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Rod bearing comments from Rennlist


944-Spec#94

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944-Spec#94

Guys I Have compiled some comments from Rennlist on Rod bearings.

 

There are some intersting issues.

 

From Huntley Racing

You can change bearings all the time or you can have us upgrade the crank so this will not happen again. Here is a repost of an article we wrote for the PCA: Huntley Racing had done a lot of research over the years into EXACTLY why 944 cars spin rod bearings. What we found out over several years of searching was that there is much more miss-information that actual facts. First we found that whether in a track car, streetcar or even a weekend show car all 944 based cars including the 968 can spin a rod bearing. Second this has nothing to do with HP or TQ. Third it has nothing to do with uncovering the oil pick-up (This is a common miss-conception promoted by many many shops). Forth is that extra oil, like a half quart over the dipstick, does nothing. Fifth the Accusump and other systems don't fix this issue (other possible problems yes, but not the common rod bearing failures). Sixth no matter how many baffles you have put in your pan they will not help. I can go on and on but to get to the 'meat' of the matter....

 

What causes rod-bearing failures is 99% of the time centrifugal force. We found the solution to the mystery in an uncommon place, the Chevy world. It turns out a Chevy motor has the same problem, the 454 big block. Chevy 454 big blocks, which were designed for lower RPM operation, later became popular for drag racers. The drag racers started to turn more and more rpm's in search of more HP, which resulted in a 'new' problem developing, spun rod bearings. It took years to figure out why. The reason turned out to be so basic that the likes of Chevy and Porsche simply 'missed' it.

 

As a crankshaft rotates it has many forces acting upon it. It is obvious that the pistons push on the rods, which push on the crank and so forth and so on. What was missed was centrifugal force acting on the oil within the crank. High-pressure oil is fed thru the center of the crank to the main and rod bearings. Oil passing thru each journal is forced out of the crank onto the surface of the bearing thru the oil feed, which is nothing more than a hole in the surface of the journal. Where the 'mistake' was made was in the placement of the hole. The single oil feed hole can be drilled at any point 360 deg around on the journal, this is a decision dictated during the production of the crank. When the 944 crank design was made there was no attention given to the placement of this hole and the effect centrifugal force might have on the oil within it. Where the feed was placed just so happens to be one nearly opposite the direction centrifugal force pulls the oil when the crank is in motion. As the RPMs increase the centrifugal force goes up, eventually to the point where the oil pumps pressure simply can't overcome it. When this happens the rod bearings are starved of oil. The reason more track cars have this failure is because they are at high RPMs more often and for longer periods of time. Also track cars tend to have relatively high oil temperatures which thins the oil and causes the oil pressure to drop which lowers the RPM point where oil starvation at the rod bearings occurs. Further the high RPMs and often overfilled oil pans (to supposedly save the rod bearings) cause high windage that aerates the oil, further reducing its lubricating potential. Older motors spin rod bearings more often than newer motors since they have had more high RPM time than new motors and they usually have less oil pressure. Baffles, Accusumps, overfilling etc... do nothing to stop this failure mode.

 

Cross-drilling came out several years ago as a remedy for this issue but not because the problem was understood but because the idea was that a second oil feed hole would add more oil. There was a positive benefit from crossdrilling. The new oil feed opposite the original oil feed was not either hurt or helped by centrifugal force due to its position. This meant

that the oil pump could generally keep up with the oiling needs of the rod bearings. Huntley Racing however took the cross-drilling to the next level and developed the Perp drilled crank. We perpendicularly bore a new feed into the rod journal, which is actually taking the nemesis, 'centrifugal force' and working with it to help to actually scavenge oil to the rod bearing as the RPMs go up!! Since we have machined cranks with this technique we have 'NEVER' had a rod bearing failure in any car, ever! We started offering these in 1998.

 

This subject and its relevance to the 944 world is obvious but it is only one of many possible failures, which can and do occur to these cars. Cars that suffer rod failure generally can trace this to the above mentioned rod bearing problem as the catalyst. Main bearings generally don’t have this problem simply because they are centrally located on the centerline of the crank and have a much smaller ‘arm’ to their outer diameter which makes them far less susceptible to oil starvation from centrifugal force.

 

So in summary if you have your crank out have the process done. If your motor is still together and you want to avoid spinning a bearing without the Perp drilled crank, keep your oil temps down, limit your RPMs a bit (look at your HP peak and avoid revving past it), run a higher viscosity oil, avoid over filling, and keep the oil fresh.

 

Derrek Huntley Khajavi

Huntley Racing

 

Copywrite © 01/27/2002

 

 

Chris Cervelli - Technodyne 12/3/02

I like Derrick's explanation. I agree that the problem is not really related to oil level and such. However, a baffled pan will help out if you let the oil get low. I agree that the Accusump is worthless.

 

I also agree that RPM is a BIG contributor to the failures. I think that torque output does play a role however. Obviously the higher the torque, the higher the load on the bearing. This plays a small role, but it is important (on Turbo engines anyway).

 

Derrick's explanation makes good sense. But one question is left unanswered: Why it is always #2?

 

Comments?

 

Chris Cervelli

Technodyne Inc.

 

 

 

Chris Prack, Fairfax, VA. 12/03/02

 

BTW, there is one other thing that I have noted on this subject over the years.

 

Each rod journal is fed from a main journal next to it. So the oil flows from the main journal through the crank to the rod journal. In this journal is a chamber that kind of acts as a little resovior before the oil gets to the rod bearing.

 

I have built more than a few 944 motors and reguardless if they were N/A, S2, turbo, whatever, the chamber in the crank is always found to have coaked oil in it. I have spent countless hours with a pick and compressed air removing chunks larger than a bb. Anyone of which if it broke free in a running engine would more than plug the oil feed hole to the crank and trash the bearing. It would also reduce the amount of oil getting to the bearing by reducing the volume of oil in this chamber.

 

This deposit problem is obviously from heat and probably from a lack of proper service or inferior oil quality.

 

So when you put your new motor together make sure you get a real close look at the rod journals, you can see the coaked oil in there if you look with a flashlight. You will have to dig it out with a pick, just "hot tanking" the crank won't always remove it.

 

 

Thanks Mike B re how to post pictures. I just finished having my '86 951 engine rebuilt by Henri Costa of Refined Motorsports in Toronto, and I thought I'd share what I have discovered about the No. 2 rod bearing. Henri worked on the Rothmanns Turbo Cup cars in the mid-1980's, and he said that they never had a problem with the No. 2 rod bearings in any of the engines. These cars were prepared by the factory for about 300 rwhp, and they rebuilt the engines after each season. He worked on Richard Spenard's car, among others. Henri's view is that the main reason for the damage to the No.2 bearing is low oil level, and this has some logic.

Almost all of the engines that have the No.2 rod bearing spin have high mileage, and they use a lot of oil. My car had 100k miles, and it used a liter of oil per driver ed day, or for about 80 minutes on the track. I had to monitor it very closely. Each time the oil is a little low, the number 2 bearing is starved because it is the last in line. It seems to happen very gradually. My No. 2 rod bearing had a lot of copper showing and was loose in the rod, so it was just a matter of time. Henri carried out a number of modifications in the rebuilt engine to delay the problem, and I plan to limit revs to 6k and continue to check the oil religiously. I drive to and from the tracks, so I need reliablity.

The modifications consist of an added baffle with a trap door to control the uphill oil surge on left-hand turns, and a collar around the oil pick-up to reduce aeration. The crank is knife-deged to reduce windage, and cross-drilled. If I had read this thread before cross-drilling, I would have gone for the radial hole suggested here earlier. Anyway, here are the pictures of the modified sump and oil pick-up.

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944-Spec#94

I wonder if oil coking in the crank is causing the short time rod bearing failures?

 

It seems to me that even if you change the rod bearings on an old beat-up motor if it has crud in the oil passages in the crank it could cause the issues Chris Prack described. It may be that dirty crank passages only need a few racing hours to heat them enough to cause the exising coke to break loose and cause problems.

 

Just food for thought.

 

 

I am starting to lean torward allowing drilling of the crank to prevent rod bearing failures. There seems to be some technical justification and some practical experince from the Austraila series that allows it.

 

It also seems like a good idea to clean he oil passages in crank when doing any rod bearing replacement. This seems like cheap insurance and is 100% legal.

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944-Spec#94

Here is a long thread from the 928 Forum.

They have issues with #2 and #6 rod bearings. Remember our engine is a 4 cylinder version of their 8 so much if the internal design is similar.

 

http://forums.rennlist.com/rennforums/showthread.php?s=&threadid=92854&highlight=rod+bearing

 

 

Intersting they brought up two things Ralph Evans brought up about BMW oiling.

1) limit oil to the head using restictors to keep the oil in the bottomend.

2) Mobil 1 sucks on the track.

 

Intesting indeed!

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Paul Bloomberg

Joe,

I support the use of any rules update to prolong engine life even if they are unproven "it's their money" and in the long term it is in the best interest of the series...

The rod bearings are a concern but then again I can't think of any series in AZ that has as many racers with as many evenly prepared racecars...which produces some very close racing.

 

Next issue....split starts:)

 

Paul

#51

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944-Spec#94

Copy of discussion from split start post.

 

BTW - Att $500 for a used motor are cross drilled cranks really an option? From what I've herd from "ALLOT" of people is that spun bearings will happen. Big deal!! Put a new motor in and run another year!! I'm as cheap as the next guy (more so cuss I don't have a ton of money) but it seems as though motors are cheap and solutions are $$$

Eric

_________________

Eric Sorensen

84 Spec 944 #70

 

 

Eric,

With respect to engines. I am really thinking we need to push for legal accusumps, drilled cranks (add 1 more oil hole to rod journals), and oil pan baffles.

 

These things seem to be such that they can improve engine reliability without increasing performance. Thus those than want to spend the money can do so. Those that don't won't need to keep up on the track.

_________________

Joe Paluch

944-Spec #94

I know that we are now way off topic, (perhaps someone can move these last three posts to another thread) but I would like to know where these $500 engines exist. It seems to me that any $500 engine you could find would need a rebuild before it would be worth the R&R in your car and it is my understanding that a rebuild, depending on how well you do it (full, partial, as needed) costs $3-5k.

 

Further, I have been told that to machine the crank properly you should remove the engine and at that point why wouldnt you just do a rebuild? If that's the case, I just as soon wait for my engine to blow. Perhaps I am missing something?

_________________

David J. Marguglio

San Diego Region

#62 Spec 944

#254 LSS Boxster

 

 

 

I am all for increasing the reliability of our motor's!! I think we need to actually speak with the experts involved. Rick W. ran 15K miles on his stock motor in a 924S. And he replaced the rod bearings as a precaution. I think his input would be most valuable. It seems to me that some motors break and some don't. New motor experience the same failures as do old motors. Why? #2 rod bearing seems to be an issue but why can a 150K motor last and a new rebuilt motor die?? Glen Uslan's motor lasted 4 years.!! I have herd all the talks about cross drilled cranks, Acusumps, baffleing, and adding extra oil. What works and what doesn't. Is spending $700 for a crank worth it if you can get a motor for $500?. I'm starting to think having a spare motor in the wings for $500 is money well spent. Swapping a motor is less than a days worth of work. I'm thinking about keeping an 88 944 motor in the wings just in case!! I'll get seat time from this one and the extra HP from the other one once I learn how to really drive.

It beats saving $600 for a crank plus the complete rebuild and swapping the motor!! You can spend $4K to have a new motor that may or may/not work or spend $4k on 2 motor swaps!!! These motors are cheap so why bother!!

Eric

Just my opinion!!

_________________

Eric Sorensen

84 Spec 944 #70

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944-Spec#94

Well I am not 100% certain why rod bearings fail. I know motors are not that expensive, but I don't see any problem with giving people the option.

 

I am not certain a crank drill needs to cost $500 anyway. In any event I don't care if you just want to replace engines vs drill cranks. The end goal i am looking for is still low cost racing. Not having a reasonable solution will probably mean less drivers in the series.

 

 

BTW...

I have been hearing alot of bad reports about using Mobil 1 in racing cars. I have been running it and never heard these before and not I am thinking of switching to AMSOil or Redline.

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Well, as the latest casualty of the rod bearing fiasco let me differ with the following comments:

 

"Att $500 for a used motor"

"but it seems as though motors are cheap"

 

Not sure where those $500 motors are either (David). At $500 you are going to be sinking some money to get them ready.

 

Now these failures aren't cheap either. While I'm not going to state the exact quote, let's just say that the repair costs are approaching the rebuild costs pretty darn quickly. My failure (and the rod did NOT leave the block) requires new, or reworked crank, rod, piston, etc.......

That work means the engine is coming all the way out of the car and the costs do add up.

 

It appears no one has a definitive answer, or if they do, they aren't interested in sharing it with the group as a whole, but oil type, oil level, perp drilled cranks, accusumps, etc... don't seem to solve it. Unless of course the Huntley site can be fully believed. (And I'd love to hear from someone on that issue, true or just hype to sell product).

 

I think we need to hit up both the Aussie types and the east coast 944 series and get their feedback, because frankly, if I have to replace/rebuild my motor every 4 track days, I'm not sticking with this car type.

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Paul Bloomberg

I bought a spare crank this week and will be biulding a cost effective motor myself for a spare with some help.... I also bought 12 quarts of Redline to run in the 2hr enduro.

 

Joe,

Bought a 7,8mm, some Superblue and a power bleeder

Paul

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I think the concept of say $500 motors (give or take on actual price) is based on the theory of extendable units. i.e. Put removal and install costs aside as you encounter both with rebuilds or replacements. Rather than spend the $2-3K on a rebuild, the theory is, buy somebody used 944 which was crashed or, the tranny broke and for whatever reason it made it cheap. People are findind engines with blown head gaskets and getting the entire car for $800. Then, do the obvious cheaper items like belts and pumps etc. Then install that engine. So rather than $2-3K, it cost you maybe $1K for an engine that may keep running indefinitely? There is plenty of people autoXing and racing their 944's, they can't all be doing bearings or surely you would hear about it more?

 

I can see where people are comnig from on the replacement engine side. I take poor Jeff's recent bad run with a rebuilt engine. Rather than pay that money (sorry to use you as an example Jeff) for a rebuild, I would rather have spent a third of that on an engine I knew was running and put that into the car. UNLESS, all "stock" engines keep blowing the bearings, I think the replace an engine is a viable solution? And those cheap cars are out there and you can even make some money back on the spares. I got my car for $1K. I could have used the engine as a donor and then sold off a completely function shell i.e. doors, glass, wheels, drive train etc. So maybe you pay a little more up front and have to recover by selling the left over parts? It's still cheaper than a rebuild.

 

Just my thoughts on the replacement engine versus rebuild costs debate.

 

Cheers,

Dylan.

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Chris Cervelli

There has been a great deal of discussion regarding this problem over the years. None of it seems to have helped one bit.

 

I saw 944's blow up in 1991 when I started racing and I see them blow up now. I hate to just say that the engine is unsuitable for racing, but it seems that that is really the case.

 

Here is what I know from first hand experience:

 

Accusumps do nothing.

Cross drilling the rod journals does nothing, and may make it worse.

The oil level is critical.

The hot oil pressure is not particularly important.

Oil/Air separators and crankcase vents do nothing.

There is no correlation whatsoever between fuel mixture distribution and rod bearing failures.

 

Here is what seems to help:

 

Keeping Rpm below 6000 rpm, which is not an option except with slow 944 Turbos

Checking the oil level after EVERY session, and never running enduros

Keeping the oil cool

Keeping the oil pressure as high as possible. The racer's only means of doing this is by cooling the oil. The engine builder can use a tight main bearing clearance.

Modifying the oil pan so the effective oil level in corners is higher.

Running the oil level a little over full

 

Some observations that may or may not be relevant:

 

The stock oil pump cannot maintain 5 bar oil pressure under extreme conditions. At high oil temps the main bearing clearance become larger.

All 944s tend to run very high oil temps

The stock oil pan's sump is wide and tall, which allows oil to move way from the pickup rather easily.

The engine's design demands a lot of the oil system. The hydraulic lifters consume a fair amount of volume, and the balance shafts also take some.

Large 4 cylinder engines tend to have bad crankcase aerodynamics.

Porsche redesigned the oil pan and pickup once to improve performance under high G conditions. Only 87 cars have this in stock form.

Porsche redesigned the dipstick more than once. Each time the oil level got higher.

 

I'll go out on a limb and make this statement:

 

If you 100% guarantee a perfect oil supply at all times, and keep the RPM below 6800, you will never have a bearing problem.

 

Figuring out how to guarantee the oil supply on a wet-sump engine is the trick.

 

Here are some ways that a 911 differs from a 944. This is relevant because 911's just don't have oil related bearing failures.

 

911s have a simple but effective dry sump system.

911s have a very large pressure pump. They almost never run short of volume

911s don't have an aerodynamic mess in the crankcase.

911s tend to have better control of oil temp

911s have large oil tanks, even when you are three quarts low, there is still plenty of oil.

911s have a very open crankcase breathing system.

 

Maybe someone can add to this and help point out the solution to the problem.

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I don't know why there is such a continuing misconception but there is no such thing as a $500 engine, unless you employ Enron-like accounting principals. At a junkyard or it's equivalent, you can buy an engine for $500-$750. In fact sometimes you can buy the whole car. However, it takes about $1200 worth of labor to install it. Obviously more if you open the case up. A single oil pressure relief valve costs $300. My guess is that fewer than 10% of us can turn a wrench so its real labor costs.

 

Would you pay $1200 to install an engine of uncertain history? Would you feel dumb if the [insert favorite $30 part] broke in the first lap and you lost your $275 entry fee plus $120 hotel plus $100 in fuel AND $1700?

 

However, I do agree that there remains a lack of evidence as to why we suffer so many rod failures. There is equally a lack of evidence as to whether any of the reliability efforts makes any difference either. On the face of it, it appears as though a junkyard engine works as well as a fresh rebuild. I just don't think we've gotten to the bottom of this engine's weak link.

 

Could there be a reason Porsche quit making the large bore 4 cylinder? I grant you they made it for a lot of years, though never really raced it.

 

Edit -

Mr. Cervelli's response is the closest thing I've heard toward a conclusion. Since I have to put a new engine in my car anyway , I WILL RIP OUT ALL THE ACCUSUMP AND OTHER BULLSHIT, KNIFE-EDGE THE CRANK AND INSTALL A DRY SUMP. I WILL DYNO TEST TO CONFIRM HP, ADDING BALLAST OR WHATEVER IF THE HP RISES. THIS ENGINE WILL HAVE AN HOURMETER AND COMPLETE DOCUMENTATION OF SERVICE AND RUN CYCLE. I WILL SEND OIL SAMPLES TO THE LAB (Analysts, Inc. in Illinois). COULD WE USE A TEST MULE?

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Spec-944#70

The $500 was just a number but you can get running engines for less than $1000. Chris's suggestions are valid and confirms what RW has been telling me. Keep plenty of oil in the car. These are cheap/fun cars to run. They're not 24 hour Le Mans killers.

Eric

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944-Spec#94

Guys,

 

To make these bearings last they need oil. Anything the limits or interrupts oil flow is can lead to potential problems.

 

Here is a little bearing tech and theory

 

Rod bearing are hydrodynamic bearings. What is means is that the surfaces are completely separated by an oil film. The loads are completely supported by the fluid pressure generated by the relative motion of the surfaces. What is this mean is that the oil pressure (what you read on a gauge) does not support any loads. It does play an important role that I will explain later. The nice thing about hydrodynamic bearings is that no surface to surface contact occurs. This means little friction and no wear. Wear in these bearings only occurs at low speeds like engine start. They way these things work is that a sufficient speed there will be enough internal oil pressure to "float the bearing".

 

Three things impact the ability to "float the bearing"

 

1) Viscosity of the oil - The lower the viscosity the more rotating speed is needed to float the bearing.

2) Shaft Speed - The higher the speed the less viscosity needed to float the bearing. However any speeds beyond what is needed to float just will add heat to the oil. Heating the oil will reduce its viscosity.

3) Bearing load = More load the more viscosity and shaft speed needed to float the bearing.

 

 

Now lets look at our bearings.

When they fail it is due to metal to metal contact. This contact occurs when any of the above are not sufficient. Well one look says shaft speed is plenty high to float the bearing. Bearing load is limited by engine output and really does not play big role in these failures. So that leaves oil viscosity as the issues.

 

Now there is one major assumption in using these bearings. It is that there is a sufficient oil supply. These bearings leak oil and must be replenished with oil for them to function. This is the job of the oil supply hole in the rod journal on the crank. Interestingly this oil need not be supplied at any pressure, as the bearing will generate its own pressure. What is very important is that the oil must be supplied at a rate that is at least equal to the rate of oil lost around the bearing. This leak rate is driven by the geometry of the bearing (diameter and width) radial bearing clearance, oil viscosity, load and speed. RPM we know is a driver and viscosity is unknown with the rest pretty much the same. Looking at the charts and equations the oil leak rate and flow rate actually decrease with more RPM. This seams odd, but is related to the ability of the high speeds to create more internal bearing pressure. So this would make it seem that RPM is not bad, but we would be wrong to think that.

 

Remember that excessive RPM creates heat from friction. If this heat is not extracted away it will cause further viscosity drops eventually leading to failure. This is where the oil pressure comes in place. If you supply the bearing more than sufficient oil flow you can use this oil to extract heat. So at high RPM you need enough oil to pull the heat from the bearing. So it all comes down to oil flow and viscosity.

 

So what impact Oil Viscosity and oil flow in our engines

 

Viscosity in the bearing is impacted by

Oil grade used (SAE 15w 15, etc)

Oil Temperature in the bearing - critical as this controls local viscosity

Oil Temp in the sump - important as it determines oil temp going into the bearing and therefore impacts the temp in the bearing.

Oil Flow Rate into the bearing - more flow can lower temps while less flow increases temps

 

What impacts Oil Flow Rate into the bearing?

Oil Pressure

Oil Feed passage resistance - This causes a pressure drop in the passage

Oil viscosity - Lower the oil viscosity and the oil pressure drops

Oil Pump output - pressure and flow rate

Oil supply pickup for pump

Air volume in oil supply

 

 

So given this list what do some of proposed solutions do

 

1) Keep oil level full

- This minimized the risk of the oil being pulled from the oil pickup during cornering

2) Oil quality

- Better oils will maintain viscosity under high temps and not produce particulate mater that could clog oil passages.

3) Limit RPM's = Lower heat input in to the bearings

4) Accusump = prevent oil pressure loss

5) baffled oil pan. = Prevent or minimize risk of oil pick-up tube sucking in air

6) 2nd hole drilled in rod journals on crank = Idea is that this provides added oil flow. I am not 100% sure that does however. If there is a restriction elsewhere then two holes will supply no more flow.

7) Dry sump = Maintain oil supply to pump and minimize risk of frothing.

Oil cooler = reduce average oil temps to improve oil viscosity.

 

 

So

some of these we can do now. Like

1, 2, 3, 8

 

I believe items

4, 5, 6 should be allowed

 

A dry sump is nice, but VERY costly.

 

I believe the doing things to ensure oil quality and maintian oil flow are the biggest things

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I have yet to get into the motor to find out how bad it is but it's pretty well locked up, work and a vacation have kept this out of my mind but I need to get back at it now.

 

Kevin, man I'm sorry to hear, how did yours go? Was it a rattle? or did you notice a drop in pressure? How does it look now?

 

For a 4 hour rebuild to let go while being run with plenty of oil (full, not overfilled, Mid 210's oil temp and solid oil pressure does not bode well for the longevity of these motors. I've built a lot of motors, save 2.7 911's, I've never seen such an achillies heel.

 

A rebuilt motor will now push the cost of this project into 911 territory.

 

A few things that I am suspect of:

 

The oil pressure reading on the guage will give you the pressure in the galley, but does not take into account the internal losses. Multiple uses such as cam bearings, Hydraulic lifters, Balance shaft bearings all will pull oil away from the galley and reduce the total available to the rod bearings. As the engine heats up all these will demand more oil as their bores open up and oil viscosity goes down. Building Ford race motors you would place restrictors in several locations in the block to prevent loss of oil to critical parts and would always run a higher volume/Pressure oil pump. Is none available for the 944? or even a higher rate control valve?

 

As oil viscosity goes up, the volume capacity of the pump goes down. So getting "Stable" viscosity is the goal, not ultimately high viscosity. Right now it's hard to tell if this is a lack of volume or pressure.

 

If a rod bearing is run loose it will take a higher volume of oil to keep it lubricated, running new bearings on a old crank helps but how many of you guy's are plastiguaging your bearings to see what you are really running for clearances? How about rod end play? A rod that is within loose tollerances will have a tendancy to hammer up and down on the journal effectively hammering the oil film out of the bearing and starting a bearing failure. What do your bearings look like as they come out of your engines? Are they bright on axis with the rod or at the cap joint? Inside or outside the bore?

 

Running an engine over full is not a great idea. It leads to the crank frothing the oil with microscopic air bubbles which lead to the starvation problems that joe was refering to. Remember the oil level is well below the crank, it's not an oil bath, you want to get oil off the crank as fast and cleanly as you can. Those small bubbles don't just settle out in a few seconds, they stay suspended for hours. Windage trays, crank scrapers and baffles are designed to effectively remove oil from the crank and keep oil from being picked back up. Mod'ing the pan to eliminate starvation during cornering may be an issue, I don't like the sloped look of the pan, It's perfect for oil to run up the side of the block and away from the pickup, but who knows.

 

Larger Oil cooler- definately a good idea, I'm running the stock turbo unit, I thing a larger turbotrol is the right idea.

 

I was wondering about the perp drilled (Huntley) solution, but would like to hear more from those who did it.

 

Anyway I'll get you some updates on what I find soon.

 

Jim

 

PS: anyone have a new/old motor for sale?

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No, his car died at the track and couldn't be turned over. I don't think he got it out of AMP under its own power, as it died by the stop sign near the track.

 

Could be wrong, as I left after trying to help him jumpstart it.

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More on the 928 list about bearing failures (944's even referenced) by Kim Crumb.

 

Subject: 928 motors & reliability

From: [email protected]

Date: Sun, 2 Nov 2003 13:20:34 -0500

X-Message-Number: 21

 

928 motors, in street use, and in a purely mechanical sense (as opposed to

LH brain failure) are VERY reliable and durable. Yes, you do have to

rigorously attend to a few pesky things, like the cambelt and waterpump.

In the larger scheme of things those items aren't all that expensive, if

you do the maintenance...rather than wait for the "check to come due." I

know of any number of 928's with 200,000 to 300,000 miles on them, and the

original short block is still intact! Amazing. So, let's be clear, in

"normal use" there are no significant reliablity problems, indeed, it's

quite the opposite...the 928 engine is probably a little "overbuilt!"

That being said, racetrack use is a whole different deal. I remember when

we were doing some of what I experienced as the first development on the

5L S4's, back in 91-93. Suddenly this #2/#6 rod bearing failure showed

up, repeatedly. After the third time, I had to recognize it as "944

disease" from the SCCA Pro Racing I was involved in, back in the late

80's. (They only whacked #2, of course, but it wasn't any prettier.) I

went to some of the premier 944 racers in the country. One of them even

blew up a #2 rod bearing on the dyno, so I knew it wasn't purely an "oil

not at the pick-up" kinda thing. I knew we were in for a toughy. We were

revving these engines to 7,200...I had expected to find weakness in the

valvetrain...that didn't happen! Oil/air separators were tested, etc.

Not enough. Next idea...

I came to understand that in the typical overall development of a

street engine for racetrack use, we didn't have a long list of problems.

During this process, I watched an engineering firm under contract to a Big

Three do a full race development of a Detroit engine...in the end,

virtually no stock parts were left. While I hated the challenge we

have....we didn't seem to have that many problems! We did have a big

Gotcha. The failure mode isn't pretty. If you can shut the engine off

fast enough (when you hear the noise deep in the block,) maybe you can

save the basic engine. (Or don't, and when the rod seizes mostly you have

a big expensive "doorstop.")

I've been through this too many times, with different owners...and Mark

Anderson has experienced plenty, too. Heck even the guys with automatics

have it, and I know they aren't hitting the rev limiter. I'm a results

kinda guy, so the only real question for me isn't to look for

blame....it's: "what's the fix?" It would have been really nice if

Porsche had raced the 928 seriously, and paid for finding, and fixing,

this issue (like they did with plenty of 911 stuff.) They didn't, we're

basically on our own, at this point in time. I know Mark Anderson has had

many engine heartbreaks. And he has proven, over the last five years,

that a different crank (oiling) and a dry-sump oiling system is an

effective fix for this issue. (Mark please chime in and tell me if I'm

wrong.) Below that level of alteration, things are not as clear.

Probably because we have less consistent data. I've seen mixed results

with accusumps and nothing else...at time time, I have little confidence

that's more than an "improvement." I haven't yet seen enough examples of

different crank (oiling) and just an accusump (not a dry sump.) Looks

like Don Hanson and Marc Thomas are giving that design theory a good

long-term run...I look forward to hearing about there experience (or from

anybody else who tries it.) If we get a few more people doing that

"experimentation," we may find out a new "minimum" floor that's effective.

This is the kind of tenacity that race development is about. It's why

people buy a new "Cup Car" for really big bucks...these matters are pretty

sorted out. I am big time annoyed by this little design "inefficiency,"

actually painfully annoyed, sicne my GT has sat in the garage for over a

whole year...waiting for the money and to do the next "fix" that I've

proposed needs more testing. In my two decades at tracks, I can relate to

this this as "less" the number of problems than most folks have to face,

when racing an engine that their factory didn't...I KNOW there is usually

there's a MUCH longer list of those. And? Knowing that doesn't make me

feel a lot better when I look in my garage. Wishing doesn't change the

"score" any, in getting on with the work there is to do. My .02 worth.

Kim

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Kevin,

 

Sorry for the confusion, I often get it having 3 first names, you were helping me with number 19 ( dan's old car), and sure enough it didn't leave the track under it's own power...

 

I was wondering how your spun bearing happened. As I remember you had a pretty fresh motor similar to mine. Way too soon to be spining a bearing. How did it end up?

 

Jim (Richard)

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  • 2 weeks later...
944-spec#09

Jim

I had the next stall to Kevin and was there when the bearing failed. I know when he checked the oil after he brought it back in it was almost down to the lower mark which is very likely the cause of his failure. He is very lucky he caught it before it completely failed and put a hole in the block. By the way, I have an old 1985 block that we took out of my car when I blew the head gasket. There apparently was a lot of crud in the cooling system which got into the cylinders and a couple have some slight scoring so I don't know if it will be good enough for a race engine but it may be usable. Send me an email or call if you are still looking for an engine.

Steve Sapareto

[email protected]

(602)908-9449 cell

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My oil level was in the middle of the stick after the "event". However, after all this discussion, it seems that that is not the correct level for these motors. (who knew you were supposed to "overfill" these? ) Anyway, I will keep the oil much higher in the future, and I am going the AMSOIL route as well.

As to the signs, the dreaded knock-knock-knock down the straight was my first clue. I however didn't correctly diagnose it and babied the car back to the pits. In 20/20 hindsight, I should have shut it down out there and been towed back. Luckily, all the parts stayed inside the motor . Not having ever heard that before, I thought I had some exhaust problem, like maybe a broken header, etc, because due to the shifter opening, it sounded like it was right under that area. Live and learn I guess.

It is back together and I will be at AMP this coming Saturday. Not doing the enduro on Sunday though, don't want to push my luck again so soon.

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944-spec#09

Thanks for the correction. Glad you will be there Sat, see you then. Do you think the Amsol is that much better than Mobil 1? Was there a discussion I don't remember? Doesn't the factory use Mobil 1 in all race cars?

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Sorry Steve, didn't mean to make that as personal as it seems now that I have re-read that.

On the Amsoil, many people swear by it, but then again, people will swear to most anything. Chris (Technodyne) didn't have anything against it, Don Jackson recommends it, .........

Also, some of the 928 guys stand by it as well. So, since I did have the chance to start over with something new HA! I will try it as well. If you compare the charts on amsoil's site, with those on Redlines, vs Mobil, it does appear that both redline and amsoil don't break down as quickly. But obviously those sites may have an agenda and who knows exactly how the test was conducted.

I guess I'll see.

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Spec-944#70

How often are you guys running synthetic oil changing it? I run Castrol and change the oil after each race weekend and filter every other race weekend. I also check the level after each run and keep the oil about 1/4 qt above the full line. This is all per Rick White!! I think since most of us are running older or rebuilt motors checking the oil should be as important as checking tire presures. Knock wood but just watch next event I spin a bearing.

Eric

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