TD in DC

Since I had my engine problem, I have heard from various people that word among the 944 drivers is that you should consider backing off a little in Karussel, because it may be very hard on rod bearings for 944 variants.

It is a high-g left hander which, so I am told, is the worst combination for 944s. My knock started right after exiting Karussel. It might have no connection whatsoever, but you might want to keep that in mind when driving at Shenandoah.

Of course, I don't think it is a reason to avoid the track at all (it is one of my favorites), but I wanted to pass on what I have heard over the past week.

If you are new to this thread, please read the following clarification before continuing:

I have tried to make it clear that I do not know exactly why I had engine problems when I started this thread. There may or may not be any connection to Shenandoah, and there may or may not be any connection to G-loads. That is why I said "potential caution" etc . . .

I am not claiming that I know what happened, and I am not entirely sure that I ever will.

Also, as I stated earlier, I really like Shenandoah and do not plan to avoid it in the future.

Z-man

TD:
It's my understanding that it's the high-g right-handers that 944 owners have to worry about (ex: The Bowl taken clockwise @ Pocono), and not the left hand - high-g corners.

Can someone verify?
-Z-man.

38D

If you had an accusump, it should take care of this problem...no?

TD in DC

That is exactly what I thought, and the reason why I installed an accusump. However, I have since learned that you actually can have oil starvation despite the accusump under certain circumstances. Apparently, one or two other 944s have spun bearings at Shenandoah, and at least one of them also had an accusump. Again, this is all rumor and speculation at this point, and I have yet to tear my motor down so it may or may not have anything to do with my problems, but I just wanted to share what I have heard. It can't hurt to back off a little in one turn during a DE. If I had heard these rumors before I went, I wouldn't have pushed so hard through that particular turn. It is just so much fun that it is hard not to . . .

Z-man

An accusump would definately help with oil starvation issues. A less high-tech help is upgrading to the later type 944 oil pan that has baffles in it.

Another thing that most people forget to do is to keep an eye on the oil pressure guage. Check it on every straight, on ever lap.

-Z.

TD in DC

Ah well, in my case it did me no good. During the fateful run, my oil pressure would climb on the straights to between 4-5 bar, but then it would drop for the corners to 2-3 bar. The accusump doesn't even "activate" until below 2 bar, so I am not sure whether it even emptied. But my point is that when I looked at my gauges on the straights, the oil pressure was fine. The problem is that it dropped in the corners, which is where you aren't looking at the gauges. It made me a believer in warning lights. That is going to be one of my winter projects.

joseph mitro

was your oil level correct? any leaking of coolant into the oil? i spun my #2 going straight and i think it was at least partially from coolant in the oil. also, i installed an S2 oil cooler on my rebuilt engine to keep the temps down and pressure up. that's another thing to consider.

maybe it was a worn oil pump that couldn't keep the pressure up. i'm just thinking out loud.

evil 944t

I was always told to use 1 extra quart. Also, to baffle the pan, do a search on the 944 turbo forum and find pics. Its just a metal flap/door hinge welded in. Its harder to drop the pan then do the mod.
Then do rod bearings while your there.

KLR

Out of curiousity, how old (in miles, track hours, years, or whathave you) were your rod bearings and what RPM was the motor turning through the Karussel? What was the typical oil pressure for the motor at warm idle?

Adam Richman

I have always been told to not overfill them w/ oil. When discussing my motor's launching w/ someone that I think is pretty educated on the subject, he felt it was actually under braking that it took on the most damage, not high-G turning (said this in respect to oil flow in the head of the 944S - much of it was over my noggin'). My oil level was a quart low - that was my contribution to the problem, that and thinking the pressure was acceptable when it was in fact low (45psi which I read as 60 unfortunately).

I just wonder since you hear left, right, straight, braking and folks lean toward over filling and accusumps if its just that these motors (S and non-S) are sucesptible to momentary dry shots to the #2 bearing for one of any number of reasons and we would be wise to keep the oil temps as low as possible on track and use an oil that does a good job of coating so the bearing can survive a belch of air. I run coated bearings and an external Mocal oil cooler now but I guess it doesn't mean anything to say "and it hasn't blown up yet."

TD in DC

My oil level was correct both before and after the run. I didn't see any evidence of milkshake BUT I haven't dropped the pan yet -- I just checked the dipstick.

I was told that it is a bad idea to run with extra oil because it makes the cavatation problems worse.

Also, I have a very effective oil cooler that kept oil temps at 150-180 (usually 150) until the incident.


Thanks for the tips on the baffle. I plan to do that.

The day before the engine went, oil pressure was 3-4 bar warm at idle, and 4-5 at while on the track, everywhere, even in the corners (I can tell by watching the video). Good question about the rpm in the caroussel. I "think" that I was at about 4-4.5 K while in Karussel. I definitely wasn't lugging at all. I will try to look at the data and see what it says.

With respect to the motor, it was supposedly rebuilt a few years ago, with rod bearings, and then only used for one or two DEs (IRRC) and then parked for two years. Obviously, I have no way to prove or disprove this. Until I tear the motor apart, I will have no way of knowing for sure, and even then, I might not know.

ADAM, you nailed EXACTLY what I have been hearing. The motors can experience just a momentary burp of air and that can be enough to cause damage, despite the accusump. That is why I posted this warning for the 44 guys to consider exercising caution at Shenandoah Circuit until we find out more. Apparently, my 44 was not the first to start knocking after karussel.

RedlineMan

Well...

There are all kinds of reasons things blow up. In the case of 944 #2 rod bearings, it is a bit of a mystery. I've talked to a lot of people and gotten no clear answer.

One thing that is a bit missunderstood is pressure -vs- volume. It does not take a lot of pressure to oil a bearing as long as their is volume. 2-3 bar = 29-44psi, which is a fair amount, and should be enough to keep a bearing alive if everything is OK, and/or there are no other forces to overcome. If there is some sort of restriction, all the pressure in the world will not make up for the lack of volume.

Volume too is quite important for keeping bearings cool. As my machinist says, he would rather have 15psi and tons of volume than the reverse any day.

So too will neither pressure or volume make up for sucking air, which is usually down to cavitation. All 944 pans are baffled, the later ones better so. You should indeed keep your oil levels up. Overfilling is OK, but only to a point. Over filling to the point that the crank is whipping up the oil is REALLY BAD. I run 1pt over at most on early cars, and even/full on late.

And it IS generally long right turns where the oil cavitates away from the pickup, which is on the right side of the sump.

KLR

Interesting. One of the common explanations (besides cavitation in right hand turns or frothing due to overfilling) involves a flaw in the design of the oil galley/drilling of the crank in the #2 bearing that results in oil starvation at high RPM. I'm sure that, as we've all figured, it's probably some combination of all of these issues, as no single solution (drilling the crank, accusump, etc.) has ever solved it. That said, it's interesting to hear that you were only turning 4-4.5k RPM, as I would have guessed that the motor must be spinning faster for this to crop up if I have correctly understood the crank design issue.

If you were seeing perfect oil pressures in your in-car videos at all times the day before and lower pressures (e.g., 2 bar) only when cornering on the day that you spun the bearing, it suggests a couple of things to me. Either the bearing had already given up the ghost earlier, but not yet spun, in which case the Karussel might have been the straw that broke the camel's back, rather than the bolt of lightning that took it out in its prime.... Or, perhaps a baffle broke in the oilpan, allowing some cavitation in many corners, and finally complete starvation in the one. Do you have some video of your last couple of sessions? It would be interesting to see, although I suppose that we'll get some insight when the pan comes off. What type of suspension, brakes, and tires are you running?

As you might have guessed, I'm particularly interested because I'm taking the 951 down to Shenandoah this weekend. I'm on street tires with nearly stock suspension and brakes, so I like to think that I'm generally a poor candidate for the rod bearing issue. Nonetheless, I certainly think about it on occasion. My car's PO had the clutch, steering rack, and RMS done 15k miles ago, but didn't have the original oilpan gasket or rod bearings done at the same time . I'm sure that he didn't know any better and that his wrench didn't feel the need to suggest yet more work to add to the bill (it came to $4200), but it struck me as foolish. Hopefully, it won't also strike me as stranded some day.

Z-man

Yeah, I'm with KLR - any chance you can drop the oil pan before Friday, TD? You don't really need to go to work tomorrow, do you? ?
-Zoltan.

PS: I have had my rod bearings replaced, but did have that cracked head issue last year, where some coolant did mix in with my oil...

evil 944t

Not only can you baffle the pan but you can ad a collar around the pick up screen.

Another thought is, sometimes the pick up tubes themselves can crack and cause starvation. Some people have found them almost completely broken.