Four years ago, I did a complete rebuild of my 88 924S engine for track use only. It got new pistons and rings and all bearings, seals, belts etc were changed.

Since then I have tracked it about 6 times per year for a total of 12 Driver's Ed and 12 PCA Club Races. The club races by the way are much harder on the car. Based on an average of about 2 hours of track time for each event (Driver's eds are 2 days and races are generally 3), my engine had about 50 hours on it at the end of this year. I have religiously changed the oil (Castrol Syntec) after every two events and have generally not over revved the engine although there are a few places where you just can't help bouncing off the rev limiter (the Carousel at Nelson Ledges for one). Anyways, after a hard season this year during which we also did two endurance races, I decided to change the rod bearings as a precaution. I have read that 50 hours is the practical limit for a track engine.

Well...we got it apart last night and the 1, 3 and 4 cylinder rod bearings looked great however, number 2 looks like it might have let go on the next revolution of the engine. The difference between it and the others is amazing. I will try to post a pic later.

So my experience is that 50 hours is a good time to look at your rod bearings or you may spend a lot more!

 

What is it with cylinder 2? I keep hearing this lately. Interesting.

Thaddeus

 

Failure of the no.2 rod bearing, caused by oil starvation in high G long fast corners, is the classic 944 engine failure mode that everyone worries about. Under sustained cornering loads the oil is pushed away from the pickup.

This is why you should check your oil after every track session and keep it right at the top mark of the dip stick or a little above. I always run 1/2 litre extra. You should also add the 87 and later baffle to the oil pan as it keeps oil in the area of the pickup under cornering loads.

Cross drilling the crank is supposed to help too but I havn't done that.

 

I will add this to the mix.

I just came up to post my results on my motor. I tore the rest of it down this evening. My 1 and 4 look great, but 2 and 3 not so good. 2 is badly worn on the rod cap side, and worn in 1 area on the rod side. 3 is worn on the cap a little right down the center.

I also have some scoring that I did not see on the rebuild. Hummm.. the fate of the 2.8 looms ever closer. What the hell to do now besides open the checkbook!

So, moral of the story is to get the crank cross drilled or drive like my grandmother.

 

There ought to be a club... or rather a *support group* for those stricken by the dreaded #2. Mine let go at autocross 2 years ago. How else could I justify installing the 2.7 in my 86

Skip

 

Skip: Did you cross drill your 2.7 crank along with the transplant ?? Say with Xmas getting close (the season to be jolly) how about another Beer Night.... I would even go north. --Roy--

 

When doing my rebuild, I had #2 AND #3 cross-drilled to help avert the problem. I already had the baffled oil pan.

For what it's worth, the CAUSE of The Great Rebuild was indeed the #2 rod bearing failure, though the engine was in bad shape regardless.

Greg

 

Nope, living life on the edge... if I blow this one it goes to Milledge for ITS prep, or into a 951 tub as a 2.8 stroker. (yes, I break things just to fix them... childhood affliction ) I will do preventative bearing replacements as needed... not enough time on the engine yet though... had only 40k on it when installed. No "performance" modifications are allowed to the crank in ITS, so no other reason to fool with the crank. It does have a baffled pan, new OC seals, new OPRV, and I keep the oil topped off at all times. Measured risk, so far so good... over 25 autocrosses and no trouble yet (my previous engine let go during autocross).

Sounds like a plan... no need to come North, gives me a chance to remember why I don't live in the city Maybe the 19th? Redmond Towne Centre?

Skip

 

So N0.2 only goes dry on hard long corners, Under normal driving conditions it should be fine right? Does anyone know if the 968 suffers from the same oil problem under high G cornering? Just checking,

Thanks

 

Roberto - Mine #2 rod bearing went when I was accellerating in a straight line from a stop. Chances are the bearing was significantly worn to begin with, and the condition of the oil was questionable as I had just picked up the car.

Greg

 

Roberto, I have heard that the 968 is better, but I suspect that it is only as good as a 1991 944 S2. It does have the updated pan and/or baffle.

 

Skip: Wed 12/19 is good for me. What time & watering hole do you have in mind. --Roy--

 

Hard driven long corners like say a highway clover leaf entrance ramp? Uh-oh. I hit 4 clover leafs and 2 other high speed ramps each and every day. This coupled with the fact that my balance shaft seals are leaking make it difficult to keep the damn thing topped off.

Firestarter

 

But WHY is it the #2 rod-bearing that goes first? Figured if the problem was from the oil-pump pickup, once that sucks air and we lose oil-pressure, wouldn't the oil supply to ALL the bearings be lost? including the main crank bearings too?



Skip, I'm going to follow our suspend-the-engine-from-wooden-beams procedure to replace my motor-mounts and figured I'd do the rod-bearings too. How would you estimate for this job? Thanks -danno

 

The word from the factory and the folks who dealt with this "in the day" (Andial, Milledge, etc) is that the oiling for the #2 bearing is the worst by design... like "not all conrods are created equal". I've been told it's not only the oil squirting to the bearing, but also the delivery... which is why enlarging or camfering (sp?) of the hole doesn't always guarantee success. I guess it's a combination of the bad pickup causing starvation, and the lack of tolerence the #2 allows because of its already bad design. BTW, this was never corrected, it's just that the baffled pan and lower sump makes such a huge difference over time (less chances of starvation) that it's less heard of on newer cars... like 968's which are most barely pushing 100k miles at this point (except Rudy ). It's not that the #2 bearing is starved once and spins, it's the overall effect of the number of times this has happened, with the final blow *usually* when the engine is spinning fast, on a corner, under high G's, etc (the straw that broke the camels back)... evident by all the stories of breakdown inspections or rod bearing showing obvious signs of wear (like scoring or discoloring).

While there are many ways to combat this, probably the most effective for most is to run good clean oil, topped off, and change the rod bearing every 50-75k (this may seem too often, I'll show you my *new engine* bill to give a better feel as to why this is). If looking to prevent it in a race car, you can:
- install later pan, baffle, sump, and associated pieces.
- send off to a company that will increase the baffling (Milledge is one)
- install and accusump
- have the bearings/journals coated and treated by the same folks that build drag engines (basically a Teflon treatment)
- Have the crank redrilled and polished (again, Milledge and others)
- even after all this, replace the rod bearing after 50 hours (or less) of track duty. They're very cheap, and once you've done it a few times, create the right jigs, it's probably a walk-in-the-park.

Danno, You could probably do them and the mounts in under 8 hours... not too hard with with one-man... would be much nicer to have another hand (to hold the beer )