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Old 08-18-2011, 11:33 PM   #1
hp18racer
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Default Rod Bearing Life for 944 Race Cars

How many hours racing do you guys go in your 944 n/a cars before replacing rod bearings?

My personal experience would indicate that the maintenance interval should have been something less than 53 racing hours.
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Old 08-18-2011, 11:51 PM   #2
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great thread.....I gotta ask where did you come up with the 53 hours?

also what mods did you do to the oiling system to "fix" the problem??
928's have the same issues....just with twice as many rod bearings.. :>)

In my research....there is a grand canyon wide quality problem with 944-928 rod bearings...the glyco's that are common can be good...or can be HORRIBLE...like grendade your engine is a few hours bad... The Porsche branded bearings seem to be better....but cost much more....

I have had great success with original used engines that still have their factory bearings.....but currently have 52 hours on the engine...I really hope you are not jinxing me....but the oil analysis does not indicate excessive bearing wear...
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Old 08-19-2011, 12:04 AM   #3
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Fresh rod bearings before the first race.
53 hours was 2 24 hour races + a double duty DE.
Failed 4 hours into the next event.
Did a baffle in the pan, ran Valvoline VR1 20-50.
Monitored oil temp to verify it stayed under 250F in the sump.
Standing order for drivers on my team was shift at 5000rpm.
Really need to get in the habit of the oil analysis.
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Old 08-19-2011, 12:12 AM   #4
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Biggest benefit to rod bearing life are the oil baffles AND cross drilling the crank at least for 2 and 3 I believe. I don't have a set change interval - others I believe do yearly (off season) preventative maintenance.
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Old 08-19-2011, 12:14 AM   #5
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I was dead worried about this when I bought a 944T before the 2004 season. There were good records with the car, but no mention of rod bearings being replaced. Ran a full 944Cup schedule [14 races] + maybe 6 DE events that season. Pulled the engine and zero hour'ed it over the winter. Pulled the pan and found that the rod bearings were perfect. Replaced them anyway.
Since then, one full and one half 944Cup schedule plus PCA club races and lots of DEs. No sign of trouble.
Good oil [Redline in my case], slightly overfilled before each run, good baffles in the pan, and good oil cooling all seem to have helped. Now I hope I'm not asking for trouble having said that!
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Old 08-19-2011, 02:46 AM   #6
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It's a crapshoot. But one season is about all I would push it. I had them done before nationals each year and the last time it was opened up they showed very minor wear. But then a re-ring and fresh bearings spun number two with less than 10 hrs...go figure, there is some potential that excess balance shaft clearance is causing the starvation but we'll see when it's all apart.
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Old 08-19-2011, 08:54 AM   #7
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My experience has varied as well with my 944 cup car. Went 4 years on a set with no problems. I changed them out of caution and added the Lindsey baffle. Went about 4 races when #2 failed and killed the motor. New motor has a modified Mantis baffle, scrapper and the engine builder did some kind of voodoo to the block. Only 1 race on it, so far so good.
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Old 08-19-2011, 09:47 AM   #8
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I am on year 3 with this rebuild. 2-1/2 race weekends, and numerous DE events. No extra baffles. Change the oil almost after every event due to what ever reason, usually a hole in my auxillary oil cooler or some other such nonsense. Do you normally have your crankshaft tolerances checked? The wear patterns on them can be strange sometimes.

Did you ever get your tranny back in your daily driver?
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Old 08-19-2011, 10:37 AM   #9
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Quote:
Originally Posted by hp18racer View Post
How many hours racing do you guys go in your 944 n/a cars before replacing rod bearings?

My personal experience would indicate that the maintenance interval should have been something less than 53 racing hours.
Rod bearing failures are not strictly related to wear. It is just one factor. I suggest that 944 spec guys do it once a season at most or every other season.

However more important is checking the oil before each run on the track. Running low oil levels are good way to spin a bearing. Also running and oil cooler, using high quality oil of 15/20W50 weight. Plus any new race motor should ideally zero time it by changing rod and main bearings before racing. Changing main bearings though means pulling the engine to get to the crank.
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Old 08-19-2011, 11:21 AM   #10
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I do mine at 100 hours on the meter, which is probably 60 hours of track time with all the idling and sitting we do. The last 2 times I've done them they looked like new, so any failure in that time span would have to be an oiling issue, IMO. I got the car with 70,000 miles on it and when I rebuilt the motor#2 was showing copper, so I was just dumb lucky that I built it when I did.
Cheers
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PS - a Lindsey 3 piece crossmember makes it a 4-5hour job, no excuse not to do it regularly...
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Old 08-19-2011, 11:58 AM   #11
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The proper time to replace the rod bearings is right before they go bad. ;-)

I think Joe's advice re filling and checking oil level is good advice. You could visit 944Cup.com and see what racers there have to say.
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Old 08-19-2011, 12:38 PM   #12
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I am convinced the issue is as much the rod as the oiling. If the rods and crank were properly polished and sized during the build the rod bearing last a long time. If the rods were not done it is a crap shoot. Either way I would go no more than 40 hours myself.
As an FYI, my machine shop who has been doing 944 work for 25 years, tells me every rod they have ever received has been out of spec. Another reason why it's worth finding some forged rods or better yet aftermarket.
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Old 08-19-2011, 01:38 PM   #13
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I had a failure at about 90 hours on the meter (~60 racing hours). The engine history was unknown probably over 100k, new bearings were installed when converting it to a racecar. I was going about 100 mph when it happened and the failure killed the engine.
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Old 08-19-2011, 02:03 PM   #14
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Quote:
Originally Posted by North Coast Cab View Post
As an FYI, my machine shop who has been doing 944 work for 25 years, tells me every rod they have ever received has been out of spec. Another reason why it's worth finding some forged rods or better yet aftermarket.
^^^ I've been wondering about this. The prevalent attitude is the rods are robust and overkill for the NA application, but if it's a complete teardown the rods should be checked, the reliance on Porsche quality has to be tempered with the fact that many of the parts are Audi spec. (Not sure of the rods)

Checking means rod twist, flatness, big end for oval, side clearance and the taper of the journal bore. All of which directly affect the bearing running clearance and oiling. For the most part dropping the pan for new bearings you can only plastiguage but that's only part of the story.
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Old 08-20-2011, 12:01 AM   #15
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I've done mine every other season (120ish hours) and each time they have been fine. Running Redline 40weight oil, forged rods and the Lindsey pan baffles. Also running a pretty large Setrab oil cooler...My oil temps don't exceed 220 even during the hottest summer races.
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Old 08-20-2011, 12:01 AM
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