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935/962 bearing clearances

Does anybody know what bearing clearances were recommended from the factory for these high boost/rpm engines?
I know that, once in team hands, they would modify as they would see fit and I am sure it varied a bit team to team. Just curious what they deemed necessary for engine survival for 24 hours and sustained near 8000 rpm.
Choice of oil grade would have a lot to do with it and with titanium connecting rods clearances would probably be less than with for instance Carrillo rods.
But the mains would be similar to any other 911 engine turning 8000 rpm, I would assume. Chances are that these would be set up on the loose side, but would the racing spec still fall within standard factory clearances?

Thanks, Oliver
Old 08-31-2017, 10:10 AM
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I've been hoping someone who builds those engines would comment on this just to see what they say. I don't know the factory recommendations for those engines but I would think .001-.00125" per inch of journal diameter for the mains would be fine with 50 oil. Rods looser at .0015" - .002" per inch of journal. No way I would run clearances as tight as the std factory minimum clearances. For 3.3 turbo they say minimum is .0004" on the mains and .0012" on the rods. That sounds like a guaranteed spun bearing. Max factory recommendation on the 3.3 is .0028" on the mains and .0035" on the rods. The above clearance ratios for race would put mains at .0024 -.00295" and rods at .00325 - .0038" so at the upper end and slightly above the factory recommended max for the 3.3. But like I say I would like to see what the pros who build those engines have to say. It's probably one of those trade secrets that few want to share. Better loose than tight though.
Old 09-01-2017, 06:02 AM
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Neil Harvey of Performance Developments posts on here sometimes. Check out their web site. They rebuild those engines so he may help.
Old 09-01-2017, 10:12 PM
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The 935 / 962 engines originally used Titainium rods and the Rod Bearings had a thrust surface on each side of the rod, also the Crankshaft has a wider radius on the crank pin (both main & rod) When I was building 935 engines I typically used .003 to .0035 bearing clearance. Also had the bearings coated by H.M. Elliott Co. We also used Carrillo and Pauter Rods with the same clearances with Std. bearings but had to have the bearings chamfered.





BTW, the rods & bearings in the photos are for sale.
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Old 09-02-2017, 11:02 AM
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Was that .030 - .035" just the rods or mains too?
Old 09-02-2017, 11:25 AM
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We have never seen rod bearings for these engines in undersize sizes for the crank. When they were easy to obtain, we could mix and match uppers and lowers to get clearances where we wanted them, but over the past years you are lucky to get what they give you. The only way added clearance was ever possible was to reduced the journal size.

Running large clearances requires you to control the oil volume and pressure at the bearing. Oil grade certainly plays a role here as does the oil temperature. Unless you are trying to win a race against a fierce rival, use common sense and use typical clearances you would with a steel rod. The bearing shells will dictate what you can run and the only other way is the journal. Easy to add but dollars to tighten.
Old 09-02-2017, 07:39 PM
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clearances

As I remember the rod bearing clearance was increased by one thousandth of an inc h on the RSR and Turbo engines.RSR had double tang bearing shells with a part # ending in 148-01.Pressure was controlled by the beautiful oil filter bypass that replaced the oil cooler and shimming the O.P.relief valves.RSR bearing shells had a bevel on the outer edge of the bearing to help shed oil quicker.Fred
Old 09-11-2017, 04:07 AM
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You might pick up some ideas here: Bearing Clearances - Engine Builder Magazine
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Old 09-11-2017, 05:00 AM
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Great info Neil.
Old 09-11-2017, 06:24 AM
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