Quote:
Originally Posted by sunsweet
Some people, me included were interested to see a comparison of these clearances specs to other engines. It is difficult to get access to that documentation for more recent engines so if you have something more recent by all mean provide that info but here are some older high performance engines. A few of these are by now historical cars but the clearance numbers cannot be questionned as they come straight from the corresponding manufacturer.
(and think metric)
S65B40 (repeated for the comparison)
Main Bearing Clearance [mm]: 0.0291 - 0.0458
Rod Bearing Clearance [mm]: 0.0293 - 0.0469
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Ferrari Mondial 8/QV
Main Bearing Clearance [mm]: 0.0290 - 0.0640
Rod Bearing Clearance [mm]: 0.0460 - 0.0890
(source: pages B11 and B19 in the 281/83 Mondial 8/QV WSM specs)
Ferrari 328 GTS
Main Bearing Clearance [mm]: 0.0130 - 0.0510
Rod Bearing Clearance [mm]:
(source: Ferrari Technical Specs, Service bulletin, page 6, total 147 pages)
Porsche 924
Main Bearing Clearance [mm]: 0.0200 - 0.0800
Rod Bearing Clearance [mm]: 0.0200 - 0.0700
(source Porsche engine specs)
Porsche 912,911, 911T,911L,911S
Main Bearing Clearance [mm]: 0.0100 - 0.0720
Rod Bearing Clearance [mm]: 0.0300 - 0.0880
(source Workshop Manual on E127)
Main Bearing Clearance [mm]: 0.0300 - 0.0880
Rod Bearing Clearance [mm]: 0.0300 - 0.0880
(source 912,911, 911T,911L,911S Spec Book)
I have not searched the rod side clearance specs for the above but doing a random search:
Rod side clearance: 0.015 - 0.025 (inches)
(source: Jim Smart Senior editor of Mustang & Ford monthly "Engine Tips - Biggest Engine-Building Mistakes")
For information 2 hairs diameter is about 2 X 0.007 inches = 0.014 inches
Based on these numbers the S65 engine main/rod bearing clearances are not out of family, they seem to fit right in with these other cars. Of course there are large differences between these cars and a whole set of parameters that would have to be adjusted for : surface harshness of main journals and bearings, surface finishing and treatment, materials, engine horsepower, max RPM, dynamic compression ratio, tune, etc. I will let the expert speak on that.
Some engines have failed indeniably something went wrong but I think attributing the problem to the clearances does not seem to add up. It may be an aggravating factor but based on other engines clearances we are not there in terms of finding the root cause.
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Great post!
Is there a way to find out what was the manufacture recommended oil that went along with these engines and include them as well? I tried looking them up but probably much slower.
I am taking a machining class right now and just last class session, it was indicated by the prof and the book that the average diameter for a human hair is 0.003 inch. I would believe this is closer to what Regular Guy had in mind when he said 2 human hair. That would make the side clearance at 0.006 which is much smaller than the average of 0.015-0.030 that I randomly searched on.