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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I converted the data above to a similar table that I used on the front page. One important note: none of the journal diameters are listed in the other engine specs. Without that data, their clearance specifications don't mean very much. But I decided to convert the data anyways so we could see how the S65B40 compares to other engines even if we don't know their journal sizes.
Now, before anybody wants to messenger, let me explain this. All I did was calculate the midpoint as "nominal" bearing clearance and did a very quick internet search to find the factory recommended oil. I took the first thing I could find. In the case of the Porsche, I found a factory manual online; and same for Ferrari 328. For the others, I found other internet postings that talked about factory oil specs.
For S65B40, I also used the midpoint method to calculate nominal bearing clearance even though we know that's not correct. The actual nominal clearance values are those I posted in the first post and were determined by looking at two cranks and two sets of rods and selecting the values that came up the most often. For reference, actual nominal S65B40 is:
Main Bearing Clearance: 0.03650 mm, 0.00144"
Rod Bearing Clearance: 0.03250 mm, 0.00125"
The point is: let's not roast the messenger. The idea is to make the data as accurate as possible without bias or agenda. If somebody finds more accurate data, I'll refine and revise the list. I will also add more engines to the list should the data become available:
| Min (mm) | Max (mm) | Nominal (mm) | Min (inch) | Max (inch) | Nominal (inch) | Oil Type |
| S65B40 Main (actual) | 0.02910 | 0.04580 | 0.03650 | 0.00115 | 0.00180 | 0.00144 | TWS 10W60 |
| S65B40 Rod (actual) | 0.02930 | 0.04690 | 0.03250 | 0.00115 | 0.00185 | 0.00125 | TWS 10W60 |
| S65B40 Main (midpoint) | 0.02910 | 0.04580 | 0.03745 | 0.00115 | 0.00180 | 0.00147 | TWS 10W60 |
| S65B40 Rod (midpoint) | 0.02930 | 0.04690 | 0.03810 | 0.00115 | 0.00185 | 0.00150 | TWS 10W60 |
| Ferrari Mondial 8/QV Main | 0.02900 | 0.06400 | 0.04650 | 0.00114 | 0.00252 | 0.00183 | Agip 10W50 |
| Ferrari Mondial 8/QV Rod | 0.04600 | 0.08900 | 0.06750 | 0.00181 | 0.00350 | 0.00266 | Agip 10W50 |
| Ferrari 328 GTS Main | 0.01300 | 0.05100 | 0.03200 | 0.00051 | 0.00201 | 0.00126 | Agip 10W40 |
| Ferrari 328 GTS Rod | | | | | | | Agip 10W40 |
| Porsche 924 Main | 0.02000 | 0.08000 | 0.05000 | 0.00079 | 0.00315 | 0.00197 | |
| Porsche 924 Rod | 0.02000 | 0.07000 | 0.04500 | 0.00079 | 0.00276 | 0.00177 | |
| Porsche 912,911, 911T,911L,911S Main | 0.01000 | 0.07200 | 0.04100 | 0.00039 | 0.00283 | 0.00161 | Mobil 0W40 |
| Porsche 912,911, 911T,911L,911S Rod | 0.03000 | 0.08800 | 0.05900 | 0.00118 | 0.00346 | 0.00232 | Mobil 0W40 |
| Porsche 912,911, 911T,911L,911S Main | 0.03000 | 0.08800 | 0.05900 | 0.00118 | 0.00346 | 0.00232 | Mobil 5W40 |
| Porsche 912,911, 911T,911L,911S Rod | 0.03000 | 0.08800 | 0.05900 | 0.00118 | 0.00346 | 0.00232 | Mobil 5W40 |