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500 Sport Crankshaft dimensions

Posted: 22 Mar 2021 11:02
by Bedfordowner
Hi All,
I have a crankshaft that I believe is from the 478 engine. Does anyone know the nominal dimensions of the big end and mains please. It is unused by the looks of it so should be standard size. I checked the blue manual but could not see the dimensions. Hope you can help, thanks

Re: 500 Sport Crankshaft dimensions

Posted: 22 Mar 2021 17:48
by morini_tom
I put a brand new 500 crank on the CMM at work a few years back... Unfortunately I'd already had the main bearing ground for a roller at that point so cannot confirm new nominal right hand side main bearing size however:

LHS main bearing (the split 4 point angular contact) crank journal: 32.995mm from the CMM measurement

Big end journal: 34.994mm from the CMM measurement

so nominals 33 and 35mm

An interesting CMM measurement was that the torqued up conrod big ends without shells are 38.11mm (1.5")... A casual measurement may mislead you into thinking big end shells should be 38/35mm but they actually need to be 1.5"/35mm, which I suspect is part of the reason they are so difficult to get.

A very approximate measurement I've just done with vernier calipers of a low mileage original main bearing shell still in its housing gives me 46.4mm, which would suggest a new crank between 46.375 and 46.355mm going on the quoted clearances in the blue book.

Re: 500 Sport Crankshaft dimensions

Posted: 22 Mar 2021 18:25
by Bedfordowner
morini_tom wrote:I put a brand new 500 crank on the CMM at work a few years back... Unfortunately I'd already had the main bearing ground for a roller at that point so cannot confirm new nominal right hand side main bearing size however:

LHS main bearing (the split 4 point angular contact) crank journal: 32.995mm from the CMM measurement

Big end journal: 34.994mm from the CMM measurement

so nominals 33 and 35mm

An interesting CMM measurement was that the torqued up conrod big ends without shells are 38.11mm (1.5")... A casual measurement may mislead you into thinking big end shells should be 38/35mm but they actually need to be 1.5"/35mm, which I suspect is part of the reason they are so difficult to get.

A very approximate measurement I've just done with vernier calipers of a low mileage original main bearing shell still in its housing gives me 46.4mm, which would suggest a new crank between 46.375 and 46.355mm going on the quoted clearances in the blue book.
Thank you so much for all the details. Really helpful. I will be able to measure it against some knows now. I have two of the plain bearings that are unused but haven't measured them or tried them on the crank yet as still sorting some bits out. I do not have any of the other case bearings as the cases are completely bare so will need to sort that next particularly the crank bearings. Thanks again for your help.

Re: 500 Sport Crankshaft dimensions

Posted: 22 Mar 2021 23:26
by simonnorthroad
I know a genuine 633250C/C3 main bearing sold on Ebay for £250 recently, and I sold a genuine SKF new-old-stock one for £200 a while back, with no chance of replacing it
The clutch mainshaft bearing is similarly hen's teeth
Mdina doesnt have any in stock

Re: 500 Sport Crankshaft dimensions

Posted: 23 Mar 2021 16:26
by harrymuffin
I know where you can get some from as SKF told me they are not interested in making or modifying any bearings to fit this application.

Re: 500 Sport Crankshaft dimensions

Posted: 23 Mar 2021 18:05
by EVguru
The Germans seem to be grinding the drive side crank journal down to 30mm (same as the 350) and then using a standard QJ306 FPAC (four point angular contact) bearing. I've also seen the 350's plain deep grove ball race used, apparently without problems. It's a pretty generously sized bearing in the first place. The inner races can be ground out to 33mm, Vintage Bearing for example can do it. It could even be done in an an accurate lathe if set up correctly and using a toolpost grinder.

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