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oversized pistons for M90 engine

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janusz200
Posts: 38
Joined: Mon Mar 11, 2013 6:09 am
Location: Warsaw, Poland

oversized pistons for M90 engine

Post by janusz200 » Thu Nov 29, 2018 6:33 pm

I'm looking for +0,2mm oversized pistons for so called M90 635 CSi 1980 (3453 cm3).
QEM prod.no 11 25 1 278 112, piston dia 93,56 mm.
It's no longer available in BMW. Has anybody an experience which manufacturer still produces or where to buy?
1980 635 CSi EU
M90/L-Jetronic/manual

bpoliakoff
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Re: oversized pistons for M90 engine

Post by bpoliakoff » Thu Nov 29, 2018 7:11 pm

I had new pistons manufactured to spec by JE Pistons. in CA for approx $800. Spec being true 10:1 compression. Problem being with you in Europe you would have to send them your present piston, specify an oversize and bore your cylinders to fit. To me it is the only way to get it right. JE pistons are hi end forged pistons. Again rather than specify the exact oversize,I would add a bit and then bore to match the piston. Their pistons will come complete with rings and wrist pins. Another US manufacture of cutom pistons is Ross and well known for doing BMW pistons as well as contact VAC motor sports in Philadelphia Pennsylvania as well as Korman Auto Works. Any of the above will be able to solve your problem for sure.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

janusz200
Posts: 38
Joined: Mon Mar 11, 2013 6:09 am
Location: Warsaw, Poland

Re: oversized pistons for M90 engine

Post by janusz200 » Thu Nov 29, 2018 9:25 pm

Thank You a lot. Your advise can be really priceless. However it will take a lot of time to manage like this. So as a first I try to find ready pistons on stock somewhere here in Europe or US. I'm under time pressure a little bit. If I find something - great. If not - I'll contact both companies.
1980 635 CSi EU
M90/L-Jetronic/manual

bpoliakoff
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Joined: Thu Sep 28, 2006 9:28 pm
Location: scottsdale, arizona
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Re: oversized pistons for M90 engine

Post by bpoliakoff » Thu Nov 29, 2018 11:46 pm

Try Walloth and Nesch in Germany a real good second for original BMW parts. You can easily find them on the internet easily. Honest people to deal with and very fair pricing and quick shipping
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

janusz200
Posts: 38
Joined: Mon Mar 11, 2013 6:09 am
Location: Warsaw, Poland

Re: oversized pistons for M90 engine

Post by janusz200 » Sat Dec 15, 2018 5:23 pm

I’ve contacted Mahle – they stopped the production, nothing on stock. Kolbenschmidt even hasn’t answered the enquiry. Therefore the car part’s sellers like Pelican, Maximillian Importing Company in U.S. or Walloth and Nesch and others in Europe can’t help as well. Only way is to order custom pistons. Ross offers now for about $900 per set of 6 pistons with rings and wrist pins with snap ring. Same set at JE Pistons/Wiseco (sister companies now having common sales department) costs … $1800 here at their europe’s distributor. Hell a lot. Is it the quality difference or sales margin?

What is surprising for me – both producers recommend clearance of 0,004” (~0,1 mm) between piston and cylinder. In factory manual there’s less than half of this. Maximum allowable clearance between piston and cylinder is 0,15 mm. I’m not a specialist but it looks for me like their alloy gets higher thermal expansion than old BMW’s. Does it mean that engine is noisy being cold? Can it cause higher wear of low piston’s skirt? I suppose their pistons are very good for sport engines but not for classic car driven occasionally.

All of this and more I describe here viewtopic.php?f=2&t=30275 at Engine - Mechanical – Electrical.
1980 635 CSi EU
M90/L-Jetronic/manual

bpoliakoff
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Joined: Thu Sep 28, 2006 9:28 pm
Location: scottsdale, arizona
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Re: oversized pistons for M90 engine

Post by bpoliakoff » Fri Mar 15, 2019 9:52 pm

Hello Janusz After many years, We have finally lit my M90 engine, running JE pistons,off. I can promise you, to me at least, it is not noisy running cold. Maybe I am so excited hearing it run, I didn't enough attention, but I still do not believe it to be noisy. The valves are set at ten thousandths It does have a 284 cam and the lope is noticeable and all in all I am happy with it's sound at idle. I have not driven it yet as there are still some gremlins we are working on. I am having a hard time understanding why you can't order JE's direct from the US and have them shipped direct or to one of us and then have us forward them. It still has to be under $1000 that way. Of course providing you send them the absolute correct specs.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.

m6dave
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Re: oversized pistons for M90 engine

Post by m6dave » Sat Mar 16, 2019 2:00 am

I’m running JE forged pistons in my S38. They were supplied by Steve Nelson at Topend Performance in the US. Steve organised machining to my specs and shipped them direct to me in Australia. Nothing was a problem for Steve, service and price were excellent and product quality is outstanding. The engine block was bored to match using the JE specs and there is no problem with noise when cold. :D

janusz200
Posts: 38
Joined: Mon Mar 11, 2013 6:09 am
Location: Warsaw, Poland

Re: oversized pistons for M90 engine

Post by janusz200 » Sun Mar 17, 2019 5:48 pm

Engine parts are back from machine shop few weeks ago and now wait to be put together.
Block is done, all camshaft journals are grinded and nitrided, camshaft-rods-wlywheel-clutch assembly is balanced, cylinder head - valve guides are changed, valve seats are machined. I cross my fingers for guys in garage to put it right together.
Finally I decided to put cylinder sleeves and use original pistons. I took this decision before some people from here has convinced me that my doubts about forged pistons were not right.
bpoliakoff wrote:
Fri Mar 15, 2019 9:52 pm
... I am having a hard time understanding why you can't order JE's direct from the US and have them shipped direct or to one of us and then have us forward them. ...
The honest answer is – I haven’t get this idea… :oops:
1980 635 CSi EU
M90/L-Jetronic/manual

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