oversized pistons for M90 engine

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janusz200
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oversized pistons for M90 engine

Post by janusz200 »

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?
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bpoliakoff
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Re: oversized pistons for M90 engine

Post by bpoliakoff »

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
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Re: oversized pistons for M90 engine

Post by janusz200 »

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.
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Re: oversized pistons for M90 engine

Post by bpoliakoff »

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
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Re: oversized pistons for M90 engine

Post by janusz200 »

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.
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Re: oversized pistons for M90 engine

Post by bpoliakoff »

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.
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Re: oversized pistons for M90 engine

Post by m6dave »

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
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Re: oversized pistons for M90 engine

Post by janusz200 »

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:
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janusz200
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Re: oversized pistons for M90 engine

Post by janusz200 »

OK, engine was fantastic for first 5000 km (~3000 miles). The honeymoon has been finished after about 15 miles on highway at speed of 150 km/h. Engine… seized. Started from 1st cylinder (see the photo), than went to 2nd (looks a little better than 1st), 3rd better than 2nd, 4th looks good. Cooling system was OK. Pistons/cylinder was mounted with clearanece of 0,04 mm. I thing it was too tight.
tlok 1_08-2019.jpg
tlok 1_08-2019.jpg (71.68 KiB) Viewed 13746 times
Anyway, I’ve bought another engine. I havn't measured it yet but looks like it has to be machined to 1st or 2nd oversize. I’m looking now for new casted pistons. Original Mahle etc are no longer available – who is producing custom casted pistons? I’ve heard something good about hypereutectic pistons - kind of Alu alloy with low thermal expantion due to high content of silica. Does anyone has some experience with this stuff? Where to order them?
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Pasocb
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Re: oversized pistons for M90 engine

Post by Pasocb »

It appears that someone confused imperial and metric measurements at the machine shop.
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Re: oversized pistons for M90 engine

Post by jps635 »

Sorry to see didn't go well.

The issue could be wit the block machining, the pistons or both

I don't know a lot about engine machining but what I learned rebuilding my engine was as well as the piston to wall clearance the honing is also critical - using the correct honing stone and speed to produce the right cross hatching and finish for the pistons and rings.

When I was considering forged pistons i came to the conclusion hypereuectic were best for a street engine. I think all the main manufacturers would offer these, I know Wiseco and JE do.

I would recommend talking to your engine builder such that he makes the recommendations, sources the pistons and takes responsibility for the finished engine, else you'll be the jam in the sandwich.
'85 635csi JPS (RA2-66)
janusz200
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Re: oversized pistons for M90 engine

Post by janusz200 »

:D looks like.
(this was the answer to Pasocb post)
Last edited by janusz200 on Sat Jan 25, 2020 11:48 am, edited 1 time in total.
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bpoliakoff
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Re: oversized pistons for M90 engine

Post by bpoliakoff »

As Jeff says, let the engine builder order them. I say JE is the way to go. The cross hatching done by honing only affects ring seating and wear providing everything else is sized right to begin with.
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
flickr.com/photos/bertsphotos.
janusz200
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Re: oversized pistons for M90 engine

Post by janusz200 »

You're right I should let the engine biulder to decide and I did so. I'm also checking from my side the pistons' producers. But final decission will be done by specialists, not me. JE refused to offer saying they have only forged with 2618 alloy. As far I know Wiseco joined with JE. CP Carrillo can cast custom hypereuthectic pistons but purchasing is possible via VAC Motorsports.

Machine shop is doing their job since decades and they machine more than thousand engines per year - for motorsport as well as for trucs. Wrong measuring, bad honing etc is was not the reason rather.

Thank you for all your comments and advises - each one is helpful for me so I'm waiting for more.
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bdorey
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crankshaft for M90 engine

Post by bdorey »

I wonder where I could get a used crankshaft for my M90? The threaded end of mine broke off. Otherwise, the motor ran great with oversize JE pistons, a 284 cam, 320i intake runners and a 3.73LS diff. I want to get my car back on the road but can't find a crankshaft. Also, will an M30B35 head work on this block? Thank you for any guidance.
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Re: crankshaft for M90 engine

Post by Ralph in Socal »

bdorey wrote: Thu Mar 19, 2020 10:39 pm I wonder where I could get a used crankshaft for my M90? The threaded end of mine broke off. Otherwise, the motor ran great with oversize JE pistons, a 284 cam, 320i intake runners and a 3.73LS diff. I want to get my car back on the road but can't find a crankshaft. Also, will an M30B35 head work on this block? Thank you for any guidance.
I have one but I have to make sure I will not need it for my M90. My motor had an oil pump problem so rod bearings took a beating

B35 head will work but compression will be reduced as the B35 chamber is supposed to be larger. How much larger I’m not sure. Good luck

Ralph
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crankshaft M90 engine

Post by bdorey »

Thanks for the reply. Sorry about your oil pump problem. Keep me posted on the crankshaft situation. The M90 is a bit of a unique motor. Mine's a transplant from a 1980 E24 Euro and plopped into my 1979 E12.
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Re: oversized pistons for M90 engine

Post by bdorey »

Oh yeah, thanks for the info on the B35 head. Kind of thought that. I suppose it could be machined. Or maybe I should plop an M30B35 motor into my E12.
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Re: oversized pistons for M90 engine

Post by Ralph in Socal »

Use the B35 exhaust manifolds and downpipes as well since they are part of the upgrade to get above 200hp. B35 exhaust is dual 2 inch all the way out

I have heard the M90 exhaust is an upgrade over the B34 M30 but I am not informed well enough on that

Ralph

PS - you face a steep hill with the crankshaft. Same unit used for the M88
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Re: oversized pistons for M90 engine

Post by bpoliakoff »

M90 is 2"
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
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Re: oversized pistons for M90 engine

Post by jps635 »

The threaded end of mine broke off
Curious as to how this would happen?
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bdorey
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broken crankshaft

Post by bdorey »

Good question. I was driving relatively normally and heard a crack and thought I had driven over something. Then my battery light came on and the power steering stopped working so, of course, I pulled over. The crank hub and pulley were on the road and the threaded end of the crankshaft was broken off and missing. My mechanic has never heard of this happening. Rather upsetting, as the motor with it's upgrades of a few years ago was running great. I'm debating to find and install an M90 crankshaft and new bearings or to drop in an M30B35 motor as I love my old E12. I've had a couple of E24s, E28s, E30 etc. I'd like to find another E24 5spd and there are a few out there still.
Thanks.
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M30B35 vs M90

Post by bdorey »

Thanks Ralph for the good replies. I think I'm leaning towards the M30B35 engine/wiring harness transplant as there is one locally available in a 1991 BMW 535i 5pd.
and which means I'll have some left over M90/M30 parts.
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Re: oversized pistons for M90 engine

Post by Ralph in Socal »

bpoliakoff wrote: Fri Mar 20, 2020 2:53 am M90 is 2"
Thanks Bert. If anyone has an M90 exhaust manifold on a shelf please send/post a couple of pictures. B35 manifold design allows for each exhaust “pulse” to sit in a pocket of the manifold before flowing through to join the rest of the exhaust

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Re: oversized pistons for M90 engine

Post by bpoliakoff »

I have one Just have to remember where I "threw" it Not sure if I have the pair. They are getting major hard to find. Years ago I had a set from Metric Mechanic that were really hogged out at he the collector. However you guys are off on this. The early euro cars, and mine was original, and I have also seen original new down pipes are roughly 1 3/4" coming off the manifold at the collector for about 6". From there they go into 2" tubes. The Metric Mechanic manifolds were hogged out to 2" at the collector with a "ball" end mill allowing 2" pipes from the manifolds back. Gere Stahl's' Headers which were the gold standard for long tube headers came in three diameters and for a street motor or mildly warmed motor he recommended basically the
1 5/8" primary tubes to the collector as it did affect low end torque and then you could come off them with the 2" or what ever you wanted .. So coming off the motor with 2" tubes to the collectors as most headers are now is really eye candy and not a big performance boost, although there is some and that is why the early manifolds really do what they are supposed to do
81 Euro 635 M90 with motronic. Currently under a complete nut and bolt restoration. Pictures at
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