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Big bore M90 - any reasons not to remove head ?

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Big bore M90 - any reasons not to remove head ?

Post by jeme9 » Wed Jun 13, 2018 11:54 am

I bought an M90 (to go in e9), background largely unknown except it apparently has not been used for about 10 years.
Inspection of bores and big end bearings (from sump) and overhead from rocker cover, appear to show good condition.
However compression test does not show numbers I would like (160 psi) euro spec engine - maybe needs running to free rings.

I have been told by two sources tp just install engine and run it ("don't disturb things and cause issues"), however as I have a head gasket, I wonder if I should remove head and check gasket and head before installing in car.

My question:
is there any real reasons why NOT to remove head (considering I already have gasket and valve guides) and engine is out of car ? thanks

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Re: Big bore M90 - any reasons not to remove head ?

Post by Pasocb » Wed Jun 13, 2018 12:42 pm

I am sure others will chime in here but I would at least run a leak down test to determine if compression gasses are leaking past the rings from sitting as you mention or the valves. These engines are succeptical to head gasket failure due to their siemesed cylinders and misstreatment. I have a couple in my shop right now because of this. Your engine may be fine. Really comes down to a judgment call on your part and where you are with your project. Let us know what you end up doing and how the engine runs in the end.
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Re: Big bore M90 - any reasons not to remove head ?

Post by Brucey » Thu Jun 28, 2018 11:29 pm

I would check the ring leakage by adding oil, install the engine and run it for a while, then test it again.

You can pull the head very nearly as easily with the engine in situ so there is not much loss in doing it this way, but you will feel a bit daft if the block needs a skim I suppose.

BTW because the M90 bore size is different the head gasket is not the usual M30 one, but I guess you know that already.


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