Author Topic: Low compression when cold, ok when hot  (Read 1829 times)

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nick7nick7

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Low compression when cold, ok when hot
« on: November 22, 2018, 07:03:09 PM »
I have a 90 Bis.
Its impossible to start from cold, due to low compression on cyl1 circa 12psi. However, when warm (20c+) the compression measures 122 psi. cyl2 is constant at 126psi

Any suggestions what or how to fix it?
I think it could be piston rings. But im not mechanic.

Gadge

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Re: Low compression when cold, ok when hot
« Reply #1 on: November 22, 2018, 07:33:49 PM »
Hi nick, BIS engines LOVE eating head gaskets. I've taken heads off and the old gasket just falls apart between my fingers so I would be suspecting that this has happened to yours, although not as drastic as the one I last did. I think the reason it regains its compression is because as the engine warms up all the components expand due to the heat and it effectively re-seals itself so perhaps a pin hole sized hole has appeared. There are fluids you can use like K-Seal which works like radweld and seals the hole after you've emptied it into your water system but to be honest if a jobs worth doing it's worth doing right so I would opt for getting the head gasket done. It's actually rather easy and well within the relms of a diy-er to do
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nick7nick7

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Re: Low compression when cold, ok when hot
« Reply #2 on: November 30, 2018, 09:42:25 PM »
Cheers for that gadge. I recently had the head skinned and pressure treated.
Not done a hundred miles since.

Do you have any idea where I can get one of the copper ones? Or is it a case of making my own?

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nick7nick7

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Re: Low compression when cold, ok when hot
« Reply #4 on: December 01, 2018, 07:29:53 AM »
Cheers matey, not heard of that first shop.

Will it still eat away at the copper ones like it does with the cork version I got last time?

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Xylaquin

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Re: Low compression when cold, ok when hot
« Reply #5 on: December 01, 2018, 10:05:01 AM »
Hopefully not, though if your head gasket was made of cork I have a theory what your problem has been  :o

nick7nick7

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Re: Low compression when cold, ok when hot
« Reply #6 on: December 01, 2018, 10:08:01 AM »
Hopefully I'll get it striped tomorrow and see.
Dependant on the weather.

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dajwid

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Re: Low compression when cold, ok when hot
« Reply #7 on: December 01, 2018, 08:39:43 PM »
Are you thinking of rocker gasket or head gasket ??

Cheers matey, not heard of that first shop.

Will it still eat away at the copper ones like it does with the cork version I got last time?

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nick7nick7

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Re: Low compression when cold, ok when hot
« Reply #8 on: December 01, 2018, 08:55:17 PM »
Head gasket


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