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How To Prepare Thermostat Mating Surface


Best Answer zero_wlv , 02 August 2020 - 02:05 PM

Thanks everyone for the advice,  it's sorted now (sort of,  for the time being anyway).

 

I spent a while sanding down the cylinder head surface with a block of 120 wet and dry.   And then with a whetstone.  It didn't seem to be taking much material off so the area around the third stud hole still looks very marginal,  but it might have helped.

 

I used Hylomar Blue on both mating surfaces and left it to evaporate for half an hour before assembling (unlike rushing it like I did before).   I also made sure there was plenty of sealant around the dodgy stud hole.

 

I used a thick cork gasket instead of the skinny blue paper ones I've always used before - might have helped.

 

I also used studs - I found the joint much easier to assemble neatly compared to the bolts I had before.

 

 

After the first 1 mile run there was a fair bit of leakage out of exactly the same place  :ohno:   - the top of the third bolt  -  which is why I'm still a bit dubious that the seal might be on a bit of a knifeedge and might suddenly fail in the future    (I was actually about to tear it apart and have yet another attempt!)

Getting the engine up to temperature must have sealed the joint though as it's been perfect since and has been on a 35 mile high speed run and stayed bone dry.

So fingers crossed,  it'll stay that way!

 

I'm sort of wishing I'd been even more persistent with the wet and dry but not sure it was making much difference anyway.

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#16 madaboutcherry

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Posted 28 July 2020 - 11:24 AM

i think the indent on the gasket is for 11 stud heads.



#17 gazza82

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Posted 28 July 2020 - 04:19 PM

I Only use loctite blue sealant these days to fit thermostat housings, dont use a gasket anymore. I'd go over that with an oilstone first though

Or a diamond plate .. small playing card sized one worked wonders for me on a slightly corroded ali head! I filled the worst holes with a metal putty then polished it flat ..



#18 zero_wlv

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Posted 02 August 2020 - 02:05 PM   Best Answer

Thanks everyone for the advice,  it's sorted now (sort of,  for the time being anyway).

 

I spent a while sanding down the cylinder head surface with a block of 120 wet and dry.   And then with a whetstone.  It didn't seem to be taking much material off so the area around the third stud hole still looks very marginal,  but it might have helped.

 

I used Hylomar Blue on both mating surfaces and left it to evaporate for half an hour before assembling (unlike rushing it like I did before).   I also made sure there was plenty of sealant around the dodgy stud hole.

 

I used a thick cork gasket instead of the skinny blue paper ones I've always used before - might have helped.

 

I also used studs - I found the joint much easier to assemble neatly compared to the bolts I had before.

 

 

After the first 1 mile run there was a fair bit of leakage out of exactly the same place  :ohno:   - the top of the third bolt  -  which is why I'm still a bit dubious that the seal might be on a bit of a knifeedge and might suddenly fail in the future    (I was actually about to tear it apart and have yet another attempt!)

Getting the engine up to temperature must have sealed the joint though as it's been perfect since and has been on a 35 mile high speed run and stayed bone dry.

So fingers crossed,  it'll stay that way!

 

I'm sort of wishing I'd been even more persistent with the wet and dry but not sure it was making much difference anyway.


Edited by zero_wlv, 02 August 2020 - 02:06 PM.





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