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850 headgasket post mortem

Brendan W

Brendan W

Forum Sage
Past Site Supporter
This is the old headgasket. I don't know how old it is but I have done 9000 miles on it and it's been leaking for half of that time, bubbling out between 1 and 2. The view is the bottom side and it had the narrow side of the fire ring against the deck. There were four aluminium washers at the corners. One of the riser gallery seals was pinched but the base gasket was fine. The chain tunnel o-ring was in place but hard as glass as were the base ring seals. The head and barrel came off with almost no effort. The deck cleaned up really well with kerosene and acetone and a sharp scraper. The base area has had abuse but was sealed ok. I did find a lot of what looked like sealer in the groove between the liners and the deck. Do people use gasket sealer going back?
Would anyone care to comment on the condition or origin of the headgasket ? The pistons seem remarkably good for 48000 miles. Seven of the stem seals are leaking and there was oily crud up to 0.080" thick in places in the combustion chamber. Valves seem tight. Poured kero/acetone in there and was still all there an hour later.

 
48K? Seriously, you have another 100K left on them at least. I took my '79 apart at 140K and the pistons and bores looked like they'd just come out of Hamamatsu last week.
Re-reading your post, are you saying it's been apart before, from traces left behind? Might be time to check the flatness of the head and barrels.
 
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I reckon it has been open. Cracked fins in the usual pry points and the shims are all in the 2.1 - 2.5 range and I have stainless mount brackets.
The filter cover is black and I suspect came from another motor. There are old cam chain groves under the cam cover. I got the bike at 38k.
Am I right in thinking the wide side of the fire ring should have been against the deck ?
 
Brendan W said:
I reckon it has been open. Cracked fins in the usual pry points and the shims are all in the 2.1 - 2.5 range and I have stainless mount brackets.
The filter cover is black and I suspect came from another motor. There are old cam chain groves under the cam cover. I got the bike at 38k.
Am I right in thinking the wide side of the fire ring should have been against the deck ?
Click to expand...
I honestly do not recall for sure, but that rings a bell.
 
Brendan W said:
Manual seems to agree. Any thoughts on extra sealing around the chain tunnel o-ring like threebond.
Click to expand...

Smear of Hylomar always does it for me, most especially at the verdammt front left corner of the base gasket oil passage.
 
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