-
Hey Guest!
British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!**Upgrade Now**
(PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
The Head Gasket
- Thread starter DNK
- Start date
Share this page
Darrell_Walker
Jedi Knight
Offline
When I changed mine last year, the consensus was dry.
Do the composite gaskets crush? Not sure I would reuse any head gasket, other that perhaps solid copper.
Do the composite gaskets crush? Not sure I would reuse any head gasket, other that perhaps solid copper.
Darrell_Walker
Jedi Knight
Offline
DNK said:
I would never reuse the steel TR8 head gasket, as it it meant to crush when installed.
The more typical composite-sandwich type may be OK, but given the effort to get the heads off on the TR8, I wouldn't risk having to redo it. I don't think it would try to reuse the valley pan gasket, either (and that was much more expensive than the steel head gaskets).
Darrell_Walker
Jedi Knight
Offline
DNK said:
Wow!
Darrell_Walker
Jedi Knight
Offline
DNK said:
Oh, OK.
I would never reuse a head gasket. A local reputable engine builder had a problem with a stroker Rover V8 he had just built for a buddy of mine. The newly built engine was on the dyno and the gapless rings were causing negative crankcase pressure. He pulled the whole thing apart, bought another set of new forged pistons slightly more oversized, steel rings, and a new set of Cometic head gaskets. Point is the builder wouldn't reuse the gaskets which cost around $250 a set and he was the one standing behind the work and he was footing the bill. Engine has been in the car for a few thousand miles and so far it runs smooth and powerful with no blow by.
Something about the rings sealing when under pressure but not sealing on the downstroke under negative pressure. I didn't buy that explanation at first either, but the builder rebuilt the engine at his expense and all seems well. The folks from gapless rings told him to go back to steel rings.
Offline
Interesting. Perhaps someone can enlighten us. At the risk of straying somewhat off the topic, my 92 BMW is designed to run with negative crankcase pressure. (I cracked the oil pan at a road construction site once and drove the car fifty miles. It didn't leak much at all until I shut it off and then it drained like I pulled the plug.)
Tom
Tom
I would assume your BMW engine has a PCV hooked up to manifold vacuum. This Rover engine had nothing hooked up to it while it was getting broken in on the dyno. At first everyone was like cool no engine blowby. Then they realized the engine was consuming oil and there was actually a small vacuum being created that you could feel when you put your hand over the oil filler. Rover V8s are known to have blowby or positive crankcase pressure. The amount of blowby is determined by who built the engine, how it was built and what parts they used. The engines with really big cams that wash lots of fuel down the cylinder walls at idle seem to fair the worst as the rings never seat well and the crosshatching on the walls gets worn away. Many of the guys with the 4.6L and up engines are using a vacuum pump to draw out excess pressure and also to create vacuum for the brake booster. That is if they are using a big overlap cam that doesn't make much vacuum. Somehow negative crankcase pressure makes more HP, but the biggest advantage is not spitting out oil pan gaskets and dipsticks every time you romp on it.
TomMull said:
I don't know for sure but it seem to me that the neg pressure would be created by the PCV valve and there is no reason that the pressure can't be set for whatever the manufacturer thinks is desirable by balancing the amount of air sucked from the crankcase with the total blowby, leaks, outgassing.... if there is more sucked out then the pressure is going to go negative.
