can valve stem seals lead to lack of compression?
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cbr_veze
- Settled in member
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- Joined: Thu Mar 19, 2009 8:30 pm
can valve stem seals lead to lack of compression?
ive got a chap looking at my engine at the mo, because there was little compression on cylinder 2. it was only blowing 75psi. the other 3 were at about 190-200psi.
i took the rocker cover off and he checked the tappets with a gauge, but then i had to drop the engine out because he wanted the head off. hes had a look and told me that i need a new set of valve stem seals and said something about the shims for the valves.
i took the rocker cover off and he checked the tappets with a gauge, but then i had to drop the engine out because he wanted the head off. hes had a look and told me that i need a new set of valve stem seals and said something about the shims for the valves.
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greggo
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Re: can valve stem seals lead to lack of compression?
Yes and no.
The valve stem seals won't lead to a lack of compression. The valve has to be open for the valve stem seal to be exposed to the gases etc from the cylinder. Having said that, the stem seals may well need replacing, but you usually replace the valve as well. If the stem seal is leaking it means you are getting combustion gases passing through into the head of the engine which can damage the valve stem among other things. This sometimes causes 'sticky valves' where the valve stem collects carbon deposits and sticks in the stem seal preventing it from opening and closing properly, leading to compression loss....
The other cause could be carbon build up on the valve and valve seat preventing proper sealing. This would again lead to combustion gases going up the port to the valve stem seal. Sometimes you can get away with removing the carbon deposits, other times its a new valve and seal.
It's always worth reshimming the valves when you have the head off. Although I doubt that is the reason for compression loss (it's possible one of the valves has a stetched valve stem or knife edged at the sealing surface which can contribute to compression loss). But any valve work requires new shims. But don't worry, shims are cheap!
Hope that helps you out a bit.
You can always ask the bloke to show you on the head where the problem is and explain it to you.
The valve stem seals won't lead to a lack of compression. The valve has to be open for the valve stem seal to be exposed to the gases etc from the cylinder. Having said that, the stem seals may well need replacing, but you usually replace the valve as well. If the stem seal is leaking it means you are getting combustion gases passing through into the head of the engine which can damage the valve stem among other things. This sometimes causes 'sticky valves' where the valve stem collects carbon deposits and sticks in the stem seal preventing it from opening and closing properly, leading to compression loss....
The other cause could be carbon build up on the valve and valve seat preventing proper sealing. This would again lead to combustion gases going up the port to the valve stem seal. Sometimes you can get away with removing the carbon deposits, other times its a new valve and seal.
It's always worth reshimming the valves when you have the head off. Although I doubt that is the reason for compression loss (it's possible one of the valves has a stetched valve stem or knife edged at the sealing surface which can contribute to compression loss). But any valve work requires new shims. But don't worry, shims are cheap!
Hope that helps you out a bit.
You can always ask the bloke to show you on the head where the problem is and explain it to you.
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cbr_veze
- Settled in member
- Posts: 80
- Joined: Thu Mar 19, 2009 8:30 pm
Re: can valve stem seals lead to lack of compression?
thanks very much for that, i rang them today and they said its ready to go back together, just waiting for the parts, i think he did say he was going to re shim a few or all of the valves before it goes back together, he said the bores and the pistons look ok aswell. so thats cool. i just cant wait to get it back so i can go for a ride to the coast. my mum thinks i shouldnt because she thinks it will blow up again. lol. i imagine that is highly unlikely though.