Thread: 2.25 Petrol Valve Stem Seals

Valve stem seals aren't there to seal in the compression. They stop oil running down the valve stems.

One common symptom of valve stem seals that need replacing is a cloud of smoke when you start up after the vehicle has been sitting for a while.

It could be the valves themselves though.
Relatively easy job to remove the head, remove the valves and regrind them, new seals and head gasket.
Good job for a Saturday morning.
Make sure you have a decent valve spring compressor though.
Phil

As vnx says - valve stem seals are irrelevant for compression.

When you say the compression is "pretty low", what numbers are we looking at? And how even are they?

Rings tend to be fairly uniform between cylinders, where more variability is expected from valves, as valve seat sealing will usually get worse very rapidly, at least on exhaust valves, so cylinders are less likely to be uniform.

John

From memory a 2.25 litre 7:1 comp motor should read 110-120lb but will run smokeless at as low as 85lbs,if all are about the same then it could be that they are all worn out,if the motor has 4 ring pistons (2 oil rings) I.E. 2nd oil ring at bottom of piston then it won't burn oil,but still be very weak,I would suggest you lift the head,and shout it a new set of rings providing the bore is not scoured

You will need,1 VRSH kit,1 Sump gasket set,and when you clean the piston tops to read the bore size 1 set of rings to suit just as simple as doing a small stationary motor

cheers

BTW.the other thing could worn valve guides as compression will escape that way,they are sintered bronze and are replacable,and can be bought in sets, worn valve stems can add to the problem as well.

Originally Posted by UncleHo

From memory a 2.25 litre 7:1 comp motor should read 110-120lb but will run smokeless at as low as 85lbs,if all are about the same then it could be that they are all worn out,if the motor has 4 ring pistons (2 oil rings) I.E. 2nd oil ring at bottom of piston then it won't burn oil,but still be very weak,I would suggest you lift the head,and shout it a new set of rings providing the bore is not scoured

You will need,1 VRSH kit,1 Sump gasket set,and when you clean the piston tops to read the bore size 1 set of rings to suit just as simple as doing a small stationary motor

cheers

BTW.the other thing could worn valve guides as compression will escape that way,they are sintered bronze and are replacable,and can be bought in sets, worn valve stems can add to the problem as well.

hi uncle i have the parts for your brakes and drums for you and s3 screen and they are free jim

Originally Posted by UncleHo

....

BTW.the other thing could worn valve guides as compression will escape that way,they are sintered bronze and are replacable,and can be bought in sets, worn valve stems can add to the problem as well.

Valve guide/stem wear cannot (directly) result in low compression - the seal between the valve stem and guide is not under pressure from the cylinder. The inlet ones are below atmospheric, which is why leaky seals suck oil into the manifold and hence cylinder, and the exhaust ones are under pressure during the exhaust stroke but not compression. There is some possibility that worn stems and guides will result in poor seating, but rather than directly resulting in low compression this is more likely to result in damaged seats and valves, which then result in low compression.

John

Has anyone ever changed a valve stem seal without removing the head? I have one leaky valve seal, I spotted it when I removed the manifold (oil in number 4 exhaust that is not coming out of the cylinder). Smoke on startup is annoying!

If it was an aeroplane engine I would partly fill the cylinder with rope threaded through the spark plug hole and then turn it up towards top dead centre till the rope was compressed against the valves then use a valve compressor that held against the rocker shaft. It is an easy job on a big engine with big valves and soft springs.

Is this ever done in cars? Is there any oil additive that might work? I am reluctant to pull the head off an otherwise lovely engine.

If its a SIIa the seal is an O ring in the valve guide part way down the valve stem, to replace the seal you have to remove the valve and that requires taking the head off. Even the SIII seals which are a cap require you taking the valve springs off and to do that you need to compress the springs to refit the collets. Usually a head off job, but your rope may work.

Cookey machines the six cylinder inlet valve guides to use caps similar to the SIII 4 cyl type