2.25 Petrol Valve Stem Seals

[Series3 GT]

Hi all, I'm looking to replace my valve stem seals in my IIA, I've done a compression test and she's pretty low but its not the rings cause the reading didn't go up with oil in the cylinders, so I'm guessing valve stem seals are one of the culprits, it could also be the valve seats too. It's not a road vehicle so I'm not looking to spend massive money on it she's just a farm ute. Just looking for opinions on whether it's worth it or if it's the seats or valves themselves.

[vnx205]

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.

[Phil B]

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

[JDNSW]

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

[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.

[russellrovers]

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

[JDNSW]

....

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

[Aussie Bob]

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.

[Lotz-A-Landies]

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

[Blknight.aus]

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.

where do you think areo engine mechanics learnt the trick from? rocket surgeons?

ok sarcasm aside, yes, I wouldnt even bother with rope, roll the engine till the valve is compressed, lockwire lash the valve compressed, plug out, engine to 20 degree btdc on comprerssion, fill with engine oil till the oil comes back out of the plug hole, wind the spark plug back in. maintain effort on the crank handle rocker gear off collets out lift the cap and spring assembly, pull the seal, replace and reverse the rest. oil syringe the oil out as best you can, wad cover the vacant plug hole, wind on the starter, clean the plug, start, let it run on 3 pots for a bit till it stops blowing lots of mist, stop plug in restart.

for the II/IIA use a section of un reinforced fuel hose thats a tight fit over the stem lasts about 5-8K Km.

try running a slightly thicker engine oil or old engine formula, a cup full of 80/90 or 85/140 can help in the short term.

[Aussie Bob]

Great post Dave, and I love a bit of sarcasm. Never thought of a hydraulic lock. It is a Series 3 BTW, I dug out this thread rather than start a new one.

[101 Ron]

I do this sort of stuff all the time.

What's wrong with using compressed air on TDC and universal umbrella rubber valve stem seals.
Using umbrella seals it doesn't matter if O rings are all ready fitted further in the valve guide.
The only draw back to using compressed air is you need to stick a bar or screw driver in the ring gear to stop the motor moving from TDC.
If you don't have a cylinder leak down adaptor to to add compressed air to the cylinder, one is easily made using a old sparkplug.
While the compressed air is in the cylinder.......ie cylinder leak down test, it is the best way to check ring and valve condition.
Good way to check out the head gasket and other stuff doing it this way, and no oil , no mess.
Umbrella valve steam seals can be purchased from any engine reconditioner very cheaply and one size fits most engines.
Many a time I have made money buying a supposedly stuffed motor in a vehicle and fixed the valve stem seals in situ and resold as the motor stopped burning oil.
Ron

[Blknight.aus]

compressed air will work just as well, BUT..

not everyone has an adaptor to get the compressed air reliably on the cylinder through the plug hole and if you tap it just a little bit to hard trying to get the collets in you can drop the valve. against oil with the crank being held in the "apply force" direction the viscosity of the oil means you have a little more wiggle room if you push a little to hard.

you also may not have it on the side of the road.

that said.

Ive used

rope, shoelaces, paper, water, oil, diesel, compressed air, strips of rag, and just to proove it could be done (and we had to pull the head anyway so no loss if I got it wrong) nothing inside the cylinder.

[Aaron IIA]

Try using this style of valve spring compressor.

http://pages.ebay.com/link/?nav=item.view&id=140402538477

Aaron

[harry]

I'd indian rope it like we do on aircraft engines, lots easier than all that messing with oil and stuff.


but we all have missed the point here, where did his compression go?
on aircraft engines we do not do a battery condition test type compression check, but do a differential test where we set the cylinder on top dead comp stroke and then introduce compressed air and read the leakage on a gauge set,
no need to mess around like that for your car engine, but on the cylinder you think is crook, set it on tdc comp stroke, pump compressed air in through your plug hole and listen at the oil filler cap, exhaust and carby top to hear the air escaping.
this will tell you where the compression leak is.
there will always be air escaping past the rings which you will hear at the oil filler cap, any air at the exhaust or carby indicates a valve leak.
also check your valve /tappet clearances, at tdc, If I remember correctly , you should have .008 in clearance.
if the tappet clearance is nil, that might be a reason for the valve leaking.

[Aussie Bob]

Good to see another aircraft man Harry! My valve is not leaking, just letting oil past its stem seal. This was apparent when I removed the manifold to replace broken studs.

BUT! After running this engine a bit and going for a drive the problem is not nearly as bad as it seemed. Sitting around for a decade may have something to do with the leak, using the engine seems to be reducing it so for the time being I am leaving it.

There is a heap of good information in this thread and I thank the contributors. If I do the job I think I will first use clean nylon cord. Air sounds great but I lack the fitting and the resolve to either make one or hunt one down. Oil sounds great to me and would certainly make a strong hydraulic lock, but the mess would **** me off.

Thanks for the link Aaron, that does look like the tool I am after and for the cost, well worth buying.

[chaybra]

Just my opinion, but would it not be easier to pull the head for the cost of a head gasket? seems like a lot of effort to go though with the 50% chance of having to pull the head anyway.

[vnx205]

Disclaimer: I have no idea whether this actually works. It may fall into the same category as Hiclones and flux capacitors.

I was told years ago that some oil additives have a component that slightly softens seals that have become hardened with time.

If such additives actually exist and if they actually work, your situation might be exactly the sort of problem they are designed to cure.

[Blknight.aus]

actually true, also available as additives.

however.

once you remove the additives the situation is almost always worse than before, so treat it as a one stop just to get you to the next service fix.