Valve stem seals

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vik351

Valve stem seals

Post by vik351 »

My E24 3.5 smokes like buggery when pushing it a bit in the hills,but on deceleration only,on the move it is fine.

Have been told this is hard valve stem seals,can they be changed with out removing the head,single overhead cam motor...???

vik... 186,000 miles 1979... dog leg Getrag gear box...
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Brucey
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Post by Brucey »

in answer to your question 'how'; I've done this job on other engines but not an M30. I've looked at it though, and this is how I would try;

First comment is that there are plenty of reason why the head should come off anyway; a bad valve seat or something, so do a leakdown test if you are in any doubt. But even if the guides are worn, it would have to be very bad indeed (past top limit) to necessitate head removal (although granted, new guides might be the best thing in the long run...)

One cylinder at a time:

You need to be able to stop the engine at BDC with both valves closed, and be able to attach a reliable compressed air supply to the cylinder with about 100psi to it. This will need a special adapter which you will either have to rob from a compression tester or make from an old spark plug. The compressed air holds the valve shut; this is necessary to allow the collets to be removed and it also stops the valve from dropping into the cylinder on paralell valve engines. On this engine it may not be possible to lose the valve altogether but you don't want to find out the hard way.

Now slide the exhaust rocker and its spacer towards the back of the engine, and pop the snap ring (which is normally hidden beneath the spacer) forwards out of its groove . This will let the exhaust rocker slide forwards further than normal. Now you can push the inlet rocker forwards to give the most clearance over the inlet valve. You will need to wire it into position somehow to stop it from being pushed back by the spring.

The clearance you get probably won't be enough to cleanly remove the spring (in a straight line, anyway), but this is OK, you won't need to; you just need to be able to remove the retainer.

At this point think hard; do you have a tool or are you sure to be able to make one that will allow you to refit the valve collets in situ? If not then failure in the next steps means you are taking the head off.

Next job is to block the oil drains from the head with rags or small pieces of foam. Cut a ~1" diameter hole in a large piece of rag and fit that as best you can over the valve spring so that only the valve spring retainer is visible.

With the compressed air on, now take a suitable tube ( a long series 7/8" socket probably) and use it as a drift on the spring retainer. You are aiming to compress the valve spring about 1/4" with each hammer blow. Normally a moderate blow with a 12oz or 1lb hammer is about right, but with heavier springs a bigger hammer might be the thing. Some thin penetrant sprayed on the collets may help to release them.

Start gentle; after a few blows you should be getting a feel for how much the spring is compressing; any 'whooshing' from the TB means the collets are sticking and the valve is opening, so carry on until this sound stops at least. Suddenly the socket should pop up a load more than normal on the way back up. This means the collets have released fully. Generally they don't go too far; losing them is an irritation, but where they might wind up inside the engine is a major source of worry, hence all the rag precautions. If you can fix a strong magnet inside your drift/socket (epoxy resin probably required) this might help the little buggers stay local instead of pinging across the shop.

Why use the hammer at all? Well you might have 150lbs pressure on the valve or something, but collets can take a lot more than that to come free once they have settled into a retainer. Even if you use an external spring compressor to push the retainer down, you may find it doesn't work unless you give it a few taps with the hammer beforehand.

With any luck you now can remove the retainer from the valve assy; since it can usually tilt at 20 or 30 degrees on the valve stem, and the edge is thin, it should come out from under the rocker which may still be over the edge of the spring/retainer. You may need to remove the rocker eccentric to give a bit more clearance.

Now you can remove the spring (probably) and remove the stem seal.

A suitably placed elastic band may hold the valve up well enough that you can turn the compressed air off for a while at this stage. This will let you check for play in the guide. If there is some, don't fret; M30s with valve guides worn even to top limit reputedly stop using oil almost completely once new seals are fitted.

The last step is the most awkward; you need to hold the spring down whilst the collets are teased back into position.

I have made up tools from pieces of tube with 'windows' cut in the side for this purpose, and on smaller valves than these, you can (if you are fairly strong) just hold them down by hand. I do not expect this to be possible on the M30 engine. I expect a really clever home-made tool to be used, or perhaps an assistant working a ~3:1 lever to be necessary, most likely with a hook or tether on the lever that goes under the camshaft or something.

The most awkward part of this procedure is holding the retainer concentric enough to start the collets back in their groove. This part is bloody awkward and calls for a clever tool and/or good teamwork. Needless to say by the time you are doing the final valve it is probably quite easy but you will likely explore the outer limits of both your patience and your vocabulary en route....

Many seasoned mechanics find this process so frustrating that they would sooner pull the head and do it that way....that is how bad it is....

I hope this is of some interest anyway. Like I say, I have not tried it on an M30 but I have measured up and I think it should be possible.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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miklilmag
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Post by miklilmag »

Have you given it a Seafoam treatment yet? Try that first,
....valve job......better off removing head, any other way....no fun...!
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vik351

Post by vik351 »

Seafoam treatment , Havent heard of that in Australia...???

I presume that is an additive to the oil of some kind

Have tried Liqui Moly http://www.liqui-moly.com.au/ engine oil resealer

But they say it takes 600 klm to work if it will at all

Looks like a head job coming up...

vik...
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tschultz
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Re: Valve stem seals

Post by tschultz »

The old style breaks down. I have the same problem and am replacing them with a headgasket job at the moment.
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