Hi all,

My Daimler is starting to running extremely rough at the moment, so I undertook the job of checking and if necessary adjusting the valve clearance to 0.30-0.35.

I was absolutely confused to discover that the first exhaust valve I measured did not have ANY clearance. I always thought clearance got bigger over time. The biggest clearance I measured was 0.15 mm on the inlet valves, 0,05mm on 1 exhaust valve. Nearly all exhaust valves have no clearance.

1 year ago I had the cylinder head gasket replaced by a mechanic. He assured me that the valves were OK. (I was worried because the car is running on LPG. I bought it this way) no burnt out valves.the car has driven about 10,000 km since.

What can cause the valve clearance to decrease? How to determine which shims to order to getting right?

 

Unlike tappet operated valves which have a lot of wearing components and tend to open with time the OHC design has little to wear.
As the valve settles into its seat the clearance will decrease - although your case seems a little extreme.
There are circumstances where the valve head itself can deform (tulip) which is bad news.
I think we need help from someone who really knows this engine.

 

Frank,

Steve sent me a PM, so here goes. It will be long, and Australian, so bear with me.

Every S3 6cyl I have seen has had tight tappets. The "why is it so", ended very quickly, due to all the cars having been "played with" a long time ago.

THE ENGINE MUST BE STONE MOTHER COLD

Basically I removed both cam covers, rotate the engine by hand and measure ALL the clearances, noting them down on paper. Do it twice if its your first time, just to be sure.

Now rotate the engine so both camshaft slots are facing up, using the special timing tool if you have it. I strongly suggest getting one, they are cheap, and take the guess work out of it.

NOW THE ENGINE MUST NOT BE ROTATED.

Remove the vent housing at the front of the head, and loosen the locknut on the serrated wheel, and release the top chain tension. There is a special tool for this also, but pointy nose pliers will suffice at a pinch.

Remove the 2 cam sprockets and allow them to slide in the "rabbits ears".

Nothing will spring out and smack you, but take care not to drop stuff down the front cover, that will excite the situation no end.

Remove the 2 camshafts. Place the bearing caps in order on a clean sheeted table. Place the camshafts neatly, and labelled "inlet and exhaust" just so you dont get confused.

Remove the cam buckets 1 at a time. Remove the shim, and using a micrometer (imperial is best) measure that shim. Take the clearance you got prior to dismantling, and calculate the thickness shim you need to get it right.

Continue with all 12 buckets, taking your time, measuring 2 or 3 times, just to be sure.

When all sorted, shims ordered and fitted, refit the camshafts, again TAKE YOUR TIME, and when they are BOTH secure, refit the sprockets and tighten the chain (not too tight), and rotate the engine by HAND.

Measure the clearances again.

If you did it right with all those measurements and calculations, all will be sweet, if not, note the "dud" tappets, and do it all again.

PLEASE NOTE THE FOLLOWING:

The camshafts SHOULD only be removed when the 2 slots are facing the top, as in with that tool used to align them. Removing them with that slot in any other position can/will bend the valves, and that is NOT funny.

NEVER EVER rotate one camshaft with the other shaft fitted, that will also do obscene things to valves.

I set the clearances at 0.012" Inlet, and 0.014" exhaust. I dont talk metric, so that is Imperial.

This takes me about 8 hours to do one start to finish, and I have done about 20 in my time. It is not a "quicky" reset.

The valve tuliping that Steve discussed is real, and LPG wont help that, as it is a hotter burning fuel than gasoline.

I would not get too stressed at the whole thing just yet. the history of the engine will be vague at best, and if it was set wrong be previous spanner people, you are now addressing it correctly.

Most mechanics (spanner people) really do not understand the operation of this valve arrangement on these engines, and the V12, so what you have now is nothing new to my ears.

If you want this in a "Word" document, ask, and supply by PM your email address, and I will do it for you.



FORGOT, I do that.

NEVER, EVER rotate this engine "anticlockwise". If you go past what you need, go around again, PLEASE.

 

Thanks Grant for your elaborate answer. Don't worry about the imperial measurements, we've got conversion tools for that. That being said: I wanted an English car, so I'll deal with it!

The procedure you describe is crystal clear and doesn't differ from my Haynes manual, only yours could be executed by a layman.

I slept a night over the entire matter and came up with a solution: I basically will remove the Cam shafts, extract the shims, rebuild it and measure the clearance. That should give me the proper measurements for the shims I need to order. Once I receive them, 'simply' put them in, check the measurements and close it up.

I saw an endoscopic camera on sale last week, so I'll buy that one later today to inspect the valves through the spark pluk holes... I sincerely hope it's all OK in there. The car will be completely overhauled & restored next year, so I hoped not to have any big issues before that...

Once again, many thanks for your answer

 

We're very fortunate to have guys like Grant on the Forum - where else would you find help like that ?
If you really have no clearance cold you'll need two iterations at least because, of course, you need a measurable clearance to do Grant's thing.
You mustn't use a magnet to extract the shims - no idea why !
Added to the HOW TO's