Something's going on...

[Geoffers71]

With my cylinder head. Engine has been going well, I thought, but has always had issues when starting from cold and a very slight stumble at very small throttle openings. When cold, the engine starts but misses badly with lots of spitting through the carbs and popping through the exhaust. After about 30 seconds or so everything settles down and the engine revs normally with no spitting etc., although the very slight stumble is still there. Have tried adjusting carbs as have others, but little improvement. A new engine man has just joined our local garage and I thought I'd give him a try. Must say I was impressed! He tried adjusting the carbs, using the tube to the ear method for balancing ( said he preferred that to using the any other method) and immediately noticed an issue with the inlet to no 4 cylinder. Reckoned not much wrong with the carbs, but thought there was a mechanical issue of sorts. Whipped off the cam cover, turned the engine to give cam lobe clearance at no.4 and found there was none To cut a long story short ( bit late for that ) I set about checking all tappet clearances and changing the shims as necessary. No problem there until I came to no.4 inlet. I calculated the the size of shim required (a bit on the thin side I thought) and replaced everything. Checked all clearances again and AGAIN no clearance at no.4 inlet. Tried again and by this time the shim thickness was only just above 50 thou.....too thin. I puzzled over this for some time (my few remains brain cells take their time to get together ) and realise the size of shim made no difference as the bucket was resting directly on the valve spring retainer !!! How the hell as that happened? I'm sure that all tappet clearances were fine when I first checked, though I did collect the head with camshafts already fitted. I do think that the original head machinist I used, topped some of the valves to give adequate shim thickness and maybe that has something to do with it. Anyway I've little alternative but to get the head off to find out what is going on. Anyone any ideas?
My new engine man is sure he can sort whatever it turns out to be, but I'm a bit annoyed with the original one.
Sorry, I've gone on a bit long. Once I get going...............!

[Foxie]

Before you take the head off... do a compression test, and post the results !

If the bucket is sitting directly on the spring retainer (hard to believe) instead of the valve stem, it is very likely the collets & valve groove will be damaged

[Geoffers71]

Before you take the head off... do a compression test, and post the results !

I don't have a compression tester, but I can't see that knowing that the compression of 4 is down, which I suspect, would avoid me pulling the head.

If the bucket is sitting directly on the spring retainer (hard to believe) instead of the valve stem, it is very likely the collets & valve groove will be damaged

Yes it is difficult to believe, but inside of the bucket is circular scored to match the spring retainer . I agree about the collets and groove, which is why I have to pull the head.
Thanks for the comments though

[Foxie]

I don't have a compression tester, but I can't see that knowing that the compression of 4 is down, which I suspect, would avoid me pulling the head.

An engineer may suspect. But then he should go on to check.

[Elanconvert]

hello geoffers

you are very welcome to borrow my compression tester... although I would have thought your new engine man would keep one in his back pocket!!

fred

[nmauduit]

Before you take the head off... do a compression test, and post the results !

I don't have a compression tester, but I can't see that knowing that the compression of 4 is down, which I suspect, would avoid me pulling the head.

If the bucket is sitting directly on the spring retainer (hard to believe) instead of the valve stem, it is very likely the collets & valve groove will be damaged

Yes it is difficult to believe, but inside of the bucket is circular scored to match the spring retainer . I agree about the collets and groove, which is why I have to pull the head.
Thanks for the comments though

I guess you have checked that you did not have a broken spring, and as a result a somewhat sticking valve (less strength plus bits moving around)... removing the springs without taking the head off using compressed air to keep the valves closed is not very time consuming (you may inspect the valve grove then, though I hardly see how they would get damaged gradually just like that).

[Craven]

Unusual but there has been some concern over the quality of some valves in they do stretch, compare the overall length of your valves. There is some data on valve stem length but it?s difficult to relate this to an actual valve.
Ron.

[rgh0]

What was the shim thickness to begin with and what is the pad thickness in the bucket? It is quite possible for the face of the bucket to hit the retainer with a bucket with a small shim pad and using a thin shim or with the end of the valve stem machined to try to achieve an acceptable shim thickness. its one the routine clearance checks you need to do.

Once the bucket contacts the retainer even if only slightly then the collets and retainer start to wear and it becomes progressively worse until loss of compression or total failure and the valve is dropped.

Looks like you were lucky and the loss of compression picked up first.

cheers
Rohan

[Geoffers71]

The original thickness of the shim was only 69 thou, tooo small!, despite the original machinist assuring me that all shims were around 100 thou. Lying **????&@$ !!!! It is also clear that this valve had been topped to achieve even this figure. Whatever has happened it means that the spring retainer and valve end are lower than they should be allowing the bucket to rest on the valve retainer. Maybe it IS a broken spring, or the collets and their retaining grooves are damaged in some way. Or something or crud is holding the valve off its seat. The new engine guy I now have assures me that nothing he sees will so far not enable him to produce a good fix. Time will tell. I am currently dismantling the head attachments. Exhaust is off ( thank god for new studs and brass nuts ) coolant drained, and heater valve & sensor off. Carbs next and then we'll see. Having to take my time as leaning over the engine bay is playing hell with my back ! :roll.

[alan.barker]

I had this same problem on a +2 where the collet/spring retainer was touching the underneath of the cam follower bucket.
I fitted a new collet/ spring retainer and a pair of new collets and the problem was fixed.
The problem was worn or wrong collets and worn or wrong spring retainer.
Alan

[Geoffers71]

Well now we know what has been going on The original bodger/builder fitted new inlet valves and seats. However the seats were too shallow and so were seated too low in the head, resulting in the valves sitting too deep. To give sufficient shim thickness he then ground the top of each of the new valves. The amount ground off was however truly shocking. The distance left between the collet groove and the ground tip was little more than 1mm The result, particularly on valve no 4, was that the collet was pushing up on the thin ring left which caused a "distortion" in the tip of the valve stem. This closed the shim gap to zero and less eventually so that the bucket was pressing against the spring retainer. There were no bottom spring retainers at all, the springs bearing directly on the aluminium head.
I think I've explained that correctly as described to me by my new engine man. I'm very shocked to learn all this as the original work was done by a supposedly reputable local engine guy (or maybe one of his employees). It's lucky I guess that this was discovered before some serious damage was done.
Anyway the new guy has impressed me with his knowledge ( he specializes in race engine prep) and I've left the head with him to sort. New deeper valve seats with new valves will be used, and he will profile the seats to remove any edge. So relieved that this problem was caught early and will be properly resolved.

[billwill]

To add one more aspect to such behavior, I seem to recall Rohan putting a message on this site saying it was a really BAD idea to grind off the tips of the valve stems as they are hardened there, so you may end up using soft-tipped valves !

[alan.barker]

+1 BAD IDEA but there are many boggers about
Alan

[Geoffers71]

Yes, to say I'm cross about the original rebuild/bodge is an understatement. The new work will cost me north of ?600 but has to done. The original bill was ?670 so hardly cheap, but it was 3 years ago (unbelievable) and I'm hesitant about confronting the guy with his abysmal standard of work. What excuses could he use to mitigate the issues? P The car has done about 1000 miles since. My initial reaction is to let it go rather than kick up a fuss with little chance if getting any recompense. Am I being a bit of a wuss?

[vincereynard]

Yes, to say I'm cross about the original rebuild/bodge is an understatement. The new work will cost me north of ?600 but has to done. The original bill was ?670 so hardly cheap, but it was 3 years ago (unbelievable) and I'm hesitant about confronting the guy with his abysmal standard of work. What excuses could he use to mitigate the issues? P The car has done about 1000 miles since. My initial reaction is to let it go rather than kick up a fuss with little chance if getting any recompense. Am I being a bit of a wuss?

We will have to form a club of disgruntaled recipients of other wa***rs bodging.

Name and shame the bludger before he screws someone else. I had no quarms.