Tappet Shim Escapes!

[Elanintheforest]

I've just made an interesting discovery with my engine whilst diagnosing a very light ‘tappety’ noise whist it ticks over. The engine started instantly, revved cleanly and ran on all 4.

The cam cover came off to measure the clearances as the first measure. I’ve recently re-built the engine so it seemed quite possible that a gap had opened as things settled down, although the engine had only been run for 4 or 5 x 20 minute sessions.

All the clearances were as I had recorded except No 2 exhaust, which had none!

The cam came off, and it was pretty obvious that something was wrong as the culprit shim bucket was sitting up quite a bit higher than the others. On removing the bucket, the shim had popped out and was sitting happily on the side of the valve retainers.

In the normal course of running a 145 thou shim can’t get out of a 9 thou gap, so what happened?

The only thing I can think of is that the bucket somehow became stuck or sticky, allowing the gap between the valve top and the bucket to open up and allow the shim to be displaced. But I’ve not heard of this happening before!

The head is a very early one, from April 1963, so the buckets run in aluminium, and not in steel tappet sleeves, which may have contributed to the problem.

About the only thing I didn’t replace when building the engine was the buckets, valve guides and valve seats, as they all looked so good. The buckets have some wear marks on them, and they did go back into the position they came from.

The last couple of times I ran the engine I was testing out the fan otter switch to make sure it all worked, so the engine was taken up to 95 degrees or so on those occasions, which of course would have made everything expand.

Any other thoughts on what may have happened here guys?

I am now thinking through the next step. If it can only be a stuck bucket, the simple one is to pop a new set of buckets and see what happens! The obvious proper thing to do is to get the head off and get the bucket housings sleeved, as all engines were after mid 1964,...... and put a new set of buckets in!

But I would love to hear your views on what else may have happened first. The strange thing is, after I could hear the light ‘tappety’ noise (only heard on tick-over) the engine still ran as sweet as a nut!

Mark

[2cams70]

Did you replace the valves? Did you properly lubricate the valve stems before fitting them? Did you check the valve stem to guide clearance and for any burrs that might exist on either the stem itself or inside the valve guide?

Sounds like it might have been caused by a valve sticking in it's guide. Exhaust valves in particular are prone to do this because they run hotter than inlets

[Elanintheforest]

New valves & springs and checked the guides and valves in guides which all measured up fine.

I didn't check for any burrs on the stems, but had a good look at the guides! I didn't replace the guides, which I really should have done.

I always use Graphogen on an engine build on all bearing surfaces, and plenty of oil for good measure.I lubricated each valve stem before it went in and moved it up and down several times to ensure each one was well covered, and moving in the guide smoothly.

But you are right that's the only other thing that could have caused the issue.

Getting the head off and valves out will reveal all I'm sure.

Mark

[stuart]

Hi Mark

got about 1000 shims if you need any!!

regards
Stuart

[Elanintheforest]

Thanks Stewart. The shim is OK, but the bucket looks decidedly 2nd hand underneath!

Can't see any more damage luckily.

[Elanintheforest]

I replaced the bucket and shim, and all is back to normal with the same gap it had before.

I've now completed a coupe of running cycles up to 95C and back to cold, with no issue. The compression in all cylinders is a healthy 210 psi.

I still don't know what happened, but another theory of a bit of carbon stuck in the inlet manifold for the dormant 35 years may have become unstuck and jammed up the valve. I did clean it out thoroughly, but I'll probably never know the cause.

Another few hours running the engine should prove it's all OK.

Mark

[Hawksfield]

Mark

I bet that's a relief it could have been worse

Hope every thing continues satisfactorily good luck