Over the last few weeks, I’ve re-built the ‘best’ engine for my trials car. Essentially, this has involved building the ‘old’ engine into a better crankcase, fitting new Honda pistons and re-metaling the rods. Everything else is as before. On the bench, I very carefully adjusted the tappets and checked them four times as adjusting tappets on this engine in-situ means removing the manifolding and carburettor.

Once fitted, the engine fired up straight away but with a significant tappet rattle. I therefore removed the manifolds and carb and re-adjusted the tappets that were all 10 – 11 thou ie. 4 thou greater than I had set them. Checked them twice again turning the engine a few times on the handle between checks. After re-assembly, I again fired up only to be greeted with the same tappet rattle. After dismantling, the tappets again measured 10 –11 thou. I set them again, same thing happened.

The tappets aren’t loose. The camshaft is not bent. The tappet blocks aren’t sticking. What on earth can be causing this? Any ideas?

I am minded, next time, to set the things to 2 – 3 thou. to see what happens!!

STEVE

It would be interesting to know how often this would continue to happen, but I suspect you are not prepared to find out!

Well, either the block or valves are moving upwards or the tappet assembly is getting shorter, or the camshaft is wearing out rather rapidly....I vote for blaming the tappet assy. You've not refaced the tappets, have you Steve? Or reground the base of the tappet blocks?

Very mysterious!

Await next instalment with interest,

Regards, Stuart

I came across an engine a few months ago that gave lots of "tappet" noise, it turned out that is had cam followers which were not hardened...

If your followers were ground down or have been heated up, you may like to try centre punching them to see if the are still hardened..

I set all my tappets to 6 thou..

Good luck,

Ruairidh

Thanks boys. Tappets have not been re-ground and all the 'bits' have run together previously, without problem, for about four years. Block is certainly not moving, obviously can't see what's happening to the cam lobes but the tappet rattle is instant on re-starting the engine after the tappets have been adjusted rather than gradually increasing. As it's a 'new' engine, it has only been run each time for a few seconds. Leaving new rings/bores to tick over is the best way to glaze the bores. I too set to 6 thou.

Even tried an alternative set of feeler gauges in desparation!

STEVE

So do all the clearances open up by a similar amount each time? I take it the locknuts are still tight.

The fact that the problem appears to be instantaneous does make one suspect an anomaly in the setting process. I can quite see why you tried another feeler gauge!

I would much rather know why, but I think there is some merit in the idea of setting at 2 thou. If you're only running for a few seconds it won't do any harm. The interesting question becomes, what happens next?

Regards, Stuart

I think the answer to this question will be, "There is no base gasket but Loctite"! However; you've not fitted a thicker base gasket so the tappet adjusters are now fouling the tops of the tappet guides where they didn't before? Can't see it really, but thought I'd ask.

Regards, Stuart

.

A wild thought!

Have a look at the threads in the lock nuts. That is unless you have changed these already.

Except for speed there is nothing different happening if you turn the engine over twenty times (or even many more!) by hand. You could try doing this and checking tappets every so often.

Plugs out you could probably motor it with a 3/4" drill and a suitable socket. At least this would save keep removing the manifold and save stretch on those poor little studs, not to mention gaskets. You might just spot something.

Mike

PS ... Camshaft bearings?

Come to think of it, you would get the same effect if the deck height of the new crankcase above the camshaft was greater than that of the old one, if the old crankcase had been refaced a few times, say. Probably wrong but the first idea I've had that I could almost believe!

Regards, Stuart

Steve

Have you had work done to the block?
If you had seat inserts fitted that were working their way out this would move the valve away from the tappet and give you trouble?
Measure the fitted height of the valve spring before the next test and then check again when you inspect to see if it is different?


Steve.

Have you put the tappets back in exactly the same guide and the same way round? If the tappet and guide have run in to each other there may be an unworn part to one side. Reassembly even in the right guide might result in an unworn edge being the contact point that then wears in very quickly. I've also experienced tappets sticking - they can crack down the flat side if the taper nut is overtightened and then not reseat properly on the back of the cam when the spring pressure isn't active. I like the proposed idea of cranking the engine over to settle things in.
Dave

Base gasket Stuart?? I thought you knew me better than that!!

Not absolutely sure yet (Granddaughter’s 4th birthday stopped play early afternoon) but I think we may have the answer. As Stuart will be aware, I posted my question on the VSCC Forum also and Dave Dye gave me the clue.

If you use re-radiused followers, you often need to reduce the height of the tappet block guides to stop the locknut fouling the guide – even with a standard camshaft. In my case, I used standard radius tappet blocks with a Rawson Trials cam, the same set up as in the ‘old’ engine with the guides at standard height. No problem in the past. On taking the thing to bits this morning, it was obvious that the locknuts were fouling the guides and so, after removing the head, I was able to remove one of the tappet blocks. Comparing with another block, it was 1.0 mm shorter – perhaps the radius had been ‘cleaned up’, but not changed, at some time? I’ve now changed all the tappet blocks for an alternative set, all the replacements being 1.0mm longer than those previously fitted and, with the tappets adjusted again, all locknuts are clear of the guides. Will probably be Tuesday before I can run the engine to see if this has worked but I will report back.

One last thought. Assuming I’ve solved the problem, why did the same bits work fine in the ‘old’ engine? Could it be that the ‘old’ crankcase was die-cast whereas the ‘new’ is sand-cast? Perhaps the line of the camshaft and crankshaft is very slightly different?

Thanks ever so for all your ideas. Isn’t this Internet wonderful?

STEVE

PS:

Yes, I also thought of cranking the engine over. After I'd changed all the tappet blocks and re-set the tappets, I spun it over on the starter motor for a few seconds before I put the head back on. Very minor adjustment needed afterwards. Spun it over again, no further adjustment needed.

Thanks again,

STEVE

Have been following this thread whilst looking at my own engine which I have rebuilt and bench testing. Although I have checked tappet clearances which I set to 8 thou all round and which dont seem to be changing, there does seem to be a little more noise than I was expecting from the tappets/valve gear. There are one or two valves which, when fully closed, have the locknut appearing to rest on top of the (bronze?) guide in the block. I thought up to now that it was because I have deliberately set the clearances on the generous side but in the light of Steve's problem, I am wondering whether I have the same problem?

The tappet heads were reground to remove indentation from the valve stem but I would have thought that the effect of this was to effectively shorten the tappet assembly and thus move it slightly away from the shoulder at the top of the tappet guide??

Am I on the right lines or talking b*****s?