Top end clatter - diagnosis help please!

[Hugo]

Come on, that's all far too modern for me Which reminds me - I've just started a Corvair breeding programme here in Florida (program I suppose I should say). I have three with a fourth on the way. They are fascinating cars - tin-plated pistons - ever heard of that? Flat six air-cooled in the back (very popular engine in home-made aircraft), drives through the differential to a two speed automatic which then drives back via a concentric shaft to the diff - and it's all one unit. You can push-start them too, if you can get to 25 mph which is certainly faster than I can run. Manual convertible top that you can raise and lower one-handed in about two seconds flat. I needed a pair of front brake shoes & ordered them yesterday (Sunday) from the local Autozone - they were here 19 hours later - and that's for a 1964 car - try that in Halfords! Oh dear I seem to have gone rather off-topic again!

[chrisfell]

Two things suddenly clicked: massive noise like a valve and zero valve gap. I know what this could be. I hope I'm wrong.

Sorry to have to break this to you, but the one fault that fits these symptoms is a dropped valve.

What happens is the valve collets give up, either because they are faulty or poorly fitted. The noise is valve piston contact.

To check, remove the inlet cam. If the valve has dropped the valve spring should be loose under the tappet.
If this is so, the head must come off and the damage inspected. Suspect piston damage and a very bent valve at the least maybe worse.

[kingzetts]

Not a dropped valve. Inlet cam is off and the valve stem tip is in the right place. Inlet manifold is off and I can see the back of the valve head and the valve seat. No sign of anything wrong with the valve seat from that side, but there is some carbon buildup on the back of the valve which is unusual for an inlet valve (especially with only 2500 miles on the head) and suggests the valve has not been fully closing. No obvious issues with the valve springs.

I tried reshimming that valve with the thinnest available standard shim, which is 10 thou thinner than the one which was in there - still zero clearance (or at least less than 2 thou which is the thinnest feeler gauge I have), which suggests that the clearance before was at least -8 thou and the valve could not have been closing fully.

I'm wondering if maybe the seat insert was not fully seated in manufacture before the seat was machined - maybe a tiny bit of swarm or dirt in the way. Then over the first few hundred miles, it has been pushed home by the valve, and the noise is Christopher's suggestion of the valve stem tip hitting the tappet and the cam lobe due to negative/zero clearance.

In any case, the head still has to come off for further investigation.......

[Hugo]

Nope. I don't buy it I'm afraid. It might explain your negative clearance but not the noise. If you have zero or negative clearance it will be silent. The other possibility of course is that something had been sucked in & hit the piston, & maybe pushed the centre of the valve in a bit, although that last must be at the edge of what is possible. Can you look down the plug hole & see what the top of the piston looks like?
Of course you might have two unconnected faults - Something may have got in there somehow & made the noise, & the valve seat may have gone further in due to being incorrectly fitted, but again this must be at the edge of what is possible. More likely the seat has fallen out & got smashed back further in.
If I recall, the only reason you suspect this cylinder is the lack of valve clearance? Have you checked the other tappet sleeves to see if one of the others might have ridden up & hit the cam?
Get that bloody head off & put us out of our misery!

[kingzetts]

An update - the head is off but the whole thing remains most puzzling.

There is absolutely no sign of anything untoward around #1 inlet valve seat.

Nothing at all unusual on any of the pistons or bores.

No signs on either inlet or exhaust bank of any metal to metal contact between lobes and tappet guides or anywhere else. All except #1 inlet valve clearances were normal, #1 inlet valve has less than 2 thou clearance with an "A" (86 thou - thinnest standard) shim fitted.

I took off #1 and #2 inlet valves and put #1 inlet valve, springs, retainer and collets, "A" shim and tappet into #2 position and got zero clearance. With #2 valve etc into #1 position I got a normal clearance.

So the clearance problem seems to lie with the #1 valve or its tappet etc, not with the valve seat. But I can't yet explain the difference as the valve seems to be the same length as #2 with the kit I have available (vernier caliper - I don't have a long enough micrometer).

I tried #1 valve (back in its own spot) with no shim at all under the tappet. That gave a 21 thou clearance. With no shim fitted the tappet sits on the spring retainer and there's a gap between tappet and valve stem tip. As near as I can measure it by adding a shim and seeing how much the top of the tappet rises up, that gap is around 57 thou.

That suggests if I had a 66 thou shim, I should get a clearance of about 12 thou. But according to Haynes the thinnest standard shim is an 86 thou.

None of this explains the noise, either, as Hugo pointed out. Since the valve was running with less than zero clearance, then a gap would never open up between cam lobe and tappet and shim and valve stem, so it should make that valve dead quiet, not noisy.

Maybe tomorrow I'll play mix and match with the spring retainers and collets to see if that makes any differ nice but I can't see that it would. Sounds like either trying a new valve,finding a slimmer shim, or grinding the valve stem are the other options to solve the clearance issue.

[cactusman]

All was initially well so something must have altered somewhere.. I am no expert but I seem to recall the valve stems are hardened...would grinding them be wise....others will know for sure. I would look elsewhere before resorting to the grinder though...

[288gto]

Jonn,

Assuming #1 and #2 valves are the same length and you say the problem seems to be somewhere in #1 valve components, have you checked the tappet is of uniform thickness. If it is thicker on one side and rotated it would close the gap up.
Admittedly another long shot but easy to check.
Did you try swapping just the tappets, #1 to #2?

Simon

[mgcjag]

Hi John....dont just concentrate on inlet 1.....what about exhaust 1.....and all the others...... as others have stated something has changed to cause your noise...dont be to quick to start changing shims etc.....there must be signs of something wrong somewhere.....also overall measureing valve length is misleading as they sit in the seats....are all the other seats ok........all the best.. Steve

[Hugo]

............... Sounds like either trying a new valve,finding a slimmer shim, or grinding the valve stem are the other options to solve the clearance issue.

This is how you adjust the valve clearances on Astons - they don't have shims so you can grind up to 0.020" off the tip of the valve before you go through the hardening. The trouble with that is you never know if they've been ground before! Other than that it's grind the valve in to reduce the gap, or get another selective thickness cam follower. Those nasty old Ford 1172 sidevalves didn't have adjustable tappets either, but for a different reason!
As for the rest of it - weird!
What was the story again - you got a nasty noise coming from the top of the engine on the inlet side? Did it come on suddenly? Did it go away & come back? Just walk us through it again.
Could it have been a sticking valve do you think? But that normally happens on the exhaust side.
And you say # 1 & # 2 valves are the same length? But when you swap them over, the negative clearance follows the valve? Are you swapping the valve, cam follower and shims over as a set? Is the shim on #1 cam follower going right home in the cam follower? It couldn't have bounced out of its recess if the valve momentarily stuck open & then jammed in the wrong position?
Questions questions questions I'm afraid.
I was going to suggest you may have different diameter cam lobes if it has been reground (nothing wrong with that) but if the clearance issue follows the valve, it rules that out.
Real head-scratcher, isn't it!

[kingzetts]

Nasty noise, top end, inlet side as far as I could tell, appeared somewhere between Calais and Nice, not sure when as I use earplugs on long motorway runs. Frequency follows rpm. Noise has remained ever since, would occasionally fall silent at idle but not always, and reappeared as soon as rpm increased.

Negative clearance follows valve. So far I've only swapped the valves over as a complete package, springs, retainers, collets and tappets. I said the valves are the same length "within the limits of my measurement tools", not sure I would be able to detect a 20 thou difference as I don't have a long enough micrometer, just vernier calipers.

The shims are definitely correctly seated and there are no visible signs of anything amiss anywhere else. #1 & 2 tappets measure the same thickness on a micrometer to within 1 thou. I will try mix'n'match parts between 1 & 2 valves tomorrow.

Thanks to you all for the ongoing suggestions.

[Hugo]

Digital calipers should easily be good for 0.020". Maybe you need to start pulling pistons & checking small ends? If it was a big end it would all have fallen to bits by now. How good is your ear - can you tell whether it's half engine speed? Is it worse under load, over-run, both?

[Hugo]

Just going back to your orignal post, you said that #1 inlet valve was between 0.7 and 1.0mm too high. Now you say the clearance seems to require a shim 0.020" thinner than the thinnest one. Given that these were very rough measurements, they look fairly consistent with each other. You say that #2valve in #1 hole is normal, and #1 valve in #2 hole is wrong, so it must be #1 valve (or tappet/shim ass.y). Where it all goes wrong is that you say the valves measure the same.
I know you've only been doing rough measurements, but unless I've mis-understood you, they are contradictory so it's time to take a deep breath, make a pot of tea and start doing some really careful measurements.
I know you don't need me to tell you that, and that you expected to see something obvious with a quick measure. So would I, but this one is clearly not going to play.

[288gto]

Hi John,

Sorry to hear about your ongoing problem.

Try Googling " stretched inlet valve" there is a lot on there about it. It can also be called "tulipping".

Just to recap.

All other clearances are ok inlet and exhaust?
On checking #1 inlet, no clearance.
Putting #2 inlet valve into #1 gives a clearance.
Both#1 and #2 tappets are within 1 thou.

Everything points to the #1 inlet valve stretching or deforming.

Before you get too involved stripping and swapping more bits, it might be worth accurately checking the length of #1inlet.

As regards no valve clearance someone has already mentioned that this will make the engine noisy.


Simon

[Hugo]

Hi John,
Try Googling " stretched inlet valve" there is a lot on there about it. It can also be called "tulipping".

As regards no valve clearance someone has already mentioned that this will make the engine noisy.
Simon

Why would one valve out of twelve suddenly decide to stretch after a few hundred miles normal road use? If any valve is going to do that it should be an exhaust valve as they have a much harder life.
Why would lack of clearance make an engine noisy.? Just because somebody else said it doesn't make it true

[Series1 Stu]

I agree with Simon's suggestion to check for a stretched valve.
It might also be worth comparing the relative heights of the valve heads. If number 1 valve head is thinner then it would sit higher in the guide, even though it's the same length as the others. The same goes for valve head diameter too.

Regards

[Hugo]

Still doesn't account for the noise though

[288gto]

Hi Hugo,

I wasn't trying to disagree just for the sake of it. I was going off what Steve said from his own personal experience.

.

Hi John....when i first got my E it had bad tappet noise..on checking there was almost no gap on the inlet side, set them correct and made the tappets much quieter.......so reduced gap can make more noise.. Steve

If Steve says it's true, that's good enough for me.



Anyway at least we agree accurately measuring the suspect valve is a starting point.



Simon

[Hugo]

Not good enough for me I'm afraid - if you can give me a plausible explanation for how you think this works I might be persuaded. Until then it makes no sense I'm afraid.
Not that I have any better ideas I must admit. Well, actually, I think I've put forward a lot of better ideas. Unfortunately none of them appear to be correct.
This is why I would never make a surgeon. With things like this you can go home & sleep on it & tomorrow the job will still be there. If you have a patient on the operating table you can't really do that.

[JagWaugh]

Maybe tomorrow I'll play mix and match with the spring retainers and collets to see if that makes any differ nice but I can't see that it would. Sounds like either trying a new valve,finding a slimmer shim, or grinding the valve stem are the other options to solve the clearance issue.

I wouldn't be topping a valve, or grinding a shim until I'd traced the problem conclusively. And I still wouldn't grind a shim undersize or change the thickness of the cup.

[chrisfell]

Once a valve has receded to the point that the shim required to maintain a gap is smaller than 86, the head needs a rebuild.

Grinding the valve stem or the shim won't do much as the top of the spring will begin to bear on the under side of the cam follower.