Valve clearance not set by the shim

[johnetype]

My no. 4 inlet valve clearance was 8 thou with a "R" valve pad/shim (0.102) in it so I changed it to "U" and still the clearance was 8 thou. I changed it again to "Y" and it's still 8 thou.

Clearly the valve shim isn't setting the 8 thou clearance so what is and any suggestions on what my problem could be?

The remaining 11 valves all were a few thou below spec but have all adjusted up fine. Before checking the clearances the engine was running fine except for a tappet noise coming from around the centre of the engine, ie could be no. 4 inlet.
The tappet guide appears to be firmly in place and there's no obvious sign of what's wrong.

[mgcjag]

Hi John....what gaps are you working to 4 & 6 or 12 to 14 If your at 8tho and increasing shim size you will reduce gap....if its for your 69fhc you should be 12 to 14 Steve

[johnetype]

I'm working to 4 and 6thou. I have two hole camshafts, no grove and oil holes on the back of the lobes. My engine was made just before the change.

[mgcjag]

Have a look to see if the shim is sitting proud of the retainer.....sounds like the cam follower is sitting on the retainer and not the shim.......does your data plate say 4/6 .. Steve

[johnetype]

The shim is sitting proud of the retainer. Even with an "A" sized shim the shim surface is still 20 to 30 thou above the retainer.
You can also move the shim on the top of the valve to check it isn't fouling the retainer and is truly on top of the valve stem.
Compared to the adjacent valve, valve length and position appear to be the similar. As best as I can tell looking down the side, the valve springs on the two valves look the same. (no broken or misplaced bits)
Comparing cam followers shows no obvious differences.

So, I am still looking for any suggestions as to what I've missed; I'm on first name terms with my inlet camshaft bearing caps but it hasn't helped.

Steve, this isn't a what the clearance settings should be issue. All the signs tell me I have an engine with 4/6 clearances but even if I didn't and it should be 12/14 I've tried shims with a greater range then that and still always get around 8.

[mgcjag]

Hi John....this does sound very strange.....so engine was working fine with a bit of tappet noise...just an out of the box thought if your useing digital guage to measure shims is it reading correct..iv had one read wrong when battery was low...does the inside of the cam follower look correct so that it sits on the shim and not the retainer... one other thought your not overtightening the bearing caps.... Steve

[JagWaugh]

Is the seat area of the tappet the same thickness as the others?

If the valve hasn't been topped and the tappet is the same thickness, then it could be:

Something trapped between the valve seat and the valve.
Valve seat dropped.
Broken spring(s).
Bent Valve.
Tight valve guide (debris?).

[kingzetts]

When I had some mysterious issues with one inlet valve, I found a methodical approach ofswapping out one component at a time between the problem valve and one which was not giving the problem (in my case I swapped parts from problem #1 valve and good #2 valve) allowed me to narrow down the issue. I’d try exchanging the following one at a time, replacing each one after each check, and see which one(s) move the problem to the other valve;

Cam follower
Spring retainer
Collets
Valve

Mine turned out to be an issue with the retainer which allowed the tappet to hit the retainer before the shim, which meant the collets got loose and then slammed back in place with each cam rotation making a heck of a top end clatter.

[PeterCrespin]

I've tried shims with a greater range then that and still always get around 8.

OK. This is so bizarre that it cannot be true. By which I mean not what it appears, rather than an untrue description. There is no way a gap measured between any two fixed objects ( cam heel and valve stem) can stay fixed when a variable filler piece (shim) is inserted to take up part of the space.

What, exactly, do you use/do to measure the gap?

[johnetype]

Peter, I use a set of feeler blades to measure the gap between the heel of the cam and the tappet with the camshaft rotated so the lobe is pointing away from the valve stem. I believe I'm using the correct measuring technique because I've used it on my Twincam engine and my other 11 valves give reliable readings that match up when you change from one shim of a known thickness to another.

It is clearly bizarre and as you suggest, difficult to envisage in what is a relatively simple mechanical situation.

I fitted the "Y" shim and a new tappet and ran the car for 100 miles. Whilst the tappet noise was improved the engine had a misfire at idle and no compression pressure in no. 4 at idle. At the end of the 100 miles, the clearance now measured 2 thou.

I have reverted to an "R" shim, this gives a clearance of 8 thou. Engine now does not misfire at idle.

I plan to run the engine like this for a while. As the no.4 inlet runner is almost straight I'll see if my endoscope USB camera can get far enough down to see the valve.

Noting that if the XK engine is positioned with no. 1 cylinder at TDC, no. 4 inlet valve is open fully. My engine has stood unused for nearly 30 years and I suspect some corrosion issue between valve stem/guide and seat is responsible for the bizarre clearance issue which I will only fully resolve by removing the cylinder head and removing the valve to check.

[mgcjag]

Hi John...i did ask before but are you actually measureing the shims prior to fitting them...or just assuming they are the correct size becaus they have an R or a Y stamped on them..... Steve

[johnetype]

Steve, I measure them with a Moore and Wright (made in Sheffield) micrometer, the new ones and the old. The measurements of the new have corresponded to the micrometer readings. I haven't looked for the markings on the old ones, just gone by what they actually measure.

[abowie]

. Whilst the tappet noise was improved the engine had a misfire at idle and no compression pressure in no. 4 at idle. At the end of the 100 miles, the clearance now measured 2 thou.

Are you sure the valve spring isn't broken?

[johnetype]

No I am not sure the valve spring isn't broken. It looks alright and similar to the other springs if you observe it without the tappet in place but the view is very restricted. I could try the rope trick to allow me to remove the retainer, collets and spring but I'm not confident I'd be able to get the valve retainer and collets back on under those circumstances so would have to pull the head anyway.

[abowie]

No I am not sure the valve spring isn't broken. It looks alright and similar to the other springs if you observe it without the tappet in place but the view is very restricted. I could try the rope trick to allow me to remove the retainer, collets and spring but I'm not confident I'd be able to get the valve retainer and collets back on under those circumstances so would have to pull the head anyway.

Yes. I've been thinking about this for a while. The only way I can see that you got the measurements you did is if the valve stem is moving down when you push the feeler gauge in. With a broken spring and less tension you might be fooled. It would be interesting to see what happens if you try to get a much thicker feeler gauge in.

While I am aware that you can get the collets off with the head in situ I've never done it myself. It would be worth it though IMO.

[Polse7317]

Sorry about that but what does "IMO" mean? I have a poor english ... I know! But i can follow the thread

[mgcjag]

Hi Yves...IMO....in my opinion. ..Steve

[Heuer]

And IMHO is 'in my humble opinion". Please feel free to ask for an explanation for anything you do not understand - we are here to help.

[Polse7317]

Thank’s David ,i’ll Write that in my English book ......ASAP!