Pitted tappets

[rblumsom]

Hello all, I wonder if I might pick the brains of the knowledgeable folk of the forum ?

My car is a 1965 4.2 S1

I am adjusting the valve clearances (hopefully) to eliminate top-end noise (compression test and leak down test all good). On the exhaust side two of the tappets/tappet buckets are quite pitted. They are the centre two:

Tappet bucket.jpg (22.47 KiB) Viewed 4386 times

I haven't read about this issue anywhere else on the internet or having searched this forum.

Does anyone know what might cause this ? The cam lobes look fine although the clearances were around 7 though too large. Should I replace the buckets with new one (I assume so) ?

Also, following on from this, some of the exhaust clearances, which is the bank that the noise was coming from, were way out and in one case I need a 122 thou shim to replace the existing one. Does anyone know where I might source such oversized shims?

Finally, I am in North-West Hertfordshire, roughly between Hemel Hempstead and Ayesbury. One of the aluminium cam covers has a small crack in it. Would anyone have any advice as to where I might be able to get this welded ?

I hope that I have posted this in the appropriate manner but if not then please let me know.

Thanks in advance to anyone who can offer advice,

Richard.

[paulsco]

Hi Richard,

Chrisfell has mentioned pitted tappets in another thread, which may be of interest.

viewtopic.php?f=5&t=16314

Paul

[rblumsom]

Thanks Paul, I missed that post which is very useful.

Time to research checking out the oil feed, but my suspicion is that the cam followers might have been reused after an engine rebuild some years ago.

Richard.

[mgcjag]

Hi Richard i would re check your measurements.....as to why you need the extra large shim....check out the thickness of the cam followers...also look at the top of the valves. ...have they been ground down at some time....also look at long skirt cam followers.....as cam followers wear they become barrel shaped and rock in the bore causing noise (you can measure to see if they are barrel shape)......the longer ones are less likely to rock...but before anything check the oil feed is ok.....what do the cam bearings look like....also see similar topic listed below.....Steve

[chrisfell]

Curious. Not the tappet wear, which is due to the breakdown of lubrication, the cause of which needs to be identified and rectified. No, curious that you have experienced increasing valve gaps.

If all is well, the only adjustment should be to correct reducing valve gaps as the valve slowly recedes in its seat. The cam heel cannot wear, the tappet only ever wears if there is poor oil delivery, the shims and valve stems cannot wear, although I have seen substandard, non hardened shims develop annular indentations from the valve stem.

I'd check those shims very closely.

[mgcjag]

Iv also seen plenty of shims with a well worn indent from the valve stem....Steve

[1954Etype]

[rblumsom]

Thank you all for your observations and advice which are much appreciated.

The history of the engine is that it was rebuilt around 15 years ago, when I had neither the time nor inclination to do such things myself by a local mechanic who I am still in contact with and use for other vehicles.

I have just spoken to him and he recalls that the head was re-built with new valve seats (unleaded) and valves. He thinks it extremely unlikely that the valve stems were ground down so perhaps the seats were not ground enough. Since then I estimate that the car has covered perhaps 15K miles. After this rebuild I noticed that the engine was "tappety" but as it performed really well have not addressed this until now.

The compression test, with a recently run engine, showed 160 psi across all cylinders to within 2-3 psi either way so I took this as a good sign.

The leak down test had similarly consistent and positive results with a little air heard to be escaping past the rings (the engine had cooled a little by then) but a stable and strong reading with no discernible leak past either bank of valves which suggested to me that they were seating properly.

I am certainly not beyond making a mistake with measurements but have checked and re-checked and also had a friend confirm the readings so I'm reasonably confident of the measurements (we even checked the feeler gauges with a micrometer).

The bases of the cam followers measure 223-224 thou on the inlet bank, with the exhaust bank the same except for the two pitted cam followers which are 221-222 thou. The cam followers are, I believe, the long skirt type (1 inch from top to bottom).

When I removed the cam covers they were "full" of oil, i.e. oil was sitting in the outside parts of the cylinder head below the drain holes to just above the lower edge of the cam cover, spilling out when I removed the cam covers.

So I think that the next steps (as suggested) are to examine the top of the valve stems for evidence of grinding; check for barreling of the cam followers; check the oil pressure independently of the dash gauge (which shows pressure off the scale but I understand that the pressure senders are notoriously unreliable); check the oil feed pipe to the camshafts. Any additions/corrections to this plan will be gratefully received, particularly re: potential oil feed issues.

After this, if nothing obvious, then perhaps replace the pitted cam followers, obtain over-sized shims (Rob Beere ??) put it all back together and check again after 1,000 miles.

Again, thanks to all,

Richard.

[rblumsom]

Hello again everyone, the project continues and I'm back to tap into your knowledge base again please. I have searched the forum and could find an answer to my problem but if it exists already and I have missed it then please forgive me for asking a question that has already been asked and point me to the answer.

I removed the cam followers and shims and measured both with a good micrometer. I then ordered new cam followers and measure each of these. Surprisingly (to me) there was quite a bit of variation in these ranging from 210.5 thou to 226 thou (the old followers, despite being pitted were much more consistent in their thickness).

Having assigned the new cam followers to their valves, I then calculated the size of the shims that would be needed, taking into account the difference in thickness between the old and new followers to arrive at the shim thickness for each valve.

I have fitted the new shims, replaced the camshafts, torqued each one down (15 lbft) and remeasured the clearances. Irritatingly each one is too narrow by 2-3 thou with the inlet gaps being 1-2 thou and the exhaust 3-4 thou. I did coat everything with clean 20W50 engine oil before reassembly, including the shims and inside and outside of followers but I imagine that this effect might be in the order of 1/10,000 inch rather than 1/1,000 - please correct me if I am wrong on this. All the followers rotate in their buckets so there is some gap at least.

So my question is to ask whether the shims need to "bed in" ? Should I run the engine for a few minutes (I seem to recall reading that it should be initially run at 2000 rpm for a period of time after shim replacement) and then remeasure or is this likely to cause damage ?

Many thanks again for your wise counsel,

Richard.

[mgcjag]

Hi Richard......the new followers should all be the same size.....i fitted a set recently and the outside diameter and thickness of the shim contact area were all the same......did you get them from one of the usual suppliers or ebay?......also haveing changed followers and shims your base measurements taken befor you started are not really to be relied on.......so you take measurements now then shim as required.....but im not happy with your different size followers....Steve

[abowie]

Hi Richard......the new followers should all be the same size...

Indeed in a perfect world they should. But at the end of the day errors in bucket head thickness, or valve length, or valve seat height are irrelevant as they are compensated for with shims.

[mgcjag]

Hi Andrew...yes you are correct.....however a 16thou difference in a new set of followers should be flaged up to the supplier if they came from one of the usuals....Steve

[rblumsom]

Thanks for the responses thus far.

The new followers were purchased from a large and well known supplier (am I allowed to name them on this forum ?).

The old followers although worn were quite consistent in their thickness ranging from 221.5 to 224 with the vast majority being 222-223.

The new followers were very inconsistent: 210.5, 219.5, 219.5, 222........ 225, 226.

I spoke to the parts guy at the supplier and he, like you and I, was surprised at the variation and said that he would reflect this back to the appropriate person.

I took the view (perhaps wrongly) that as they were consistent in their diameter and fitted snugly into the collars, I would be able to compensate for the variance in their thickness with shims.

As an example, Exhaust valve #6:

Original valve clearance 16 so 10 thou too large
Original shim 108.5
Original follower 222.5
New follower 225 so this takes up 2.5 of the original excess gap leaving me requiring a shim 7.5 larger than the original, i.e. 108.5 + 7.5 = 116.
So, 116 shim purchased and fitted - gap remeasured at 4 thou not 6 !!

The curious thing to me is that ALL of the gaps on both banks are 2-3 though too narrow having followed the above approach so I have somehow made a consistent error on all 12 valves.

Could this be due to temperature, the oil or something else perhaps ? I wonder why my "logical" approach appears not to work in practice. I have checked the feeler gauges with the micrometer and the two tools yield consistent measurements.

So, given that the gaps are now 1-2 thou inlet and 3-4 thou exhaust, would the advice be to start the car (I think that I remember reading that it should be run at 2000 rpm for a certain period of time post this work) and then re-measure or should I give it up as a bad job and start again ?

Cheers, RIchard.

[mgcjag]

Hi Richard.....as i posted above.....measure gaps then shim to get them in spec.....its very easy for errors to occour when measureing.....obviously something has not gone to plan......so if it was me i would double measure all the gaps again and reshim........Steve

[mgcjag]

Just to add...are you useing all new shims or some old ones....used shims can have a wear mark ftom the top of the valve.....so in position can be thinner than if you measure across the shim not taking into account this wear...

[rblumsom]

Thanks Steve,

I was hoping that the advice would not be to do it all again but better safe than sorry! 10 of the shims are new but I re-used two (on the inlet side) so I'll replace them all.

Back to the drawing board then.......

All the best,

Richard.

[abowie]

As an example, Exhaust valve #6:

Original valve clearance 16 so 10 thou too large
Original shim 108.5
Original follower 222.5
New follower 225 so this takes up 2.5 of the original excess gap leaving me requiring a shim 7.5 larger than the original, i.e. 108.5 + 7.5 = 116.
So, 116 shim purchased and fitted - gap remeasured at 4 thou not 6 !!

Cheers, RIchard.

Unfortunately, and annoyingly, although it should work like this it just doesn't.

When I sit down with a head on the bench to shim, you would think that I could measure the gap, measure the shim, calculate the necessary change, check the new shim, install it and have the gap perfect.

For whatever reason an error of a couple of thou is common, and as I said I often end up having to re-correct several times.

I'm very fortunate in that I have a box with a couple of thousand shims in it, so all I need to do is measure another shim to ensure it's what I need and put it in.

For you, while the expectation should be that you buy your 116 shim and it fits, the reality is that you need a couple of shims in a range to ensure it's all correct.

You could perhaps use the variations in tappet thickness to your advantage in trying to improve your situation, but the likelihood is that you're going to need to buy a number of extra shims and you'll have some left over at the end.

[abowie]

Thanks Steve,

I was hoping that the advice would not be to do it all again but better safe than sorry! 10 of the shims are new but I re-used two (on the inlet side) so I'll replace them all.

Back to the drawing board then.......

All the best,

Richard.

Keep all of your old shims and reuse them.

Flip the shim so that any divot left on the face by the valve stem tip faces the tappet, so that the flat surface of the shim rests on the tip of the valve.

Also, when you measure the gap, you need to do this with the cam installed and torqued down to 15 lbft. If you try micing the thickness of the tappet and shim separately not installed you will introduce error.

[rblumsom]

Thanks Andrew, I have removed the cams, switched some of the shims around, re-measured and ordered some more shims.
My expectation now is that this could take a few more attempts and I'm going to be happy with a gap up to one thou too large on any valve - particularly given the tendency for the gap to reduce over time.
All the best,
Richard.

[christopher storey]

For you, while the expectation should be that you buy your 116 shim and it fits, the reality is that you need a couple of shims in a range to ensure it's all correct.

You could perhaps use the variations in tappet thickness to your advantage in trying to improve your situation, but the likelihood is that you're going to need to buy a number of extra shims and you'll have some left over at the end.

One thing which might help is that in the last few years it has become possible to get shims in 1/2 thou sizes - for some reason I have a better record of hitting the spot with these ( probably erring on a 1/2 thou thinner than arithmetically calculated ) and IIRC they are cheaper too !