Valve clearance / Shims less than 0,060

[SENC]

I'm not seeing anything obvious, but welcome more trained eyes that might see something different in the pictures.

[SENC]

#4

#3

#2

#1

[promotor]

#4

IMG_20220403_162822.jpg

#3

IMG_20220403_162849.jpg

#2

IMG_20220403_162911.jpg

#1

IMG_20220403_162936.jpg

Where the shim sits in the recess of the retainer it looks like the shim could have been seating on the retainer itself - the retainer looks to be polished there, possibly from contact with the shim? Or am I imagining that?

How far above the bottom of the retainer recesses are the valve tips sitting? If the valve tip is lower than the bottom of the recess, that's your problem. The retainers will be curved here too so the shim might be seating higher up than you might first think?

How far above the collet tops are the valve tips? Doesn't look like much from the photos, but perhaps it is the angle of the photo?

[SENC]

I'll try to get a couple measurements this week - I need to see if I have a depth gauge small enough or make one.

I was thinking the shim may have been in the retainer, too - but tried a top hat shim (should avoid that problem, right?) with no change. I may try to turn a few smaller diameter shims next weekend if the above measurements aren't revealing.

I need to recheck with my dad (prior owner). He had the head redone by Bean probably 20-25 years ago, I think and need to confirm to big valve specs, in which case valves etc. should have less than 15k miles.

I appreciate the questions and guidance.

[rgh0]

The valve tops appear to have been ground / machined in some way, so valve stem top possibly too close to retainer and shim hitting retainer on No 4. The others do not look much better. This was probably done due to the valve seats having been recut to much and the valves shortened in order to try to get acceptable shim thickness

Personally I would pull the valves out and start again with new valves and possibly also new seats, retainer / collets and springs depending on what you find when its apart.

cheers
Rohan

[alan.barker]

For me wrong Collets fitted. I would try fitting new collets on valve stems. I had this problem with my first 1968 Elan +2 where the wrong Collets had been fitted. This meant the Shims contacted the Retainer and not the end of the Valve Stem to open valve.
New Collets very cheap and worth a try imho.
Alan

[promotor]

I'll try to get a couple measurements this week - I need to see if I have a depth gauge small enough or make one.

I was thinking the shim may have been in the retainer, too - but tried a top hat shim (should avoid that problem, right?) with no change. I may try to turn a few smaller diameter shims next weekend if the above measurements aren't revealing.

I need to recheck with my dad (prior owner). He had the head redone by Bean probably 20-25 years ago, I think and need to confirm to big valve specs, in which case valves etc. should have less than 15k miles.

I appreciate the questions and guidance.

If the top hat shim isn't solving the problem I would want to rule out that the top hat shim bottom isn't contacting the collets. You could be seeing two different issues even though they could be related - ie, the position of the collets in relation to the valve tips and retainer bottom.
In both cases you will likely need to remove everything as has been said by others to check more closely, but before that you could try a very thin smear of that red grease in your photos (or engineers blue etc as it can be applied thinly) on the valve tips fit the shims and see if it is spread out completely. If it isn't in both cases you know the shims aren't seating.
After that you'll be wanting to check if the valve heads are pulling through the seat or if the seats are receding.

Let's hope its none of those things though and that it's something simpler and doesn't require any money spending!

[ncm]

Looking at the picture of the inside of your cam followers and spring caps it looks as though the follower in No 4 is possibly sitting on the spring cap. There appears to be a witness mark inside the follower and the cap top surface has picked up from the follower rotating on it.
Brian.

cam follower.jpg (61.74 KiB) Viewed 408 times

[promotor]

Hello Henry,

Just a couple of photos for you to show where collets sit on a standard valve:

and how close a top-hat shim comes to the collets (obviously, that depends what the spec of your top-hat shim is, but I guess they are similar).

.

HTH.

[SENC]

Good eye, @ncm. And Alistair, I'd say even without looking I don't have that much valve stem above the retainer. Perhaps Rohan is right, or Alan that the collets aren't right. Thanks to all of you, extremely helpful!

Will check these things and grab some measurements this week or weekend and see where we go from there, but seeming more likely the head will need to come off.

[rgh0]

Standard valves have 0.1 inch / 2.5 mm from top of the collet groove to top of the valve stem. The top of the collet normally sits flush with the top of the collet groove on the valve stem.

The distance from the top of the exhaust valve stem to the cam centre line for a correctly seated standard exhaust valve is 0.920 inch / 23.27 mm. Exhaust valve seats tend to need to be recut much more frequently than inlets so you often find exhaust valves that are recessed to far into the head and have had the tips ground off them to try to get enough clearance for the shims. This however creates a whole set of potential interference problems with the retainers and followers. Standard exhaust valve length is 3.850 inch.

It could be that the collets and valve stem and retainer are worn also especially if the follower has been hitting the retainer causing them to move relative to each other slightly during operation

I agree that unfortunately you need to remove the head and remove the valves and do some detailed measuring to see what needs correcting

cheers
Rohan

[2cams70]

The distance from the top of the exhaust valve stem to the cam centre line for a correctly seated standard exhaust valve is 0.920 inch / 23.27 mm.

You do need to get yourself a reference dimension between the tip of the valve stem and the cam base circle diameter or some other hard point on the head that locates the cam - eg. the cam bearing tunnel. It doesn't necessarily have to be an absolute number just a comparison with the other exhaust valves to see where the offending one sits. If the offending one sits a lot higher then you've probably got excessive valve recession in the head.

Actually there's an idea for a special tool!! - If you have a scrap camshaft lying around get all the lobes ground off so that it's just the base circle diameter left. With this you could then easily measure the reference dimension from the tip of the valve stem to the cam.

[rgh0]

The distance from the top of the exhaust valve stem to the cam centre line for a correctly seated standard exhaust valve is 0.920 inch / 23.27 mm.

You do need to get yourself a reference dimension between the tip of the valve stem and the cam base circle diameter or some other hard point on the head that locates the cam - eg. the cam bearing tunnel. It doesn't necessarily have to be an absolute number just a comparison with the other exhaust valves to see where the offending one sits. If the offending one sits a lot higher then you've probably got excessive valve recession in the head.

Actually there's an idea for a special tool!! - If you have a scrap camshaft lying around get all the lobes ground off so that it's just the base circle diameter left. With this you could then easily measure the reference dimension from the tip of the valve stem to the cam.

I use a special tool that was made for me many years ago that can be sat in the cam tunnels (without bearings) over each valve and is the tunnel diameter. It has a flat milled on the centreline with a couple of holes vertically through the milled flat. Then using the end of a caliper you can measure down to the valve tip and spring pocket base etc through one hole and also use one of the holes to line it up at the valve angle as the holes are the valve stem diameter and you can pass a cut off valve stem through the hole and the valve guide. A sketch drawing is attached

All my valve train rebuild spreadsheets are based on the cam centre line reference point this provides

twin cam valve position tool.pdf

(449.2 KiB) Downloaded 179 times

cheers
Rohan

[SENC]

Brilliant! I recently added a small metal lathe to my shop and needed a learning project... this may be just it!

[2cams70]

quote="SENC"]Brilliant! I recently added a small metal lathe to my shop and needed a learning project... this may be just it![/quote]

As you can see there's a few ways you could go about determining this measurement all equally good.

If you decide to use an old scrap camshaft I suggest taking it to a cam grinder and asking for the lobes to be ground off and the cam base circle diameter to be ground so they are consistent across all four lobes - there could be a small variation in base circle diameter across the 4 lobes otherwise.

Then with the assistance of feeler gauges, a known standard thickness follower and a known standard thickness shim you should be able to accurately determine the stem heights of 4 valves at a time. No need to install the caps - the modified cam just needs to rest in the lower bearings whilst measurements are taken.