Cam Followers - Different Types - Help Needed

[4129R]

I have just has 3 x Weber heads overhauled with new guides and valve seats fitted where needed, and gas flowing on the ports, by a specialist Lotus engine company, Scholar Engines in Suffolk.

I am now shimming up the cam clearance and here is where I am hitting a problem.

The thinnest shim listed by QED are 61 thou, and I need 51 thou on 2 cylinders on the inlet side.

I have loads of spare cam followers/buckets, and they come in a variety of thicknesses when measured cam face to shim face.

Most are in the range 213-221 thou.

I have some in the range 154-159 thou which are thinner walled and lighter.

I have 1 at 128 thou which is 2mm longer at 26mm.

I have several at 154, 163, 170, 190, 198, 202 and 212 which are 25 thou bigger in diameter and shortest at 22mm long.

My questions are:-

1) are the thin walled and thick walled cam followers interchangeable? I need the thinnest possible to get the correct thickness shims.

2) I was advised by Scholar, that one of my heads has oversized followers, probably from a Jaguar, as Lotus didn't make/use different diameter followers, and QED don't stock bigger ones. Has anyone come across bigger diameter cam followers and where do they come from? Jaguar XK or XJ series engines?

To measure the clearance between the follower and the cam (10 thou exhaust and 6 thou inlet) I was struggling, as with my thinnest shim, (69 thou) I had negative clearance. So to measure the correct shim, I needed a known thickness shim about 45 thou thick but they are not available. I had a think outside the box...... where can I find a circular disc about 45 thou thick. I had a rummage around my extensive foreign coin collection, and bingo, I found a suitable small coin, which is so small, I cannot read the print on it where it came from. 45 thou. So now I can actually get a gap to measure, but the thinnest gap is requiring a 51 thou shim, but only 61 thou are available, so I need to fit a thinner cam follower, hence my query about thinner followers.

(It turns out the coin is a 1 cent piece from South Africa with Isewula Afrike 2001 stamped on it.)

Failing this, I will probably have to take 15 thou off the end of the valves. Can this be done by simple careful filing, or do I need to get this done by a machine shop grinding a bit off the end?

Last resort is to try different inlet valves to see if any are shorter from the collet to the end where the shim abuts the valve. 

 

[BDA]

I would not use a coin as a shim as it is surly to soft and will be thinner in short order. I would either trim the end of the valve or grind (or sand) a shim or a combination of the two.

You can sand a shim with wet/dry paper for small changes or a few shims, but otherwise, I’d see if a machinist could help you out.

Sorry I can’t help you with the followers except to note that Burton Power lists two followers, one called oversized OD. I found with my BDA, there are standard and oversized followers. In reality, even the standard followers were oversized so presumably, the oversized followers were more oversized (I didn’t buy any but I’m confident they are). In fact Burton listed my standard followers as 1.200” but in fact, they were something like.008” larger requiring my machinist to open up the bore. I would expect you to have a similar experience. Unfortunately, you’ll have to buy one to find out.

As for interchangeableness, if the bore and effective thickness are (the BDA has a post in the inside of the follower) good, the only worry I would have is the radius of the crown on the follower. I don’t know if it’s critical or different from engine to engine. My guess is that it isn’t critical but an engine builder might be able to help you there.

[4129R]

Thin coin was only used to determine the correct shim thickness, as I couldn't get any gap with the shims I had.

[jbcollier]

Valve ends need to be ground in a special machine to keep them square.  Do not file them!

You can also cut off too much and have the valve shim hitting the retainer before the actual stem.  Just something to watch for.

To me it sounds like you do the valve ends (carefully) trimmed.

[BDA]

Yeah, I figured you knew better but I added that in case someone else might have thought it was a good idea.

[Richard48Y]

Correct procedure would be to either have some shims thinned on a Surface Grinder, or to have the valve stem shortened by a machine shop.

Both have possible issues to watch for.
Thinning a shim may weaken it?
You need to check for surface hardness after, if you go through the hardened layer the adjustment will be short lived.

Shortening the valve stem may be best as any machine shop doing head work should be equipped for it.
.010" should not be an issue, I would take a little more to allow for the next valve grind and adjustment.
You will need to ensure that enough valve stem remains above the keepers to ensure they are not disturbed in use.

Surprised your head specialist has not made a suggestion.

[4129R]

But why is there such a variation on cam follower thickness?

Using the thinnest cam followers means I can buy the correct thickness shims from QED.

[BDA]

Correct procedure would be to either have some shims thinned on a Surface Grinder, or to have the valve stem shortened by a machine shop.

Both have possible issues to watch for.
Thinning a shim may weaken it?
You need to check for surface hardness after, if you go through the hardened layer the adjustment will be short lived.

Shortening the valve stem may be best as any machine shop doing head work should be equipped for it.
.010" should not be an issue, I would take a little more to allow for the next valve grind and adjustment.
You will need to ensure that enough valve stem remains above the keepers to ensure they are not disturbed in use.

Surprised your head specialist has not made a suggestion.

I’m confident that shims are thin enough that they are hardened all the way through. At least that’s what I found on my BDA shims. It’s pretty easy to tell because of how you quickly wear out the paper!

I agree that especially since the problem is finding a shim thin enough, grinding the valve stem is probably the best solution. It surprising that his machinist didn’t suggest it.

It might be a good time to mention that there are two styles of shim: the flat biscuit type and the valve cap or top hat type. The latter are thicker than the biscuit type. Because they fit on the valve stem, the distance from the top of the valve keeper to the top of the valve stem must be longer than the valve cap is deep. Like I say, it’s not a worry here but it might be useful information to someone.

[4129R]

If I need to thin the shims, I can hold them in a spring cap and use a rotary sander with abrasive paper to take off a few thous carefully.

When fitting the cam follower on the him, I just need to make sure the cam follower is actually bearing on the shim, and not fouling on the cam cap.

But why are there cam followers which are thick and thin? Are the thin ones standard, or non-Lotus ones?

[Richard48Y]

"If I need to thin the shims, I can hold them in a spring cap and use a rotary sander with abrasive paper to take off a few thous carefully".

It is your engine, but the Only means of ensuring a Truly Flat shim is to use a surface grinder.
Should not be expensive at all as it is only a small area to be worked and a quick job.

[Pfreen]

The standard Lotus follower pad thickness is .216".  The thick pad follower is .245".

I think that will solve your shim issue.  I believe they are Jaguar XK. 

In my case, I needed the thick pad follower because my cam had been reground and my required shims were very thick.

I bought my thick pad followers from RD Enterprises in the U.S.

You can have a shop spark off the valves, but you will need to disassemble the head. 

[4129R]

QED Engineering confirm the thin and thick cam followers are interchangeable.

As for the oversized cam followers, they suggest fitting new original sized steel sleeves for the cam followers into the head, providing the aluminium casting of the head has not been over-bored to fit the bigger cam followers and sleeves.

They have posted me the shims I need today, so hopefully tomorrow I can complete shimming the cams and start putting the head back on, so I can get the engine back in to 2520R.

Got to keep busy during lockdown.

Most of us Europa owners must be in the "vulnerable" category, being dinosaurs.