valve shims after lapping

[lee]

I'm getting ready to order valve adjusting shims after installing new valves and hand lapping them in to ensure good seating. By using the existing shims that I have it is not too difficult to calculate what thickness I need, except that I'm wondering if I need to subtract a thou or two to compensate for the wear-in on the lapped surfaces. Your experiences and advice would be much appreciated. Thanks in advance

[bitsobrits]

Using feeling gauges is not super precise, so your measurements may be out half a thou or so. I always ordered the exact size I think I need for each valve, plus one thinner for each. (I'd rather end up +1 on clearance rather than -1). Over the years I've accumulated many extra which I trade with others.

[512BB]

My understanding of shims is that they have a hardened surface finish, or always used to, and that by lapping you will have destroyed that finish. Having said that, I have observed that shims that I bought recently, from QED, do not have the same look about them as shims from 30 years ago, so whether shims supplied today are in fact hardened, I have no idea, so bit a pointless post really

FWIW, I make no allowance for shims bedding in, but fit them so the clearance is at the top of the range to allow for valves bedding in.

Leslie

[rgh0]

I think the question is around do you need to allow for seating in of the valves after lapping them in by setting the clearances a little on the high side. The thread has drifted to, do the shims also bed in especially newer one ?

The shims need to be hardened if not they will develop a recess where they are hit by the valve stem very quickly.

With good components and good lapping of the valves in their seats the movement of the valve train as it initially beds in is very very small in the 10th of thou range. I normally set the valve clearances in the middle to top end of the range to allow for wear over time.

cheers
Rohan

[Mazzini]

My understanding of shims is that they have a hardened surface finish, or always used to, and that by lapping you will have destroyed that finish. Having said that, I have observed that shims that I bought recently, from QED, do not have the same look about them as shims from 30 years ago, so whether shims supplied today are in fact hardened, I have no idea, so bit a pointless post really

FWIW, I make no allowance for shims bedding in, but fit them so the clearance is at the top of the range to allow for valves bedding in.

Leslie

They should be through hardened not case hardened.

[englishmaninwales]

My purchases of shims from QED in recent years, I have been assured they are through hardened.
Malcolm

[lee]

My fault for the confusion--sorry. I was referring to the valve seats and the valves since they are no longer smooth, but now rough surfaces created by the lapping compound ("fine grade"). Looks like I also need to factor in shim distortion into the process too. If my thinking is correct maybe they will cancel each other out! A sharp file stroked on the edge of a shim should tell me if it is hardened, right? I've developed the habit of always adjusting to maximum valve clearance, especially on exhaust valves, based on a lot of experience with air cooled Porsche motors, but perhaps it should not carry over to Lotus twin cams???? Thanks for the thoughtful responses.

[AussieJohn]

I always set for top clearance because most times they close up, it's not such a big job to re-shim after maybe 300 to 500 miles. Usually after one adjustment they rarely move much. [ My friend made a tool that allows the cam pulley to be moved off the cam and onto the tool without having to re-time the engine, makes life very easy.]

[Foxie]

<Snip>
[ My friend made a tool that allows the cam pulley to be moved off the cam and onto the tool without having to re-time the engine, makes life very easy.]

I don't understand what this might be. And do you mean the cam sprocket ?

Any pics ?

[2cams70]

I'm getting ready to order valve adjusting shims after installing new valves and hand lapping them in to ensure good seating.

The practice of lapping in valves by hand should largely exist in the "old wives" tales category these days. Certainly if you are installing new valves you should be getting the valve seats lightly re-cut with the correct tooling rather than trying to make things match by grinding by hand. The valve contact width on the seat, the seat angle and the contact patch on the valve are all critical to valve and seat longevity. It's impossible to get it correct grinding by hand. A bit of a light grind with fine paste after they have already been recut may be OK but in this case it's really just a precaution in order to observe that the valve to seat contact patch is OK rather than to improve the sealing.

You certainly won't find any busy bodies lapping in valves by hand on an engine production line.

It's also a waste of time grinding or re-cutting seats and valves unless the valve to guide clearance is within spec.
It may be worthwhile attempting to bend a spare shim. If it breaks it's likely to be through hardened if not then probably not.

[reb53]

Leslie[/quote]

They should be through hardened not case hardened.[/quote]

My testing of a selection with a portable hardness tester suggests that this is the case.
When I tested a selection at different places, including the indentations in the centre of some, there were no
discernable differences.
Suggesting they are through hardened, not case hardened.

Ralph.

[Craven]

Leslie

They should be through hardened not case hardened.[/quote]

My testing of a selection with a portable hardness tester suggests that this is the case.
When I tested a selection at different places, including the indentations in the centre of some, there were no
discernable differences.
Suggesting they are through hardened, not case hardened.

Ralph.[/quote]
Having access to a surface grinder have adjusted shims thickness to suit, no sign of any change in hardness same applied in resurfacing of cam follower buckets.