Grinding valve stem tips

[olr159w]

Always the gift that keeps giving.

Regular readers may recall a thread about my Sprint busting a valve spring. The damage itself was not too bad but the car has basically been in bits since August. Some of this has been waiting for overseas parts, some of it has been repeated trips to the cylinder head specialists and some has just been slack behaviour

The head has now had three separate trips for engineering work - bolt removal and helicoils for two bolts on the water jacket end plate, four new valve guides seat recut and one new helicoil for a cam bearing cap when the thread stripped a week or so ago.

Prior to the valve guide work all valves were lapped in. Then I did something exceptionally stupid and it went in to get fixed plus a couple of other opportunity fixes at the same time.

It is only this weekend that I've been able to look at resetting the tappet shims for the four new valves. I don't have shims thin enough nor do they seem to ever have been available. The workshop must have recut the seats enthusiastically and to say I'm p155 would be an understatement. If it comes to it I'll be back there to demand they fix it but I note from the BL repair manual that the valve stems can be ground down a little.

Question - how much is possible? My preferred amount is probably around 0.5mm

Has anyone ever done this?

thks

[cliftyhanger]

Not myself, but the chap over the road worked for an engine builder "back in the day" and did a lot of Stags. He was telling me how they had to regularly grind the valves to get the correct clearance. I expect for the same reasons as you are experiencing. So I cant see an issue as long as they have a good finish.

[xvivalve]

What size shims would do the job?

[PaulB]

QED motorsport sell shims down to 61 thou if that helps. They are the same as Lotus Twin Cam

[olr159w]

There were four inlet valves replaced also with new guides and recut seats.

Of these one has the thinnest shim I have at 86 thou and is showing a clearance of 12 thou. So that one has a clearance 2 thou in excess of the target and is OK

For the other three :
- clearance 3 thou with 89 thou shim, so to reach 10thou clearance need 82 thou shim
- clearance <1.5 thou and quite possibly zero or negative using 95 thou shim, so to reach 10thou clearance 85 thou shim or less
- clearance 3 thou with 95 thou shim, so to reach 10thou clearance 88 thou shim

I was thinking in the process I would take a little more off and return the shim thickness into the more usual range. But if I can avoid so much the better.

The two things that trouble me, other than taking a file to the valve stem at all, are :
1. Perhaps I could make do with thinner shims if I could get them - QED an option thanks so there is a potential easy solution given Rimmers, Robsport etc have nothing below 90 thou - but of course the shim has to sit proud of the valve collar or the cam follower will just bear on that rather than the shim. It's all bolted together at the moment so I need to disassemble again and check. But I have a feeling the 86 thou one is pretty flush, there won't be much in it. And OEM was minimum shim thickness 90 thou presumably for that reason
2. if the stems are to be ground back the key thing is that the valve stem must still "protrude above the internal shoulder of the collar" . Until I get it apart I'm not sure what that means.

[xvivalve]

Looking in my shim pot, I have two shims that are 70 something thou' and a selection that are 80 something thou' (a while ago I separated them into multiples of 10 thou' for ease of finding). All of these have been taken from used Sprint or 1850 heads.

I'm due out on business shortly, but will measure the individual shims when I return; happy to post them to you if I have what you need...

[xvivalve]

If you want them, I have an 82, an 85 and an 88 sitting here on my desk...

[olr159w]

Hi Alun / all

Thanks for the offer. I spent a little time double triple checking the measurements for all valves. I'm happy I've made no errors although there is one change where I must have slipped up before.

The details :
Inlet 1 - clearance 3 thou with 94 thou shim, so to reach 10thou clearance need 87 thou shim
Inlet 2 - clearance <1.5 thou and quite possibly zero or negative using 95 thou shim, so to reach 10thou clearance 85 thou shim or less
Inlet 3 - clearance 12 thou, shim 87..............however read on
Inlet 4 - clearance 3 thou with 96 thou shim, so to reach 10thou clearance 88 thou shim

My issue is that when I look at Inlet3 with the shim in place its debatable whether it clears the collar. It looks like it might - see photo - but then see also the photo with the steel rule across the top. This was actually the cylinder that had the busted valve spring which is why the top of the collar is slightly bruised in case you are wondering.

Knowing that the stock shim sizes went down to 90 thou and seeing the way it is makes me wonder whether the shim is even clearing the collar.

I'm thinking I need to take say 15 thou off the valve stems and thus put the shim thickness back in the normal range. But something doesn't make sense about it - shorter valve stem + thicker shim = std valve + thinner shim - is still going to mean the same overall "height" and if that sits beneath the collar then I don't really understand what is going on

Actually no pictures because yet again the stupid rules on this website make it a pain. Although I have pics I don't have time to step through all the hoops that are required in order to actually post them. I can't even remember how to. But take it from me that on Inlet 3 the end of the steel rule bridges the top of the valve collar, resting on both sides and not standing proud due to the thickness of the shim.

m

[Mad Mart]

It's not ideal but if you look inside the cam followers there is a protrusion that sits on the shim but inside the collar, so the collar will still clear, if that makes sense.

[tony g]

I can add another idea, get a reground cam and all the shims need to be thicker. I have one and still idles nice and pulls better than stock (once dialled in properly)

Tony

[Sprintparts]

It's not ideal but if you look inside the cam followers there is a protrusion that sits on the shim but inside the collar, so the collar will still clear, if that makes sense.

Agree.

Over the years depending on the condition of a cylinder head, the number of times the valves have been cut and if the camshaft has been reground, have used shims as thin as .055" and up to .170"+, might have even been .200"!. The extremes are not always ideal, but what is the alternative.?

Around .080" is not a problem. If you are really worried you can always remove some material from the valve spring cap edge to give some more clearance to the bucket, or rocker. The rocker should be sitting central to the valve spring cap, so the rocker will clear the edge of the cap.

The only question that I have is the camshaft grind OEM? If OEM, the valve clearance should be .018", if reground then what the grind recommends, which usually varies from .008" to .012".

Mark

[xvivalve]

So an 85, 2 x 87 and an 88?

[olr159w]

Thanks for all the input.

I was thinking I needed to go back to the engineering workshop and have a difficult conversation but I'm now thinking Marts info might save the day

First up the cam was a new billet (ie not reground) fast road cam from Moss say 25 years ago and pretty certain made by Kent cams. Previous clearances 10 thou and in earlier thread about all this 10 thou is the target intent.

Four valves and guides were replaced. No 3 is Rimmers valve and new cam follower. The other three just new valves from Robsports. All four had the seats re-cut. All 16 have the original springs as sat unused for 20 years and substituting after one of the uprated single springs failed. All springs were within height tolerances

My thoughts on it :
1. The cam lobe is a fixed location and the gap between it and the end of the valve stem is defined by the thickness of the cam follower and the thickness of the shim. Decrease the stem length but increase the shim the same amount results in no change.
2. Recut the valves and the tip of the stem moves closer to the lobe.
3. Also the recess on the stem for the collets also moves closer to the lobe. If you recut enough this means the spring collar moves so close to the lobe that the perimeter of the collar is what engages with the underside of the cam follower and the shim becomes irrelevant
BUT what I think you are saying Mart is that this isnt the case because there is a raised protrusion inside the cam follower thereby preventing this effect to the extent of the protrusion?
4. The repair manual says the stem length can be reduced but on no account should the retaining collar be reduced in height
5. So its my view that the minimum shim thickness that sits level with the collar is about 90 thou. No point fitting anything thinner........... except that the cam follower protrusion avoids this to the extent that it protrudes.
If you have used 55 thou Mark this suggests the protrusion is at least 45 thou.

Which means the forgotten protrusion saves me from a difficult conversation. Yay.

In terms of sizes Alun one of those 87s is the current shim resulting in 12 thou so :

Inlet 1 - clearance 3 thou with 94 thou shim, need 87 thou shim
Inlet 2 - clearance <1.5 thou and quite possibly zero or negative using 95 thou shim, so there's uncertainty with this and to cover possibilities thinking ideally 86, 85, 84, 83 thou
Inlet 3 - clearance 12 thou, shim 87, need 85 thou
Inlet 8 - clearance 3 thou with 96 thou shim, need 88 thou

So to plan ahead and hopefully avoid disappointment and delay I'm thinking 83,84,2x85,86,87,88

Do you have all those perchance ?

Thanks everyone

[Sprintparts]

Don't get to hooked up chasing .001 - .002". If really depends on how good your feel is with "feeler gauges". Also removing and installing the camshaft caps can sometimes see a change in reading.

If the head is being done off engine on the bench, which is the way that I usually do it, there could be a slight variation when the head is torqued on to the engine.

Personally on NON OEM camshafts which are usually around the .010" clearance I work on up to +,002" tolerance, which will allow the valve to settle in to the seat and a close up when the head is retorqued.

I am sure everyone has their own ideas and opinions.

If you have spare shims that are oversize, why not get them ground to match what you need?

[Mad Mart]

Don't get to hooked up chasing .001 - .002".

I quite agree. I used to spend hours getting the clearances to within 0.001" of 0.018". Then I realised a lot of people didn't even use this figure.