Cylinder Head Componets. Replace?

[TeeJay]

Hi,
Looking for some clarity & inspiration.
I have examined and measured the head valve gear and I am a bit undecided on the way forward.
Do I go for a complete renewal of seats, guides, valves and spring sets etc?
Or do I select and only replace the components that are outside of specification?

The measurements are:-

Cam Shim Thickness 1 2 3 4
In 0.0695 0.0722 0.0670 0.0695
Ex 0.0745 0.0690 0.0719 0.0669

Inlet Valve
Stem Dia STD 0.310_0.311"
Stem Dia Act High 0.3101 0.3101 0.3101 0.3102
Stem Dia Act Low 0.3096 0.3094 0.3095 0.3097
Max stem wear 0.0005 0.0007 0.0006 0.0005
Side Movement with dial indicator
0.0050 0.0050 0.0050 0.0040

Exhaust Valve
Stem Dia STD 0.310_0.311"
Stem Dia Act High 0.3100 0.3101 0.3101 0.3100
Stem Dia Act Low 0.3091 0.3092 0.3082 0.3079
Max stem wear 0.0009 0.0009 0.0019 0.0021
Side Movement with dial indicator
0.0070 0.0050 0.0090 0.0080

Anyone have a view on what is the maximum wear before renewal?
As I understand, this is any wear greater than as the Specification of ?stem clearance in the guide? and shim thickness less in the 0.060-0.070 range?
i.e. Inlet 0.0003/0.0023, therefore anything greater than 0.0023? gets replaced
Exhaust 0.0025/0.0030, therefore anything greater than 0.003?
At present I have not been able to measure the bores of the guides, no ball gauge, but I have measured the valve sideways movement when at maximum lift, as recorded above.

The Head Thickness measures 4.637? and is uniform over its surface area. This suggests that it can not be further skimmed as it is just outside of the specification of 4.638? to 4.643?.???

Finally the valve seats do indicate some receding as can be seen from the cam shim thicknesses, but is it possible to recut, perhaps with new valves and remove a little off the top of the valve stem?

As you can guess I am a little reluctant to heat the head to remove/replace components, but, has the head reached the point where I have to bite the bullet and replace all valve parts?

Thanks for any replies.

[Lincoln62]

On the valve issue. I can't see the thickness of the shims making a difference for a road car as long as the clearances are correct.

When I rebuilt my engine I found the valves receded in the head significantly. They had been purposely ground down into the seats by a previous owner. He told me this was common when the cars were raced as it allowed you to use more lift without the valve hitting the piston. It ran perfectly like that for 10 years. To rectify this I had the machine shop make some new valves with slightly larger heads and very slightly larger stems to bring them higher on the existing seats. They had a selection of blanks and just cut them to length and machined the collet groove. I kept the existing guides, they just reamed them to suit the new valves. It seemed a good solution, didn't have to replace seats or guides and the valves weren't expensive.

For the shims, the machine shop had a box of them, apparently the same size as a Morris/Austin 1500OHC and some SAAB models which they lent to me. I trial fitted with some undersize shims to get measurements. I chose some slightly larger than needed and asked them to machine them to the sizes I specified.

That was 12 years ago and it still runs perfectly.

Hope this helps.

Pete

[rgh0]

Hi Teejay


A few comments on your questions

Shim minimum thickness due to valve seat recession is driven by a lot of issues. You can engineer around most of them if you know what your doing but generally easier to return to a standard set up by replacing the valve seats.

Issue to watch for as you approach the thin end of the valve shim spec which you are at

1. Interference between top of bucket and valve spring retainer. How thick a shim depends on the details of your buckets and vvalves and retainers all of which have some variation from different suppliers
2. Spring installed load. As the valve recesses the installed spring load gets less which can give valve float problems at high revs
3. Shim breakage - as it gets thinner it is more likely to break. I have seen them break around 1.5 mm or 0.060 inch so you are near this possibility

Bigger valve head can move the valve out so going to 1.625 and 1.4 inch valve heads and recutting the seats may get more life out of the existing seats depending on exactly how they have been cut previously. If combined with the matching porting and cam this can give you a substantial performance improvement also.

The side ways movement of your valves implies a bore clearance of around 0.003 to 0.005 inch on inlets compared to a spec of around 0.002 max and 0.004 to 0.009 for exhausts compared to a spec of 0.003 max. I would check with bore gauge, the guides wear in an hour glass shape but it looks like guide replacement is due. If burning signficant oil and leaving a blue trail then defintely due.

The head can be machined down to around 4.500 inch thick if really need to get straight and still be usable. so no problem with the head and if still substantially flat and no problem with blowing head gaskets no need to machine in anycase. What limits minimum thickness is compression ratio and valve clearances to piston both of which can be managed via thicker head gaskets and head material thickness to the water jacket under the exhaust port which can be managed by repair welding if you get to thin in this area. In the end the only thing that truely condems a head is softness not dimensions.


cheers
Rohan

[TeeJay]

Thanks Rohan and Pete for your inputs, interesting and most useful.

With the comments on issues, re shim thickness and that the ex. valve guide indeed does have a clearance as suggested off 0.009, it means replacement.
Therefore as the head now has to be heated all the guides and seats will be replaced as well as all the valve gear.

A previous thread by Rohan and Keith (thanks) of "cold" removal by spot Mig weld on the seats will be adopted. So hopefully the head will only need one heat cycle to replace the guides and "cold" seats.

Then off to the machine shop for completion.

This will add the engine to the "completed" list of rolling chassis and gearbox. Next is the body, including respray, hopefully with the project nearing completion next summer.

Thanks again for helping me make the decision.