Valve stem seals & tappet clearance.

[Marcusj1000]

Hello everyone.

I am setting the valve gaps on my 1974 v12 2+2. The gaps are all over the place and vary from 0 to 0.58mm! The gaps are generally too tight and only a couple are too tall. Many of the tappets are very pitted so I have purchased new ones and measured the effective thickness. I am currently working out the shim thickness I require for each valve and most of them work out less than the thinnest available to purchase. I am confident everything is seated correctly and suspect it to be a result of head work taken out by the previous owner.

My first question is this. Is it generally ok to surface grind the shim thickness down to suit or will this cause problems with the surface hardening that I assume is carried out on them?

As I have the top of the engine in bits (heads still on) I am going to replace the valve stem seals. The car has previously been stood for about 7 years and is smokey when cold. This stops when it has warmed up and I suspect the seals have hardened and are only effective when warmer and more supple. Does this sound like a plausible reason for the smoke?

I would like to change the seals without removing the heads and I have heard of a couple of ways to do this. One is by filling the cylinder with rope through the plug hole (sounds iffy!) and the other is the use of compressed air in the cylinder to stop the valve dropping. (This also sounds a bit dodgy!) . Does anyone know of any other tricks that will avoid me having to take the heads off ?

Thanks in advance for your help.

Marcus.[/b]

[MarekH]

Dear Marcus,

The scope for reducing shim thickness below the "A" size is severely limited because the tappet cariers risk hitting the spring retaining collars before they hit the shims as your camshaft pushes the valves go up and down. A safer option is to remove the tappet carriers and skim them instead so you can use shims of a thickness within the usual operating range. Typically, if a head has been skimmed excessively, the valve stems are often cut down instead.

kind regards
Marek

[Marcusj1000]

Hi Marek,

Thanks for that, I hadn't thought of removing material from the tappet carrier.
I will work out exactly what shim sizes I need and plan accordingly.

Does anyone out there know how much of an undersized shim I can get away with? It would be easier and cheaper if I can get them machined individually.

Also, I have been researching using rope to hold the valves up as I replace the stem seals and it seems quite common practice so I might give it a go and keep my fingers crossed! I have purchased 24 valve stem seals but I am aware that only the inlet valves use them. Is it possible to seal all 24 valves? Do the seals fit both? What are the reasons to only seal the inlets?

I shall let you know how the rope trick goes, hopefully I won't lose a valve as I'd rather not be taking the heads off!!

Thanks again for your help.

Marcus.