OSULemon

I purchased a '99 with no compression in one cylinder; turns out an exhaust valve had a hole in it

My brother has been doing all the work on this one (it will be his daily), took it to a machine shop he trusts, they did a port/polish and re-seat/3-way grind? (showing my ignorance here)

Anyway, the final result was movement of the valves such that the shims we have will be too thick to use for any of them. Was this a mistake? Probably. Too late now.

Far as I can tell, we have the following options:

1. Buy thin valve shim, use it to measure required shim thicknessses for all 16 cylinders, order all from cylinderheadsupply @ $20/4 for a grand total of $120 (plus shipping)

2. Grind the valve stem tip to match factory clearances? Head is already disassembled, this could be an option if it won't cause issues with the valve stem hardness. Not sure at this time how much material we would need to take off.

3. Use surface grinder (I have one at work I might be able to use) to grind existing shims to proper spec. Again, not sure how this would affect surface hardness.

4. Convert to SUB style for more money up-front ($200-$220 plus valve lash caps), but future-proofing for different cams or higher RPM's, plus less reciprocating weight.

5. Other?

Can anyone advise on which method is best moving forward? I think I've read near every thread I can find on every Miata forum about this subject, before anyone asks.

That said, I'm still an engine-building newbie. Thanks in advance for any advice!

Stealth97

iTrader: (5)

Since you have the means, I would just grind the shims.

Alumilo

iTrader: (1)

As Stealth said, tip the valves if you have a method to predict how much to take off, otherwise you'll be tipping valves and buying new shims.

albumleaf

iTrader: (7)

Correct me if I'm entirely wrong here.. but you're removing material for the valve job. so shouldn't the shims be too thin?

ryansmoneypit

iTrader: (6)

Think about that....The valve sits deeper in the head, this tightens clearances at the cam.

albumleaf

iTrader: (7)

ahhh right, my bad. Carry on.

Savington

iTrader: (31)

Grinding valve tips is SOP for most machine shops. Nobody has a full shim library for every head they work on. They cut the seats which sinks the valve ever so slightly, then they tip the valve during assembly to reset the valve lash.

OSULemon

Thanks y'all. I was also told to check the installed spring height to make sure spring tension is maintained, then correcting that with shims before grinding anything off the valve tips. I will relay all that information to the machinist.