anybody got a success story where aftermarket oversized valves have brought back to life a head where the seats were too worn to install stock sized valves? I found a T 140v single carb head but it looks in very questionable shape--- ie- deep pocketed and nicked up seats-- gasket surface and combustion chamber nicked up-- guides probably bad also-- without the head in my hands is there a way to measure if oversized valves will " go get" unused seat surface? I know these heads are getting rare so I'm seeing if this head can be brought back. thanks, Bob
"A T140v single carb head" is in actual fact not that, it's a TR7 head, but we all know what you mean. The smaller ports are a boon, do NOT go bigger!
First I'd like to know how deeply recessed the valve seats are. It usually looks worse than it is. Up to 2 mm or .080" is tolerable. If there's an edge from the cutting tool it needs to be blended in, especially on the inlet. The closer it is to the valve, the more important.
Not nearly as important on the exhaust. I've made up some simple tools on a drill to do this, but it can be done by hand. Stick an old valve in there to protect the seat and use a Dremel if you feel confident.
Your valve springs may need spacing/shimming under the spring seat to regain lost seat pressure.
The valve train geometry will be slightly altered but in the case of these engines it's not detrimental. I've done it with no obvious issues even in the long run.
PeteR (RIP) actually claimed sunken valves could be better. (His posts are still to be found on this site, bless him.)
I've used oversize valves to reclaim both inlet and exhaust seats. There are two important things too look for if you do this:
Make sure the valves don't sit too low, if the valve stem protrudes too little on the spring side, the springs may become coil bound. Not good.
You will also need to pay attention to your valve timing so they don't collide on overlap, especially if both valves are oversize.
Nicks and scratches in the combustion chambers aren't very important unless really bad. They will be smoothed out by carbon build up very quickly. To polish the sharpest nicks and edges, I use a soft stainless steel rotating wire brush on a drill. This leaves a very nice surface with any sharp edges eased down.
To restore the gasket surface I glue emery paper on a glass plate and run the head over it to flatten any protrusions. No need to overdo this, or you'll run into trouble with the push rod tubes later. Some kind of sealer can be used if the surface still has a lot of nicks and scratches.
NB! Chances are your cylinder head will be slightly bowed, in which case it may need to be straightened to be able to restore the gasket surface. Or not:
Deft hands and some emery paper may be all you need, carefully smooth down what you can and use the head as it is, with a careful re-torque regime, all will be fine.
This is my "fisherman's approach" anyway, akin to a Hillbilly
, we had to make due with what we had. I found out decades ago that these old things can take a beating...