Valve job

[monsterm20]

Ok so I turbo'd my m20 then due to horrible tuning done by me the head gasket blew. Now the head is off and look very good. No cracks. While it's off I would like to do a refresh I have new seals and was wondering if anyone has ever regound the seats using valve grinding compound? I've seen it done and my experience with it is on iron heads. So my question is would it be a good idea to do on my head. The valves don't wabble but with over 200k on them I'm sure there is some pitting. So yea or nea? Speedy replies appreciated

[downforce22]

I just did it. Head is not installed yet but why not? After looking at the seats mine were very shiny with pitting. Everything I read pointed toward getting rid of the pitting for a dull grey color. Why not? I have just heard not to get too aggressive since its aluminum

[monsterm20]

K that's what I was thinking. My compression was good before I blew it up but I was on the same kinda thought pathas you. Why not? But at the same time it seems when I have those thoughts alot of people think they are retarded. So just making sure. Also you know those cylinder glaze removers do those work? I'm not rebuilding this motor cuz I have a turbo motor in the works but it would be great if I could get a year or two out of this one.

[jlevie]

At 200k, there is a good chance that the exhaust valves are now too thin to be ground. That would be even more important in case of FI. The head will definitely need to be surfaced. My advice is that you send the head and a new set of exhaust valves to a shop. Have a three angle valve grind done and the head surfaced. The cam may well be worn, have it profiled to check for wear and if worn it can be re-ground back to spec or replaced.Depending on the wear new rockers may be needed.

Once the head comes back it would be smart to lap the valves in until there is full contact across the sealing surface. If the shop did the work correctly full contact will immediately be established. If not have the shop redo the head.

[digger]

the lapping compound used properly checks the integrity/quality of the valve job as a last step. it is NOT to true things up and take metal away

[monsterm20]

I don't want to do a full rebuild cuz like I said I have a m20 in the works that will be built with turbo charging in mind I.E. Low compression pistons, Shrick 288 cam, balance and blueprinted bottom end etc..... So I just need this engine to last a year or so doing like 5-9 psi. On a war chip. I just figured while the head was off I'd get rid of some of the pitting on the valves.

[MonkeyMan]

Once the head comes back it would be smart to lap the valves in until there is full contact across the sealing surface. If the shop did the work correctly full contact will immediately be established. If not have the shop redo the head.

how do you check for this?

[jlevie]

The "color" of the seat and valve will change as you lap. so it is pretty easy to tell if full contact across the seat surface is present.

[ForcedFirebird]

The "color" of the seat and valve will change as you lap. so it is pretty easy to tell if full contact across the seat surface is present.

Dye can also be used.

I also have found the typical high mileage m20 has worn valve guides, the valves themselves are usually in tolerance.

[jeffnhiscars]

Here's a freshly machined valve before and after hand lapping. It shouldn't take more than a minute or two with fine compound if everything is right to get a perfect grey circle. Problems can come from worn guides or valve stems (most common), a bent valve, an improperly dressed valve facing stone or a bad seat cutter. Keep in mind the seat cutter uses the guide as a pilot so if the guides are worn its impossible for the seats to be concentric