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Pitted valves and valve lash

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Hello everyone,

Recently got work done at a machine shop and need some opinions before I take it back.

The shop replaced a seat (burnt valve) and did a grind on all the valves (even though I didn't ask for it). The valve stem tips were also ground to set the valve lash (bucket lifters).

Grinding revealed a lot of the valves were pitted, see pictures, the badly pitted valve was in the same cylinder as a burnt valve.


1. I will be replacing the severely pitted valves, but some valves have very minor pitting, Could/should light lapping be used to remove minor pitting?

2. After assembling the head I found the valve lash on all valves to be 0.10mm OVER allowable tolerance. Could there be something that I missed?



Attached Files

I'd take a guess that you're dealing with a machine shop who doesn't work with performance engines too much. What they've done is probably quite acceptable for an average road going engine. It may even hold up in a performance application but it certainly isn't pretty. I'd personally replace the pitted valves and know that the seat finish is in perfect condition.

Lapping valves needs to be approached with care. It was a technique that was common a couple of decades back but these days it's rarely used because it results in a concave/convex interface between the valve and seat that almost guarantees that the only time the valve seals properly is when the engine is cold. Light lapping can be used to remove minor chatter marks left from the valve seat cutting tools but you're not going to be able to lap out the pitting that is visible in these pics.

Andre, you guessed right, am still surprised the shop didn't tell me about it.

I am going to replace all the valves, since the seats and valves were machined for the old valves, should I get the seats/valves machined again for the new valves?

Considering that this will be a high performance engine, should I be concerned with the valve seat that this machine shop replaced it with?

Appreciate all the help!

You will need to make sure that the valves are ground to the same angle that the seats are cut on so some care is required here. I'd recommend finding a more competent machine shop and having them go over everything to make sure your valves are seating correctly and make any required adjustments to the installed height. A point here is that this is one area a light lapping can help as it will quickly show you the seat contact between the valve and valve seat and you'll be able to see how wide the contact is and how even it is.

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