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Non-sealing exhaust valves after valve job?

K

kopeck

Member
Good Morning,

Quick back story. 15 years ago I had the rebuilt on my '47 A when I replaced the head gasket. The new head gasket didn't solve my problem so it got tucked away until now. I don't think the valve job has more then 10 hours on it, at the very most 15.

Fast forward to today. Complete engine overhaul. Last night I removed the valves as I was going to have the shop machine shop run the head through their parts washer (it's been sitting for a long time and was pretty grimy). This is what I found:


IMG_0923.jpg


This is the worst of the bunch, it's kind of hard to see in the picture but the you can only see the ring on about 2/3s of the exhaust valve face, the rest is just soot. There at least one other like this as well but not quite as bad. The intake valves look OK.

What would cause that? Did I get a poorly done valve job?

K
 
your guides are not true too the seats allowing stone too be cocked off to side when being ground . will probably brake in and be alright but
would i would measure everything and go from there and do it again , but i have a valve grinder
 

The valve lash could have been set too tight preventing the valves from seating. In this case there may not be a problem with the valve job itself.

You should be able to check for valve sealing on the seat (proper valve job). I am not an expert on this and would like to see others comment on how this would be done.
 
clean the valves then lightly lap them and check with some prussian blue. that will tell you if the valve is sealing correctly. if they check out then it could be the valves were set too tight
 
OK.

I was under the impression that new guides were installed but that was a long time ago.

I think I'll still have them wash the head. I'll clean the valves and give them a light lap and see how it goes. Like I said the intakes were fine...

I guess the lash could have been off, I would guess not but that doesn't mean anything.

K
 
Use some 3M scuff pad chuck each valve in a drill and give the face a quick polish job. Use the
scuff pad by hand on each seat in the head using a "washing machine" motion. Assemble the
valves in the head with springs on. Place the head on the bench so the valves are level. Put a
couple of tablespoons of diesel in each combustion chamber. If the diesel has not leaked
completely out of the combustion chamber in a minute or so your valve job is adequate.
 
wire brush it all, get some lapping compound, put a good layer on the valve face. put the valve in the head, then chuck it up in a drill. run drill slow and pull up and seat the valve. do it a couple times. take valves out and check them to see it they sealed all around. works good, I have even "fixed" a few cars this way, but with ne compound, just spinning them and putting pressure on the seat.
 
I showed the guy at the machine shop I'm having work done and he thinks he can touch them up pretty quickly. It looks to me that only the center to exhaust valves are wonky.

He agrees that the seat isn't square with the guide. Not idea how you do that if you're paying attention.

The one thing I didn't think I was going to have to mess with was the head...

K
 
clean them with a wire brush lap them and they should work fine, when lapping make sure the valve and seat have a lapped surface if any portion of either doesn't then you will need to re-grind them,man I worked with years ago would lap the valves of a reconditioned head before installing them, I asked why? he said unless I know who done the work it was easier to lap the valves to start with than to have to pull a head back off at his time and expense and lap them he said he put one on a 350 Cummins time it started it had a slight miss,pulled the head back off to find someone cleaned 2 valves and reinstalled them they weren't seating and that wasn't the only one he had problems with, filling the port with diesel as mentioned before works good also.
 
The guy that fixed a rebuilt head I bought said they did a poor job of setting up their machine to cut the seats. I'm
guessing you got the same set up...

GReg
 
As IK already said below, not enough valve lash could keep a valve from fully closing. That would be an easy thing to fix.
 
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