1990 4.3LX Rebuild - Worrying Cylinder Heads

[ba5e]

Hi all! I'm renovating my second 4.3LX, I'm ready to start to put the thing back together after ny new sump arrives (had a pinhole in it near the oil plug) but have hit a problem with the cylinder heads after getting them milled and cleaned.
The outer valve seats look lovely but the inner valve seats are pitted and extremely worn. The engine has only done 300 hours so I'm wondering what would cause such valve seat damage only on the 'middle' cylinders given the others are in such good condition. Second question, if I lapp these valve seats will I make a discernable difference? FOr some background, the engine did smoke a bit at low revs but compression figures over the last 3 years have been on the limit of 10% of the others.

Bad valves (one from each head)

Good valves:

 

[Bondo]

Ayuh,.... The center cylinders sit right under the riser/ manifold gasket,... Probably rust pittin',.....

You sent the heads out to mill 'em, 'n didn't have the valves done,..??

SoP is grind the valves, 'n seats, then hand lap 'em in,.....

I donno's hand lappin' will be enough, alone,....

 

[tpenfield]

Yea, looks like the seats were not ground/cut . . . A few might be questionable and need a new seat. Lapping won't do the trick . . . these heads should go back for completion of the needed work.

 

[NHGuy]

Agree. those seats won't do. No sense assembling til fixed.

 

[ba5e]

Ayuh,.... The center cylinders sit right under the riser/ manifold gasket,... Probably rust pittin',.....

You sent the heads out to mill 'em, 'n didn't have the valves done,..??

SoP is grind the valves, 'n seats, then hand lap 'em in,.....

I donno's hand lappin' will be enough, alone,....

Just got the cylinder heads back again. Went to another workshop as the first one was aweful! Pressure tested the heads and then cut all the exhaust valve seats and its looking good now, will upload some shots this weekend.