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Two destroyed exhaust valves [with pics] - replace valves or entire head?

  • Thread starter Thread starter TheDuke
  • Start date Start date
Even if you buy a new head your gonna need to inspect and probably repair to an extent on the new one. As already stated the seats are very durable, the valves burn partially because they don't make contact with the head when out of adjustment and as a result don't cool properly. As long as the seats can be cleaned up I'd replace the bad valves and go with it.

Cheers
 
Maybe, maybe not. If they were .010mm looser maybe none of them would not have burnt, maybe the other valves are fine. Or maybe they are burnt to shchitt too. Did you check the compression?
 
Yes, and 1 and 4 were fine. But I suppose it is best to replace them all while I have it all apart.
 
How about some shots showing the valve seats after a good decarboning? As far as replacing all the valves, I'd measure the stems first and then decide. A quick spin on a valve facing machine and old valves get a new life so no need to replace them unless they are worn.
 
I plan to apply some elbow grease on Sunday or Monday and will post some pics of the seats then. Would lapping in the old-but-usable valves be sufficient? Or do I have to get those two survivors machined?
 
TheDuke said:
I plan to apply some elbow grease on Sunday or Monday and will post some pics of the seats then. Would lapping in the old-but-usable valves be sufficient? Or do I have to get those two survivors machined?
Click to expand...

I'd get them all faced. Should only cost a few bucks each. If the head has thin shims installed already, I'd have them shave a few thousands off the stem too, since that will shift the shim thickness range up the scale.
 
Good advice. I should have pics up this evening of the cleaned seats.
 
C1 intake
cdm4.jpg


C2 intake
l119.jpg


C3 intake
4pum.jpg


C4 intake
gwjy.jpg


C1 exhaust
j1r5.jpg


C2 exhaust
u4of.jpg


C3 exhaust
kzjm.jpg


C4 exhast
qxjy.jpg


Also, all of the seats appear normal, no gouges or scratches jump out at me. However, I did notice some odd pitting/texture with some carbon build up that I couldn't scrub out. I circled what I'm talking about below. Is this normal or should I get the seats machined too?
04x6.jpg
 
Those seats look fine, I'd lap them, leak check them and call them good. Not so sure about how new valves will fit the old seats. Are the valve guides good and tight?
 
The pits in that exhaust seat will not hand lap out. If you put a new valve on that seat it will just end up burning again.
 
Agree that those pits don't look good. Seat looks wider than the service limit too. I suspect the engine would get down the road for a good long while regardless so it's a judgement call.
 
I would give the seats a lick round with a seat cutter, then grind the valves in and call it done, plus, maybe, maybe not, take a gnats cock off the stem like Ed says, depending how much was needed to be removed on the seat 'cut'.
When a valve is "Lapped" it has been ground too far causing lines and steps in the seat and valve. Just sayin......
To take those pits out simply by grinding will take a long time, likely cause Lapping and cause the seat angle to change too much, leading to...overheating, burnt valves. Those valves are probably the worst I've ever seen. Well done. :)
 
tatu said:
I would give the seats a lick round with a seat cutter, then grind the valves in and call it done, plus, maybe, maybe not, take a gnats cock off the stem like Ed says, depending how much was needed to be removed on the seat 'cut'.
When a valve is "Lapped" it has been ground too far causing lines and steps in the seat and valve. Just sayin......
To take those pits out simply by grinding will take a long time, likely cause Lapping and cause the seat angle to change too much, leading to...overheating, burnt valves. Those valves are probably the worst I've ever seen. Well done. :)
Click to expand...

I bought a set of Neway cutters when rehabbing my 1000S head. Pretty nifty tools. Watch ebay and you can find them for cheap sometimes. The seat width is what surprised me when measuring my old head, which only had something like 20k miles on it; all the seats were wider than the service limit. I suspect this spec is a little off in the manual. And speaking of off spec, the valve to stem clearance service limit is unbelievably sloppy in some GS manuals. Suzuki is a little inconsistent in this regard from manual to manual. At any rate, working on stuff like this is the fun part of old motorcycle restoration. Requires some precision and care.
 
Last edited:
Nessism said:
Agree that those pits don't look good. Seat looks wider than the service limit too. I suspect the engine would get down the road for a good long while regardless so it's a judgement call.
Click to expand...

Agreed

Valve seats should be narrow. Wider is not better

I'd get the seats cut and lap in the valves

Check the valve guides and replace if necessary

If it takes a lot to get clean seats, trim .25mm from the top of the valve stems to regain some clearance
 
tkent02 said:
Those seats look fine, I'd lap them, leak check them and call them good. Not so sure about how new valves will fit the old seats. Are the valve guides good and tight?
Click to expand...

Didn't notice anything loose with the valve guides (but I also wasn't looking for that)...but how much play is acceptable? No wiggle? I will go out and recheck them if you can give me some guidance.

Also, I took a look at Ebay for the seat cutter and they run around $350...which is way beyond the budget of this build. I will call around to find a machine shop and get a quote to get the seats and new-to-me valves touched up.

So, the general consensus is lapping will not suffice?





On a side note, this....
9cwb.jpg
 
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