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Two destroyed exhaust valves [with pics] - replace valves or entire head?
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TopTechRacing
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.
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Forum LongTimerGSResource Superstar
Past Site Supporter
Super Site Supporter- Mar 2006
- 35641
- Torrance, CA
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.Ed
To measure is to know.
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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.sigpic
Don't say can't, as anything is possible with time and effort, but, if you don't have time things get tougher and require more effort.
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Forum LongTimerGSResource Superstar
Past Site Supporter
Super Site Supporter- Mar 2006
- 35641
- Torrance, CA
Originally posted by tatu View PostI 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.Last edited by Nessism; 11-02-2013, 08:09 PM.Ed
To measure is to know.
Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182
Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846
Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf
KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection
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Originally posted by Nessism View PostAgree 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.
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 clearance1978 GS 1000 (since new)
1979 GS 1000 (The Fridge, superbike replica project)
1978 GS 1000 (parts)
1981 GS 850 (anyone want a project?)
1981 GPZ 550 (backroad screamer)
1970 450 Mk IIID (THUMP!)
2007 DRz 400S
1999 ATK 490ES
1994 DR 350SES
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TheDuke
Originally posted by tkent02 View PostThose 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?
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....
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