Pitted Valve Seats

Husbyb86 · Post by **Husbyb86** » Sun Mar 30, 2014 1:12 pm

I've got my CB160 head on my desk right here and I need some guidance. I understand this is primarily a 250/305 forum, but the 160 is very similar in a lot of aspects.

I bought a 160 here a while back and the engine was froze for I'm guessing quite a while. Understandably, I encountered some rust in the engine when I took it all a part. My question is, are my valve seats to far gone? Will a valve grind get rid of all the pitting? I tried a little valve lapping, but the pits are way to deep. I used some paint thinner in attempt to test for leaks, and the valves leak like a sieve.

Thanks!

jensey · Post by **jensey** » Mon Mar 31, 2014 3:10 pm

Hi,

First of all, lapping is a final step, it doesn't repair a bad valve seat.
Milling (cutting) is the only way in this case. How are the valve's ?

A machinist will tell you if there's enough meat to mill (re-cut), I think there is.

Jensen

Husbyb86 · Post by **Husbyb86** » Mon Mar 31, 2014 6:29 pm

The valves are so-so I think. A little pitting here and there, and especially on one valve. I would like to find some NOS valves as I'm not sure I would feel comfortable reusing these. Tell me what you think.

Hahnda · Post by **Hahnda** » Mon Mar 31, 2014 8:59 pm

that one valve would concern me a little also. It might be ok though as most of area that does the sealing is above that.

The seats are a bit pitted but will probably clean up pretty good.

Jensey is correct, the seats need to be cut. I use Neway cutters and then do a light lap to confirm and measure the seat width and location on the valve face. Then I fill the heads up with alcohol and check for possible leaks. I little weep after a minute is ok but if its flowing right away there might be a problem.

jensey · Post by **jensey** » Tue Apr 01, 2014 1:39 am

Replace the valve with the severe pitting, before the pitting gets worse.

Rebuilding an engine is to replace everything what is not good or what is out of specification. Sometimes you get away when the part doesn't have a really important function but a severe pitted (exhaust !) valve is definitely an important part, there are no back doors, it's a little time bomb in your engine.

btw, this is how re-cutted valve seat's look like (not a CB77)

jensey · Post by **jensey** » Tue Apr 01, 2014 1:53 am

A pitted exhaust valve leads to glowing / burning around the pitted area. In the picture below you see the results of that. Another thing is that the heat won't be transferred to the sealing area, leading to heat build up in the valve stem, destroying your valve stem and valve guide. All just a matter of time.

bonjour · Post by **bonjour** » Tue Apr 01, 2014 12:06 pm

ouch !