[roccitycafe]

What's the verdict on refacing cb350 valves? I set up my surface grinder and whirlygig and refaced a set of them, they look perfect, but the more I heard about it, if you take more than a few tenths off the face, you've cut through the stellite coating and the valve will prematurely wear out. Then some other people cited articles about stellite being only on the stems, then others said it was stems and faces, then... on it goes. I'm not above buying a new set of valves, but ****, if I've got the tools to regrind them, why not?

 

[doode]

Others can confirm but I think it's safe to take some off BETWEEN the stem and a few mm before the seat area for intake only.
Nothing near where it meets the seat

 

[TOOLS1]

I have ground several of them, no problems yet with any of them. A valve is well worn out before you grind through the coating. Somewhere I have some valves that were oxidized and then bead blasted, you can see how thick the coating is on them. It is pretty thick.
TOOLS

 

[JamesPal]

These are the Honda Factory Service Manual descriptions and inspection requirements for the valves in the CB450 DOHC. You can see for yourself Honda says the valve can be refaced. There is a limit to how much material can be removed. I'm willing to bet there is similar specs in the CB350 FSM. The valves in my 450 have been refaced and the bike has 2700 miles on it. I have read there are some good repo out there for the 350. If they are reasonably priced it is the best option. It is i little harder to source new valves for the 450, but then again it is only money.

 

[doode]

From the 250/350 manual

 

[JamesPal]

From the 250/350 manual

Early Honda shop manuals had a lot of information describing the designs of the engines. I have a circa 1965 CB450 FSM and the last version that covered all of the 450 DOHC. The later was the former plus a differences section. It is interesting the CB350 manual drops the stellite description and it was written for a 1968 model. When I was riding and working on my C100 in HS (1969) it was fascinating to read the FSM because it held so much information. It went way beyond what was needed to maintain the bike and went into the design philosophy.

 

[doode]

So it looks like it's within service limits that 0.5mm (0.25mm per side) can be removed from a NOS spec, and the stellite does not extend up the stem

 

[Lefty]

It would be interesting to section, grind and acid etch a old valve. I bet you see how the face was shaped before the stellite was welded on.

 

[JamesPal]

So it looks like it's within service limits that 0.5mm (0.25mm per side) can be removed from a NOS spec, and the stellite does not extend up the stem

For the 350 valves, .6mm is the service limit for the valve head thickness. If it was me and I was forced to regrind used valve, I would look for a valve that could be cleaned up closer to the standard value of .85-1.15mm. Especially for the exhaust valve. The exhaust side runs hotter and usually wears faster.

 

[longdistancerider]

There's a couple of different methods for hard facing the valves, Stellite and Nitriding. Stellite is a plasma spray method and Nitriding is a salt bath. Nitrided valves new have a black appearance. In either case the hardening is only @.002" thick, in many cases it's thinner. Here's a couple of articles
https://books.google.com/books?id=d...e&q=honda motorcycle valves hardening&f=false
https://www.motorcycleproject.com/text/valve_jobs_done_right.html

 

[TOOLS1]

According to Mike Nixion there, there might only be three or four people in the known world that are capable of doing a proper valve job.
TOOLS

 

[JamesPal]

Don't reengineer a valve job. Any machinist should be able to cut new seats and face the valves. As long as the factory specs are met and the bike runs well just ride and enjoy.

 

[roccitycafe]

I think I have the answer. I took an HSS end mill and scratched the valve face that I reground, I couldn't scratch the tip, I think the answer is that any hard coating on the valve face was removed by the grinding process. that valve wouldn't have lasted all that long imo

 

[TOOLS1]

The tips of the valve are a lot harder than the face. Try scratching the face of a new valve. The tips take the real beating.
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[Boomer343]

For the 350 valves, .6mm is the service limit for the valve head thickness. If it was me and I was forced to regrind used valve, I would look for a valve that could be cleaned up closer to the standard value of .85-1.15mm. Especially for the exhaust valve. The exhaust side runs hotter and usually wears faster.

My experience with the 350 valves is that the Intakes show much more wear than the exhaust valves. I have a bag of serviceable exhaust valves and no Intakes.

For the price I just bought new.

 

[NighthawkCharlie]

Honda used Stellite surfacing on many of their valves.
Remove any of it at your own risk.
Have spares for when they start to make noise, unless they get tight and burn.
But it's a reality we face fixing old bikes, so you do what you have to and maybe don't visit redline as often as you'd prefer.

 

[mountaingoat]

My experience with the 350 valves is that the Intakes show much more wear than the exhaust valves. I have a bag of serviceable exhaust valves and no Intakes.

For the price I just bought new.

This goes with what my machinist told me while working on my head. The exhaust valves were ok and one Intake valve was out of spec. The other was ok.