This is a discussion on this will probably start a fight within the Technical forums, part of the Caferacer.net Forums category; if you're prepared to pull it apart again and fit new valves when it turns out to be a crap idea, reface them. if you're ...
if you're prepared to pull it apart again and fit new valves when it turns out to be a crap idea, reface them.
if you're not, don't.
Do the valves look like they may have been ground before? Probably not easy to tell if it was a light skim and if you don't have a NOS one to compare it too.
You're welcome for the copy of the bulletin btw.
"Non urinat in ventum"
I don't think that CB350 valves were stellite tipped or on the seat faces. Honda, and others used two piece valvee with different head and stem materials. Heads used to be heat treated or coated with something to get that hard skin, but teh valves were OK to grind, even though Honda said don't do it.
The problem with two piece valves is that on a race motor that is revved hard, every so often a head will fall off and punch a hole in other parts. We had that happen on a CB160 years ago. On a street motor, not an issue, on a racer that's ridden hard, fit new valves.
roc that is a good point and the gist of the question
the reason they did the hardfacing in 79 and later is the ban on leaded fuel ewh ?"as you promote the 350 twin is early 60's tech when unleaded fuel was non existent nno ?
aoso if you bakcut the valve @30 degees you can actually bring that angle into the worn cupped area of the valve
effectively narrowing the contact area ,then you are not tricked into grinding the contact area all the way up into the backcut because its nolonger there
on the ex valve especially the contact wants to be pretty close to rhe outer dianeter any way to enable onseat closed time to have the best abjlity to cool down because vthe hottest zone is the outer edge
and that is the only way nthe ex valve can be cooled is on seat time
of course the intake valve wants to have the contact zone nearer to the middle area of the seat angle cut for best flow at low lift time
most of the bused valves i have inspected have not insignificant stem wear anyway and the stem to guide service limit is reached quite often with combined stem and guide clearance it is a bit tricky to measure the stem to guide clearance
but should be checked as layed out in the FSM
i cant remember if FSM mentions this here part but the clearance bmust be checked with clean dry stem and guide
"Non urinat in ventum"
valve seat recession used to be a common topic on may forums as leaded fuel became less available. It was rarely an issue with valves - just seats and only for machines not designed for unleaded gas. TEL is of course one the earliest and most used knock inhibiting compounds which all gasoline is laced with because it all has a naturally low resistance to detonation (knock). Then it was replaced with nice clean MTBE which turned out to be worse than lead. Alcohol - ethanol and methanol have much higher knock resistance than gasoline and diesel is way up there.
:I don't see any fights happening here, seems we are all pretty much on the same page.
Did you ever notice how Hydrocarbon fuels including Octane contain exclusively Hydrogen and Carbon molecules, right up until somebody comes along and tries to improve it with an additive, which usually messes it up for either the machinery or the environment :|