Topic: valve work on cb500

[haill]

Getting ready to start with the valve seating on my 71 CB500 four. The rest of the motor is being rebuilt due to a bad primary chain.  Anything special that should be done with the valves and their seats. The motor has 23 000 miles showing.
Have the valve seals which came with the gasket kit so they will be replaced.
not looking for a race motor type set up just a well done job.
Any mods to stock that have proven over time to be an improvement over the stock values etc?
thanks Keith

[Sam Green Racing]

Check for wear in the stem to guide area and for any pitting or burning in the seat and valve contact areas.
If they are OK, just give them a quick lap in with light valve cutting paste.

Sam.

[haill]

and if there are pits?  sending it off to a engine builder to have the valve  work done and the cylinders honed. he recommended grinding the seats and the valves and finally lapping them in. he also spoke about machining the surfaces to get them flat for the gaskets. there was/is some pitting around the cylinder bores and he was going to hone the cylinder check for spec before getting into to boring them out.
if one does bore the cylinders one size up, do you have to get large pistons as well or just larger rings?
the compression in the motor before starting to take it apart was 100 across the set.
the primary chain was the reason for taking the motor apart but the compression didn't show well either. wasn't fouling the plugs with oil but the compression was low.

[bryanj]

Rebore means new piston kits complete, make sure you get them BEFORE having machine woek done so as to get size correct

DO NOT grind the surfaces on the valves as they are surface hardened ---lapping in with paste is OK

[haill]

spoke with the machinist yesterday. he said one of the exhaust valves is worn on the stem area tappet contact area. the valve seats were in bad shape so he ground them and have been reseated.
the intakes where in better shape. he said if wanted perfect job to get a complete set of exhaust valves or less than perfect just replace the one.
he moved them around from the original order so when i checked  the tappets off the cam locations couldn't get a read from them.
some of the tappets have some light pitting on the ends but are not worn off shape.
going to the machinist today to pick the head up so can have a look at the valve condition and guess make the call.
the cylinders honed out to spec so that will have the original pistons installed with  new rings.
thanks Keith

[Big Jay]

A head that old, and the guides were OK? 

[Tnutz]

my honda mechanic said mt 500/4 guides were okay too with 21,000 miles on them.

[MRieck]

A head that old, and the guides were OK? 

Jay....I look at a million old CB heads and believe it or not the old guides in the 550's can be good and tight. The smaller stem and angle play a large part. UNFORTUNATELY the valve faces are junk 95% of the time. The 750 guides are junk 50% of the time with the valve faces junk 95% of the time.

[Tnutz]

yup, the guy who did my head work said the same on my 500...guides were good, almost all my exhaust valves were shot though.

[haill]

when you say junk... do you mean throw away or able to renew. the machinist ground the seats and the valves and lapped them in on my cb500. does this have a negative affect on them. increased wear? please just say things are OK go about what your doing and enjoying driving the bike down the street.