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Valves

mcycle-nut

mcycle-nut

Forum Mentor
Past Site Supporter
Charter Member
Ok, so I'm rebuilding a head for my 8 valve GS750. I have had the seats cut by a motorcycle mechanic using a cutter made for motorcycles. I have ordered new valves. The particular mechanic that did the cutting suggested I do a light lap with the new valves. I have had another motorcycle mechanic tell me NEVER lap Japanese motorcycle valves. Apparently he toured the Honda factory, and he was told this, something to do with the valves being microwaved for hardness and lapping will take away the hardness.

Our good friend Mr. Clymer says lapping can be used as a "touch up" for GS motorcycles, but gives directions on seat cutting if that doesn't work. I know the Clymer manual for Honda 50's says DO NOT LAP VALVES, buy new ones. So, is this do not lap thing a Honda thing, or what? Should I do a light lap as told, or not?
:-k
 
Unless someone here knows something special about the GS valves, I know I would lap them. It finshes the valve seats off to match the valve.
 
Re: Valves

mcycle-nut said:
I have had another motorcycle mechanic tell me NEVER lap Japanese motorcycle valves. :-k
Click to expand...

Suzuki genuine valves should not be lapped, the outer surface is specially hardened, and lapping will remove this.
 
Wow, no lapping. You learn something new every day. Thanks for correcting me.
 
Hmm. These aren't Suzuki valves, they're aftermarket. Then again, my buddy who runs the shop from where I ordered them from has found that the valves come in EXACTLY the same package as the Suzuki valves, except that it doesn't say "Suzuki" on the package. Once out of the package, you can't tell the difference. Oh yeah, they're about 1/2 the price of Suzuki's.
 
valve lapping.

valve lapping.

OK, all or most Honda manuals state do not lap valves in, I have 2 honda's that the manuals state that.
I have had 3 GS's and I have lapped the valves in on ALL of them and NEVER had a problem with seating them in, even on new ones.
 
Good old Clymer. They say to use a slide hammer to remove the rotor too.

The factory GS1100 manual says not to use lapping compound after the final cut. This is kind of strange because it doesn't even mention lapping compound in any part of the valve fitting process. They do mention using Prussian blue for checking the contact area.

Steve
 
Valve surface treatment

Valve surface treatment

Back in the '70's when we all stopped using leaded gas, Suzuki started coating the valves with Stellite as we no longer had lead to lubricate the valve faces. I think Honda did the same. I rebuilt a 1982 Honda XL185, and though the manual cautioned about lapping in the valves, my local shop (who I've been dealing with since they opened 30 years ago, and I trust) said it was fine to lap the valves, which I had them do after they cut the seats. No problems so far!
 
As quoted from Suzuki Manual:

"After the desired seat position and width are acheived, use the 45* cutter very lightly to clean up any burrs caused by the previous cutting operations DO NOT use lapping compound after the final cut is made. The finsished valve seat should have a velvety smooth finish and not a shiny or highly polished finish. This will provide a soft surface for the final seating of teh valve which will ocour during the first few seconds of engine operation."

Valves are hardened for a reason. It's your engine...
 
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