Topic: CB750 K3- 3 angle valve grind?

[GreenHorn]

Sadly, the winter in Northern Ohio has begun and I performed the yearly ritual of "winterizing" of my summer toys.  But the season is bittersweet as it is now time to turn some wrenchs!

I suspected I did not have a good seal on my head gasket due to the increased film of oil forming on the fins of the cylinders and the outboard carbs.  I pulled the motor from the frame on my K3 and unbolted the head- the 4 phillips head bolts that are located in the center of the head and are recessed had never been tightened.  Someone had there dirty little fingers in the engine at one time and left them standing 3/4" proud of their seats.  Maybe this is the problem, maybe not, but it can't be helping!

So, now that I have the head off, what can I do for some more pep?  I can't find a cam for under $200 that is made for the standard displacement (they all seem to be oriented for the big bore kits).  How about a multi angle valve grind?  I've read that the OEM valves should NOT be reground due to being surface hardened and coated.  Even if I was to get some aftermarket valves, is it even worth it to do a valve grind alone?  I mean, I know it will help flow, but will it even provide a noticable improvement in performance?  My guess is probably not... anyone else's take?

[Gordon]

How about a port an polish instead?  Hondaman has a good write-up on specifics of what to do in the FAQ under "The thoughts of Hondaman". 

[Whaleman]

You do not say how many miles the bike has. If I had a head off I would, at the minimum, clean the head of carbon, wire brush the valves, lap in the valves and replace with new valve guide seals. You most likely do not need the seats ground. I would not worry as much about carbon in the exhaust port. The cleaning and lapping of the valves and new seals are a must if you get to this point. Some people say if you pull the head you will loose the seal of the base gasket. I believe it has to do with how much rubber mallet work was done on the head to get it loose. I do not want to start an argument but my opinion is if you go this far I would pull the cylinder, clean the pistons, hone the cylinders and install new rings. Dan

[crazypj]

I would clean up the ports and do 3 angle, been doing it routinely for at least 30yrs when I get head off bike

PJ

[Big Jay]

It will need guides, so plan on a valve job. But go with a radius valve job that will give more flow past the seat.

You can  have the valves ground. Won't be a problem.

Be sure and put some big studs in it to make the gasket seal.

http://cbrzone.com/sohc.html

Jay

[bucky katt]

how expensive is a multi angle valve job compared to a single angle? i know how to do it myself if i had the tools but i dont so.............

[Nikkisixx]

how expensive is a multi angle valve job compared to a single angle? i know how to do it myself if i had the tools but i dont so.............

A good machinist shouldn't charge extra for a 3 angle job, as this is the only way to keep the sealing surface narrow and in specification.  If you can find a shop that uses a Serdi machine, all the better (IMHO).  The cutting bits available for these machines create really nice and consistant multiangle valve jobs. 

As for Honda having coated valves that can't be resurfaced, I've never had problems provided the valves were not worn to the point that they became thin after grinding.  In fact, I'd insist on grinding the valves to be sure the seat and valve angles match.

[crazypj]

how expensive is a multi angle valve job compared to a single angle? i know how to do it myself if i had the tools but i dont so.............

If my auntie had balls, she's be my uncle..............................................
It depends if they are using SERDI or NEWAY.
 Neway is more versatile but takes a lot longer to do 3 angle PROPERLY with it.
 Serdi cuts all 3 angles at one time.
 Either works but both are expensive *Neway cutters about $150~200 each, $1200.00 for set with pilots ( they used to be about $1600 so price has dropped)

PJ

[Yoshi823]

I had a decent 30/45/70 valve seat job done after new valves and aluminium/bronze valve guides were installed.When I checked the valve sealing with parafin once the valves were installed with the S&W springs there was a perfect seal.


When people say 'grinding the valves in' do they mean using course and then fine grinding paste or just lapping them in with a bit of fine paste?

[Nikkisixx]

When people say 'grinding the valves in' do they mean using course and then fine grinding paste or just lapping them in with a bit of fine paste?

Well... people say all kinds of crazy things and I never know what they mean. 
Usually I say "cutting" a surface when I use a hard metal bit, "grinding" when I use a stone or abrasive.  The kind of machine work me and crazypj are talking about uses carbide cutters to put the seats back in shape. There is another method that involves using stones to "grind the seats".  The tool/machine used to reface the valves also uses stones, so you could say "grinding the valves in" for that operation as well.

Information you may know/or not want to know:
Carbide bit cutting type machines look like a fancy drill press, with a pilot that goes down the valve guide that centers a tool holder and carbide bit.  The carbide bit has the profile of the finished seat, and the tool holder and bit rotates and cuts the seat. Sometimes the tool will chatter as it cuts, which does not make for a great seal.  To check for a good seal and clean up small imperfections, one can "lap" the seats and valves using abrasive compound.  This lapping process also can help reseat an old valve job, but is by no means a viable fix for motor you want to keep in the family for a while.  Another common practice is to use a vaccum pump on each runner after machining the seat and valve to test the seal - no spring or oil/lube required since the vaccum is pulling against the seat.   The machinist just drops a valve in the guide onto the seat and pumps the runner empty to verify a seal.  If the seal is good, no lapping required.