Topic: Valvetrain component compatibilty

[seventytimes7]

Hey everyone!

New to the forum and also new owner of a 74 CB750.

I am in the middle of a top end refresh that is turning into a top end overhaul.  After talking to my local motorcycle shop (Cycle Specialist- Larry McBride) they have suggested I buy new valves, valve springs, and guides.  While I am looking to buy quality products, I am also trying to keep cost down.  My question is whether CycleX super flow valves are compatible with KPMI valve springs (using stock retainers) or do I need to spend the extra money on CycleX race springs?

Thanks!

[Harsh]

My first thought is why do you need the new parts.  Is there something wrong with what you currently have?  Are the valves bent, spring out of spec, etc?

[MRieck]

Hey everyone!

New to the forum and also new owner of a 74 CB750.

I am in the middle of a top end refresh that is turning into a top end overhaul.  After talking to my local motorcycle shop (Cycle Specialist- Larry McBride) they have suggested I buy new valves, valve springs, and guides.  While I am looking to buy quality products, I am also trying to keep cost down.  My question is whether CycleX super flow valves are compatible with KPMI valve springs (using stock retainers) or do I need to spend the extra money on CycleX race springs?

Thanks!

Yes.

[seventytimes7]

Cliffs: Shop said my valves are no good.....are they?

I had a shop look the bike over and the compression numbers came back 140 90 130 140.  A few calls were made to surrounding shops and they all said it would be in my best interest to take the job on myself.  So I bought a manual and tore the top end down.  The only problem I could see was massive carbon buildup on the pistons, valves, and head.  I called back to the mechanic and told him what I had found and he suggested the valves were probably sticking due to all the buildup.  I was referred to Cycle Specialist to have the cylinders honed and head cleaned up.  After arriving at the shop I explained what I had going on and that I'd like to have the head cleaned up.  He said they don't "clean up" and that I was the mechanic and he was the machinist, so I needed to tell him exactly it is that I'd like to have done.  I once again said I'm learning as I go along and that I think I had sticking valves.  So we came to the conclusion I needed a valve job. I showed him my valves that had been sitting in parts cleaner for 48 hours and asked if they were any good.  He took one to the back and cleaned it up and said they were no longer good because the coating had been pitted.  He suggested I buy new valves, springs, and guides since the bike was older and I do not know the history.  The odometer is showing around 17k miles, but there is massive carbon buildup so I'm not sure if it is accurate.

Pics:




The one he cleaned:

[Vinhead1957]

Not looking at the clean one the others look pitted. I had the same with my fatboy and the machinist reground the valves in my case the manufacturer used the wrong seals.

[trueblue]

Not looking at the clean one the others look pitted. I had the same with my fatboy and the machinist reground the valves in my case the manufacturer used the wrong seals.

I wouldn't say pitted from just the pictures, I would say that they need a good clean then check them over.

[MRieck]

Pictures are not a good diagnostic tool in general. Those intakes look like the valve faces are beat (not a surprise). Look at the width of the valve face contact area....that is supposed to be .040. Looks like double that. Than there is the condition of the tips and guide etc.
 Honda valves should not be ground. I have personally seen ground Honda valves out of low mileage 550/750 engines and the valve faces were very beat up and the margin gone.
 I am sure you could wire wheel the valves and lap them for 5 minutes and they would seal. You can also be assured of low performance.
 McBride just may know a couple of things about engines....that's just a hunch. The only things they forgot to mention is you will need a valve job if the guides are replaced. Also...the ports have to be bead blasted to remove the guides. That valve job would be far superior to the factory one Honda did and actually provide a nice improvement in performance..

[seventytimes7]

Thanks for all the responses, guys!  I'm going to go ahead and replace them.

Exhaust valves seem to be hard to come by....Partsnmore and CB750supply seem to be sold out.

[MRieck]

Thanks for all the responses, guys!  I'm going to go ahead and replace them.

Exhaust valves seem to be hard to come by....Partsnmore and CB750supply seem to be sold out.

Buy a full set of valves from CycleX. Very, very reasonable and they can be ground if you ever rebuilt the head again. OEM exhaust valves are expensive in comparision....you can get the full set from CycleX for about the price of 4 OEM exhaust valves.

[seventytimes7]

Will do.  Thanks again!