Valve Question

[wingedwheel]

1978 CB750A. I started as a basic restore on a bike that sat for 26 years. Everything was stuck, half seized or rusty. After I pulled the engine to work on the frame and swing-arm I noticed what looked like the head gasket was leaking. I have all the gaskets so I figured just replace everything. Pulled the head and the jugs, ordered new rings and while waiting for them to arrive I started replacing the valve stem seals. The #2 intake valve would not slip out past the retainer groove so I had to drive it out. I've only gotten to the intake side so far and #2 was the only one like that. I'm assuming the valve might be bent? First time running into this and need an opinion. Does that sound like a bent valve shaft? do I replace the valve and the guide? I also have no idea why it would be like that. The cam shows no indication there was a problem. what would cause this?

 

[dirtdigger]

There was probably a slight bur where the valve keepers touch the valve stem. If you would have taken a fine file or even some fine sand paper to dress the edge it would have slipped right out. beings you drove it out you probably ruined the valve guide and probably the valve also. You will have to send the head to a GOOD motorcycle shop and have the guides replaced, most automotive repair shops will do more harm then good. After this long and probably a fair number of miles....all the guides are more then likely too loose and all should be replaced. After guides are replaced you have to have the seats ground as they will no longer be concentric with the new guide. I recommend APE or Cycle X to have head work done. Unless you have the correct tools to pull out and pull in the new guides and have valve seat cutters, you need to send them to a good bike shop that specializes in japanese bikes. None better then APE or Cycle X.

 

[amc49]

It depends on how much force was used to drive the valve out, if a lot then likely the guide may have damage now. If only a little bit then go on about business.

The later DOHC does it on almost all of the intakes, I have a flat very fine tooth file just for lightly removing the burr that occurs as the valve impacts the locks to make it.

 

[wingedwheel]

Thanks guys, yep I used a brass hammer to tap it out but I'm sure the guide needs to be replaced as I tried cleaning the valve off afterwards and it won't go back in. The miles aren't high on the engine and the other valves were fine so probably just the one will need to be replaced now. Crap.....everything on this machine has been an issue as far as having to do "something" I know someone with the correct cutters so that's not an issue, just more time and $.

 

[amc49]

The guide scars up its' ID when you force the valve past it with a burr that then cuts the guide all the way down. I have even recouped those before to run fine provided the overall clearance is still OK. I work mainly on DOHC though, guide wear is almost never an issue on those like with a SOHC.

I'd take that problem valve and one of your good ones and flip the stems on each other (both clean of course) to roll them around for a quick straight valve check.

 

[wingedwheel]

I actually chucked a couple up in the drill and spun them. The good valve spun fine, the bad valve had a slight wobble to it and i chucked them above the retainer groove.. Not much wobble but I could still see it. I'll try your method also but I'm pretty sure it's bent at the retainer groove. I found no burrs, nor can I see any marking in the guide where it might have been scratched. I had to tap the valve pretty good to get it out, thus leading me to believe it is bent.

 

[amc49]

It likely is. ANY wobble is unacceptable.