Topic: Mushroomed valve retainer grooves?

[seanbarney41]

I am trying to rebuild a cylinder head and can't get the valves out because the groove in the valve stem for the keepers is mushroomed enough that the valve stem will no longer fit through the guide.  I guess I will have to file or grind the mushroomed part but can the valve still be used after this?  The motor in question had 150-160psi compression prior to teardown and filling the combustion chamber with light oil revealed little leakage after 15 minutes.  I just wanted to check the stems/guides for wear and do some port clean up.  Also, one intake valve stem tip has some nasty pitting.  Are lash caps the answer here?   Should I just put it back together? (yes, I am a cheap bastard)  Can these valves be fixed?...or should I just spring for new valves?

[w1sa]

From what you say (if it were me), I would replace damaged valves/keepers (valve/seat grind(s) as appropriate), fresh valve seals, and re-assemble.

[dave500]

 pictures!

[seanbarney41]

pictures!

sorry, wanted to get some but didn't have a camera with me...the mushrooming is very slight, just enough to prevent the stem from sliding out of the guide

[PeWe]

I have had this problem in my CB750. I had to grind the sides of the valve stems to be able to remove them. I bought new valves.
The reason was most likely that the valve stems hardened surface was damaged by the workshop that tuned my engine by grinding the stem surface so the hardened steel became softer after max 5000 miles.

[Old Scrambler]

Sean........the keepers have been slamming into the stem collar because of a deeper recess at the valve-seat.........or a high-lift cam with stock-length guides.  This is somewhat common with partially rebuilt heads. Yes, you will need to grind the mushroomed area to save the guides........and you will need new or good used valves, along with new seals and new keepers. You may have to grind the seats. If all else is set to spec, you should not need lash-caps.  Check your rocker/tappet adjusters for wear.

[seanbarney41]

Damn, not one of you is yet to confirm my cheap ass bastard ways...I was afraid of that.  Thanks for the good advice.  I will still try to get some pics up for others use.

[MCRider]

Damn, not one of you is yet to confirm my cheap ass bastard ways...I was afraid of that.  Thanks for the good advice.  I will still try to get some pics up for others use.

Did I miss it? What bike is this?

Was there a reason you can suspect why this happened?

[seanbarney41]

geez, total newbie mistake...it's a '76 cb750 motor that I was gonna swap into my '74...tore it down for a head gasket, now it's getting expensive...I don't yet know the cause of the mushrooming.  What I can see of the seats looks fine, they sure seemed to be sealing ok...cam sure looks like a stocker, although the pistons are .010 over, so someone has been in here before.

[TwoTired]

You can check for valve guide wear without removing the guides.  It's called a "wobble test", to see how much the stem tip wobbles from side to side while the valve is in its seat (No springs).

Personally, I'd remove the mushrooming from the stem keeper slots, and reuse, if the guide wear is within limits.  Unless this was a a Hi-Po build with non-stock cam and valve springs. Then it would be all new parts, assuming you want some sort of longevity from the engine.

Cheers,

[camelman]

That mushrooming could be from excessive valve clearances. I've run across it on four engines now. Just sand the sides down with Emory cloth and slip the valves out like usual. It should not take much sanding to remove them. Clean the valves well before removal so you don't scratch your guides. The valves will be fine to reuse as long as the shafts are within tolerance.

Camelman

[Jerry Rxman Griffin aka MuthaF'er]

From what I've heard the Manley valves had the mushrooming issue. Measure the size of the head. You never know but Manley made stock size valves too.