250 scrambler valve job

[Adam]

Hi All
Working on the top end this weekend. Bike is a 1966. While the Pistons moved freely, everything else attached to them was stuck on pretty good. Finally got the valves out. Tried tapping out the valve guides but they seem pretty frozen. Walkers book shows to drive them out from the inside and that this can be done cold. All this is doing is deforming the brass guide which is not moving. Is there a better way to remove these?

Thanks

Adam

[Rick]

As you've found out, driving them out from the combustion chamber just mushrooms the guide and makes them about impossible to get out.
An 8mm valve stem is a good fit for a 3/8" tap- tap some threads through the inside of the guide and pull it out from the spring side of the valve- I use a piece of threaded rod, a sleeve around the rod, and a nut to pull them out with a wrench- some guys use a slide hammer.
If you've hammered the guide into a bell shape you'll probably need to grind it flush to avoid galling the bore in the head.
Rick

[ducwiz]

In any case you need a stepped drift which tightly fits into the valve bore, to tap the guide out. Such a tool prevents "mushrooming". If you want to tap from the valve side, you should carefully remove all carbon deposits around the protruding part of the guide, i. e. by shot blasting. Otherwise you may damage it's bore in the cylinder head.
My version: drill or countersink the protruding part of the guide off from the spring side, then tap the rest out, towards the valve side.

cheers Hans

[frankfast]

Assuming everything is out of the heads, have you tried heating the head in an oven?

[Adam]

An 8mm valve stem is a good fit for a 3/8" tap- tap some threads through the inside of the guide and pull it out from the spring side of the valve- I use a piece of threaded rod, a sleeve around the rod, and a nut to pull them out with a wrench- some guys use a slide hammer.
If you've hammered the guide into a bell shape you'll probably need to grind it flush to avoid galling the bore in the head.
Rick

I didn't get too crazy with it so I wouldnt all it mushrooming, maybe deforming the top end on the valve side. Went with your recommendation and all was good gathering materials. the sleeve material fit around the replacement guide nicely, too nicely. Got it home and the current guide stop(thats what i'm calling it) is about a 64th too wide so the sleeve doesn't fit around the guide. Figures. I could just get a wider sleeve cut but those roll pins are preventing that. Might have to cut the next sleeve around those.

what did you use for the sleeve and how far down did you run the tap?

Thanks

[Rick]

You could try just running a 3/8" bolt into the threaded guide and hitting the end of the bolt with a punch from the combustion chamber side- the force acting on the internal threads won't bulge the guide like driving from the end will.
Rick
edit: you should probably stop the bolt in the length of the guide that's supported by the head casting- if the bolt ran out into the unsupported guide in the chamber it might still mushroom out.

[Adam]

In any case you need a stepped drift which tightly fits into the valve bore, to tap the guide out. Such a tool prevents "mushrooming". If you want to tap from the valve side, you should carefully remove all carbon deposits around the protruding part of the guide, i. e. by shot blasting. Otherwise you may damage it's bore in the cylinder head.
My version: drill or countersink the protruding part of the guide off from the spring side, then tap the rest out, towards the valve side.

cheers Hans

Thanks for the advice on the stepped drift. I'm sure I'll be in this situation again somewhere on another bike. Will keep this in mind.

-Adam

[Adam]

Assuming everything is out of the heads, have you tried heating the head in an oven?

Considered heat but figured that would also heat the guide.
-Adam

[Adam]

I ended up going with a 3/4" sleeve as the 1/2" wouldnt fit. Filed notches where the pins would interfere and went to work. That was a good diameter to work with. Both valve guides came out with no issue or marring of the path. Thanks Rick for the advice. I found an example of what you described here. https://www.youtube.com/watch?v=iod2WuV1iYM

[Nick]

The proper way to remove valve guides is to first machine off the top of the guide (using a stepped drill bit or custom cutting tool), then drill out the the guide to a larger diameter (but not so large as to break out into the head), and to then knock the guide out from the valve-cover side into the combustion-chamber. This eliminates two possible problems: scarring of the guide bore due to carbon build up on the guide, and expanding the guide bore by simply knocking out the un-drilled guide.