Thoughts on swappling valve-train to new head?

Quick run-down of what's gotten me here:

Engine that was in the bike when I bought it is completely froze.

I bought another engine for it but the head on this engine had a broken exhaust stud boss.

Pulled the busted head from the new engine.

Tonight I'm pulling the good head from the bad engine.

So I Popped the cover off only to be greeted with major rust on the cams.

The whole valve-train looks pretty nice in the other head so I'm thinking about just doing a swap on the internals... if that's a thing that can be done?

I know the cams ride directly in the heads (no bearings) so I'm not sure if there may be a mis-match in wear. But then, can the cam of one head be used in another head using the recipient head's cam caps?

...

I'm starting to confuse myself.

I guess I'm just wondering if it's alright to swap in the cams and valves from a different head. The valves will be lapped.

As always, input will be greatly appreciated.

~Rev.

 

If it is still in spec, you could use it, remember to fit new bolts to the cam caps.

 

I would get a mic and measure the cams where they ride in the bearing journals and compare them to make sure you have the proper clearances. if the replacement is too big, you could have galling from being too tight and if they are too small you could have oil starvation from pressure loss.

CN

 

Try it. Can't be any worse than what you have now.

 

There is more to it than that.

If the cam journals and head/caps are not obviously worn or grooved, then the swap can be attempted.

You will need to install the replacement cams, and then use Plastigauge to check the cam-to-cap/head bearing journal clearances. This procedure is covered in the factory service manual but apparently completely overlooked in the Haynes.

If you don't have a FSM, PM me with your email address and I'll send you a scan of the page.

 

IMHO extract/replace the broken exhaust stud.

Roc

 

I'm guessing clean/polish surfaces, Place plastigauge torque down cap, Then remove cap and check the squishage of the plastigauge?

If clearance is too loose, can I just wetsand the flats of the caps to tighten it up?

The actual casting into which the stud screw into is broken off. I'd have to have someone build the material back up with a TIG, then have it srilled and tapped. And even after all that, I'd still have to replace all the other studs as well because they are all bent beyond saving.

If the clearances are good in the other head, it'll be less hassle to just swap heads.

 

Unfortunately not. the bearings will be ovoid if you do that. If you want a visual, take a peice of cardstock and cut a circle from the center of the card. Then cut a strip from the middle of the card stock the the hole is in. Now tape it back together, minus the strip. You have now made an ovoid.

A machine shop can trim the caps and rebore the bearing surfaces though.

 

I thought that might be an issue. I've got a pretty good machine shop down the road from me but hopefully I won't need to pay them a visit.

Thanks for the input.

 

this won't work. the cam journals will still be too wide at the mating surfaces to be rebored smaller.

CN

 

if they have the equipment to do it, your looking at 100$/hr

 

Yikes.

The bearing surfaces are cleaning up nicely and I've got some plastigauge. Here's hoping I don't need to employ such services...

 

Yep. Brain fart on my part, but if the fit is just barely out of spec it can be done as a cheat, and will work.....for a while. Really not worth doing, especially if you have to pay someone to do the job.

What I do know can be done is one of two procedures.


• Weld (or metal spray) and remachine the bearings, which is standard practice. (relatively low cost, but still likely more expensive than finding another engine)

• Machining the existing cam bearings in order to fit bearing inserts (the inserts would likely need to be made as well, or modified from inserts that are close to the corrrect dimentions) You're looking at a considerable cost for this; well beyond the cost of an entire running XJ.