Bushing rocker spindles

Hi,
My downdraught dominator head has very worn rocker spindle bores so I’m in the process of bushing them. Currently in early stages of experimenting with shrink fits of the phosphore bronze bushes I’m making in the head. I’m finding an intereference of 0.015mm is a sliding fit with a 200c head temperature and the bushes shrunk in dry ice. Once the temperature has equalised it takes some significant tapping with a hammer and drift to get the bush to move. The OD of the bushes is approx 15mm. I’ve experimented with pieces of plate and I’m now fitting bushes to a junk head before tackling my good one.
If anyone else has done this I’d be happy to hear your thoughts on the process and what kind of interference you used.
Cheers,
Pete

If its only the outer bore that is worn then it would be easier to bore the minimum out to make the bore concentric and then have the rocker shaft copper plated on the outer end to restore the fit to the larger outer bore. Its a routine job in a platers to blank off where plating is not needed, any excess copper on the rocker shaft where it fits the bore is easily sanded down as the copper is soft.

Cheers. Unfortunately it’s mainly the inner bores that are loose.

First fit of a bush into an actual head. Seemed to go well.

Peteyoung75 said:

First fit of a bush into an actual head. Seemed to go well.
View attachment 123457

View attachment 123458

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Why did you choose bronze, versus aluminum for a non rotating shaft?

Suggesting here that a same material bush, shrunk in place would be held secure, and do the job just fine. (like thousands of original heads)

Just food for thought. Clearly you have the needed skills & resources.
Good luck with the repair. (I know "luck" has NOTHING to do with it, but everyone says it...)

I like the old horizontal mill.

concours said:

Why did you choose bronze, versus aluminum for a non rotating shaft?

Suggesting here that a same material bush, shrunk in place would be held secure, and do the job just fine. (like thousands of original heads)

Just food for thought. Clearly you have the needed skills & resources.
Good luck with the repair. (I know "luck" has NOTHING to do with it, but everyone says it...)

I like the old horizontal mill.

Click to expand...

I’m using phosphor bronze as it’s a bit tougher than aluminium but has a similar thermal expansion coefficient. It’s a pretty thin bush so I think an aluminium one would run the risk of getting hammered into submission a bit easier.
The mills great. It’s a 1951 Fritz Werner 5.160WS horizontal and vertical mill. It’s very original and still has all its original controls and wiring including a Siemens timer relay that uses a v low geared motor to flip a mercury tilt switch to turn the motor brake off after 5 seconds.

That is a nice little mill. Looks stout for its size.

Did you end up using a .015mm fit, and did you line bore it after fitting, or just fit a final size ID?

I went for 0.020mm on that one and it slid in ok, I’ve got my indicating mic set to a +0.015 - 0.020 tolerance now. That bush needs cutting and dressing back flush. Next I’ll fit the outer bush, then I’ll run a 12.66 machine reamer through followed by a 1/2” flex hone to deburr it all (especiallly the oil hole). I did this in my test pieces and it gave me a sliding fit with the test piece hot and the spindles cold. With the test pieces and spindle hot the spindle would pull out and the bush would stay put.
I’m doing this a bit differently now as I want to keep the machine set up throughout the fitting and finishing of each pair of bushes. To do this I heated the head locally with a torch and used a temperature crayon rather than heating it evenly in the oven.
They cant be line bored as such as the inner bores are all effectively blind holes.

Triumph cam bushes have one through, and one blind, and the line boring kit is a large bearing to push through the through-hole and a hand reamer, with a (mostly) ground off taper to finish the blind. I did my first set well before my metal working career really started, but by the time I had done my next, it shocked my "machinist sensibilities", but it works every time.

I do really appreciate your thoroughness, not giving you a hard time!

t ingermanson said:

Triumph cam bushes have one through, and one blind, and the line boring kit is a large bearing to push through the through-hole and a hand reamer, with a (mostly) ground off taper to finish the blind. I did my first set well before my metal working career really started, but by the time I had done my next, it shocked my "machinist sensibilities", but it works every time.

I do really appreciate your thoroughness, not giving you a hard time!

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Ha ha no - I appreciate the info! I’m new to engine work so have no previous experience of this stuff. My main concern is not needing to do it again! Or wrecking my downdraught 88 head!

t ingermanson said:

Triumph cam bushes have one through, and one blind, and the line boring kit is a large bearing to push through the through-hole and a hand reamer, with a (mostly) ground off taper to finish the blind. I did my first set well before my metal working career really started, but by the time I had done my next, it shocked my "machinist sensibilities", but it works every time.

I do really appreciate your thoroughness, not giving you a hard time!

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Yep! Push the ball through and be amazed! All very simple on a Triumph - haven't found a similar kit for Norton.

Peteyoung75 said:

Ha ha no - I appreciate the info! I’m new to engine work so have no previous experience of this stuff. My main concern is not needing to do it again! Or wrecking my downdraught 88 head!

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That's fair. These old motors are tugboats. You probably could have knurled it and it woulda been fine! Ha!

Well I guess I’ll keep updating this as it may be useful for someone in the future and might prompt discussion of things I haven’t considered. It’s taking ages as I rarely have a chunk of time to put in to it. Got the outer bush roughed out last night.