Stering Peg

[Steve Simmons]

Hi all, I was helping a friend with his TC this evening and told him I would get more opinions on his issue. He has a brand new steering peg and a brand new worm. The peg is from one of our current suppliers. The worm as far as I know is a NOS part from 1960 so probably a BMC factory replacement item. I don't recall ever looking this closely at brand new parts, but if you examine the attached image, the tapers are just a little different. I'm sure they would wear in to each other but is this normal? His old worn peg turned to the least worn side fit better than the brand new peg, but that doesn't tell us much.

[Duncan M]

Did the car not come with a worm? Or, what is perceived to be wrong with the old worm?

[Steve Simmons]

Other than showing wear, it had a few chips along the top of the grooves. Then while trying to remove it, the owner kind of banged up the top bearing area. So he wants to replace it. None of the suppliers seem to have them so that's when I gave up one of my NOS pieces.

[jddevel]

On the assumption that the worm is in fact NOS then the peg is to the wrong specification and personally would return it. Although no engineer what`s the point of two items that are to run in tandem not making full contact. Surely in this particular case stress on a specific point can only lead to potentially a long term break. To me it`s like have one piston ring in contact with a bore and waiting for it to wear until the others make contact. I would also add that in a perfect environment both peg and worm surfaces would benefit from either being "hardened" or possibly a chrome finish to give them an extended life. Perhaps a local engineer could turn down the peg to give a more suitable fit. That`s assuming those surfaces as suggested are not already hardened.

[Steve Simmons]

I agree, and I had the same thought about hardening. I have no idea what type of hardening was done on either one of these pieces.

[ROGER FURNEAUX]

hi Steve - both worm and peg should be case-hardened (at least 10-thou deep) and ground. The Bishop cam co. who invented the thing, also made special machine tools to produce them, and it seems that nobody since has been able to reproduce them correctly! Eric Worpe has done a lot of research into worms, and should know what the angle is. One machinist I use has a shadow-graph, so we should be able to measure it: I have a new repro worm made here in England by a chap called Ray Tutt, and a Morris 8 worm, which has a different pitch, but the angle should be the same.

As is well known, parts suppliers do not always get it right (or rather, the suppliers to the suppliers) and who these days has any factory drawings? They do exist, Gerry Goguen had some, so perhaps AS have the correct pegs. Theirs should be spot-on, at $58 each! Moss in the UK only want 12GBP...

Roger

[Steve Simmons]

Thanks Roger, that rules out machining and re-hardening the peg, which is something we shouldn't have to do anyway. I'll have to check with Eric and Abingdon Spares to see if either has more info. I don't suppose your machinist would share his graph? It would be nice to know which of these parts (if either) is correct. Doug Pelton says they made their pegs based on original worm samples, but that means the worms were likely worn, so all bets are off.

I mentioned on the email list that the worm gears I have were made so long ago that I can't imagine anyone was making aftermarket repros. They have the same part numbers stamped into them, the same type of date code (except 1960 instead of 1948) and the bronze finish is identical to other BMC products of the era that I've seen. So while I can't be 100% certain, I have little reason to doubt their authenticity.

[ROGER FURNEAUX]

As a first approximation, I machined a cone on an Al. rod, by swivelling the top slide, and 12.5 degrees looked good on both worms I have. You could possibly get that done in California. The pegs could be ground, but are tricky to hold. For something so critical, they should have been checked using NOS worms.

Roger

[Tom Lange, MGT Repair]

I believe I still have an NOS peg and worm, that came with a TC many years ago. I'm happy to go dig them out and compare them, if there is interest.

Tom Lange
MGT Repair

[jddevel]

Tom, Might I suggest for a long term investment if a 3D printer is available that a "pattern" is made which would allow when metal printing becomes more reasonably priced worm and pegs reproduced for those concerned with originality.

[Steve Simmons]

I'd love to have a look at those items, Tom.

[Duncan M]

When I rebuilt the box I used the original worm, so it is on the car. Likely the original peg pictured. It did match up to the new peg I installed. Using a digital dial caliper I got the shaft that presses into the sector shaft with a slight taper. .439" tapering to .449" (diameters)

The angled peg is .579" and the small end is hard to measure because it is slightly rounded, but pretty close to .426" (diameters)

Holding my original peg up to the peg you picture, they look like the angle is identical. I'd say the worm that is pictured is different than original.

IMG_1727.JPG (30.33 KiB) Viewed 3059 times

[ROGER FURNEAUX]

Jan - I am no expert in these matters, but I suspect that 3D printing would not have the strength for worms and pegs. Being built up from fine particles it is akin to sintering.

Thanks to Digby Elliott who has loaned me some worms, i now have several to try: the difficulty will be to mount them in such a way that I can measure the "lift" of the peg in the central position, as done by Eric Worpe. This will hopefully identify any non-standard worms.

Roger