GIbson Crankpins

[JamesTMaxted]

Hi , I'm having problems achieving 90 degree, normal alignment between AG crank pins and the outer face of the boss on AG plastic centred wheels. The wheels are relatively new purchases with a molded hole for the crankpin on all six wheels of 0.85 mm diameter. I'm using my Unimat milling set-up to both counter sink the large rear boss and start a 14BA tap in the rear face to encourage the pin to go through square. Needless to say I am hand turning the chuck carefully with no belts attached! I have checked to ensure the end of the crank pin is fully flush with the rear of the wheel and completely clear of the rear boss. Despite this , in all cases the crank pin once screwed in fully has a very slight lean off normal from the outerface of the central boss. The lean varies a bit in direction from wheel to wheel. I'd appreciate any advice on how to rectify this.. I am loathe to go down the route of completely drill out the molded hole , filling and starting again. Equally I'm a bit nervous about tweeting the pin once the epoxy has set to bring it back into alignment. So any advice much appreciated.

[Philip Hall]

Unfortunately, on some AG driving wheels the crankpin holes are not at right angles to the front face of the wheel. This problem was covered at length by Chris Pendlenton in his 'Wheel Derangements' articles in MRJ 219 and 221, along with his solutions, and I would recommend a read. However, I have always just bent the crankpin straight and so far had no problems. This is definitely not precision engineering, but it has worked.

Philip

[JamesTMaxted]

Many thanks Philip,

I was hoping for a reply like this , I've been using my stock of Sharman wheels up till now , so this was my first venture into the DIY cranckpin fixing game, hence the call for advice . Anyway with your encouragement and having re-read Chris' helpful notes in the MRJs you refer to, I have gone for the "fix it and tweak it" method. On a practice wheel, I glued the 14ba screw supplied in place with epoxy (plastic padding steel) and after 24 hours hand spun the wheel lightly secured by the crack pin in the jaws of the chuck of my Unimat. I then reduced the wobble to a minimum by finger adjustment on the rims . I used a suitable pointer fitted to the tool post and then lined up by eye on the inside rim of the wheel - as a sort poor man's DTI ! It seemed to work for the first wheel at any rate!

James

[JackBlack]

I think I've always had a problem with Gibson crankpins coming through at *not* 90 degrees. Just give them a tweak with a pair of pliers and job done.

[David Knight]

One trick to get the crankpins straight that I learned from many years ago on e4um was to tap in from the outer face and use a long crankpin bush as a guide.

HTH

David

[Philip Hall]

I have done the same with a piece of brass drilled with a clearance hole to hold the screw vertical on the back of the wheel. However, sometimes the problem is that the hole is actually moulded at an angle, so bending the screw afterwards (or doing it Chris's way, plugging the hole and re-drilling) is the only option.

Philip