Front fork pinchbolts

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56G80S
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Front fork pinchbolts

Post by 56G80S »

No help required but just an observation.

I thought I'd replace the front fork oil seeing as how I'd just done the gearbox, engine and chaincase oil (suction). Got my SAE 20. Drained 5 FL Oz from nearside slider. Filthy and of course less than the 6 that I should've got. I did thoroughly work the forks but with hindsight had unscrewed the cap bolt first

When refilling oil poured out of the headlamp shrouds.

The pinchbolts weren't pinching!

The tube had dropped.

Fortunately I had long ago made up a tool for drawing the tube back up and did so. Then the problem of how to tighten the pinchbolt as this was custom made with an extension for the Avon handlebar fairing. I didn't want to remove the fairing because it was a nuisance refitting it.

Some time ago Colin Farrington had made me some custom pinchbolts out of hexagonal stainless steel which he'd turned down to round at the yoke end. Unfortunately the threads were now tired (stainless is hard to work with and had a difficult time when I came off on the way to Nijmegen and then repeated the trick on the way to Stirling the other year) and the engagement into the bottom yoke could've been greater.

A local engineer had made up some further ones for me providing more engagement into the yoke but made them from round bar and machined two flats for a "C" spanner. I'd shunned these flats and as the extensions for mounting the fairing were quite long enough wound a nut to the bottom of the extension thread and tightened with that using a ratchet, two extension bars and a socket!

On releasing the fork tube puller the tube dropped again.

I didn't know why but the only answer I could come up with was that the pinchbolt thread was bottoming out in the yoke. Rather than shorten the thread I found a washer in my box of washers and filed down the outside diameter to match the pinchbolt, put it in and when tightened up the tube remained in place! The difference can't have been much more than a turn but it seems that was all that was needed.

Why this happened I can't guess, but it worked. Ironically, the fork leg other side was a doddle with no movement of the fork tube, although the custom pinchbolts were a matched pair. Also, the oil out of the offside (second) leg was so clean that I doubt if it really needed doing.

The whole lot is coming out next winter as the nearside leg seals are weeping and the slider extensions (which I had re-chromed 30 odd years ago) are flaking. I know from when I replaced the bushes quite a long time ago that there is quite a bit of pitting on the tubes above where they enter the bottom yoke although not so much as to be a hazard as yet (I hope). Saving up now.

Johnny B
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Rob Harknett
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Re: Front fork pinchbolts

Post by Rob Harknett »

Seems replacement pinch bolts when fitting the fairing were a bit complicated.
I had a fairing on a 55 G3LS back in 1956. Allen head pinch bolt replaced with standard length hex head bolt to hold the L bracket supplied with fairing to the forks & faring. So when I got another 55 G3LS in the 80's I simply bent up and drilled an L bracket, picked hex head bolts out the tin of spare mixed fittings. Handle bar fittings & clamps from jumble stalls. Struts bent up using stainless round bar.
56G80S
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Re: Front fork pinchbolts

Post by 56G80S »

For some reason I didn't want to have the bracket bearing onto the face of the bottm yoke. Probably would've been simpler if I had!

Johnny B
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Rob Harknett
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Re: Front fork pinchbolts

Post by Rob Harknett »

Long time since I fitted my last fairing, maybe I could go and look. However, I seem to recall cutting a bit of tube a little longer than the recess the allen head bolt goes into, then a washer behind the inverted L bracket. I probably found an old spacer to cut in the box of bits, not tubing. I also seem to recall I did this for the same reason as yourself. I think the L bracket needs to be a little proud of the bottom yoke to fit properly. Once the bottom is secure, alignment for the headlamp beam is done by adjusting the round rod struts in the clamps on the handlebar fitting. I am sure I recall bending the first strut with the leg too short. So I cut them long enough to be sure I could dip the fairing enough for the beam to be correct, with perhaps some adjustment to the L bracket angle. Once set up, cut the strut legs leaving about 1/2 " hanging out the bottom clamp. These fittings I made for the fairing fitted in the 80's, from memory of fairing's fitted to a new bike in the 50's. Which were Avon and Westlight. Westlite had a ridge that swept back from the headlamp to handle bar ends, a bit like the ridge in the mud guards.
MikeM.
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Re: Front fork pinchbolts

Post by MikeM. »

I too have an Avonaire handlebars fairing on my Twingle which I fitted many years ago, I sourced the handlebar fittings from various places but made up my own brackets for the fork fixtures. I used longer Allen screws and made up a pair of sleeves to enable me to have the brackets clear of the top fork covers. These have been in place for over 30 years without giving any problems. I have taken a photo of the bracket etc but know not how to post on forum (yes I'm too thick to know how to🤣) pm me your e-mail address Johnny and I will send you the photos. MikeM
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