Worn long Roadholder sliders.

There was a recent post I cannot find where some fork lowers had bronze liners fitted by persons unknown and needed sizing which the poster had done, it included pics of a boring bar that piloted on the bottom hole and allowed them to be sized.

Hi Peter,

I was who has posted.

Search for "What to do with a worn Roadholder fork leg?" posted on August 16.

The attached picture shows a home made boring bar that worked well.

Regards,

Hans.

Found it.

The pre 65 trials boys, bore them out and fit a turned down mazarochi leg inside.

I have a large enough lathe for the job, the OD of the top bush is 38mm. I have also tracked down some aluminium alloy tube nominal size 1 5/8" OD or 43.1mm and an ID of 1.5" or 38.1mm. Just need to track down a piloted boring bar that does 43.2mm bores and a scrap fork bottom to practise on. Tube will be loctited in and the seal will also retain the tube. The tube is seamless and comes from the same source where I buy the alloy tubes to make cartridge fork inserts so I know the surface finish is good.

John, you may well be very busy shortly! If you get stuck, I might have a spare fork bottom

Dan, could you measure the depth of the bore in the fork bottom of the long fork holder.

For a Commando the bush bore length is 220mm and total length of the bore plus a few mm clearance is 270mm including the fork seal retainer. So for a Commando boring tool the bar length needs to be 270mm plus enough to be gripped by either the chuck or the tailstock chuck say 50mm.

I was concerned for the Disc fork lowers as they are oval and would not mount in the 3 jaw chuck and be centralised but by adding the fork seal retainer that gives a circular OD to be used as a datum at the top end plus the 3/8 hole at the bottom gives another datum. As a 250mm 3/8 rod could bend under the cutting forces of 1 cutting edge especially in the middle of the travel giving a bell shaped bore that is out as a solution. So the tool needs at least 2 cutting edges, it needs whats called a balanced borer which are thin on the ground. So it looks like a copy of Hans boring bar but for 43.2mm would be best.

Okey dokey will have a look this afternoon

The bore appears to be 214mm using a tape measure, 242mm to the top of the threads, both measurements are from the bottom of the. Bore not the damper seat.

Hope that helps

dan

Thanks, Hans kindly emailed me more detailed pics so another project for the winter. Triumph pre oif fork bottoms have the same ID, I use the 38mm reamer to clean out their bores from dings etc, but being steel the wall may be 2 thin to take a liner.

I've been away for a while so just trying to catch up....

(a) Would it not be beneficial to insert a thin steel liner (rather than alloy) into a bored slider - that way it would be possible to make up some bespoke bronze bottom fork bushes, rather than using the steel OE bushes that cause slider wear, and are invariably a sloppy fit? (Velocette fork sliders are steel).

(b) The alternative might be to fit an alloy tube liner, just as John Holmes has suggested, and then make the bottom bushes out of one of the new plastic bush materials, eg Turcite

These are already available for short Roadholders, but are pricey:

http://www.jsmotorsport.com/products.asp

(c) John Bould was looking into all this, and its such a shame that he has suddenly passed on.

Unfortunately I don't have the machinery to experiment myself, but I'm interested to hear from anyone who takes the initiative and does so.

If someone will donate an old fork bottom that would otherwise be scrap, with no promises you would ever get it back, I have the equipment and will buy the tooling and materials to try out a fix.

A thin steel liner with the internal spring already providing rust to make the oil into grinding paste is going to be worse, without the heat of combustion to drive out moisture staying with alloy would be better. If the liner works then replacing it with another should be easy.

I'll have a look, I think I have one. Remember that the trials boys regularly bore out roadholder legs to insert turned down mazzochi legs (cheating in my book!) so the principle should work.

ill venture into the shed after Christmas.

dan