Rear Chain Adjusters - what thread size?

The adjusters on my Domi are 1/4" x 26tpi. These adjusters are distinctly under-engineered and prone to breaking off. Some owners, on having an adjuster break, have fitted snail-cam adjusters instead. As for removing the broken off adjusters, easy-outs won't work. A pillar drill and patience are required, followed by Helicoiling or similar. All in all a guddle.

Previously richard_evans wrote:

The two rear chain adjusters on my Dominator 99 (1957) have both broken off and will have to be drilled out. I've bought two beautifully engineered stainles steel adjusters to replace them from CPC Engineering (www.cpcengineering.co,uk) which I assume are the right thread.

Measuring the thread of the new 1/4 inch diameter adjusters with a thread gauge, with a view to tapping the holes out, expecting them to be 26 TPI (Cycle Thread or BSF), I found that they are actually 28 TPI which equates with 1/4 UNF, which seems a strange size for a British bike of that era.

Any ideas, not only on the sizes, but also on the practicalities of extracting the old adjusters which are broken off flush and have been like that for the past 50 years. I suspect they made be a bit harder than mild steel. I use 'Plus Gas' as a penetrating oil which is about the best in the business and I do have a set of 'Easyouts'..

Is theswing arm in a finishedstateorcan you heat it? Ihave had success with "Eas-out's" (West German manufacture....) afterapplying heatand chill through thedrillingwith afreezer spray. I'mprettysure they were 26tpias I fittedsomespare bolts I had in the pot...

This ad says they are identical to the original:

http://www.ebay.co.uk/itm/Norton-88-99-650-Featherbed-R-WheelChain-Adjuster-Bolts-nuts-Stainless-03-0500-/162191498010?hash=item25c35ddb1a:g:9QMAAOSw34FVGws4

NOC SHOP has a version too.

Les

I think you will find the steel used is not particularly hard just normal bolt (mild) steel. As they are broken off, it is most likely to mean they are as good as being welded in, as original attempts have sheared them, so I would imagine you'll have no luck with an extractor apart from snapping this off too, which would be really difficult if this snapped off flush as they are really hard metal.

I would attempt to drill them out.....Do this with ever increasing drill sizes from a small pilot drill size, but keep the maximum drill size just below the correct tapping size as you are likely to wander off slightly....Quite often when the hole you are drilling is getting near the correct size it will expose one side or parts of the thread as bits break away so at this point I would get a first taper tap of the correct thread and carefully wind this in gently in and out, after a while you may be lucky to get the tap going in and removing the original remains of the bolt, Procede until the rest of the old bolt flakes comes out. Finish off with a plug tap. I personnally would undertake this freehand as trying to mount this in a drill stand would seem near impossible. Remember they are quite rudimentary and don't require microscopic accuracy like an engine repair would.

If your endeavours destroys the thread you could Heli coil the thread or make up some adjusters with the next size up thread....no-one is going to notice and they'll be stronger too.

Les

The early s/arm chain adjuster (I think the changeover is in 1957) needs a different fork end. This is formed by inserting flat steel into the end of the tube and flattening it. The axle slot is machined to an open end.

I like the snail cam idea. Let us know what cam you choose, and how you get on. Make sure you incorporate a means of adjusting wheel alignment.

Paul

Previously richard_evans wrote:

Another solution occurs to me if I fail with the type I am dealing with and that is the earlier Dominator (1952) had a different type of chain adjuster. One that had a plate on the rear end of the swing arm through which the threaded adjuster passed. More in keeping with the model and vintage of the machine than the snail cams.

I don't see them listed anywhere so they may have to be fabricated.

There are quite a few solutions to this problems of duff adjusters in Featherbed Swinging Arms. Often the broken section won't budge and the end result can be a broken drill bit or extractor end adding to the problem. I like the cook and freeze idea to help free the broken end. Some people have soaked the threaded hole with Cola overnight and this has also worked.

I have played about with the problem in a number of different ways. Drilling out the stuck chunk has usually messed up the inside thread. If I was in a quick-fix hurry. My solution was to drill and tap an extra half inch of 1/4x26tpi Cycle thread. There is enough room to do this. I then found a bolt that was half an inch longer than the adjuster, file the head round, then ran up and threadlocked a nut under the rounded head. In essence just making a longer adjuster.

If you are thinking of a helicoil solution.Much easier, if you have the tools, is to drill and tap the old hole up to Commando size. Again there is room to do this. As the attachment shows the Commando adjuster is longer and much beefier. The only problem being the AF spanner size nuts.

So thats what my Atlas has, Always thought it was another AMC "improvement".