Hutch’s workshop tips
Hutch has to get it on with a late 1960s Bush
This month, Hutch show the benefits of using a reamer on a gearbox bush
Ihave a ‘69 Triumph T100C engine in for building on the bench at the moment. It was delivered to me in my favourite condition – already in bits, just as the present owner got it as a project bike. As is the way with these things, not all the parts appear to come from the same engine... just to make the jigsaw a little easier.
The crank assembly is now together and installed into the cases with new bearings all round, so it was the gearbox's turn next. After a good degrease and clean up, there was quite a lot of part numbering going on; fortunately the Triumph gears all carry identification numbers, making life a little easier. The gears were all in good useable condition and only a few small parts were needed. One part that did need replacing was the layshaft lower gear bush which fitted on the layshaft like a slack thing in slacksville (I've replaced Hutch's 'workshop term' for the easily offended – Matt).
Along with the other small parts, a new bush was ordered and soon delivered. Upon
inspection, the new bush wouldn't slide onto the layshaft, even before it was fitted in the low gear. Sticking my finger into the bush revealed a bit of a burr on the scrolled oil way on the inside diameter. A bit of light de-burring with some emery paper didn't solve the problem so I decided, due to the thin wall thickness of the new bush, to fit it, then de-burr or open up the ID (Inside Diameter) a little with a reamer.
A quick measure of the layshaft and a glance inside a Zeus book (an essential machinist's guide to measurements) showed the shaft OD (Outside Diameter) to be 11/16th; unfortunately, while I have lots of reamers, I don't appear to have one of that size... isn't it always the way. However, what I did have was an adjustable reamer that spanned 11/16th.
First things first, remove the old bush. I retired to my machine shop, cup of tea in hand (thank you, Chelley), measured up the new bush and made a sketch of a small press tool of OD and ID just smaller than the new bush that could be used to remove the old and fit the new.
A bit of a sort through the scrap boxes under the lathe came up with a suitable piece of alloy, which would be fine for this one-off use. From the scrap piece I
turned up the small stepped press tool as I had drawn.
Setting the gear on a couple of vee blocks on my small fly press, using the alloy tool and noting the bush would only come out in one direction as it was staked into the gear, I gently pressed (not swinging the fly handle) the old bush out. Using a similar set-up I fitted the new bush, paying careful attention to pushing it in so it was flush on both sides of the gear.
With the new bush fitted in the low gear it would, unsurprisingly, still not fit on the layshaft. Holding the gear in the vice, I adjusted the adjustable reamer until it opened up to just touch the bush.
The gear was then repositioned in the vice so I could ream vertically; reaming horizontally would give far more chances of the ream being all over the place. Once I'd passed the reamer through the bush, remembering that a reamer turns in the same direction both in and out, and the cut being so small I was more just de-burring at this point, I tried fitting the layshaft into the gear/bush assembly held in the vice. Happy days! There was a nice sliding fit and no further adjustment of the reamer or cutting was needed.
All that was left was to return to the workshop, throw all the gears in a box and shake them up in hope they assembled themselves in the right order.