classic motorcycle forum

Ditto. Also time to check the main shafts for wear and roundness - the wear is some distance in from the end so if the shafts are not parallel and round your new bushes will be wasted.

Also the bushes need to be in line when you're all done. I usually make them a thou (0.001") under size, then ease them out with an adjustable reamer fitted with a pilot. The pilot fits into the bush in the opposite side of the crank case to keep the reamer parallel while its cutting. Not a difficult job, but you need the right tool. (I borrow my adjustable reamers from a friend who has a boxed selection - last forever if only used on phospor bronze.)

Leon

Is it sucking in false air through the bronze bushings on the crankshaft?

It will if the main shafts or the bushes are worn: the shafts and bushes need to be round with only a thou or two clearance (say 0.025-0.05 mm). You definitely should not feel any movement if you grab the flywheel and try to move it up and down. If it clunks you're in trouble! The other place that wear occurs in early two strokes is in the bore: not so much up the top (as it is in four strokes) but above and below the ports where the rings jump across. And the rings, of course.

If these parts are worn the bike will probably still run, but will get hot an bothered when riding. If you've got good compression - it really should be quite "sharp" as you kick it over - then wear is probably not the problem at the moment.

Leon

The booklet "The Story of Bennett and Wood Pty. Ltd." was published in 1949, the year that the company's own Acme motorcycle gave way to the BSA Bantam. Unsurprisingly, the Acme motorcycle is not mentioned at all. But they do comment that the motor cycle factory was established in Wentworth Ave "over ten years ago" - say around 1938/9 - which ties in nicely with the beginning of Acme production for 1939. They could enamel sheet metal (see attached), they had a plating works (shown plating handlebars that they presumably made), they had frame jigs and brazing in the Speedwell Cycle Factory, and a huge spare parts and accessory department. In a nutshell, I believe that they did "manufacture" the Acme motorcycle.

Leon

I've looked pretty hard, but I have no direct evidence of local manufacture. However if a local firm of repute (like Bennett & Wood, one of the best known cycle/motor houses in Sydney for 50+ years) say that their bike is "Manufactured in Australia" there's every chance they are not lying. Simply not worth making something like this up if it isn't (largely) true.

There are comments in the 1939 press like, "... an unusually large proportion of the Acme motorcycle has been locally built" and "In appearance, this newcomer, with its Australian-built frame, is "easy" to look at."

It wouldn't surprise me if the frame was locally built, and maybe guards, tank, spokes, rims, handlebars, levers,... leaving the engine/gear unit, fork, saddle, lights... imported from the UK, then the whole thing assembled here? More or less.

We mustn't forget that there was active industry in Australia at the time. Beginning around 1940, for example, Tilbrook in Adelaide made a wide selection of parts and accessories for motorcycles.

But yes, it would be fun to know exactly what went on!

Leon

Unlike Williams Bros' Waratah, Bennett & Wood's Acme probably had a decent amount of Australian content. At least if claims in the contemporary press are to be believed.

In particular, the frame was said to be made in Australia. This is possible: I've not seen a British lightweight with a frame of the Acme design. Happy to be proved wrong!

Leon

"I'm just pondering the wisdom of splitting the crank up to check the big-end bearings..."

Yes it's a tricky one, perhaps depending on what you want to do with the bike. If you do pull it apart keep in mind that it is tricky to get it back together and running dead true. If you've not done it before best left to an expert? I've done it lots of times, and most often it's gone ok. Only once did it defeat me entirely (i.e. no better than a couple of thou run-out on the shafts after trying everything I know) and I had to pass it on to the expert who used appropriate (unknown to me) magic to get it running just so.

The epoxy is interesting. Often cases an an engine can be quite porous to oil and painting the inside with something (glyptal, expoxy of some kind) can keep the outside clean. Hopefully there's no major corrosion being covered up.

Leon

There seem to be a lot of GY-prefix engines used in little Francis Barnetts in the 1930s, like this one: https://cars.bonhams.com/auction/29728/lot/229/1933-francis-barnett-148cc-lapwing-27-frame-no-c27176-engine-no-gy-4934/

Some of them have a GYF prefix. What does the 'F' mean, and was there a serial number reset to go along with it?

Leon