Burman B52 conundrum

[enigmas]

Hi Rob, I'm just trying to repair a gearbox for a friend...not trying to steal anything!

Thanks again Grolly and 1608. We had most of the gearbox apart but didn't remove the gearbox sprocket as that looked and felt ok, but perhaps I didn't look hard enough. All the rotary selector mechanism looked fine but what didn't, were the 2 bent and blued selector forks that moved the dog clutches. Seeing these, I presumed that these were the primary cause of the faulty operation.

I like to run the bike on a stand with the back wheel in the air so there's no 'real' torque loading on the mainshaft sprocket and see if it selects 3rd and 4th more easily. After that test refocus on wear in the selector mechanism.

We refitted the the outer cover using anerobic sealant so there is no gasket. The original was very thin and I did read some tech literature stating to leave it out to reduce tolerances on the gearchange mechanism. The box does select 1st and 2nd fine.

Perhaps the indicator mechanism is binding (nut too tight or not enough clearance when tightened, but I doubt it as 1st and 2nd are fine.)

It worked fine on the bench so I 'd say the issue has to do with torque loading.

As 3rd and 4th are the most used gears I'd like to revisit that particular dog clutch as I did notice the tapers on the engagement segments of the dog were rounded.

I also read that reducing the distance this dog clutch moves by placing a thin spacer behind one of the gears can cure the engagement issue on 4th.

Any observations on these considerations?

[robcurrie]

Hi Rob, I'm just trying to repair a gearbox for a friend...not trying to steal anything!

We are very suspicious of queries from your corner of the empire
Maybe it would sound less like a decree if I said : "Non-members do not have access ..."

Rob C

[enigmas]

Rob, frankly I don't particularly want to go there but the tone you use and the condescending nature of your comment is not well taken.

I'm grateful to the contributors who have assisted in my quest to repair the gearbox and as a consequence keep another fine English motorcycle on the road...even though it is not in 'mother' England. I didn't really think it mattered as to what country I'm in (and I do take offence at your aspersions on Oz and the 'empire' comment) as I imagined the aim of the club was to keep these fine motorcycles going in whatever part of the world the motorcycle happened to reside.

For your information I'm a member of of 3 clubs and have posted to 4 tech forums for approx 16 - 20 years. Sharing technical info was never an issue for non paid members on these forums but certain aspects of the clubs were reserved for members, such as first 'dibs' on parts and club projects...which I believe is fair.

End of rant!

Thanks to the other helpful guys who are trying to assist me with the gearbox repair. I post further details as they come to hand.

~ Vince.

[1608]

Hi Vince, I'm running out of ideas now. The placing of a spacer behind the gear may prove or disprove wear on the selector train, But, anything like spacers or shims would very quickly wear if placed agin any rotating parts. And therefore be a very temporary fix. I'm off on a weeks rally later today, but I'll ask somebody thats v.g with g/boxes and if he replies in time I'll let you know.
What ever hapens please keep us updated when sorted.

[clive]

Vince as well as advice just occasionally the piss may be taken, the clue is in the I thought it was quite funny and that you had set yourself up for it by saying "I am not trying to steal anything" which had never been suggested. Yes many of us who spend time giving advice are happy to help keep an AMC bike on the road anywhere in the world and even if the owner is not a member of the club.
Personally I cannot help with your query, I had two large boxes of gearbox bits and although they all look like they should be interchangeable they are not. I gave up and bought another gearbox!

[enigmas]

Thanks 1608 and Clive. The bike's at my friend's home about an hour away. For the moment, I'm just trying to collate all the possible mechanical issues that could cause this situation and then tackle it with that information at hand.

Since it engages 1st and 2nd without issue it then must be something that affects the mainshaft or functions on the mainshaft.

The first test will be to get the rear wheel off the ground, get it running and run through the gears. There'll be minimal load on the gearbox sprocket. If it then runs through all the gears without issue, it's likely to be torque loading that's causing the issue. So it could then possibly be the mainshaft bearing or a worn 3 - 4 dog clutch.

Well it's worth trying. The bike has been assembled from mixed parts so this may compound the problem.

NB. When we refitted 3rd and 4th gears to the mainshaft there certainly didn't seem to be excessive play.

Will get back when there's some fresh info to report.

~ Vince

[1608]

Further, sleeve bush on the main shaft coming adrift has been known to prevent engaging 4th but not 3rd. One other thought, and I know I keep banging on about the selector train being worn in different places. But, when I stripped my box I noticed that the 1st and 2nd gear locating dimples in the rear of the selector drum are close together, there is a noticeable gap from 2nd to 3rd and then 4th. So, any wear will become more apparent when selecting 3rd and 4th. Hope this makes sense. Anyway, away for a week now so good luck and do give us an up-date with the result, I'm interested. I've no way of contacting you again.

[Andy51]

Hi Vince, arrived late in the game. Things to check: are all the various bronze bushes in the gear pinions secur? They often work loose but a drop of loctite will secure. Is the mainshaft straight? Check between centres on a lathe or v-blocks with a dial guage - you should be looking for total indicated runout (TIR) ideally of less than 1 thou but a couple of thou is OK - and don't try to straighten them (how do I know?!). The dogs on one pinion (can't remember which) take the form of 5/6 'prongs' that engage in holes in neighbouring pinion on layshaft - these are susceptible to wear. Check tooth numbers against parts list (see Christian's archive) and make sure they are paired off correctly - it is possible to put them in the wrong order, and all looks well until you try to assemble the main case and the kickstart case (they will then go together with a rubber mallet but nothing will turn!) - the 2 case parts should go together easily and all parts move freely. If the 'box is a bitza, check opposing pinions for width, etc - they should match, but there appear to have been changes over the years. Finally, check layshaft and gearbox casings against parts list, as these changed mid-1954 - I have a thread on this at the moment as I have 2 autojumble 'boxes I am trying to sort and one contains a mixture of parts across the years which may or may not affect operation. Hope this helps and doesn't come too late, Andy.

[enigmas]

Hi guys, I believe we've resolved the problem. The owner of the bike (Francis) lives some distance from me. We've managed to resolve the conundrum over the ether via sms.

By loosening both the primary and secondary chains it became evident that there was movement in the mainshaft bearing through some muscle being applied to the clutch basket. Once the chains were loosened off, the bike could be ridden and changed gear reasonably well. 3rd and 4th were the problematic gears. There were no issues with 1st and 2nd.

The bike was then stationed so that the rear wheel was clear off the ground and thus unloaded from any 'driven wheel' torque reactions. Starting the engine and running through the gears in this manner enabled all gears to function. So there was no issue with the selector drum or the selector forks for the sliding dog clutches.

This final issue stemmed from the worn mainshaft bearing on the clutch hub side. We shouldn't have missed it but we did? Unfortunately when the box was first dismantled the most apparent issues were the 2 bent and heat blued selector forks working on the dog clutches. These were severely bent so masked the probable cause of the bent forks...which was the worn mainshaft bearing allowing the mainshaft to move both fore and aft, and up and down.

NB.
Interestingly, according to C.W. Waller in his book, 'Ariel' (Motorcycle Maintenance and Repair) covering the years 1948-60...he states on p.151, (in relation to Burman gearboxes) "Test the shafts in their respective bearings and bushes and note the clearance wear of .005"- 007" wear is permissible before renewal."

Thanks 'Basil' for the loan of the text.

~ Vince