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M49 rear wheel spindle reassembly


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Hi all, I think I have got the rear spindle in wrong but not sure how to correct it..

Initially I put it together "spindle, snail cam, swinging arm, brake plate, wheel, speedo drive, spacer, swinging arm, snail cam, washer, nut.

This was fine - chain runs centrally over the tensioner and rides ok but clearance between tyre and chain is very limited. so much so that fitting the Sammy Miller Chain guard will rub the tyre.

So following the book I moved the spacer from the nut side to the "tommy bar" side. Bit more clearance but chain out of alignment.

Can anyone give me the right reassembly order

Am I missing any bits? It seems a bit odd there is nothing between the brake backplate and the swinging arm when set so the chain run is straight

Best regards


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You had the order correct initially, there is no spacer between brake plate and swingarm

The clearance is tight anyway, but the guard should fit although very close to the tyre so you will probably get some rub occasionally. Has the wheel been rebuilt with the wrong offset at some time maybe?  What tyre is it? Looks like a Pirelli which is blown up quite hard?  It may rub less with normal trials pressure

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Try adjusting the snail cams until the tire moves away from the swing arm. On my M49 I discovered when my rear fender was off that the tire was not centered to the middle of the frame when the snail cams were adjusted equally (mine was rubbing the exhaust). I set the cam on the chain size to the 8 mark and the speedo on the 4 mark. The trick was removing the rear fender (and seat / tank) so you have a point of reference for the alignment.

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Wheel spindle enters swing arm and brake plate from drive side. No spacer between brake plate and swing arm lug. Non drive side should be speedo drive (if fitted) spacer and additional thin spacer if no speedo or replacement double shouldered spacer. Then you have snail cam and thin washer. Some rear wheel spindles also had a thin washer on the drive side, between the spindle shoulder end and snail cam, this brings the spindle slit pin hole into line more for the castleated nut. Take the chain guard off and use a good straight edge on the rear sprocket and align the gearbox and rear wheel sprocket. Tighten spindle nut and look at exhaust where it is closest to tyre. You may need to adjust the rear silencer if the tyre rubs. It’s more important that the chain is true as this could cause serious wear to the sprocket teeth and possibly take a bit of power away from the engine. 

As Woody says you may have the tyre inflated too high but if the pressure was reduced to say 4 psi you might have more rubbing issues due to tyre flexing on the rim. There never has been much room for the back wheel in most Bultacos a design issue but then they tend to be slim which helps the rider. A bit of rubbing here and there will always happen when the bike is in action, you may get it all set lovely with no rubbing but after use the alignment fairies with have been busy shifting thing around for you so it all rubs on everything! 

If you search on this site you’ll find some tips on wheel alignment if you are the fussy sort and must have a perfect bike....and why not! But it wouldn’t be a bad thing to check front forks for correct alignment then check front to rear. 2-3 mm out is not significant ( watch me get pilloried for that comment) as it’s the chain which is important. You will not notice that small measurement when riding unless your an alignment fairy or Toni Bou. I wonder how many frames the works boys throw away after each trial because they’ve been used so hard. 

Last piece of advice if you are having problems still, then I would either remove the swing arm and get it on a surface plate at a local engineering company to make sure it’s not twisted. That’s fairly easy to sort with a bit of brute force or a hydraulic press. If you can’t go there then again on this site is the pics and info to help you DIY. Hope you get sorted and don’t forget you can always gain a little extra clearance on the exhaust back box by deft use of a......BIG hammer.?? Erm number plates could be covered next time ??

Edited by section swept
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Hi Woody, 71Z man and Section Swept. Many thanks for the words of wisdom. Woody - you are right both wheels have been rebuilt and re booted (Pirellis) on the original rims and hubs by Trials and Tribulations in Church Stretton so should have the correct offset. I will try lowering the pressure.

71Z Man - I like your thoughts on offsetting the wheel on the snail cams. Measuring the offset against the front wheel should also help the setup.

Section Swept - Interesting point re an additional washer on the drive side. I had to put an extra washer behind the nut on the speedo side to keep the nut off the unthreaded length.

I could never be described as a perfectionist so having made sure the chain run is right I will use the snail cam move and leave well alone. I live on a farm (they use the woods and stream above us on the Vic Brittain) so these days I just use the bike for a bit of fun and the odd trip to the shops on a busy Saturday. Lastly good point re. number plate. Laziness on my part, used a photo required by my insurance people...



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Might be worth also checking the swingarm to see if it's bent. I had one which must have been clattered on one side as both arms were pointing to the right when you looked at it from the back of the bike with the wheel out and I had to straighten both back into line using another arm as a guide. If you look at your bike from the back are the shocks upright as if the are leaning a bit, it could show the swingarm is out of line?  You shouldn't have to offset snail cams really, I have a few Bultacos and have never had to do that. The chainguards all run close and rub a bit, even the tensioner can rub on them. The spindle on the speedo side is wasted for the threads so a larger diameter washer is needed where the solid part of the spindle protrudes by a mill or two and has to be that thick otherwise the spindle nut won't pull up against the arm, just the ridge on the spindle.

You let Spence loose on your wheels.....   only joking, he's a good bloke.

I've probably ridden past your 'back garden' on many occassions over the years

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Could well be bent. Its certainly got a ding plus wear where the chain rubbed the swinginging arm pivot so had a lot of use / abuse prior to 1980 when it was laid up. Still finding the odd bodge... I will take it out and check after the Cleobury Mortimer Show. Could be another winter project...

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