gazzaecowarrior Posted January 22, 2013 Report Share Posted January 22, 2013 (edited) As some may know Im currently restoring and rebuilding a Mont MH123. I've had both wheels respoked. Turned out yesterday that the front wheel has been respoked at the wrong angle and had a bias to the left by about 4mm. Obviously I've started to panic whether the rear one is also spoked wrong but it is far harder to check. The wheel seems to line up straight but only when the snail cams are adjusted in a non symmetrical manner . The chain sounds and looks like it's running straight. But the adjusting cams on the rear spindle are not in symmetrical positions to achieve this and are a few notches different to each other. They are identical cams. On my beta the cams were allways in pretty much identical positions either side. Is it common for the positions of each of these cams to be so different or am i correct in thinking maybe the rear wheel has also been spoked incorrectly ? Edited January 22, 2013 by gazzaecowarrior Quote Link to comment Share on other sites More sharing options...
b40rt Posted January 22, 2013 Report Share Posted January 22, 2013 If your swinging arm has a slight twist (like my bsa) you may need to compensate . Quote Link to comment Share on other sites More sharing options...
gazzaecowarrior Posted January 22, 2013 Author Report Share Posted January 22, 2013 If your swinging arm has a slight twist (like my bsa) you may need to compensate . Hi B40RT. No i don't think it's that. The bike has never been trialed. Frame and swing arm look true. I've got a horrible feeling the wheel isnt right. Quote Link to comment Share on other sites More sharing options...
pete_scorpa3 Posted January 22, 2013 Report Share Posted January 22, 2013 If the wheel is out then the sprocket would not run true when the wheel is aligned. Use a long straight edge from the back wheel to the front, then measure the distance from the straight edge to the front wheel rim. Do this both sides and adjust the cams until you will get the same measurement, the wheels will then be in a straight line. Now look at the sprocket and see if it is running true. If it is, then the chances are that the swinging arm is bent, if it isn't then it's probably the wheel out of true. Hope this makes sense. Pete Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted January 22, 2013 Report Share Posted January 22, 2013 I don't think I ever had a bike in that era that was not like this. Spanish materials and build quality were not of the highest order so swingarms could twist or the frame be off true anyway. Rear wheels were sometimes set off-centre to allow the chain to clear the tire - bear in mind that the motors were basically designed for use in road bikes with much narrower tyres. If the chain is running straight between the sprockets then your wheel is pointing "straight forward", assuming the motor is too (see above re build quality). If the rear wheel is a bit to one side of centre then that is not critical on a trials bike, indeed Sammy Miller once said that made it easier to balance the bike. Whether or not that was the case or just BS to cover for what was coming out the factory we'll never know. Notwithstanding the above I would imagine that having the front rim central in the forks would be advantageous. Quote Link to comment Share on other sites More sharing options...
b40rt Posted January 22, 2013 Report Share Posted January 22, 2013 Best way I've found to check sprocket alignment is steel channel, B&Q sell it. Quote Link to comment Share on other sites More sharing options...
pete_scorpa3 Posted January 22, 2013 Report Share Posted January 22, 2013 I've had one of these for the road racing bikes for many years, it is available from Maxton. It makes aligning the rear wheel really easy as it bolts two pieces of box section through the rear rim. Alignment is crucial on a road racer that may be touching 180mph and the factory marks are never spot on. http://www.maxtonsuspension.co.uk/files/wheelalignment.htm Quote Link to comment Share on other sites More sharing options...
b40rt Posted January 22, 2013 Report Share Posted January 22, 2013 I've had one of these for the road racing bikes for many years, it is available from Maxton. It makes aligning the rear wheel really easy as it bolts two pieces of box section through the rear rim. Alignment is crucial on a road racer that may be touching 180mph and the factory marks are never spot on. http://www.maxtonsus...elalignment.htm Dont think that will help align sprockets ? Quote Link to comment Share on other sites More sharing options...
gazzaecowarrior Posted January 22, 2013 Author Report Share Posted January 22, 2013 If the wheel is out then the sprocket would not run true when the wheel is aligned. Use a long straight edge from the back wheel to the front, then measure the distance from the straight edge to the front wheel rim. Do this both sides and adjust the cams until you will get the same measurement, the wheels will then be in a straight line. Now look at the sprocket and see if it is running true. If it is, then the chances are that the swinging arm is bent, if it isn't then it's probably the wheel out of true. Hope this makes sense. Pete Hi pete Yes that makes good sense. Sadly the front wheel has gone back to the wheel builders to be corrected so i can't do what you say. I ran a straight edge from the rear sprocket and it seemed to hit the front sproket true. This was at the same time as the tyre looked central at the front of the swingarm. But there is about 5 notches out on the snail cams. I'm only paranoid of the rear wheel as the spoker made such a botch of the front. Surely he couldnt have got two wrong ? Or maybe he jsut got his mesurements for each wheel the wrong way round. Quote Link to comment Share on other sites More sharing options...
gazzaecowarrior Posted January 22, 2013 Author Report Share Posted January 22, 2013 I don't think I ever had a bike in that era that was not like this. Spanish materials and build quality were not of the highest order so swingarms could twist or the frame be off true anyway. Rear wheels were sometimes set off-centre to allow the chain to clear the tire - bear in mind that the motors were basically designed for use in road bikes with much narrower tyres. If the chain is running straight between the sprockets then your wheel is pointing "straight forward", assuming the motor is too (see above re build quality). If the rear wheel is a bit to one side of centre then that is not critical on a trials bike, indeed Sammy Miller once said that made it easier to balance the bike. Whether or not that was the case or just BS to cover for what was coming out the factory we'll never know. Notwithstanding the above I would imagine that having the front rim central in the forks would be advantageous. Thanks for that. No wonder the spanish economy is in a bad way. So it could simply be that maybe the lugs that the snail cams notch onto are not equal or maybe as you say there are other imperfections in the frame / swingarm. Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted January 22, 2013 Report Share Posted January 22, 2013 (edited) Hi pete Yes that makes good sense. Sadly the front wheel has gone back to the wheel builders to be corrected so i can't do what you say. I ran a straight edge from the rear sprocket and it seemed to hit the front sproket true. This was at the same time as the tyre looked central at the front of the swingarm. But there is about 5 notches out on the snail cams. I'm only paranoid of the rear wheel as the spoker made such a botch of the front. Surely he couldnt have got two wrong ? Or maybe he jsut got his mesurements for each wheel the wrong way round. If you have the wheel in a position about the middle of the swing arm and the sprockets lining up (by string line or chain should be accurate enough) then you're fine but five notches does seem a lot. Try measuring the distance between the cam stops on the swing arm and the centre of the swingarm spindle to see if they are the same. If the dishing was wrong then you would not be able to correct things by use of the snail cams. If you had the wheel centralised under such circumstances then it would not be pointing dead ahead. Pete - I tried for ages to get a straight edge that would work on the road bike but the answer eventually came from Kevin Cameron's "Sportbike Performance Handbook" (not an appealing title but a really useful book full of his distilled knowledge) - two fluorescent tubes. Cheap ie free, guaranteed to be straight and set up like your device but measurements at the front are taken to the "front and back" if I can put it that way, of the discs. Allows very fine adjustment of alignment and "centre lining" of the rear wheel by tweaking spacers if necessary. Edited January 22, 2013 by 2stroke4stroke Quote Link to comment Share on other sites More sharing options...
gazzaecowarrior Posted January 22, 2013 Author Report Share Posted January 22, 2013 If you have the wheel in a position about the middle of the swing arm and the sprockets lining up (by string line or chain should be accurate enough) then you're fine but five notches does seem a lot. Try measuring the distance between the cam stops on the swing arm and the centre of the swingarm spindle to see if they are the same. If the dishing was wrong then you would not be able to correct things by use of the snail cams. If you had the wheel centralised under such circumstances then it would not be pointing dead ahead. Pete - I tried for ages to get a straight edge that would work on the road bike but the answer eventually came from Kevin Cameron's "Sportbike Performance Handbook" (not an appealing title but a really useful book full of his distilled knowledge) - two fluorescent tubes. Cheap ie free, guaranteed to be straight and set up like your device but measurements at the front are taken to the "front and back" if I can put it that way, of the discs. Allows very fine adjustment of alignment and "centre lining" of the rear wheel by tweaking spacers if necessary. Thanks for that info. wheel builder just rang to say the front wheel is now ready and correct. So at least the front of my bike will go in the right direction. Im in no rush anyway as my I only had my knee reconstructed two months ago so no riding for me. Quote Link to comment Share on other sites More sharing options...
2stroke4stroke Posted January 22, 2013 Report Share Posted January 22, 2013 There's always this of course http://www.probike.co.uk/it110009.htm but it only checks the chainline, not the wheel alignment. Quote Link to comment Share on other sites More sharing options...
b40rt Posted January 22, 2013 Report Share Posted January 22, 2013 Hi B40RT. No i don't think it's that. The bike has never been trialed. Frame and swing arm look true. I've got a horrible feeling the wheel isnt right. Hi B40RT. No i don't think it's that. The bike has never been trialed. Frame and swing arm look true. I've got a horrible feeling the wheel isnt right. If your using the same hub and spacers, the only thing that has changed is the dish of the wheel. Front to rear alignment is meaningless unless you have the pre rebuild dimensions to compare. Quote Link to comment Share on other sites More sharing options...
pete_scorpa3 Posted January 22, 2013 Report Share Posted January 22, 2013 Dont think that will help align sprockets ? No, but ensuring that the wheels are inline will provide a base point to make further investigations. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.