Various Questions

[Ozmadman]

Rotor

[Remington]

Hello Paul,

As far as I remember my sprocket is the same as yours although the extended part faces outward towards the alternator otherwise the chain would gouge lumps out of the stator as it did before, and the chain would not run parallel with the wall of the chaincase. I think that the exploded diagram for the G2 shows the sprocket teeth inward. 'Stripping the Lightweight Engine' which I recall can be downloaded from Christian's archive also shows the 350cc sprocket with the extended part facing outwards. If yours has been installed the other way round this may explain the need for shims between the rotor and sprocket to avoid damage to the rotor.

My 'bike has a Lucas alternator and rotor (reasons unknown) unless the original was damaged at some time in the past. It has occurred to me that the rotor may be deeper/thicker than the original and therefore takes up more than the .20 thou. slack with the shim installed, although without the shim the chain would not run parallel with the inner chaincase (not much in it, though). Perhaps all is fairly well inside the engine and, because of the slightly different size Lucas rotor, the nut has not been very tight for decades? It is held in place with Loctite/Threadlocker and a tab washer which does have a spares part number (unable to remember offhand). The handbook and workshop manual are incredibly vague about the shim and only mention that one or more may exist and to make sure that they are replaced when reassembling the drive side of the engine.

[Ozmadman]

Hi, this 020 thou thing has nothing to do with the possible different thickness of the rotor or whether it is Lucas or not. Whatever is on the end of the crank is irrelevant because once that nut is tightened it pulls everything towards that side and as long as the sprocket face or shims are pulled up tight against the outer bearing there should be no locking up. Leaving the nut loose is not the answer. The reason for the approx .020 thou, and the exact amount isn't written in stone, is as far as I am aware to allow for expansion when hot. Once the crank is pulled to the left hand side you will then have the 020 thou or so gap at the other end of the crank ie, between the flywheel and timing side bush. Once things warm up you need that gap to ensure the engine doesn't seize. The sprocket saga is a mystery as there has been discussion on this before. I will have another look when I come to put my engine together but when I have tried it before the other way round the body of the sprocket hits the casing a long way before it bears against the bearing so much so that I would need a serious amount of shims to space it enough and then it will probably space the rotor out too far so it hits the casing?? I must admit that way round does make sense as you say to avoid the chain rubbing the rotor. Will get back once I have another look.

[Ozmadman]

Can't find the publication you mention plus I have never seen a picture of the engine showing the position of the sprocket. Maybe someone else can intervene here and inform us the proper way the sprocket goes so I can put mine back correctly

[Remington]

Paul,

Many thanks for explaining the .20 thou. requirement - back to the drawing board for me.

Christian's archives can be found on the following: http://archives.jampot.dk/http://archives.jampot.dk/ Hopefully this will work for you.

You need to find the Technical page, then Specific Models, and then Stripping the AMC Lightweight which is a document containing photographs and descriptions of how to dismantle the engine. The images are of the 350cc model and quite clearly show the chain sprocket in place.

I wonder why your sprocket hits the casing before it reaches the bearing as mine sits comfortably without any binding (as in the archive document)? Interesting also the damage to your rotor where mine is not marked although the alternator stator suffered damage from the chain when the sprocket was the wrong way round. With your sprocket installed teeth outwards, does the chain not run at an angle to the inner chaincase, or has the clutch basket been shimmed out as well to compensate? I have a photograph of my incorrectly installed sprocket and chain (before corrective surgery) which I shall attempt to attach to this thread if I can work out how to do it (and if I can find the photograph!). Is it possible to stuff 350cc innards into a 250cc engine case or is this just mad thinking?

[Remington]

Ooops,

I don't think the link works - it may need a little fettling unless someone else can supply something different. This was the address supplied to me although there may be something misquoted between jampot.dk and /http://archives.....................

If you are unable to access it still I could forward the document to your e-mail address if you let me know what it is.

[Ozmadman]

Ooops,

I don't think the link works - it may need a little fettling unless someone else can supply something different. This was the address supplied to me although there may be something misquoted between jampot.dk and /http://archives.....................

If you are unable to access it still I could forward the document to your e-mail address if you let me know what it is.

Thanks Philip

This is the site now http://archives.jampot.dk/ actually I have seen this before, I even have printed this out in the past but never noticed the sprocket!!

this will take you to the actual file https://www.dropbox.com/sh/8ns2c6cv3kb5 ... s.pdf?dl=0

The plot thickens.. Looking at picture 3C yes it does look like the longer side of the sprocket body faces towards the rotor but now look at picture 3D, the bearing in this picture is totally visible and flush with the casing, now have a look at mine?? my bearing is recessed a bit and sits behind part of the casing so only the inner track and a small portion of the balls are visible and this is why my sprocket hits the casing before hitting the bearing. maybe there was a modified casing?? and possibly sprocket as well (will have a look at the parts books when I get a mo...) will get to the bottom of it though and I am glad we found it before I put my sprocket on?? Also, at present my chain runs in line with the clutch basket and you can't really shim out the basket itself as it just slides onto the gearbox out put shaft, there is nothing behind it to shim against. Out of interest my primary chain case(the bit with the stator attached to it) is part number 04460L could be worth having a look at yours see next comments..

As for " Is it possible to stuff 350cc innards into a 250cc engine case or is this just mad thinking?" as far as I am aware the only difference(apart from the obvious bore and stroke length) is in the primary casing, as the duplex set up needs a slightly deeper casing than the simplex set up and it is only the standard 250 (non CSR's )that had simplex anyway. Again, no personal experience with this so maybe Colin B can step in here and correct if need be..

[Remington]

Hello Paul,

It is a while since I worked on my engine but I am pretty sure that the bearing balls are not visible as they are covered by a disk which the sprocket sits against and this stops this bit of machinery from rubbing on the casing which I have not, as yet, removed. I wonder which 'bike has been modified? I would imagine that the longer portion of the sprocket acts as a spacer to prevent the chain from chewing up the rotor and it seems to work on my engine.

I understand what you say about the clutch basket so no need for shims there. I shall check the primary chain case number when I next remove it - presumably it is stamped or moulded on the inside somewhere?

It could be that my engine is slightly non standard although picture 3D does definitely show the bearing visible behind the sprocket which I don't recall seeing on mine. I shall have to delve deeper. If I hadn't had the butchery, er, work carried out on my 'bike we would probably never had started this thread although it has thrown up one or two interesting conundrums which probably need to be solved before too long.

[Rangy65]

Hi Chaps, mine bike is still in bits as work & family stuff has kept me out of the shed. I have had a close look at my bottom end, its the only thing that came complete with bike.

My front chain sprocket short side faces inwards & there are two shims against the bearing, unfortunately i cant put it all back together because i haven't had time to finally fix the gear box.

I have tried to take a few photos showing the crankshaft & bearing without the shims in place ( pic 1) the shims (pic 2) and finally ( pic 3) the crankshaft & bearings with the shims.

IMG_0001_2.jpg

IMG_0001_3.jpg

IMG_0001_2.jpg

Hope this helps a bit.

Oh and if you're reading this Colin wishing you a fast recovery & all the best!!

Cheers
Steve

[Ozmadman]

Thanks Steve for coming in on this... Looks like we are getting somewhere... Yours looks exactly the same as mine and I do have two shims as well but when I took the engine apart they were one the drive side of the crankshaft between the flywheel and inner beating. I left them out on reassembly as I knew they shouldn't be there so it looks like those are the ones that should space the sprocket?? Will put them on and try the sprocket again when I get chance, hopefully tomorrow as I am going to work in a mo! Yes Sunday.. I know a bit of a drag! Thanks for your input, hopefully between us all we can solve this and the engine locking problem as well

Paul