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Changes in the A65 idler pinion?? #779080 07/18/19 10:57 pm
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Chopper Rob Offline OP
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Hey Guys,

Putting together a narrow crank 1965 A65 engine and running into issues trying to install the idler pinion. (i know the part that just slips in) The issue is at the crank pinion as the two do not want to mesh. I've checked my parts books and can see the crank nut has always been the same part number, but there are two different idler pinions. (early 68-0114) and (late 70-9104). I tried all the idler pinions i have (they all look the same 44 tooth) to no avil and wondering if maybe I need an earlier idler pinion? Or at least what the differed between the two idler pinions was? If its any help a few other observations are...

1. It seems the idler is just to close (the gear teeth engaging to deeply) into the crank nut
2. The idler pinion and cam pinion engagement is fine
3. If I flip the idler pinion (timing marks and shorter shaft towards the case) It engages the crank nut much easier, but this may because the shorter shaft does not require the idler pinion to be perfectly centered before engaging the crank nut
4. The crank nut is in correctly with the tapered edge towards the case, and the gear puller hooks on the outside.

I've been scratching my head on this one most of the day so any and all help is greatly appreciated,
Thanks! -Rob

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Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779082 07/18/19 11:07 pm
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NickL Offline
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Have the cases been bored to fit a larger diameter special t/s bush to correct crank mis-alignment?
The pitch on the cam-idler-crank pinions did not change over the production time, the idler changed shape etc
but that's all. Try a different crank pinion, you may have a duff one if it's 'new'.

Last edited by NickL; 07/18/19 11:11 pm.
Re: Changes in the A65 idler pinion?? [Re: NickL] #779086 07/19/19 12:18 am
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Chopper Rob Offline OP
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Hi Nick,

Thanks for the reply. Yes the cases have been bored to accept the larger T/S bush. I have tried a different crank pinion with slight improvement, but I would still need to tap the idler cam to basically force it on. The first one I tapped on was causing some binding when I tried to turn the engine over so I then got the pleasure of prying it back off.

Anyway thanks again, will see if i have a more worn out crank pinion and give that a try.

Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779111 07/19/19 6:52 am
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Allan Gill Online Happy
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the later idler pinions were deeper because they stopped using a top hat bush but that is all as Nick says.

If your having to tap a gear on it is too tight. You need some lash in a set of gears and running something like fag paper between the teeth should show a minimum gap. If you don’t they will whine until either the bush wears out or the shaft seizes in the bush and then the bush spins in the case.

Another thing is, has the inner timing cover been changed? Or have those bushes been replaced? The bushes for the idler need to be line reemed with the inner timing cover bolted to the crank case.

Reamer size from memory is 11/16” can be done in situ but don’t recommend it and is better when all the cases are apart.


beerchug
Re: Changes in the A65 idler pinion?? [Re: Allan Gill] #779120 07/19/19 12:44 pm
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Chopper Rob Offline OP
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Hi Allan.

Thank you for your reply. I have been following your posts for many years and trust your expertise. The bushs have been replaced and they were line reamed along with the inner timing cover (or so I'm told). This engine has been in many hands before mine and all the machine shop work including the bushings were done before it came to me for assembly. I guess my next question is... If the idler pinions are interchangeable what do you think is the cause of the binding?

Thanks in advance,
-Rob

Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779122 07/19/19 12:58 pm
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If the gears are binding then the holes are too close together, you have to suspect the line reaming has moved the crank centre position on the timing side and now the idler gear needs to be moved outwards from the crank axis. Before doing that I would be checking the crank is freely spinning and not out of line or you could end up chasing a few thou around the cases from one component to another.

Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779129 07/19/19 3:40 pm
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DMadigan Offline
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Also possible the idler bush was line reamed off centre. What is the fit between the idler and cam gear? Tight too?
If both are tight, a CRINGE WORTHY suggestion, put lapping compound on the gear teeth and spin the gears until they run free. They are a hunting tooth pair so only come to the starting alignment around 41(?) revolutions. Otherwise you will have to fix the bushes.

Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779148 07/19/19 7:29 pm
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No Hunting tooth on the A65 David, 22t crank and cam and idler are both 44t. The A10 might be hunting tooth but it’s been. Very long time since I’ve paid that much attention to an A10 timing side.

Rob, many thanks for your kind words they are most appreciated. Some good advice above and the only other thing I can think of is to check that...:

A) there is no bits of fabric shoved in between the teeth, I’ve seen that before
B) there are no burrs on the edges of the teeth, I’ve found burrs on the backs or front faces of the teeth before now, if the alignment has changed from previous then the crank pinion might be rubbing against the burred part of the teeth?

Two other things to ask, is it only binding when the inner timing cover is on or both on or off? If it’s only when the case is on you might have a later timing pinion and the binding is against the case and not another pinion??


beerchug
Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779170 07/19/19 10:15 pm
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DMadigan Offline
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Should have checked the book first. Memory still had triple information in EEPROM.

Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779172 07/19/19 10:40 pm
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NickL Offline
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The 'Way-out' with the matter is to move the idler pinion by replacing the bushes and boring them off-centre a thou or so..
The oil seal will allow for a few thou run-out. Everyone will probably scream 'bodge' at this but as i say it's a way out.
The only other thing to do is to have the cases bored again and new TS main made. A lot more expensive.
I know which way i'd go on it, but the perfectionists will have you spending fortunes getting a couple of grands worth
of bike to 'blueprint spec'.

Re: Changes in the A65 idler pinion?? [Re: NickL] #779209 07/20/19 6:58 am
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Allan Gill Online Happy
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Originally Posted by NickL
The 'Way-out' with the matter is to move the idler pinion by replacing the bushes and boring them off-centre a thou or so..
The oil seal will allow for a few thou run-out. Everyone will probably scream 'bodge' at this but as i say it's a way out.
The only other thing to do is to have the cases bored again and new TS main made. A lot more expensive.
I know which way i'd go on it, but the perfectionists will have you spending fortunes getting a couple of grands worth
of bike to 'blueprint spec'.


Did the factory even make them to blue print spec? laughing

How does the idler compares to against the cam pinion with the crank pinion removed?


beerchug
Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779214 07/20/19 9:23 am
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Arnstein Offline
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The teeth edges are often the "binding" points, grinding the edges a little or as DMadigan says use grinding paste might help. Anyway, if there is only a light tap that is needed for to make it fit I would use it as is.. because when the crankcase expand / heats up the center of the cam - idler - crank will move away from each other more than the steel in the pinions expand. Also after a few miles the bushes will have been "run in" and all is ok.

If this seems not possible the easiest way might be to bore the idler pinions bushes off centre as NickL says.


Arnstein

BSA Spitfire MK3.800cc (also engine 850cc 90degree)
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Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #779302 07/21/19 5:00 pm
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DMadigan Offline
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If the pinion or gear are only surface hardened the lapping might wear through and wear during use will be accelerated, one reason for saying "cringe worthy".
Running gears that are binding might also over heat them and cause breakage. They are not going to "run in" without something to cause wear. The sliding friction might just gall the surface and cause fretting.
Was the TS case bore out of round, needing to be bored? If that was the case then it appears that the shop did not locate the crank correctly.

Re: Changes in the A65 idler pinion?? [Re: DMadigan] #779332 07/21/19 10:13 pm
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Arnstein Offline
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The case hardening is usually ca 0.5mm deep, so a lot of lapping is needed to wear through. And the binding must be extreme to cause overheating and breakage. As said, if only a light tap is needed I think it will be ok when the crankcase aluminium heats up and expand.. the clearance will probably be enough and the bronze bearings will wear a little if not too tight. Anyway, the light grinding of the teeth edges where they engage might be the solution, I know this has worked in a similar situation.

Not knowing exact how tight these pinions might run, it is hard to advise what solution is best.. so only guessing.


Arnstein

BSA Spitfire MK3.800cc (also engine 850cc 90degree)
Honda CB450T -71
Laverda RGS 1130cc -85
Ducati 1098 -08
Re: Changes in the A65 idler pinion?? [Re: Chopper Rob] #780612 08/05/19 2:55 pm
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I recently installed new idler bushings in a '66 Spitfire case. They must be reamed to size after installation using the inner timing cover as a pilot. If someone ahead of you reamed the bushings independently of each other, you could have a big problem.
If I were in your shoes, I'd turn a small pin on the lathe the exact same size as the idler shaft and fit it into the bushing. Then I'd measure the centers of the idler bush to the crank T/S bush. I have plenty of other A65 cases around here or available to me.
I would then check them for the same dimensions. That would tell me where the center of the hole was. Now remove the idler bush in question and measure over again. I'll bet you the idler bush was reamed off center.
You can be pretty sure the T/S bush is centered or the crank would not turn freely (unless the clearance was excessive).


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