Author Topic: Behind the clutch  (Read 1332 times)

Offline Swarfcut

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Re: Behind the clutch
« Reply #30 on: 17.07. 2020 09:30 »
Denis..The more I read your previous posts, the more i hope this machine was a bargain. From the pictures posted the state of it reflects abuse, ignorance and neglect big time by a succession of previous owners.

  The crack in the crankcases look to me to be fatigue rather than accident damage, most likely cause being a loose through stud allowing movement and the wear to the casting you now have to rectify. A length of threaded bar was the usual backyard fix, but of course a poor engineering solution.

 How you proceed depends on the state of the build. With the cases unassembled, checking for an internal crack is easy, but in any event I would V out the crack and build up a substantial alloy weld web to beef up the lug on both cases. Then accurately drill the through hole to clean it up so that your new sleeve fits firmly, but with no strain on the castings, and a new plain through stud which fits closely to the sleeve ID. What you are trying to do is make the through stud fit the cases with the minimum scope for up/down and forward/backwards movement. This will prevent further damage and also secure the engine unit more positively to the frame, good for reducing vibration.

 The difference between inner frame and crankcase is interesting. Is this measured with the rear wheel in place? This may be pulling the rear together, opening up the front.  Assuming the frame is undamaged, fitting the rear wheel first means the frame will be under less stress if you simply make larger top hat bushes to fill the gap. The brim of the top hat will clamp the crankcase nicely between the frame members, far better than the usual assortment odd washers most folks use.

  I think the reason the bar you showed not fitting across the frame is due to the wear pattern in the holes at the end of the frame. This can be rectified and new bushes made to fit, rather than forcing the frame to where you think it wants to go, and being under strain, a recipe for cracking. If it is as GB suggests, accident damage, you can carefully heat it up and carefully bend it, but only do this if you are super confident and know what to do to control the bend without crushing the frame tube. It is a shame the very dimension you need is missing from the frame drawings. Installing the basic engine unit (crankcase and gearbox) will show where any misalignment lies, use the front mounts and seat pillar/gearbox mount as a starting point, see how the through hole lines up. Aim for a frame and engine in place without any strain.


 Swarfy.

  Additional.  Just done some measuring.

 Plunger Crankcase is 80mm wide at lower through stud lug position.

  Unassembled plunger rear section of frame,,,,Inner sides of frame tubes are 95mm apart at the frame section join, flat cheeks of the join  are 115mm apart.

 Not saying this is how it should be, just that this frame section looks to be a good one. So like yours there is some gap, depending on the width of the front frame section joint lugs.
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Offline denis

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Re: Behind the clutch
« Reply #31 on: 01.08. 2020 07:29 »
Thanks Swarfy, Morris and Greybeard,

Just the fact that you hope this bike “was a bargain” cheers me up a bit, I must admit my enthusiasm about rebuilding these boxes of bits into a bike sort of faded away over the years, luckily other bikes kept me on the road and busy.  I think this lot was more the rejected parts off other bikes the guy had. 

Anyway, I always wanted a rigid a10, and I’ll rebuild it.

I took the rear wheel of as you suggested but the measure at lower through stud lug didn’t change a bit.

The tube at the connection of the front and rear section ‘at the saddle’ , (yes, bolted on frame) is not moving a bit and ID is bigger on one end. ?  the only reason I would take it out is to see how much tension there’s in the frame, should I persist you reckon?  My grandma as a child told me to not use a hammer on a bicycle, so I’ll make a puller as I don’t like hammering things to bits.  Although tempting + it’s not a bicycle.
 
Top hat bushes, ... why did I already turn a straight tube and fitted it in? ... top hat bushes is a far better idea, will do that next week.  Cheers. 
Today I’ll put the engine in (again) to check how far out it is now, or how close in, (think positive!)

Anyway,  cheers all for your input, measures and all.  All very much appreciated.
Good day, Denis
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Offline Swarfcut

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Re: Behind the clutch
« Reply #32 on: 01.08. 2020 20:25 »
Denis The frame join under the saddle is a cross tube for location, and a through stud, threaded at both ends to draw the two frame components together. There is  little chance that anything is amiss here. might look that way, but in any event tightening the nuts each side will keep things in place and located well enough. Not worth trying to drive the tube out, they are usually a tight fit in the front frame lug.

 The real test is how the engine unit you have aligns with its mounting points.  Datum (as a suggestion) is the chain alignment from rear sprocket to gearbox sprocket.  With the age and abuse over time, custom spacers may be required to ensure the engine aligns without any strain on mounting points.

 Even though the parts you have could be the worst of the best, they were made to the high standards of metallurgy and hardness of OEM parts, unlike some repro's. Retain original parts if you can.

 Swarfy.
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