Building a Scrambles G80 Bitsa

[RichardS]

I need to repair one of the fork sliders which has the standard Roadholder pinch-bolt crack. Not a great design detail that in my experience

Mine neither.
Tightening up the pinch bolt on an N15 last year, ohhh joy...
IMG_20220924_210057.jpg
Way too much clearance between the hole in the slider and the OD of the spindle.
New slider from Andover Norton and I sleeved the spindle to a close fit.

Youch! That's the worst I've seen, no way can you "repair" that.
I've had three over the years and all came to me pre-cracked just adjacent to the pinch bolt. A couple IO had welded and it was adequate, though not wonderful. The other I changed the forks so it became irrelevant.

[RichardS]

Every time I see the Bosch logo on a washing machine or anything else they make these days, I smile and ask myself how many folk know that it's a magneto armature.

I didn't know that. But now I do... I'll be dropping it into conversation any chance I get

I always thought it was an electric motor, it is very similar to the standard schematic representation for a motor. As you say, an amusing factoid

[RichardS]

I need to repair one of the fork sliders which has the standard Roadholder pinch-bolt crack. Not a great design detail that in my experience

Mine neither.
Tightening up the pinch bolt on an N15 last year, ohhh joy...
IMG_20220924_210057.jpg
Way too much clearance between the hole in the slider and the OD of the spindle.
New slider from Andover Norton and I sleeved the spindle to a close fit.

Youch! That's the worst I've seen, no way can you "repair" that.
I've had three over the years and all came to me pre-cracked just adjacent to the pinch bolt. A couple I had welded and it was adequate, though not wonderful. The other I changed the forks so it became irrelevant.

[RichardS]

Does anyone have any good suggestions for an oil tank - beyond the obvious "yeah mate, I recon you're gonna need one"? Photo's? Drawings? (well I can dream)

I have an old pre-'55 type that is nowhere near to fitting on the RHS
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IMG20231022094402.jpg

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and also a late -CS flat type that is equally no good to fit on the left for various reasons.



So I think I will need to make a custom central-ish tank.
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IMG20231022094436.jpg

How should it be mounted? A clamp around the down-tube in front of the rear wheel and some tags to the engine plates seems reasonable. I had a central oil tank on a Wideline NorVin, but it's too long ago to remember how it was mounted. Tags welded to tanks are notorious for cracking so I'm a bit nervous about how and where to site them, but equally how to avoid them?. Anybody got any experience of a central oil tank on a G80?

I think I'll start with a cardboard version and then use that as a template for a real one, but some initial pointers would be handy.

[dave16mct]

There's lots of room between those engine plates. Why not make a trials type to drop in there.
Dave.

[spookefoote1956]

Ditto

[mdt-son]

Re. oil tank, take a look at the oil tank for the G85CS.

The triangular space formed by the subframe and the seat post is suitable for a decent air filter. See images of the 1966 ISDT bikes. Side covers are made of GRP.

- Knut

[RichardS]

Sorry for the tardy response, been otherwise engaged....

Yes, a twixt the plates tank seems the way to go, I have recon something up like this:
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IMG20231104130814s.jpg

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Think I'll need to get some special tape to make sure it doesn't leak
It does vee down between the front of the gearbox and back of the crank case giving a shade over 4 pts whcih is close to what it says in the book.

After some soul searching and I decided to take the nulclear option for the magneto. I thouhgt about chasing about for another with the correct mountings, but what are the chances? eBay one might crop up tomorrow, or maybe not till the next millenium - you can't tell, and it could be a scrapper anyway. So, I re-tapped and plugged the original mounting holes which were a very very lose 5/16 BSW - so lose I looked for other sizes, but nothing realistic except maybe 9mm which does exist, but it jsut too weird to comtemplate. I then machined off 10mm to come down to the assigned 35mm mounting height and then re-tapped 1/4 BSW on a standard AMC mounting plan.
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IMG20231106184707s.jpg

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And it all starts to look a lot more sensible
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IMG20231106185636s.jpg

[RichardS]

I need to repair one of the fork sliders which has the standard Roadholder pinch-bolt crack. Not a great design detail that in my experience

Mine neither.
Tightening up the pinch bolt on an N15 last year, ohhh joy...
IMG_20220924_210057.jpg
Way too much clearance between the hole in the slider and the OD of the spindle.
New slider from Andover Norton and I sleeved the spindle to a close fit.

Here's my take on the repair I needed to do
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IMG20231028150539s.jpg

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IMG20231028150636.jpg

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I know the AMC has a steel insert cast into the end cap, but that's the point, it's case. Mine is a rolled 7000 series alloy so I'm happy it will be good enough as it is. I bored the hole out slightly then turned down and sleeved the axle so it's a very snug fit in the casting. I had some 015" shim under the end cap while boring it so there is a little space for it to lock down tight onto the axle. After some careful meashurement of the casting and a bit of 3D modelling I was pleasantly surprised there is comfortable space for a couople of 5/15" studs for the end cap. They are off-set, but in plenty of meat so I'm comfortable it will be robust.

I'm almost ready to put the wheels on and put it on the floor, but while I'm still fiddling with the oil tank and some engine studs it's at a more convenient height being on the old tresstle.

[RichardS]

So what's the deal with Push Rods? I have seven to choose from and they're 3 different pairs plus a stranger.

I have a 'long' pair of alloy push rods with a 0.400" dia ball foot, but until I tinkered a bit they're just too long by 1/16" for my long stroke engine. I turned a bit off the top of the threaded end and also thinned down the nut so that I can just get some clearance to adjust out. I assume alloy pushrods go with an alloy barrel.

I have a pair of steel pushrods which I assume would go with an iron cylinder and they're maybe 1/8" shorter than the two alloy ones

I have another pair of alloy pushrods, close to the same length as the steel ones, but with a much smaller 5/16 ball foot

and finally the odd-ball is alloy with a 5/16 ball foot, but significantly (1/2") shorter

The spares lists are not particularly helpful, they do list a couple of different push rods, but they don't seem to be associated in any way I can make sense of.

The '49 trials bike was using what I suspecct are technically wrong push rods with the smaller 5/16 ball end. It was 40 years ago I put it together and used whatever came with it in my youthful naievity assuming what came with it must go with it.