Re: Building a Scrambles G80 Bitsa
Posted: Mon Oct 16, 2023 4:26 pm
It's been a while with business committments really getting in the way of progress, but I have finally dragged this project forward.
After cleaning the spurious maybe-a-tank-mounting off the top tube I sent the frame for powder coating and it came back looking pretty good. Compared to some powder coating I had done some years ago which wsa utter rubbish, this is actually as good as real stoving as far as I can tell.
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I assembled the fork yokes and needed to decide what to do about adjustment. The original yokes had a nice fine thread and matching locknut, but the Commando yokes I'm using with the Roadholders have the tube down from the top (not up from the bottom) and a short, coarse thread on the bottom. That's not really suitable for adjustment purposes and although the thread is OK for just clamping, it's too short to allow double nuts. So, I made a spacer to go between the taper roller inners, deliberately slightly too short and then shimmed it to the right length to get a very slight bearing pre-load. I hate shims as a rule, but sometimes they're a necessary evil.
I was a bit concerned at the nut potentially coming loose, so I added a radial grubscrew to lock it with a slug of lead down the hole before the grub screw so I don't mangle the thread.
I wanted to have the top and bottom dust caps in stainless, but I found it too difficult to work - no great surprise, but a bit annoying. I ended up spinning them from alloy which flows easily. I added some felt rings inside to keep the dust and bugs out and the grease in.
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I seem to have spent an inordinate amount of time making various odd thread nuts, but it keeps me off the streets at night. The rear end is nearly sorted with SS nuts for the wheel spindle and brake. And the alloy chain guard I got at an auto-jumble eons ago is rather fetching too - I believe it is genuinely AJS, 'though may be an after-market product not OEM. It has the right mountings in precisely the right places and the right profile, was an alloy guard an option?
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I have also now added the proper barrel and piston to stop the cob-webs and bird's nests while progress is slow. On dismantling the donor for the cylinder and piston, I was disturbed to find that there was an evident "A hits B" issue with the exhaust valve.
- -
This is worrying and odd for two reasons. The parts are all standard, the cams were standard, not wild high lift ones and the piston also standard AE from the late '70's when I bought and fitted it. It is weird again because after initially rebuilding the engine way back, I did have a broken head sleeve nut (I still have the fragments) and subsequently replaced it. I am sure I would have noticed the piston damage then had it been there. So how did it happen later? Sticking valve? Maybe, but there is no evidence of that, the valve is perfectly in order, undamaged as far as I can tell, not bent and no obvious sign of collision.
After cleaning the scuffed area of the piston I coated it with marker and assembled the head on the engine and turned it slowly by hand. No scratches evident on the piston so I conclude it is at least clear now.
After cleaning the spurious maybe-a-tank-mounting off the top tube I sent the frame for powder coating and it came back looking pretty good. Compared to some powder coating I had done some years ago which wsa utter rubbish, this is actually as good as real stoving as far as I can tell.
- -
I assembled the fork yokes and needed to decide what to do about adjustment. The original yokes had a nice fine thread and matching locknut, but the Commando yokes I'm using with the Roadholders have the tube down from the top (not up from the bottom) and a short, coarse thread on the bottom. That's not really suitable for adjustment purposes and although the thread is OK for just clamping, it's too short to allow double nuts. So, I made a spacer to go between the taper roller inners, deliberately slightly too short and then shimmed it to the right length to get a very slight bearing pre-load. I hate shims as a rule, but sometimes they're a necessary evil.
I was a bit concerned at the nut potentially coming loose, so I added a radial grubscrew to lock it with a slug of lead down the hole before the grub screw so I don't mangle the thread.
I wanted to have the top and bottom dust caps in stainless, but I found it too difficult to work - no great surprise, but a bit annoying. I ended up spinning them from alloy which flows easily. I added some felt rings inside to keep the dust and bugs out and the grease in.
- -
I seem to have spent an inordinate amount of time making various odd thread nuts, but it keeps me off the streets at night. The rear end is nearly sorted with SS nuts for the wheel spindle and brake. And the alloy chain guard I got at an auto-jumble eons ago is rather fetching too - I believe it is genuinely AJS, 'though may be an after-market product not OEM. It has the right mountings in precisely the right places and the right profile, was an alloy guard an option?
- -
I have also now added the proper barrel and piston to stop the cob-webs and bird's nests while progress is slow. On dismantling the donor for the cylinder and piston, I was disturbed to find that there was an evident "A hits B" issue with the exhaust valve.
- -
This is worrying and odd for two reasons. The parts are all standard, the cams were standard, not wild high lift ones and the piston also standard AE from the late '70's when I bought and fitted it. It is weird again because after initially rebuilding the engine way back, I did have a broken head sleeve nut (I still have the fragments) and subsequently replaced it. I am sure I would have noticed the piston damage then had it been there. So how did it happen later? Sticking valve? Maybe, but there is no evidence of that, the valve is perfectly in order, undamaged as far as I can tell, not bent and no obvious sign of collision.
After cleaning the scuffed area of the piston I coated it with marker and assembled the head on the engine and turned it slowly by hand. No scratches evident on the piston so I conclude it is at least clear now.