SOHC.co.uk Forums > CB750

Crankcase disaster.

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Orcade-Ian:
That's a bummer Johnny,
I don't think you need to be too fussy about getting in with a thin disc as both cases will need work anyway. Graham will no doubt have thoughts on the best way but I would be inclined to chain drill a series of small holes across where the original joint line should be.  Either way, the output shaft on the box is getting in the way.  You may need to put that rod nearest the damage halfway down on the exhaust or power stroke so it's out of harms way when you break through.
David Henning might have some suitably shaped pieces of casing to fit the gaps.  I'm not sure if Frankie Bain is still doing alloy welding - he's the best man up here, as you probably know.
Also in the second pic, is there a half broken hole?

Ian

Johnny4428:
Thanks Ian for advice. Yes the rear lug (broken) catches the case that goes over the drive sprocket, I suspect the damage was probably all done together, would explain why there was no sprocket cover with the bike. Haven’t seen Frankie Bain for a while, I knew him quite well from Flotta working days. There’s another guy Kevin Tait, think he is up in Sandwick somewhere also welder in Flotta.

Trigger:
I have done quite a few like that, some that look the same, some that had a plate over the hole with the plate held on with screws that went through to the cogs and some that have had a lot bigger hole than that. I even had one that was welded up and they had not removed all the old broken bits from the inside  :o

The way forwards is a dremel cutting disc which is the easy part. The hard part is getting it welded by someone who knows about heat distortion on this type of alloy. The last one i did, the hole was that big, i had to make a jig up from a 27mm plate to stop distortion from the heat. Weld for 15 seconds and leave to cool for an hour. And when you have spent more days on it than you can remember, you have to mill it flat for a good old Honda mating surface  ;)

Johnny4428:
Thanks Trigger, I’m amused about the plate with the screws. I was thinking this repair was a bit industrial, although effective. I will post progress (good or bad) on the forum in the coming days and weeks.

royhall:
Quite surprised the alloy has not bent in and been catching the mechanisms behind it. There's next to no room at all behind there.

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