750 F2 chain damage to gearbox

[McCabe-Thiele (Ted)]

DK do a reasonably priced delivery service with a fair returns policy - worth speaking to them I would have thought as you have dealt with them before.

[JamesH]

What’s the engine number on the cases you’re trying to replace?

[johnm37]

Engine No. B750GE-1004112
I've had some good luck on this, I hope. Since TIG welding doesn't work, I decided to try some of these wonder rods that weld aluminium at low temperature. My local stockist (who I tend to trust to sell quality stuff) sells Durafix. Not cheap but worth a try. So far all I've done is tin the part that's broken off. The rods worked really well even at my first attempt. Having put a pool of Durafix on the metal, I ground it back with a power file. It's harder than the aluminium and certainly adhered well. Tomorrow I will try welding the pieces back together and let you know how it goes. Fingers crossed.
There's various video's of Durafix on Youtube.
Also, I have no connection with the company.

John

[royhall]

That sounds interesting. Take some pictures along the way so we can see the process. Best of luck with it. The cases for sale at cb-four are in the correct number range for your engine should the weld not turn out well.

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[Matt_Harrington]

John, I also would be interested to see how the Durafix rods work. I have some ally to try and repair and was thinking of this approach. It may also work to replace a fin on a cylinder barrel I have (maybe)

[Laverdaroo]

My thinking also, intrigued to see not only the process but the results you end up with. I’ve had a quick look on the net but the difficulties of your repair really would highlight it’s usefulness and versatility if it proves to be a winner for you.


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[paul G]

The issue I had with it is getting enough heat into the material you are repairing.

[clinto]

Did some fin repairs on CB350 and found that it required a tremendous ammount of heat,and of course the instant you go above your left with a blob!
Took an assistant with oxcy/acet keeping head hot and holding repair peice in position while I held,another torch and filler rod.
Will never attempt again.

[johnm37]

You're right about the amount of heat needed. Aluminium conducts it away too well. I started with a blow lamp but that took ages. Oxy acetylene worked better. The biggest problem was not hitting the rod with the flame. Do that and it turns to paste and won't flow.
I managed a reasonable repair. It's certainly strong. I hope I've sealed all the cracks to stop oil leaks. I welded the big piece back in. Then I put a piece of stainless steel behind the hole to support the weld puddle. That worked well. The Durafix didn't stick to the stainless allowing me to fill quite a large hole.
I've taken pictures but they're over the 3Mb limit for posting. I will try again tomorrow.
Tomorrow it's the turn of the top casting.

[royhall]

Be careful you don't get too much in there as the gears behind the repair are very close to the casing.

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[K2-K6]

For risk of leaking, many casting when they were more porous are painted internally to prevent this.

A decent coat of something oil resistant may be worthwhile here.

[johnm37]

Well the top casing was much more difficult to weld. Durafix doest like vertical use. It just runs off into a large puddle. Its I also almost impossible to weld both sides of the casing. Heating up for the second weld just melts off the filler from the first. I went through a couple of rods before giving up.
My next attempt was better. I lifted the engine so the area to be welded was nearly horizontal. That gave a reasonable weld. Certainly strong enough for such a small area on the casing.
Having welded the inside of both cracks, I am going to reinforce the outside with epoxy putty. I use evostick putty. It's 2 parts of putty which you break off and nead together. I've used it before and it sets very hard. It can be sanded, filed, drilled and tapped. It also sticks to almost anything including hands so use gloves when handling it.
There's more room to use this on the outside. This should be the last step in the repair of the casings.
I would attach pictures but they're above the 3Mb limit on this forum.

[johnm37]

I coated the inside repairs with Evo-Stik epoxy metal. It's more liquid than the putty stuff so can be spread on easily. The idea is to cover any remaining cracks to prevent oil leaks.
I will still reinforce the outside with epoxy putty.

[philward]

Great work there John

[Matt_Harrington]

John, that is good work. Based on that, I'm going to have a go with Durafix on one of my fins that has broken off. I think I'll use a copper (or s/steel) wedge between the fins and just weld from one side and see how it goes.