Broken Mag Engine

[Andy Cawley]

   

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    N

Patience, it takes ages to do it in an iPad 

[Nick Turley]

How on earth did that happen ?
It's a fair welding job ahead.

[Andy Cawley]

'[attachment=9710]

Oops, does that look like a crack in the corner?

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[attachment=9711]

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[attachment=9712]


There you have it 

What I thought, when I heard the bang, was a broken crank shaft  I declutched immediately. 

Now the engine is out the external view suggests something slightly more awful than a simple broken crank


Right then you experts, before I take it apart, what happened?


Answers before lockdown finishes please

[Ruairidh Dunford]

I can see the crack at the front but is that a casting mark at the rear?

[Andy Cawley]

    I seem to have made a mess of editing. Here are better pictures of the damage.

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    Here is another one.

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I thought originally that this one was a casting defect but it really is a crack. There appears to be a splodge (technical word) of weld at the top end.. 

I will strip it down but thought speculation from the group might be fun

[Steve Jones]

When Ang showed me the close up photo yesterday, I initially feared it was the new engine you've just finished putting together. At least that's not the case!! When I had something similar happen back in around 1997, the crank had broken across the rear crankshaft web. The front three quarters then flailed around inside the the crankcase thumping the side and punching a hole through it. That happened in the very few seconds it takes to hear the bang, de-clutch and stop. That was a 1 5/16 crank. Assume this is a 1 1/8?

As to repair, your laser welding man, whilst expensive, is, probably, your best bet.

Steve

Edited: The sploge of weld is a casting mark.

[Alan]

Broken crank or something has come loose and jammed the gears

[stuartu]

Pleased to hear that's not the new engine, Andy!

Regards,

Stuart

[Nick Turley]

I fear some nasty problem with the gears at the front !

[Andy Cawley]

Nick, I’m inclined to agree. Cranks usually break at the rear. I need to think positive and imagine that I have a pristine crankshaft??.