Welding magnesium alloy crankcase

[Toleman]

The 'crankcase' is usually 4 pieces.

Two halves of the crankcase proper (where things like the sump plug live) sandwiched between the generator and clutch covers.

The two outer covers will be the magnesium parts. The actual case is more normally alu.

This is my understanding. Again limited knowledge.

I’m not sure what other bikes are like but these off road bikes come apart really easily. 1 hour yesterday evening and 1 hour tonight the engine is out and I’ve never done this before.

Whilst looking on eBay this crack is a common problem. I looked at 3 suitable crank cases and they all had it cracked in the same place with some form of glue smeared all over it.

@Richard.

I have the m14 tap, 12.7 drill and the new sump bolt. Can I send you this to add onto the job or would you prefer not to?

I’ll post the part and come and collect it afterwards to save you having to mess about packaging it and taking it to the post office yourself. I’m several days off as I need to beg, borrow or steal various tools to do this.

 

[Richard.]

This is my understanding. Again limited knowledge.

I’m not sure what other bikes are like but these off road bikes come apart really easily. 1 hour yesterday evening and 1 hour tonight the engine is out and I’ve never done this before.

Whilst looking on eBay this crack is a common problem. I looked at 3 suitable crank cases and they all had it cracked in the same place with some form of glue smeared all over it.

@Richard.

I have the m14 tap, 12.7 drill and the new sump bolt. Can I send you this to add onto the job or would you prefer not to?

I’ll post the part and come and collect it afterwards to save you having to mess about packaging it and taking it to the post office yourself. I’m several days off as I need to beg, borrow or steal various tools to do this.

Yes mate I’ll tap it out.

 

[Toleman]

Being a right pain in the rear end.

These things aren’t built for chippies to disassemble.

I’m going to have a go at making a pusher to split the cases to save me £80 or so. I’ll keep you posted.

 

[wyn]

I always used to take the left hand case off. Using the holes where the stator bolted on, to bolt a plate and push on the end of the crank.

 

[Toleman]

Cheers wyn. Managed to get it sorted tonight. The crank gear needed a 2 foot pair of Stinsons and a 2 foot breaker bar to get it off.

I can’t get the power valve mechanism off as the screws are soft as hell and have been thread locked in.

@Richard. would you be so kind to send me your address again please mate. I have the section separated although as mentioned above I can’t get that part off. There are also pressed bearings still installed, I’m just concerned about the rising cost if I damage them punching them out.

Cheers

 

[Richard.]

Cheers wyn. Managed to get it sorted tonight. The crank gear needed a 2 foot pair of Stinsons and a 2 foot breaker bar to get it off.

I can’t get the power valve mechanism off as the screws are soft as hell and have been thread locked in.

@Richard. would you be so kind to send me your address again please mate. I have the section separated although as mentioned above I can’t get that part off. There are also pressed bearings still installed, I’m just concerned about the rising cost if I damage them punching them out.

Cheers

You better send me some clear pictures of the part and what is and isn’t still bolted to it. Bearing in mind it’s going to get very hot, properly decreased, etc. Bearings might not be happy about this. Please send the detailed pics before hand.

 

[Toleman]

If you think it’s best I’ll have to get them out. How many pieces will I have left over afterwards?

All components removed so far

 

[Richard.]

Ok.
Looking at the arrows I’ve put on your photo.
Green arrow- can you confirm this is where the crack is you need welding and the drilling tapping done?
Red arrows- 3 bearings that are not too concerning. They are quite a way from the repair and they are not sealed bearings so if the heat and decreasing drys them out you can re lube them.
Blue arrow- this is a concern. Looks like a sealed no serviceable bearing sitting right next door to the repaired area. If that can come out I’d be happier. Let me know.

 

[roofman]

Matey a heat gun on the cases around the bearings (not the bearings them selves) and they will almost fall out...thats why they have retainer tabs to stop them falling out..

 

[Richard.]

Just the sealed one near the crack and I’ll be happy to do that.

 

[Toleman]

Your a top bloke mate!

Green correct. Space is tight inside. You’ll see what I mean when you see it. If your not happy to drill and tap then don’t.

I’ll get the blue one out for you.

 

[Richard.]

Address will be sent to your pm.

 

[Toleman]

Matey a heat gun on the cases around the bearings (not the bearings them selves) and they will almost fall out...thats why they have retainer tabs to stop them falling out..

It’s the main crank one which are sweated in and needs knocking out that I’m concerned with.

I’m also a bit anxious about it ever running again. First time for all this.

 

[Richard.]

Space is tight inside.

I assume I’ve got space to get to weld it.

 

[Toleman]

 

[Toleman]

View attachment 132997 View attachment 132998

 

[Richard.]

The welding side is very accessible.
Not much room for a bigger hole mind.

 

[Richard.]

Looking at the state of that heavily oxidation on the casting that’s gonna weld like a bag of ...........

 

[Richard.]

Got some more questions.
Obviously by tapping this out a bigger size your going to be making the material thinner. You say this is quite a common area for cracking on these. Are you not risking it being even more common.
Would it be worth building it up abit around that area to give it back some meat.

 

[Toleman]

Possibly but unsure how I’ll get it to seal. I trust your judgement. I’ve got your pm and I’ll give you a message once it’s on the way. Cheers