Motor rebuild/rephase

[Purplezinger]

They crack exactly where the welds are. I've magnafluxed several and always the same result I've done many cranks singles to fours and don't weld any of them anymore I haven't welded a crank in 15 years and its never been an issue but do as you will your just supporting your economy for doing it

Regardless of what srimer says, back in the day when Yamaha was racing these 650 with 750 kits. They welded the crank pins after truing the crank...

 

[Purplezinger]

Back in 1974 my XS2 torqued a flywheel and Yamaha's instructions were "True each flywheel and weld each pin. After doing that it ran another 15000 trouble free miles. I sold it, still running sweet.

 

[Highside]

Sreimer,

I love ya man, but these XS's are a MUST when it comes to welding the cranks. Even if they crack, they still hold together better than non-welded cranks. I've got cranks here that have "walked" apart just from the big-bore kits... Not a pretty sight inside the cases, and not a good thing for the rods.. But yes, I agree that the welds to tend to crack from time to time... I won't run ANY XS crank that hasn't been welded, causes too much havoc on rods and charging systems...

Not knowing a thing about the materials involved, after welding, can't you just anneal the weld area with a rosebud torch to avoid cracks? If you were afraid that you made that area too soft, couldn't you just re-heat treat the crank??

Just asking dumb questions.

 

[Purplezinger]

Not knowing a thing about the materials involved, after welding, can't you just anneal the weld area with a rosebud torch to avoid cracks? If you were afraid that you made that area too soft, couldn't you just re-heat treat the crank??

Just asking dumb questions.

I doubt that would be successful. This is a pressed together assembly, the rod bearings and main bearings are already in there, there's a good chance of ruining them and then you're back to square one.

 

[Highside]

I doubt that would be successful. This is a pressed together assembly, the rod bearings and main bearings are already in there, there's a good chance of ruining them and then you're back to square one.

Then if you're having problems with cracking welds, hitting that area with a torch might be an option worth looking into.

Welds always crack at the edge of the heat effected zone. By hitting it with a torch, you make the zone wider and less distinct, therefore less likely to crack.

 

[Punkskalar]

Then if you're having problems with cracking welds, hitting that area with a torch might be an option worth looking into.

Welds always crack at the edge of the heat effected zone. By hitting it with a torch, you make the zone wider and less distinct, therefore less likely to crack.

It's all about amperage control

 

[Highside]

It's all about amperage control

Is that what is suspected in causing the cracked welds?

I don't see how too much current would cause a problem, but too little would give a lack of proper penetration.

 

[Punkskalar]

Is that what is suspected in causing the cracked welds?

I don't see how too much current would cause a problem, but too little would give a lack of proper penetration.

Too much will heat the parts too much, and as they cool, they will contract and crack. To little and then you won't have enough penetration.

TOO Much heat is a bad thing

It's a fine balance, which has taken me some time to get just right

 

[irristeve]

weld or not some say you can press apart & resemble a crank 3 times so unless you know your engines history big call but when its welded thats it no more rebilds which isnt to much of a drama as these cranks do last,oil is cheap change it regurly,but there will come a day when all the good s/hand ones are gone & lots of dead welded ones that will be only good for scrap food for thought

 

[Punkskalar]

weld or not some say you can press apart & resemble a crank 3 times so unless you know your engines history big call but when its welded thats it no more rebilds which isnt to much of a drama as these cranks do last,oil is cheap change it regurly,but there will come a day when all the good s/hand ones are gone & lots of dead welded ones that will be only good for scrap food for thought

Bone stock rebuild, I agree. 750 Kit, Or Rephased, or both, I'd weld it up...

I have a STACK of cranks here at the shop, I'm not to worried about my supply

 

[Highside]

Too much will heat the parts too much, and as they cool, they will contract and crack. To little and then you won't have enough penetration.

TOO Much heat is a bad thing

It's a fine balance, which has taken me some time to get just right

Ahh, you're right. It was late last night and I wasn't thinking right.

That's what made me thing of the rosebud trick. Heat it up and let it cool slowly.

Might not work in this application though.

I was just thinking of how cast iron repair is done, (although AFIAK, most of that is done with a gas welder and nickel filler rod).