Crankcase repairs - advice needed

Moa

Moa

Been Around the Block
If you have read my Stinger thread you will know that it came with a blown crank. I suspect it was caused by wear to the crankcase where the left main bearing sits. You can see the damage in the pic, the metal has worn away and an edge has formed. It gives a good 0.07mm of clearance in the worst spot.

Anyway, I'm not going to rebuild the motor with the cases as they are. I need some advice on how this could be repaired (can it be repaired?). My idea was to bolt the case halves together, then have a machinist enlarge the damaged area by about 3-4 mm diameter and have a shim thing made to fit into the machined space to make the bearing seat surface level. This seems quite complicated, what are your thoughts?


 
Locktite and several others make a bearing seating product to fill the gap. I have used it once on a garden tractor engine end bearing and it worked great. YMMV.

Sent from my LePanII using Tapatalk 2
 
pidjones said:
Locktite and several others make a bearing seating product to fill the gap. I have used it once on a garden tractor engine end bearing and it worked great. YMMV.

Sent from my LePanII using Tapatalk 2
Click to expand...


+1. Had that done on one of the mains on my old GS1150 crankcase some 15 years ago. Motor's still running fine today apparently.
 
Another idea would be to source a slightly Larger OD bearing with the right ID and machine to that size, not sure if one exists but a phone call to a bearing manufacturer and you may luck in.
 
Replace the cases. Can't be that hard to find a new set and guaranteed they will be cheaper than having that machined out and magically finding the right size/type of crank bearing.
 
I am an advocate of Loctite products where it is useful,many places it is but a 2 stroke crank is
running bearings with extra clearance and they are designed to have a slight amount of radial crush
also it is pretty important that they be aligned coaxially very precicely
the Loctite cannot guarantee accurate coaxial alignment in this situation
im not saying it won't work but I think cases should be easy enough to find replacement s
 
Moa is in New Zealand - and this is for one of your NSR motors? Not going to be easy finding a spare set of good cases laying around...


Best way is to have the cases machined and shimmed, but I have had Loctite done on a 4 cyl roller crank and it worked. I can't see it matters whether it's a 2 stroke or 4 stroke - a roller crank is a roller crank is a roller crank.
 
hillsy said:
Moa is in New Zealand - and this is for one of your NSR motors? Not going to be easy finding a spare set of good cases laying around...


Best way is to have the cases machined and shimmed, but I have had Loctite done on a 4 cyl roller crank and it worked. I can't see it matters whether it's a 2 stroke or 4 stroke - a roller crank is a roller crank is a roller crank.
Click to expand...

i agree it could work,and you have proven that
if he can find a competent machinist boring out the one journal is a relatively simple job ,if i was to do it i would turn a piece of stock to fit and clamp the cases on it and bore in the lathe
having 2 journals to clamp onto a turned mandrel insures concentricity
as i understand it he is working on the lil SUZI T125 twin stinger cases
 
It's not worth it. If it doesn't work you're fucked even harder, possibly causing more damage and more money.
 
Yeah, this is a Suzuki T125 Stinger crankcase. Actually, a much rarer bike than the NSR down here. In saying that I found a good used crankshaft for it, so I'm sure there are crankcases about. I'm skeptical about making the repair using stuff that comes in a tube. Just doesn't seem permanent enough, plus I wouldn't want to block the posiforce lubrication holes.
 
if you consider boring the cases then the way to do it is still using the standard bearing and machine a sleeve or ring whatever you want to call it, to fit over the bearing
the sleeve could be made with a zero interference fit and then plus on the diameter whatever the interference crush fit is supposed to be,of the bearing in the cases
figure this out by measuring a bearing and the case bore in a known good location
1mm wall thickness with a steel sleeve will be plenty
you may need longer locating pins
i think the biggest issue is finding a job shop to do this type of work
back when i worked in a machine shop as the master journeyman machinist in charge we could have done this ,however, i had 4 "machinists" working under me but probably would have had to do the job myself to get it right , sad as it was :'(
 
If you lived closer you could ship it to me i would weld the bearing surface for ya so a machinist could cut back into spec
 
I appreciate the suggestions guys. I ended up getting a good set of used cases instead.
 
A friend repaired his H2,by simply cutting a beer can and wrapped that around the bearing...and it worked good luck
 
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