• Husqvarna Motorcycles Made In Sweden - About 1988 and older

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Backfire cracked case

Dave Mills

Dave Mills

Husqvarna
AA Class
Any one know how much it is to fix a cracked case by the kickstart idler? I was just getting ready to take it out tomorrow and it backfired and cracked the case. I don't think you can weld it (magnesium?), or JB Weld it. I have only ridden it for about 20 mins on the new top end when the old expansion chamber broke, paid a small fortune for a Dynoport chamber that took forever to get, now this. Anyone in the market for a nice 1985 500XC sans cracked case? It did start though. Any takers?
 
Common problem usually cracks the left side case in a triangular pattern above the idler gear shaft.
Only solution is new case so total strip and rebuild you have probably got the timing set up with too much advance causing a backfire and with the kicker engaged this forces the idler gear upward cracking the case.
Check the idler gear and clutch gear for misalignment and broken gear teeth or wear then set your timing to 1.5mm advance.
Do you have a standard ignition system? .
 
Did it start and backfire at essentially the same time? That is a phenomenon I have had happen but I do not believe any one else has commented it happened to.

I bought one used engine with a repaired case but the repair had failed. I am using the clutch and starting gears out of it. I can not see how the crack can be fully welded and if so the distortion would be significant. I do believe more engines go down/out of service/become parts piles due to things other than that cracking phenomenon. It happened once to me on a set of cases I bought used and someone for some reason had removed the 6mm/10mm head bolts on that intermediate shaft. The new/replacement cases come with those bolts and steel piece the intermediate gear rides on. I would think an ignition that has variable timing or at least a special starting circuit is worth considering. There are chainsaws selling for around (no more) $300 that have smart coils, even less expensive ones may. It is kind of frustrating what stuff costs, kind of frustrating how much effort goes into using a bike in this section vs buying a new or unused one.

The case is the same for the 400 and 430 so long as it is for a mono shock. It can be which one do you want the bent one the busted one or the rusted one as was common saying when there were swap meets before ebay. You or whoever you sell the bike to chances they are will end up knocking out the insert and installing it into a case or case set. with loose rear. I was buying used cases like crazy years ago I think I ended up with more than I knew I had. One has good inserts but corrosion in the crank area, the rest have missing inserts, some get so bad they crack at the rear I only got those as whole bikes. I am running one I did a weld repair and epoxy install without taking it apart but the weld probably was less than an inch.

Those cases are probably the weakest link and I can only imaging how much someone would charge to make new sets. The bore for the clutch actuating shaft wears, the pocket for the bearing with the clip around it seems always a drop in fit, the pocket at the chain can also seem larger than what one would think the spec limit would be.

I have had a tooth come off one of those starting gears I do not think is was at the exact time the case broke but it was the same bike. It is now set at 12 degrees spark timing not the 18. It is a water cooled 430. The air cooled 500 if it does kick back does not do it as hard.

Fran

Fran
 
jo360 said:
Common problem usually cracks the left side case in a triangular pattern above the idler gear shaft.
Only solution is new case so total strip and rebuild you have probably got the timing set up with too much advance causing a backfire and with the kicker engaged this forces the idler gear upward cracking the case.
Check the idler gear and clutch gear for misalignment and broken gear teeth or wear then set your timing to 1.5mm advance.
Do you have a standard ignition system? .
Click to expand...
i also like to install a fresh idler bearing every so often...backing off the timing really does work well
 
Yeah, my fault. I was f-ing with timing and had it advanced to far. It does have a new Electrex ignition too. So Fran...k, Is it possible to do a epoxy repair and have it work? I haven't cracked it open to look inside yet. I saw one case on ebay and it looked pretty worn, corroded and crappy.
 
Welding is quite possible. I have had several magnesium cases weld repaired. Take it to someone who does aero engines and othe aircraft repairs as they will have the vapor degreaser, the correct filler wire and understand how to weld it without destroying it. Expect to get some porosity in the repair but it will be quite serviceable.

There may be some distortion of the cases which can be corrected with a light file to get the joint surface flat again. Not too difficult if you are patient.

Good luck!
 
This happened to my brand new 1981 430 CR.. came from the factory with too close timing set... they replaced the cases FOC.. but .. they can be welded .. the upgrade steel plate is a must do .. and the occassional bearing replacement doesn't hurt either..
 
watto450 said:
This happened to my brand new 1981 430 CR.. came from the factory with too close timing set... they replaced the cases FOC.. but .. they can be welded .. the upgrade steel plate is a must do .. and the occassional bearing replacement doesn't hurt either..
Click to expand...

Where does the plate go and bolt to?.not heard of this before but may be good iinsurance against a malfunctioning ignition this is the trouble with mag cases and the sem combo.
 
have the case split and have it welded correctly. epoxy will only contaminate the case material and make it harder to repair correctly down the road. do it the right way it will pay off in the end.
 
jo360 said:
Where does the plate go and bolt to?.not heard of this before but may be good iinsurance against a malfunctioning ignition this is the trouble with mag cases and the sem combo.
Click to expand...
i think hes referring to a piece the 81 bikes were missing. behind the idler gear, the bushing had a plate. i believe all later years had it
 
I'm going to ask a stupid question so bare with me , I really don't want to crack a case so here goes. Is a back fire the same as a kick back ?
 
I have 2 bikes that give a kick back every once an while should I be concerned and should I retard the timing ?
 
I will have to re check , there's no way I could remember that long ago even tho it was less that 2 years ago. lol
Seems like when they kick back they do it more than once , like 2 or 3 times in a row but sometimes they never do it and they just start right up like normal.
 
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