Husky SMR450 bottom end issues?

[MotoRad-ical]

Bottom end on my 07 Husqvarna SMR450 has gone for a second time which is why I ask.
Is anyone else in this boat?

Has anyone found a solution?

The motor has less than 30hrs from the last re-build. The motor was assembled by a experienced and competent mechanic. I has got a few trick bits in it but they are all after market factory parts.

There is a few theories on why but no cold hard solution that promises to fix it.

Some say run Synthetic some say run semi.
In looking around on the net there is one place that says to run a KXF250 bearing to reduce the clearance and that this bearing has 19 rollers instead of 18 which gives a better land/ contact patch

Any ideas people? Is anyone else suffering this?
I'm abit lost as to what to do

[Dodgey Dave]

I wouldn't have thought changing from 18 to 19 rollers will cure your problem, the difference is minimal.
Ive got a 06 TC450 which ive converted to motard and it sees plenty of track time and no problems with main bearings.
I replaced the mains 18 hours ago just after I got the bike which had done at least 50 hours prior and the old bearings were fine but did bearings, rings and camchain to be safe.
what sort of hot up bits have you fitted?

[MotoRad-ical]

I would agree that 1 extra roller would do sweet F.A. I think the clearance was the advantage. I read on one web site that the oil pressure is too high and it hydraulically seizes the bearing as 2 years after they changed the oil filter with a pressure valve (Only what I heard might not be true) hence the more clearance the more room for the oil to disperce. But advice is only owrth what you pay for it and well the internet is cheap.
The bikes got aftermarket cams piston and rings and some porting and polishing. Nothing really that would weaken it I would have thought.

The first bottom end was hardness tested and came back fine.
I was wondering if this was the weak spot on them and the racing we do in Christchurch (Mostly full track stuff) was killing them as another racer has done 3 bottom ends on a tricked up KTM450 SMR.

[The Pink Panther]

Is that Phil's old bike

[Dodgey Dave]

Yeah I know that these type of engines (this goes for most MX based engines) are not designed to be held at full throtle for extended periods of time so it could be the long straights that are killing the bearings. especially as you've got a SMR with cam etc, Have you checked if TC Bearings are the same as the TC is a full HP engine from factory and therefore they may run a different bearing to handle the extra HP. SMR's are a resticted engine similar to TE engine to allow for a 24 month warranty and road use and the original bearings may not be upto the abuse your dishing out.

[MotoRad-ical]

Hmmm I was not aware of that I'll have a look at the part numbers and see if they are similar.
Talking to the dealer today who races a SMRR 450 and comparing gear ratios I'm perhaps best to over gear it abit just to keep the revs down.
I can feel the parts bill getting bigger by the day my wallets shaking at the thought.

Thanks for ya input dodgey dave its much appreciated.

[CookMySock]

Sometimes changing to an odd number of rollers or teeth can isolate a torsional vibration problem.

What exactly broke? Did it spin a bearing outer or what exactly? Does it do the same thing every time?

Steve

[MotoRad-ical]

It has worn off the bearing surface from the big end of the conrod. Last time it took off the surface from the big end journal/pin which was tested for hardness and came up fine.

I sort of understand what you mean by torsional vibration but I wouldn't have thought that one extra out of 18 would do it. Perhaps if there were less I could understand but I'm not up with the play with the exact causes of torsional vibration.

[CookMySock]

It has worn off the bearing surface from the big end of the conrod. Last time it took off the surface from the big end journal/pin which was tested for hardness and came up fine.

Is it a plain bearing, as in not a roller bearing? Does it wear it evenly all around, or just off the side towards the conrod?

I sort of understand what you mean by torsional vibration but I wouldn't have thought that one extra out of 18 would do it. Perhaps if there were less I could understand but I'm not up with the play with the exact causes of torsional vibration.

Sometimes having an odd number of teeth, rollers, blades, or cutting edges instead of an even number will clear up some TV issue. I would be surprised if that comes into play here.

Steve

[MotoRad-ical]

Roller bearing its worn on the end facing the piston.

[CookMySock]

Roller bearing its worn on the end facing the piston.

Are you sure the engine hasn't had a surface planed, inadvertently raising it's compression? Can you get its' timing dynamically checked to see it's not over-advancing. Is it's oil pressure up to scratch?

Steve

[MotoRad-ical]

Its high compression already it has a high comp piston factory also.
I can't imagine the timing is out it runs sweet and i would have thought it would show up in a cooked inlet valve or pinking / Detonation.
Oil pressure is good. Oil pump is new.
I'm begining to think I was just over reving it and the taller gearing will hopefully solve this.

[CookMySock]

As you say, maybe just sustained high rpm/load combined with the piston upgrade, and its not coping.

Good luck.

Steve

[Southmotian]

I had a good chat with a very experienced race bike mechanic about a gearbox issue I'd had with my 510. He said without a doubt run a thicker engine oil in these bikes, a 5w-50 or 10w-50. He said the 10w-40's are great for the road bike engines but too thin for the tards.

This was relating to a gearbox issue, but might apply to your bearings too.

[DesmoDAZ]

Howdy, try running a 10w60 oil like elf or plutoline, and change it every 100 ks, Plutoline @ $20 L and elf @ $34 L it's a hell of a lot cheeper than bearings. I'm picking with the hi comp setup and long straights at WOT are a big part of it. My SXV550 runs plain big ends and mains and fully relies on a film of oil at 80psi to keep metal components apart.
How long are you going between oil changes? At the top end of the engines stress you want an oil that can handle the sheer preasure and if your running a 40w it will not take the hammering your asking of it a 60w will hold up a lot better, And change it all the time. Cheers