13 replies to this topic

[juzz80]

Done my first trial today on my recently brought Sherco 290 and 2 sections in she started really knocking and cut out, my mate said it may be the crank gone :-(. When I got home I stripped bike and removed the engine, I took the top of the engine of to expose the piston, and you can put 3 fingers on it and twist it slightly each way..
Does anyone have any ideas what maybe up with it? I'm hoping it's not the crank as iv looked on splat shop and they are like £450 :-(.

Cheers Justin

[zerorev3rev4]

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[zerorev3rev4]

did you try and restart it after it had cooled down or when got it back home

[totalshell]

slow down!!! hardly likely that the crank has gone after 2 sections.. there will be a little movement of the piston forwards sideways the lot it will move.. not much but it will.. id put it back togetehr and understand what the noise is rather than take one persons off the cuff remarks as gospel.. ( unless he can feed 5000 with 2 loaves and five fish)

[monty_jon]

Really you need someone with some experience to have a look, you need to put the engine on top-dead-centre and try to lift the con-rod up and down without turning the crank

Any play there would indicate a blown crank (if it is the bigend you can have the crank rebuilt with a new con-rod kit)

But two strokes will tend to run even with a knackered big-end (very noisily until something gives!)

how old is the bike?

Edited by Monty_Jon, 22 January 2012 - 09:23 PM.

[bazza1]

hi,put the engine back together, check for a good spark first, faulty plug etc. if you have nothing, email bradford ignition they will give you resistance readings for the stator, also check the keyway in the crank for the flywheel. if you are happy you have a good spark then check the fuel and carb, i have engines pink and knock due to fuel starvation

[copemech]

Try rotating the flywheel by hand to ck for smooth rotation of the bearings. Lift up and down on it to ck for slack.

With piston halfway down, rotate flywheel to ck for lost motion in the conrod.

[juzz80]

Cheers all for the replys, the bike is a 2001 the guy I brought it of said that the previous owner had the engine apart and has replaced all the gaskets but doesnt know what else was done. When I was riding to section 3 it died like it had run out of fuel, I pushed it about 100yrs and I fired straight back up. But the engine just sounded very knockey bit like a old diesal engine, it's rather like theirs no oil in their. My mate who was with me is a mechanic with the AA he said the knocking is that loud he could hear me behind him over his bike,

[monty_jon]

If you have the head off you might as well remove the barrel & have a look at the crank

It shouldn’t cost a fortune to rebuild, new rod kit, main bearing +seals, gaskets and a new set of rings

It would be better than buying a second hand motor as you may buy another rough one!

(Also check the barrel, any flaking or score marks then you can add £££'s)

Edited by Monty_Jon, 23 January 2012 - 07:43 PM.

[joeninety]

Bit of a thread hijack here, but today I had the same symptoms as the original poster.

The engine tone changed, then the bike felt sluggish, when you closed the throttle rather than just coasting like its always done it was like I was applying the brakes. Then the engine stopped. Tried kick starting it but the kick just felt totally lifeless when being kicked if that makes sense?

Anyway, got home removed the head, carb and fly wheel cover and when I tried to rotate the flywheel it would at certain positions be almost impossible to rotate then it would free up. Couldn't even get it past these sticky points using the kick start by hand.

Then after sometime rotating the flywheel backwards and forwards it started to free up and seem fine but then suddenly the stickyness appeared again.

On inspection the barrel looks quite good and there's no obvious signs that the piston is worn. Does this point to main bearings?

The bike is a 2004 Sherco 250, if it's main bearings is it a crankcase split job, never done that before and at the moment it all seems a little daunting.

Any help much appreciated.

Cheers,

Gary.

[zippy]

I am inclined to think Crankshaft bearings (main bearings). (Please notice I did not say this is a definate, just what I think it may be) Yes it is a split cases job. If you already have the head off then the coolent is already drained (small bonus there) Follow the manual here http://sherco.com/EN/wayne_corner.html (Engine Teardown and Assembly Manual. much good info here) I would suggest if the following has not been replaced before than with the cases already split now is the time to do it. Rings, Crankshaft Bearings and Seals, small end bearing, wrist pin, Piston (if it is worn too much, manuals cover measurements and such) Look at the reeds and replace if necessary. Look at every moving part to make sure it is in usable condition.

Edited by ZIPPY, 09 April 2012 - 07:14 PM.

[joeninety]

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[joeninety]

Thanks for the reply Zippy. I thnk the next move is remove the barrel and have a closer inspection of the crank.

If it is the crank big end whats the most ecnomical route to repair, is it £400+ from Splat / Rathmells or can it be reconditioned?

Whats the best was to determine if its the big end bearing or the main crank case bearings as from the following copied and pasted thread it seems fairly economical if its main crank bearings.

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well guys, ive copped out im afraid....
i was recomended to use a bloke who's local and after speaking with him thought it easier to hand it over....

cop out i know, but i suppose in theory doing the job is one thing, but i could imagine a whole load of things that could go wrong and i just couldnt ber that sinking feeling of kicking it over to get nothing when ive rebuilt the bugger...hahhaha
i took it over to him tonight and we run the bike.....
it seemed alot quieter then it did before it threw its hand in....he said he'd heard plenty worse sherco's...
he looked at the flywheel and everything seemed ok, he said the bearings just felt a bit notchy, probably due to the bike doing so little work and probably being stood still in the previous owners garage for some time.....
but still, something wasnt quite right....
he stripped the clutch housing off and had a fiddle with the kick start mechanism... and allthough there were no teeth broken or any visable signs of damage, it didnt seem quite right either....

ive left the bike with him so he can whip out the clutch and have a look deeper into things...

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well, its all done.....
what a differance, its like a different bike !!
soooooooooo quiet and smooth...... the crankshaft bearings, one of them had melted !!!
cost about £90 for all the bits/ bearings ,gaskets, oil n coolants etc, oh an a new spring in me kickstart mech.... but worth every penny.....

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[zippy]

I personally have not had to do a big end bearing, so I don't have a clue on replacing that.

[joeninety]

Got barrel off now and big end appears to be okay and it looks like main bearings are the culprit so a bit relieved!

Many thanks for your help and advice.

Gary.

[zippy]

You are welcome. May the repair be swift and pain free