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Help from the tech heads "2 stroke"

2K views 12 replies 8 participants last post by  ZoomSplat 
#1 ·
Hey guys maybe someone can help... iv been offered an Aprilia RS 125 at a really good price... only thing is it needs the big end bearing replaced! anyone got any idea of how hard it would be to do and what is involved "the engine has already been pulled"? thought it could be a fun little project to do on the side!!! anyone that can help your wisdom will be much appreciated.

Thanks in advance!
 

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#2 ·
On a single cylinder 2-stroke, replacing a bearing is a piece of cake. Yeah you gotta split the cases and take the crank shaft out, but nothing has to be timed when you're putting it back together. The only complicated part is the tranny, I'm not sure if it'll have to come out or not, I've never worked on an Aprilia motor. Just make sure you get it back together the exact same way it came apart. Draw diagrams if you have to, or take pictures.
 
#3 ·
Never worked on Aprilias but it appears to be constructed the way other 2 strokes I've worked on are. You will need to take it to someone who knows how to rebuild the crank. Usually only requires a jig to make sure the left and right crank halves are aligned correctly. The crank pin is pressed into the flywheels. The big end bearing is a caged needle bearing. So you press the crank pin out of one flywheel, R&R the bearing, and press the crank back together.

You will probably need some special tools to pull the magneto off the end of the crank. The primary gear looks like it is splined on so it will most likely come off pretty easily.

You can take a look at the parts diagrams here:

Products at Aprilia Genuine Parts, Aprilia Parts, Aprilia Spare Parts, Aprilia Accessories, Aprilia Motorcycle Parts
 
#6 ·
I'd do a bit more research before I committed. The parts on the web site I linked make it about $300 for the connecting rod kit. You will need a gasket kit as well. Plus if it requires any special tools like for pulling the magneto you might be into the job for a fair amount of money even if you do most of it yourself. I don't recall what it cost to rebuild a crank the last time I had it done. Think it was $80 for pressing it apart and back together but I could be totally wrong there.

You could probably check with some shops and see what they want for the job.
 
#7 ·
dude... buy it and do the job. That's a kick ass little track bike!
 
#9 ·
Make sure you replace the crankshaft bearings and seals that go in the case, at the ends of the crank, as those are also a wear item.

I would want to know why it needs a con-rod bearing, if the fuel mixture was off or it had water in it, chances are it needs a top end too. Keep in mind with two strokes that replacing the piston and ring, and having the cylinder plated, are common maintenance items that you should never have to do on a four stroke, so factor the price of those parts into your maintenance budget.

Personally, I really want one of those cute little 2t track bikes, but if one needed that much work I would pass on it pretty quickly, even though its not a super huge deal to do the work.
 
#10 ·
Just one other thing to check out. Parts availability. I've talked with other people who have had Aprilias and they said getting parts can be a problem. Add on stuff like pipes and what not aren't an issue. Replacement hard parts that have to come from Aprilia they said can be hard to find or take a long time to order.
 
#11 ·
if the big end bearing has gone i can bet my life the others are not far behind.
i always replace the big end bearing, conrod, small end bearing, both main bearings and both crank seals. new gasket set and new rings and you have a motor that will last a bit... use the BEST fully synthetic 2 stroke oil you can get.
the little aprilia engines are a highly stressed motor so need rebuilding more than usual.
 
#13 ·
its a two stroke, they spend just as much time on the work bench than the do in service, if not more.
 
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