KR-1S.co.uk Forum

hey guys, i just brought a kr-1s and was out for a blat on it when it lost all power and sounded a bit louder than normal. now the engine is really hard to turn over and wont start. all oils are full. any ideas on what could be wrong???

Sounds like the top end to me. When was the top end last rebuild? If its hard to turn over sounds like she may have nipped up in which case you'll need to get a new top end fitted, which is about an hour's work. Worse case is if you have damaged the bore then you'll need to replate the bore as well.

Strip the top end off and check for damage. Remove the exhausts, rad and power valve motor. Then undo the 8 nuts holding the cylinders down to the crankcase and remove both cylinders and the head as one unit. If the cylinders are OK this will save you a head gasket.

For a top end you'll need new pistons, rings, little ends, gougen pins, circlips and two base gaskets.

Where abouts in the country are you? If you unsure now to do it I'm sure that there will be someone from here who lives near to you who can give you a helping hand.

Yeah, that's precisely what I was thinking.

If that is the case, make sure that the oil injection system is working (unless your running pre-mix), or your new top-end could go the same way as your old one.

ScottaKR wrote:Yeah, that's precisely what I was thinking.

If that is the case, make sure that the oil injection system is working (unless your running pre-mix), or your new top-end could go the same way as your old one.

Yep, check that the pump has pressure and that the pipes arn't blocked or have air in them. The trick is to run it on a tank of premix while you setup the oil pump. That way your sure that the engine is getting oil even if the pump isn't working. Also as you assemble the top end dip all the important parts like small end bearings and powervalves in new two stroke oil before fitting them. That'll give them some lub when you first start her up.

the-elf wrote:The trick is to run it on a tank of premix while you setup the oil pump.

But as your jetting is adapted to the use of the oil pump, wouldn't the engine run too lean if you run it with premix without changing the jetting? Or isn't this something to worry about, as it's only for a short while and you won't rev the engine too much?

Charles wrote:

the-elf wrote:The trick is to run it on a tank of premix while you setup the oil pump.

But as your jetting is adapted to the use of the oil pump, wouldn't the engine run too lean if you run it with premix without changing the jetting? Or isn't this something to worry about, as it's only for a short while and you won't rev the engine too much?

Your second part is correct. The premix is there as a fall back if the pump isn't working or your trying to bleed the air from the oil lines. Your not running on premix but setting the oil pump up. Think of the premix in the tank as a safety line so that even if the oil pump has failed completly you should notice the problem before you've seized the engine. Once you have a working pump set up as per the manual you can even drain the premix and/or just top it up with more fuel till its all gone.

thanks for your explanation!

awsome help, thanks guys! ill get down and dirty with it in the weekend and check it out.

Charles wrote:

the-elf wrote:The trick is to run it on a tank of premix while you setup the oil pump.

But as your jetting is adapted to the use of the oil pump, wouldn't the engine run too lean if you run it with premix without changing the jetting? Or isn't this something to worry about, as it's only for a short while and you won't rev the engine too much?

I run mine on pre mix and am now running 130 main jets and the plugs look perfect Think standard is 135 so really don,t think there is anything to worry about

right, i took the head and cylinders off together today. bit of damage to the left cylinders head internally. and the left piston is scratched so will be needing another one of them. all due to the main bearing on the conrod doing something bad. i think a piece of bearing managed to get sucked up to the top of the piston to make the marks. the cylinder itself looks pretty unscathed luckily. going to get the crankshaft out next weekend.

OUCH!!
By the sounds of it, youll need to rebuild the whole engine. Hope the cranks and rods OK, or that's going to be pretty expensive.
PS. Don't just replace the one piston unless they have both been replaced VERY recently.

Good luck mate,
Scott

If your crank has gone then you've got away with it very lightly as that normanly results in a lot more damage. Can you get the crank rebuilt locally, as its a specialist job requiring special jigs and parts? BDK and Stan Stephens can both do it over here but the postage costs would be huge

If the piston is only lightly scored and is relativly new (ie its not very long since it was rebuilt) then it can be touched up with some very fine wet and dry, same for the head as well but you can be a lot harder on cleaning that up. If your unsure of the age of the pistons then I would do a full top end rebuild as well as the crank.