11 replies to this topic

[2wheels]

The piston (Kimpex) on the rigth, PTO side, was replaced this winter. It as about 2 tanks of gas total run time.

Any opinions on how the fuel mixture is?

Attached Files

•  Skidoo 521 Apr 2012 (2).JPG   83.61K   0 downloads

[corcan]

I'm not sure how quickly the piston crown changes color.
Any pic's of the spark plugs?

Why did you open the engine back up? was there a problem with it?

[2wheels]

Here are the spark plugs.

Why did I open it up? Well 2 reasons and both a little embarrassing.
First the piston is not correct, I thought it was. But the bottom ring gap lands on a intake port.
Kimpex part number 09-741, apparently not the right piston for my cylinders.

Second, I had some seepage of antifreeze out the lower end of the jug. I did not replace the gasket and I'm guessing that's why it leaked. All the work was done outside in the winter so it wasn't the best work environment. My knowledge is quite limited as well when it involves engines.

Attached Files

•  Skidoo 521 Apr 2012 (3).JPG   69.05K   0 downloads

[58kafer]

By the top pic it looks as if your still running the injection. Both plugs look the same to me, but hard to judge so far away in the pic, but they look fat. But I'd rather be a bit on the fat side than too lean. It's amazing the beating that the PTO dome took yet the bore is still clean or is that a new jug? I'd say put the correct slug in that jug and put NEW gaskets on and enjoy it. You can never cheat an old gasket, if that base gasket would have been leaking air you could have leaned out that jug right quick. Consider yourself lucky that she leaked antifreeze out and not air in. Oh yeah, always compare the piston you took out to the one going in, never trust anyone. Pop it together and

[2wheels]

Thanks
So Fat means a little rich?

Still running the injection. But also used 50 to 1 mix on the first tank and 100 to 1 mix on the second tank.
The PTO jug is original, just honed a little. Yes I was very lucky.

I'm looking for a new piston that has the ring ends in the correct spot. I can get proper doo's but it's over 200 dollars.
Also looking at a used doo piston I'll see how it looks.
Or maybe use my Kimpex piston and not install the bottom ring.

[Old Sled Nut]

Thanks
So Fat means a little rich?

Still running the injection. But also used 50 to 1 mix on the first tank and 100 to 1 mix on the second tank.
The PTO jug is original, just honed a little. Yes I was very lucky.

I'm looking for a new piston that has the ring ends in the correct spot. I can get proper doo's but it's over 200 dollars.
Also looking at a used doo piston I'll see how it looks.
Or maybe use my Kimpex piston and not install the bottom ring.

09-741 is the correct piston for a 521cc. The bottom ring opening on this piston should be on the intake side but doesn't your cylinder have a protrusion down from the top of the intake port to carry the ring opening?

[corcan]

Yep, that head took a good beating! LOL!
My little ZR500 had taken a similar beating but runs good with the head as long as its cleaned up pretty good.
I agree, plugs look rich (black) which is always better then lean (grey-white). Double check for the correct jet's and make sure the carbs are on the correct side. Some engines require the larger main jet carb to be on the PTO side.
I usually buy all my pistons from Royal Distrubiting.

[2wheels]

The intake side of my cylinder has a port in the center.
The Kimpex piston lower ring is dead center. Right over the port.
The upper ring ends just to the right, the ring sort of hides the land in my picture.
But the top ring is good.



The carbs have the correct main jets, I have been through this with some help from folks here on the forum. And are on the correct side, they are different.
One of this summers jobs to to remove and check the midband () jets and needle to see how they look.

Attached Files

•  Skidoo 521 May 2012.JPG   42.84K   0 downloads
•  Skidoo 521 May 2012 (1).JPG   63.98K   0 downloads

[75tntrv]

Its hard to tell from the pic. of the head but it looks like you might have some high spots. Make shure you sand the head smooth you dont want any hot spots it will give you a detintion proplem.

[2wheels]

I'll try another picture, better shot of the spark plug too.

I carefully went at it with the dremmel grinder to remove high spots. I was concerned about sharp edges getting really hot and glowing, causing all kinds of problems.
I was also thinking if I remove too much the compression would be low.
It did seem to run OK though.

Attached Files

•  Skidoo 521 May2012(5).JPG   54.49K   0 downloads

[Doh]

@ 100-1 mix, the Plugs are still "Too early to read".

That Dome is pretty nasty (I have used them like that before) and will give you false readings. As shown by the ring's Detantion troubles on the top ring. That Ring was "HOT", and the Gap is a little exessive.

I would clean up that Dome. Bore it .010th over, rehone it. And reasemblem with SLP's not Kimpex. .010th's even only PTO side.

[2wheels]

Thanks, all your comments are much appreciated.

The motor really needs re-bore and new pistons I guess. That is over my budget and frankly, over my head. I will try putting it back together. But I think my focus this summer is to find another engine at a good price that has a winter left in it.

I think by carburetor jetting must be close and that is good to know.