Piston ID

[hjsmith00843]

I was told this was a 440. It was my first atv so I was unsure about it so I bought it anyway. I got a hair up my *** today and pulled the top of the motor apart.

On top if the piston it just has this.

In and the letters KCY

I think that I might have a stock bore engine with a factory piston. Am I correct?

[hjsmith00843]

I am pretty sure it is stock piston and bore. It also has a stock cam. I figure this because it has a compression release on it.


Since i just run in the woods and around the house should I replace the piston with a higher compression one. Or leave it alone. I filled the cylinder up with some marvel mystery oil and it has not leaked down very fast and no ridge on top of the cylinder bore.

I was thinking about just cleaning everything up well. Lap the valves and ride.

I am kinda relived it is stock. I am looking for relability out of this machine. Not racing or any any hard driving. Just want to spend some time with the wife. I am getting her an atv shortly.

I might install a sparks key in it.

[hazlettEX]

Leave the engine stock. Get an exhaust and air filter and open the airbox up. The sparks key wouldn't hurt either.

[hjsmith00843]

Originally posted by hazlettEX
Leave the engine stock. Get an exhaust and air filter and open the airbox up. The sparks key wouldn't hurt either.

I am 90% sure that is the route I plan on taking.

Where is the best place to buy gaskets at.

[hjsmith00843]

Here is what I am looking at at the current stage of checking out the top end.

Going to install a hot cam (not sure of the stage)
Keeping the rest stock
Lap the valves and clean the head up very well. (should I get new springs)
Clean the cam cover and check out everything to make sure it is ok.
Gonna install a sparks timing key.

I am kinda relived that the motor is not a 440 big bore kit.

Let me know if I am missing something that I should replace/repair

http://i910.photobucket.com/albums/ac309/SmithRacing00x/102_1068.jpg
http://i910.photobucket.com/albums/ac309/SmithRacing00x/102_1066.jpg
http://i910.photobucket.com/albums/ac309/SmithRacing00x/102_1062.jpg
http://i910.photobucket.com/albums/ac309/SmithRacing00x/102_1067.jpg

[Claas900]

Replace valve steem seals
You can remove your base gasket to help up the cr a little.
That does look like a stock piston

[hjsmith00843]

So taking the gasket from below the cylinder will increase CP. Will this casue a leak. I am not looking for every little bit of power just a little.

I think a Stage 1 cam and a sparks key will help out alot. Maybe clean the ports out a little.

Valvesteam seals are a good idea. I will try to find a set of them.

I just want a decent fast machine and a relaible one at the same time.

[Claas900]

Yeah just use like a silicone or something. You can also clean up the welds in your head pipe.
For valve stem seals you'll want to use like a Viton type seal.
Also if you want to get a little more CR you can mill the cylinder and aim to get around a .038 squish piston to head clearance.

[rob_990]

id replace the timing chain to while your in there with a crf 450 one and throw in an xr400 head gasket if you wanna up the compression a little.

[hjsmith00843]

Since I have decided to use a 11.1 piston and a stage 2 cam

Would it help not to use a gasket between the block halves and the cylinder. Or will this cause too much popup or too much compression.

Going to be using a combo of racing fuel and premuim fuel. 50/50

[Claas900]

If you want to get the most out of it,check your piston to head clearance. If you want to play it safe use a base gasket. I'm not 100% sure but I don't think your need any race fuel with 11.1?
Getting the most out of your comb/parts is the different between a strong runner and an average runner.

[TRX01]

yes with 11:1 you can still run pump gas