Sudden loss of compression

[2strokeDude]

Hi I have a 2003 yz250 that has an 295 kit in it. Yesterday I was racing a hare scramble and about 40 min into the race when someone fell in front of me and I stalled my bike. I kicked it to restart it, and noticed it was considerably low on compression. I never did get it started and had to get pulled out of the woods. I can now press the kickstarter down with my hands just like a 125. I had the 295 kit done in March and have a fair amount of hours on it but nothing close to being worn out. took off my head pipe on looked into the cylinder and I could still see the cross hatching, and didn't look scored at all. What could be causing this low compression? Could there be something wrong with the power valve? I really dont want to take my cylinder off right away if I don't have too because I don't want to have to go through ordering the oversized gasket kit.

[94cr rider]

broken rings

[adam728]

Powervalve won't cause it. If compression is low, it's time to pull the cylinder. No way around it.

[s14 2510s]

If its still full of coolant id say your best bet is to pull the top end. His gasket kit is an oem style kit that he just slits and puts his steel head gasket in. You can do it with a oem gasket kit as long as you dont pull the head off. I have reused the head gaskets though. Somebody some time ago had a cracked 295 jug. Maybee yours cracked or your rings failed. Either way gorr will probly fix it for free. Best bet is to contact him and pull it apart. I can put new pistons in my 250's in 45 minutes. Tare down is fast as long as you get the propper tools set out and start droping the coolant first. He has a year warantee on the work.

I have seized pistons in his plating and never had to replate. I have been doing rings in my 295 at 40 hours and piston/rings at 70-80. I have 190 hours on my 295 jug Im running now. Has always looked like new every time its been apart. But I had another 295 mid high 110 olney with ported piston built that I plan to install any day for ice racing. My other 295 is mellower for woods.

[2strokeDude]

Ok, looks like I'll be pulling the top end after work today. I should probally do the top end anyway since I have around 80 hours on it. No matter what the problem is I will never go back to the 250. Gorr's 295 kit is great!!

[USED YZ426F]

One possibility, although very uncommon, is a broken spark plug. Only takes a minute to check, just replace the plug.

But, I agree that it sounds as though you have a piston / ring problem that needs to be checked.

[2strokeDude]

So I pulled my top end off today and found the unthinkable. Apparently the screws in the power valve vibrated off and the power valve and what looks to be a screw made its way into the cylinder. It scratched up my piston pretty bad but I lucked out bacause my cylinder walls didn't have a scratch on it.

This leads to my next question. The power valve broke so I need to order a new one. Can I just order an OEM one or does Eric cut them?

[s14 2510s]

Gorr cuts them. Call gorr he can get the powervalves cheap and might even fix it for free if you explain what happened. I always take all the screws out of the powervalve once I get the cylinder back to loctite them with 243. I dont think he loctites any screws in there. Its not him its probly some dum kid working in his shop that dosnt loctite the screws. Some peoples kids..........

This is why I do rings at 40 and pistons at 80. I like inspecting my internals regularly for ware, to make shure the PV isnt gunked shut, and to make shure everthing still tight. I can rering my bike in 45 minutes from start to stop if nothings wrong.

Ive had 8-9 jugs done by eric over the years and I had screws come out once so ever sense I just pulled the apart and loctited them.

[hardhitwarrior]

how do you take the rest of the gasket material on the base with 45 min?

[s14 2510s]

Id do them so often the gasket dosnt stic realy. Lightly soak in break clean and the rest scrapes off with a gasket scraping tool in a second. I always rap the crank in rags right away so I dont drop the circlip down the case. When I replace a piston I always clean and dissasemble my powervalve. So it takes me a bit longer if I take all that apart and clean it. I use a dealt electric imapct to take alot apart makes thing fly apart and I put all my bolts in a magnet tray.

[arnego2]

I use grease on all gaskets, makes it easier to get them off.

That apart practise makes a master, the more often you do it

the betetr you become. ?

[2strokeDude]

The first thing I do when I get everything back together is to locktite those darn screws in there. Now that I'm looking at my powervalve again, it doesn't look like anything is busted off. It originally looked like there was a screw or something that was snapped off at the end of the shaft, but in all the diagrams and replacement pictures I was looking at I don't see anything. I guess I really lucked out that more damage wasn't done. From now on I think I'm going to thoroughly check all the bolts on the whole bike after every race. This should prevent anything like that from happening again.

[s14 2510s]

Buy a big bottle of 243 like I did of ebay. I use it all the time. 243 is imposible to find localy as its kinda new. 242 and 243 are both blue medium strength. 243 is made for oil saturated places while regular 242 wich is mosts commin is not for oil saturated places and can possibly fail from oil.

[Kyle.J.]

Power valves?? like thats gonna be a problem. do some research before you make yourself look stupid again.