Coolant coming out of powervalve drain tube...

[Rice#67]

So I just purchased a 2001 YZ250. My 1st question is, I have a Greyish oil coming out of the powervalve drain tube. It's only a small amount, a couple drops per 10 minutes riding maybe. I figure this is water mixed with 2stroke oil... but where could the water be coming from? I took off the head and this model has an o-ringed head, o-rings looked okay but may be a 'lil old. Could this water be coming from the bottom cylinder gasket and getting into the powervalve? I also cleaned out the drain tube to make sure it wasn't condensation and reran the bike, it didn't solve the problem. Any suggestions???

2nd question... Before taking off the head, I measured compression PSI and it was at 195PSI. I am assuming this isn't a stock compression ratio. When I took off the head, the chamber is polished, not cast looking. This isn't stock right? A stock head would have a cast chamber finish right? The bore is stock at 66mm. What octane should I run with this compression?

 

[IndyMX]

could be a bad base gasket... They are cheap, as are the head gaskets.. Might as well replace them.

I don't think you can just go by the look of the head and cylinder to determine compression ratio.

I am in no way an engineer or even a really good mechanic, but I'd say you need to measure things to determine if it's really stock or not.

If that's not possible, run a good quality 93 or 94 pump gas. If you notice any detonation at all, up the octane until it stops.

If you aren't racing, I'd run the lowest possible octane you can without detonation. What with the outrageous price of fuel these days.

 

[Rice#67]

I did measure... the compression test said 195psi. I think... stock bikes are at about 180psi but I'm not sure. So I was wondering if anyone thought I should run race gas with that.

 

[Isobareng]

One possible side thought here...... its not uncommon to see a 10% tolerance in accuracy on consumer grade gauges so there could be an error of +/- 19 psi.

 

[IndyMX]

When I said measure, I didn't mean just the compression.. I meant measure the size of the piston, the bore size, the stroke, the squish, the volume of the head. All of those factors being more likely to give you a more accurate picture of the engine specs.

Like he said up there ^^, 10psi might just be an inaccurate gauge.

 

[AV8R]

The grayish stuff coming out of the powervalve tube I always figured to be the by product of combustion plus a little oil. Moisture is one of the byproducts of combustion normally removed by the high temps in the cylinder and the temps in the powervalve drain area are relatively cool.
Mine has always done this and I have not lost any coolant that I can tell so far.
My YZ250 turns out 200 psi I am at 300ft and run 94 octane pump gas. With a FMF SST pipe I had light deto. I just put on a stock pipe and have not had any problems so far.

 

[Rice#67]

Thats true, guage could be off slightly. And for the record, I live in California the highest pump rating is 91 octane.

The reason why I was worried is because my 03 YZ125 spits out a little oil but it's pure black. I bought the bike brand new. Now I bought this 01 YZ250 just recently and it's a greyish with a little white mixed in.

 

[KX250Dad]

The 2005 YZ250 in the stable with new OEM cylinder and Wiesco piston/rings carries 210+-psi. The new cylinder is a result of grayish oil seaping from the power valve vent. Investigation proved that erosion from from the cylinder OD eventually underneath the o-ring groove permitted coolant into the combustion chamber.

This happend on both our 125 and 250.... both shortly after experiencing the powervale linkage arm breaking allowing the shoes into the cylinder and "lipping of the piston" which most likely either warped the head or generated the beginning of the erossion.

All works well now... in a emergency we did teflon tape the inner o-ring to fill the eroded spots in the cylinder, got us thru the end of the season.

Good Luck

 

[IndyMX]

Are you getting detonation on 91?

 

[Rice#67]

The 2005 YZ250 in the stable with new OEM cylinder and Wiesco piston/rings carries 210+-psi. The new cylinder is a result of grayish oil seaping from the power valve vent. Investigation proved that erosion from from the cylinder OD eventually underneath the o-ring groove permitted coolant into the combustion chamber.

This happend on both our 125 and 250.... both shortly after experiencing the powervale linkage arm breaking allowing the shoes into the cylinder and "lipping of the piston" which most likely either warped the head or generated the beginning of the erossion.

All works well now... in a emergency we did teflon tape the inner o-ring to fill the eroded spots in the cylinder, got us thru the end of the season.

Good Luck

So you think the head is probably warped... Or the cylinder is eroded under the o-ring... Causing the o-ring to not seal properly. That could be very likely, thanks for that info. If that ever happens again I would try the high temp silicone gasketmaker made my permatex. It stays rubbery and you could just coat the o-ring with it. May be a better fix then teflon tape.

 

[Rice#67]

Are you getting detonation on 91?

I haven't really ridden the bike long enough for it to get really hot. Nothing so far. I bought the bike and it ripped real nice. I checked out everything... except I didn't bounce up and down on the suspension. The shock ended up being blown and the guy just wiped the oil clean so I wouldn't notice. A day later it was leaking out. :bang: Oh well, I'll have nice new revalved suspension here pretty soon. :laugh:

 

[IndyMX]

You'd probably notice the detonation pretty quick. Doubtful it's a high compression engine requiring race gas. But, if you want to spend the extra money, it won't hurt anything but your wallet.

 

[Rice#67]

It looks like the head is warped a little. I'm gonna have it flattened slightly, and put the new o-rings in. There was no signs of erosion in the o-ring groove so it should fix the problem. It wouldn't be the base gasket because the piston doesn't go that far down into the bore. It's only a small amount of coolant leaking, there was 2 spots 1/2 centimeter wide that wiped the piston top clean on the edges, but hey better safe than sorry. It could always get worse and snap a rod possibly. Thanks for the help!!!

 

[KX250Dad]

Depending on the o-ring material silicone may not be to smart... it will soften and attack certain elastomer (rubber) compounds. Learn the flow of fuel/oil thru your engine. Base gasket coolant leak will definately get into the combustion chamber.

 

[Rice#67]

You're right... the fuel comes in through the crankcase and then into the cylinder. But the piston top is only clean on two edges... which seems more logical that it's coming from the head gasket area.