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Powervalve stressing cylinder wall. PICS

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Well, the other night I started tearing my bike down for a winter rebuild and I found this.

There are two vertical stripes on the cylinder and piston resembling cold seizure marks. They are right at the edge of the sub-exhaust ports.

I can't catch my nail in the cylinder, but I can slightly feel it. I'm going to run it as.

This cylinder was renikasiled 40 hours ago by US Chrome.

Engine was always warmed up properly.

It appears that the sub-exhaust port valves have been mushrooming the edges into the cylinder. You can see on the top of the valves where they have been hitting.

I'm planning on grinding them down to relieve the area.

Anyone ever seen this before? Any advice? Thanks

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Maybe went a hair leaner than I'd like, but I didn't expect 35 degree weather for the last race of the season!:lol:

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Edited by GMO397

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Uhi follwed by bad luck? I reckon not. My jug once looked identical. My guess is that you have it cleaned it up before taking pictures? There was no problem with it when I re-used mine.

I had a bunch of lean seizes and went from 40:1 to 30:1 that got rid of it.

If you believe the 2 auxiliary PV valves are sticking out its a good idea to dremel a bit off .5mm that should do the trick without bringing down performance.

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Uhi follwed by bad luck? I reckon not. My jug once looked identical. My guess is that you have it cleaned it up before taking pictures? There was no problem with it when I re-used mine.

I'm not followed by bad luck normally, but keeping this old yz running and me being an OCD mechanic, it's tough.

Yes I cleaned the cylinder before the pics, I was hoping some of it came off, and a lot did.

I had a bunch of lean seizes and went from 40:1 to 30:1 that got rid of it.

I'm running 32:1, Maxima 927. I'm thinking I may go to 28:1, since I have no oil pool in the crankcase, and never a drop of spooge anywhere. I never lug the bike, wide open constantly.

If you believe the 2 auxiliary PV valves are sticking out its a good idea to dremel a bit off .5mm that should do the trick without bringing down performance.

I worked them over with a hand file and emery clotch. They look better now with a small gap.

I'm not sure if the auxiliary ports are really causing this, but it's the only logical thing I can think. The only other time I've seen this is from not warming the engine up properly.

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28:1 is Ok when running it with WOT or almost at wot. Your piston looks better than mine. I do 40 hours with a piston. I run the D piston in my bikes. When they come back from the plating first a C piston than D.

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Looks like valves just gently rubbed the piston and the material taken away wore the streaks you see on the cylinder.

No worries. Ive seen it in a few Yz's Ive worked on. None of mine have ever had an issue like this so far though. I usually just clean them up enough so that they wont rub anymore. Usually it doesnt take much. If you need to take more than a minimal amount (surface layer is the best way to describe it) off Id say you have an underlying issue.

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28:1 is Ok when running it with WOT or almost at wot. Your piston looks better than mine. I do 40 hours with a piston. I run the D piston in my bikes. When they come back from the plating first a C piston than D.

Yeah, I'm thinking it needs a tad more oil because of the lack of a pool in the crankcase.

I've been running Wiseco pistons, 40 hours is the change time for the rings and piston.

Looks like valves just gently rubbed the piston and the material taken away wore the streaks you see on the cylinder.

No worries. Ive seen it in a few Yz's Ive worked on. None of mine have ever had an issue like this so far though. I usually just clean them up enough so that they wont rub anymore. Usually it doesnt take much. If you need to take more than a minimal amount (surface layer is the best way to describe it) off Id say you have an underlying issue.

Well I'm happy someone's seen this before. I wish I knew what the end of the sub PV and stop on the cylinder are supposed to look like. They both look like they've been smashing against one another for a while.

I'll post up some pics of my work on the valves soon.

My only concern is that the cylinder is cast aluminum, and those valves appear to be forged steel. Obviously we all know which wears out first.

But cycle central powersports has a cylinder for 287 and those valves for 14 $ a piece. I may just pick up a new cylinder for the next 40 hour tear down.

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Personally I don't think it looks all that bad for 40 hours of hard wide open riding. If you can't feel the streaks with your fingernail then they most likely aren't anything to be too concerned about. It does look to me like one time the piston warmed up a little too fast and just touched the cylinder, but it obviously wasn't enough for a cold seize. Everyone has it happen from time to time, it's cold morning, you start the bike, it starts to stall and you blip the throttle a little too much once or twice... not really anything to worry about.

As for the premix, if you are running wide open a lot I would run a little more oil. 28:1 would probably be alright, but you may want to go down to somewhere around 24:1 to ensure that you have lots of oil. Just make sure you jet accordingly. Going from 32:1 to 28:1 shouldn't really affect your jetting too much though.

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Personally I don't think it looks all that bad for 40 hours of hard wide open riding. If you can't feel the streaks with your fingernail then they most likely aren't anything to be too concerned about. It does look to me like one time the piston warmed up a little too fast and just touched the cylinder, but it obviously wasn't enough for a cold seize. Everyone has it happen from time to time, it's cold morning, you start the bike, it starts to stall and you blip the throttle a little too much once or twice... not really anything to worry about.

As for the premix, if you are running wide open a lot I would run a little more oil. 28:1 would probably be alright, but you may want to go down to somewhere around 24:1 to ensure that you have lots of oil. Just make sure you jet accordingly. Going from 32:1 to 28:1 shouldn't really affect your jetting too much though.

agree with everything kj said

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Looks fairly normal...

I dont think the PV is any cause of the "issue" but what you are forgetting in the big picture here is the exhaust bridge between main port and sub port gets really hot - it's not cooled by water...and its a relatively small amount of material that gets direct contact with hot exhaust gasses on all sides...

This makes it expand more...and tighten up on the piston.

On really highly stressed motors this becomes an area of issue for us...we have to drill oil holes on the piston - and in some cases hand sand the piston down in those spots.

Custom pistons can be made that have this manufactured in..but it's not really worth the cost.

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Personally I don't think it looks all that bad for 40 hours of hard wide open riding. If you can't feel the streaks with your fingernail then they most likely aren't anything to be too concerned about. It does look to me like one time the piston warmed up a little too fast and just touched the cylinder, but it obviously wasn't enough for a cold seize. Everyone has it happen from time to time, it's cold morning, you start the bike, it starts to stall and you blip the throttle a little too much once or twice... not really anything to worry about.

As for the premix, if you are running wide open a lot I would run a little more oil. 28:1 would probably be alright, but you may want to go down to somewhere around 24:1 to ensure that you have lots of oil. Just make sure you jet accordingly. Going from 32:1 to 28:1 shouldn't really affect your jetting too much though.

Thanks so much for your help.

I agree, everyone's guilty of not warming up properly. Normally for me it's not being ready to go stage and hurrying to much. Are you making this claim based on the second set of vertical stripes?

I think I'll try 24:1. I was surprised how little oil was everywhere at 32:1 with 927. I've switched to motorex cross power and it feels a little thinner, so as long as it's not spooging like crazy, I'd be more comfortable with 24:1.

Looks fairly normal...

I dont think the PV is any cause of the "issue" but what you are forgetting in the big picture here is the exhaust bridge between main port and sub port gets really hot - it's not cooled by water...and its a relatively small amount of material that gets direct contact with hot exhaust gasses on all sides...

This makes it expand more...and tighten up on the piston.

On really highly stressed motors this becomes an area of issue for us...we have to drill oil holes on the piston - and in some cases hand sand the piston down in those spots.

Custom pistons can be made that have this manufactured in..but it's not really worth the cost.

I never even thought about the water jacket.:lol: That makes perfect sense.

If I remember right, aren't the typical exhaust bridges relieved. I wonder why this area isn't relieved.

Would you suggest drilling holes in the piston?

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