Putting things in places they ought not to be (250R Hybrid Motor build)

[Billy Golightly]

The power valve can hit the piston if it is not fitted on many motors, the rotax engines (motorcycle, PWC & snowmobile) are more know for this than the Japanese engines especially if it is bored. If a non stock valve was used in your cylinder it can be worst.

The fix is easy just pull the valve out and clearance it with a dremel with a sand roll or the round end of a belt sander. (I prefer this method)

Clearance should be .016-.020 in. I prefer to run it tight but it should not hit and remember piston expansion when the engine is hot as well.

I use a feeler gauge bent at a approx. 90 degree angle, it will ruin your feeler gauge but buy another one just for this purpose & keep it around as a "special tool" for future rebuilds.

Its a easy fix.

I had checked it during assembly and found I had about .010 which is similar to what you clearance the exhaust bridges normally so I figured that was good enough at the time. I really am not so sure its the powervalve contacting the piston, because the top corner of the piston looks too perfect still, I mean there isn't any markings of any kind around on it.

Wonder if I am having contact somewhere else like on the crank webs or something...because there was zero indication of detonation on the piston everywhere I looked around at it from the exhaust and from the plug hole.

[RIDE-RED 250r]

Oneformula1 is correct about checking/adjusting clearance when boring these engines... However, being this particular Rotax top end is plated and not boreable by conventional means, and you had it freshly replated, I really do not believe this is an issue for you.

Did you buy the PV used/separate from the cylinder??

[Billy Golightly]

Yes. the PV and cylinder came separately to me.

[atc007]

I would much sooner think it traveled up from the cases... JMHO,,,

[RIDE-RED 250r]

Yes. the PV and cylinder came separately to me.

Any possibility the PV had those scuff marks when you got it and didn't notice?

Or any chance it is a PV for a smaller bore 5/6/700??? (I'm doubting this being as your piston shows no corresponding wear)

[oscarmayer]

Billy it sucks, but ya may consider taking the motor apart. Better to find no issue now than there be one and it get missed. Also finding it now also means easier to fix than when it pops.


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[onformula1]

Billy, did you get the piece out of the plug?

Is it definitely aluminum? It's hard to tell form the picture, but it kinda looks like a burned up piece of epoxy.

[oscarmayer]

Lets hope that is all it is, if it's alloy, I would defiantly want it torn down.

Any updates to what it is billy?

[Billy Golightly]

I did not get to work on it any yesterday. Maybe today. I didn't dig that chunk out of the plug or cut the threads off to look any closer at it but I will. I don't think it could be epoxy - the only places I used that are completely covered up by the base area of the cylinder. I did not put any in the transfer ramp areas. Only thing I can think of its either rubbing a tiny bit on the top corners of the crank case where i clearanced it for that stroker crank, or somewhere else? I mean the crank turned through freely with the rod and piston on final assembly after I went back and had to "fix" that area those couple times to make it clear.

I just gotta decide whether to run it a little bit more and keep checking it or tear it down. I really don't want to tear it all the way back down but I'm sure that is the most intelligent thing to do.


Also, does anyone have one of these sleds, or a buddy with one that could look up and tell me what the timing is suppose to be? Unrelated to this issue at hand at the moment, but I did quite a lot of googling and could not come up with a degree BTDC number, but I'd like to find one so I can make sure my CR ignition is as close to it as possible

[RIDE-RED 250r]

Billy, these engines do not use degrees of crank rotation BTDC to set ignition timing. They go by mm or thousandths BTDC using a dial indicator. (measured from piston top right through sparkplug hole) I'm sure that you, being an accomplished machinist, will have no trouble finding TDC with your dial indicator and checking timing using this method.

Post #2 of this thread from Dootalk.com lists timing and a few other specs you may find useful. http://www.dootalk.com/forums/topic/...p-end-rebuild/

In case the link doesn't get you there, timing is stated at .138" BTDC.

You got me strolling down memory lane searching topics over there. When I had my Doo's I spent as much time there as I spend here now! LOL!

Trikes are better!!!

[Billy Golightly]

Perfect. Thats something I can work out

[RIDE-RED 250r]

Perfect. Thats something I can work out

I have timed my Rotax sled engines a time or 2 using this method. Once the dial indicator is set, I found this method very easy to work with.

[MTS]

I got a whole manual for the 2001 here billy if you need any other info, all sorts of good stuff in it. Hoping that ball of crap was just something that got left behind upon assembly...cant wait to hear a video of it on the pipe!!

[Billy Golightly]

Billy, these engines do not use degrees of crank rotation BTDC to set ignition timing. They go by mm or thousandths BTDC using a dial indicator. (measured from piston top right through sparkplug hole) I'm sure that you, being an accomplished machinist, will have no trouble finding TDC with your dial indicator and checking timing using this method.

Post #2 of this thread from Dootalk.com lists timing and a few other specs you may find useful. http://www.dootalk.com/forums/topic/...p-end-rebuild/

In case the link doesn't get you there, timing is stated at .138" BTDC.

You got me strolling down memory lane searching topics over there. When I had my Doo's I spent as much time there as I spend here now! LOL!

Trikes are better!!!

Can you verify that timing? I'm looking at this thing this afternoon, and seems like an awful lot not sure I have enough room in my stator plate for that.

[RIDE-RED 250r]

I can't seem to find the page I downloaded service manuals from for my sleds and I no longer have the computer that has those files.

Hopefully MTS sees this and can verify those numbers for you.