os 21xm rebuild ?

[byron westman]

i'm putting a new sleeve and piston in my xm and can't seen to get the connecting rod back on the crank pin. i can get it to sit on top of the crack pin but it wont site down on it. should i force it on . it looks like the connecting rod is hitting the case when at bdc?

what am i missing. help

 

[Jerry Dunlap]

I've found it best to attach the rod to the crank pin when the crank is one side or the other just past TDC. It usually takes a little wiggling of the rod to get it to seat on the crank pin. Make sure the beveled end at the bottom end of the rod is facing the front of the engine, and the cut in the piston skirt is facing the front of the engine.

JD

 

[Grimracer]

Byron,

Just so you know.. you have to have the liner out of the case when you install the piston and rod. Like dunny said.. Install the rod with the crank pin at the top of the motor. After you have this in place slide the liner in.

Grim

 

[byron westman]

thanks guy i got it to seat ,took a little wiggling and few tapes with a wooden stick.

now just to break it in be fore the race at twin lks. hope to see ya there jerry .

 

[Jerry Dunlap]

thanks guy i got it to seat ,took a little wiggling and few tapes with a wooden stick.

now just to break it in be fore the race at twin lks. hope to see ya there jerry .

Good Lord willing and the Creeks don't rise, I'll be there in a couple of weeks.

JD

 

[byron westman]

hay jerry how many tank should i run through it before starting to race it?

 

[Jerry Dunlap]

hay jerry how many tank should i run through it before starting to race it?

I'd suggest three or four. Might want to consider restricting the cooling to build some head temp. With the cold water conditions, you can almost run w/o water cooling and still not get over 150F.

JD

 

[byron westman]

Jerry

I ran a few tanks on the bench today, I was very rich ,maybe to rich . I had the needle out to about 6 ,7 turns out. I thought the needle would fall out. Lol

Had to keep the throttle on to keep it running , I could still keep my fingers on the head.

The temp was about 125degor so. How hot should it get up to?

 

[Jerry Wyss]

Jerry

I ran a few tanks on the bench today, I was very rich ,maybe to rich . I had the needle out to about 6 ,7 turns out. I thought the needle would fall out. Lol

Had to keep the throttle on to keep it running , I could still keep my fingers on the head.

The temp was about 125degor so. How hot should it get up to?

I surprised you got anywhere near 125* with the needle about to fall out, or run at all. You need a heat gun for that kinda work,, its not a game you want to guess at.

dub

 

[byron westman]

i was using a digital thermometer so i know it got up to 125 deg. should it get hotter? and what is a proper running temp .

 

[Jerry Wyss]

i was using a digital thermometer so i know it got up to 125 deg. should it get hotter? and what is a proper running temp .

Its probably easier to explain how I do it. Now this method isn't accepted by too many people but those that I build engines for get they're o/b partialy broke in this way.

I have test bed boat that I mount o/b's on, ready to run,(LeeCraft XTR). I leave the radio system off and open the carb to about 1/2 throttle or more. Needle is set very rich, a bunch rich.

The engine is started & regulated by pinching the fuel line. I use the heat gun with the other hand. By the frequency of pinching I can regulate heat and RPM. I'll go thru 7 tanks of fuel during this process, all thru those tanks I will increase rpm and heat.

The method is like revving a dirt bike to the next gear. These engines will tolerate some fairly high RPM's using that climbing and falling of RPM's. The RPM's fall when I release the pinch,, so you end up having total control.

I get the temp as high as 270* plus with a fairly healthy chunk of RPM's towards the final couple tanks. The idea is to get the engine ready for a possile lean run during the days that follow of running or racing. If you get a lean run some time after, the engine has alreay been there,, if you know what I mean.

The final breakin is work on the pond while your progressively leaning it down carefully to find that area where it starts to wake up. That sound of a 21 o/b trying to wake up sounds an awful lot like those little cartoon Martians in the movie Mars Attacks,, the Kak,kak sound.

What this method saves you is all the tosses of the boat onto the water and never knowing if you have 60* in the engine or 100*. I have found vibrations in certain engines that I would probably never know any other way. Those certain engines get they're piston skirts trimmed to solve that vibration problem, a marked improvement is the result. The XM is one engine that doesn't have a piston skirt problem, its a fine engine the way it is.

dub

 

[byron westman]

Thanks for that. How many turns out onthe needle due you consider rich enough?

 

[Jerry Wyss]

Thanks for that. How many turns out onthe needle due you consider rich enough?

You can start at 4 turns out or more. There might be a change there if you have to pinch almost continually like in the first 2 tanks. The piped motors behave a little different than the muffler motors. The muffler motors can start whats called a "run-away" where the piped motors wont.

The "run-away" is when the whole o/b builds enough heat that it will quickly digest all that extra fuel you've been giving it and turn into a self feedin' demon. Of course it happens when you have the pinch off but stay calm and choke the carb slightly ,(I use a brushing motion with the back of my finger) and the R's will fall back down. This usually happens with the last 3 tanks and would require a click or two richer.

Be advised the entire o/b will get fairly hot. This is the advantage of semi-breaking-in an o/b. All that extra metal hangin down there acts as a great heat sink.

The other method, put the whole works on the water rich and run, run, run it in. Still a great method no doubt,, have broke-in many successful powerheads that way. But in recent years I've had several customer o/b's to build and never really trusted most of them to actually finish a solid break-in. Many just don't understand how important this process is.

dub

 

[SayMikey]

Thanks for that. How many turns out onthe needle due you consider rich enough?

You can start at 4 turns out or more. There might be a change there if you have to pinch almost continually like in the first 2 tanks. The piped motors behave a little different than the muffler motors. The muffler motors can start whats called a "run-away" where the piped motors wont.

The "run-away" is when the whole o/b builds enough heat that it will quickly digest all that extra fuel you've been giving it and turn into a self feedin' demon. Of course it happens when you have the pinch off but stay calm and choke the carb slightly ,(I use a brushing motion with the back of my finger) and the R's will fall back down. This usually happens with the last 3 tanks and would require a click or two richer.

Be advised the entire o/b will get fairly hot. This is the advantage of semi-breaking-in an o/b. All that extra metal hangin down there acts as a great heat sink.

The other method, put the whole works on the water rich and run, run, run it in. Still a great method no doubt,, have broke-in many successful powerheads that way. But in recent years I've had several customer o/b's to build and never really trusted most of them to actually finish a solid break-in. Many just don't understand how important this process is.

dub

J Dub have you used RG p/sleeves? If so do you touch the piston?

 

[dave roach]

Mikey

You you got to touch the piston to get it in,LOL

Dave Roach

 

[Jerry Wyss]

J Dub have you used RG p/sleeves? If so do you touch the piston?

The RG sleeves but never the piston. I haven't attempted cutting the RG piston. I spose it could be done but I didn't want to screw with the sweet balance of that engine.