Oh S#!T Just discover flywheel runout, Calling

[Ducman]

I'm getting the shee ready for a quick weekend warrior trip to the OR dunes this weekend. I took off the left side engine cover today to change my front sprocket. I haven't done this since the motor was built and installed, approx 100 hours on the motor now. First I noticed a small amount of sand under the cover. I think this was getting in through the wireing that comes in at the top of the case, no biggie, I think I got that issue fixed. So now I take a closer look and I see a mark where the flywheel has just barely touched my pro-design timing plate. At first I though may have been from the sand being thrown off the flywheel but as I rotate the flywheel I see that it has some runout issues. I checked the nut and it was tight. It was lightened at the time the motor was built and appears to be a good job, you can see some dimples where it has been ballanced. I measured it with a feeler guage and it is about 1.5mm away from the plate at the fartest point out and pretty much touching it at the narrowest point (180 deg of rotation between the 2 points). I started the motor and when it is ideling you can see the very slight wabble. While running I put my finger on the outer diameter and it seems to be out of round by much less than the runout, very little, you almost cant feel it but you definitely can feel the runout, and the center hub of the flywheel and the crankshaft feel like they are running perfectly true. I think the flywheel was dammaged when the motor was shipped back to me by UPS. I am almost sure of this especially since the water pump side cover was dammaged by UPS when return shipped and had to be replaced. Unfortunately I have just now noticed this after the motor has been ran like a drunk wite trash daddy beating his red headed step child for about 100 hours, mostly dune riding. It seems strange that it wouldn't make any noticeable vibration if it was out of ballance as far as the runout, I dont think the ballance is too much of an issue in making the crank move out of axis, but I don't know what stresses may have been put on the crank and bearings in the direction of the crank center line (in and out).

 

Anybody have any thoughts or experience with this type of flywheel issue? Any useful info would be appreciated.

 

I plan on replacing the flywheel. My questions are, should I tear the motor down and get the bearings and crank inspected and the crank trued if needed. That would suck since the motor is still pretty fresh and running perfect. Is there any amount of acceptable runout? The hub seems fine could the runout issue be fixed by taking a small amount of material (1.5mm) off the front and rear face with a lathe? Is there any reasonably priced aftermarket light weight flywheels out there or should I just get another stock flywheel and have it lightened. I still plan on running the sun of a bitch this weekend, focker went 100 hours and shee still runs like a raped ape, whats 8 more hours! Am I insane for doing this?

[BenBB]

I'd run it and pick up another used stocker to have lightened...mebbe try Fedex this time (either way ya got about a 50/50 chance of 'em launching it out of the truck at a high rate of speed)...

[sheefreak]

I would run it, prolly has been like that the whole 100 hrs.

[frocashmoney24]

run it for the weekend, replace it with a new one. I wouldent tear down the engine, but if a bearing goes, just replace it

[SANDSTAR]

I wouldn't just "run it". Don't rely on the problem to fix it's self. Get it fixed before your trip or you will just be worring the whole time. If it is wobbling, it could be hard on the internals. If it is rubbing, its robbing power.

[PUSH THE THROTTLE]

I

[PUSH THE THROTTLE]

I wouldn't just "run it". Don't rely on the problem to fix it's self. Get it fixed before your trip or you will just be worring the whole time. If it is wobbling, it could be hard on the internals. If it is rubbing, its robbing power.

379247[/snapback]

He isn

[Ducman]

Thanks guys. I feel a little less agitated about the hole situation now. I was thinking of buying a used set of stock jugs and trying out a port job from a local builder this summer, so I may just go ahead and pull the motor and have him check out the crank as well just to be safe. This builder does a port job that comes on very early and revs to the moon kind of like a hot MX port. He's making 72 hp on a stock stroke motor, and stock cylinders with his port work. His banshee is friggin awsome. My wife's due in mid July with our first baby so the banshee will probably not make it back to the dunes again this summer anyway and you can't ride 2 strokes in the local riding areas (CA) in the summer. Either way, blown and/or getting reworked, shee'll be down for a little while.

 

The flywheel isn't actually rubbing to make any friction to rob power. I suspect the flywheel may never cause any problems but there is no way of knowing that, and I'm sure that if there is a vibration that is being held in check now, when the crank and bearings get some slop in them over time it may take advantage of it and cause sudden crank or bearing failure so I am definitely replacing it.

[Ducman]

Talked with the local builder today, he said he could get me an aftermarket light weight flywheel for somewhere between $120 - $150. Thats the route I'm probably going to go.