blowit

My son is finally getting to that point that I need to get him some more go. Started with the a China 90. I am considering a Scrambler 90 but will admit that Polaris is not my first pick. Any other thoughts for a good performing platform? Prefer 2 stroke but not fixed on that, prefer disc brakes, manual trans would be a huge plus but.... Decent suspension and parts availability are at the top so the Polaris is a strong candidate.

You may also post something in the general or repair forums. Not sure how much traffic comes over here. Hope you find the answers you are looking for. Brandon

Post a picture of that. Never seen such a thing. Also, it is critical to transfer heat through the ring. This is the main outlet for heat from the piston crown. B

Sequential trans must have load and rotation to shift. You need to not only rotate, but sometimes torque the shafts in opposite directions and you will hear the trans pop into a gear. I suspect everything is fine but you need to study up on how to bench shift one. Basically, if it will find the gear with some twisting, it is fine. You will likely know if something is not right. They will hit a hard stop or will never free up. Mull Engineering

Yes, but you are going to need a scope for that. B

D"er ya go! Free fixes are always nice! No wait, not breaking at all is always nicer... B

You want to add the spacer and have us "add" clearance as well? I suppose setting up a head to "drop in the hole" a bit could be done if that is what you are asking but would certainly be a special design and I don't think we would have the time to do something like that. I think your best option is to bite down on that bullet (real hard) and port those cylinders like they should be. Take your time, make small adjustments, and plan to take them off and adjust things a few times. Brandon

Should not matter. but make sure you have really good contact or spark energy will suffer.

I would say you have improper parts for your installation. "soft" rings are not used in a 2 stroke. I also do not know whether you are installing forged or casted pistons. Forged clearance will be .003" * 25.4 or .07mm. Casted clearance is usually about .002" * 25.4 or .051mm. Hope that helps. Mull Engineering

Sounds like you are on the right track. If the oil level is good, you likely have compression leaking into the crank case.

Depends on "how" it dies. mechanical locking, electrical, or running out of fuel. If that gear is coming out and locking the motor STOP doing it!!! You are about to cost yourself a clutch cover and maybe more. Open the clutch cover and fix that and go from there. Probably a broken or slipped spring. Cheap fix if you act now. Mull Engineering

Wait, I thought you were going to add a spacer and chop off the cylinders. I is all confused now...

First thing is to find out why the trans locked. That cracked tooth is likely the "fuse" that took the load when the trans locked. I have seen it many times when the chain locks to the case. The instant stall of rotating, high inertial parts is never good. I am suspecting that gear is welded to the trans axle. Remove all your gears from their axles and go from there. There are 2 gears coming for welding in the Banshee. The new replacement gears will have better bronzed bearings on them and should not happen again. I think Yamaha caught this one without telling anyone.... RE: gear replacement - is is always a good idea to replace the corresponding gear that failed. IE, 2nd drive failed, you replace 2nd drive and 2nd driven. This is not always the norm but in your situation, you have over loaded that gear so it's mate may be invisibly fractured. Mull Engineering

I have no idea on the crank unless I inspect it. Feel free to call yet this morning if you like.

We are certainly swamped at the moment so it would be a few weeks before we could go over it. You sound competent enough to go over most of it. check runout on EVERYTHING. Also a good idea to "blue" up the crank and flywheel with "prussian blue" and make sure the contact is good. The damage looks something like VERY bad "fretting" and is typically caused when a taper does not seat correctly or with enough pressure and the parts wiggle around under pressure and transfer metal back an forth. I would certainly go with an impact on that flywheel next round. B

After looking more at your pics, I still cannot determine what would cause the damage on the shaft taper. Did you use an impact on the flywheel? I think regardless of what is new, you need to go through things with a fine tooth comb. Just because a crank is new or welded by hotrods does not mean it did not slip through quality control. So you developed a crank seal leak in a very short amount of time. Is the bearing toast? Does it have a lot of movement on the outer race? It is very possible if something is way out of balance to over load the bearing and cause a leak. OTOH, you should really feel that in the bars! Here is a test I would like you to do. Assemble the cases dry with no trans or crank. Torque all the bottom 6mm bolts to the light side of tolerance and have the bearing bores inspected. for roundness. Any more eccentricity than .001" could be concerning. Surely you know someone at a machine shop or something. It would also be wise to set the crank in the bottom case half and try to spin each race. None should spin free with just the weight of the crank. If one does, apply a little pressure to the crank and see if it will seat. If not, rotate just the crank and see if it changes. I am looking for a phase or balance problem with the crank. An out of true crank can certainly cause all of this. Remember, don't rule anything out because it is new. Even better would just be to get the crank to someone that is competent in checking is for true. IMO, I would not buy or build anything until the cause of the failure is known. I am suspecting the crank at this point but the tests I mentioned above are a very good idea. OR, you could just throw parts and dollars at it... B

I would suspect a simple adhesion problem on the plating due to the location. The size of that flaking along with the relatively low load area point me in that direction. You need to make sure all the bearings are free from plate contaminate. That stuff will destroy a bearing in seconds. Might not be a bad idea to show your retailer either because that just is not normal. B

Now this one is worth looking into. A crank breaking where yours did is very unlikely. I would highly suspect a severe imbalance in the flywheel or a bore misalignment which will cause excessive radial loading on the shaft. I am trying to think of some tests you could do at home but I think at the very least, you need to run down and get a mag base and .001 indicator and start there testing for runout in the crank. What a lot of people do on crank welding is true them, then weld them, then ship them. It is imperative to check after welding to test for warping which can cause a lot of excess stress on the crank. I think you should nail down this issue before moving forward. I am highly suspecting case issues but that flywheel is also suspect. You will want to put your indicator on the OD of the fly wheel as well as the front when it is mounted up and test for axial and radial runout. B

Long story short, like an idiot last year, I brought one of my bike home on an open trailer with snow on the ground and inadvertently got salt spray all over it. Totally forgot about the bike for several months and it formed rust spots on about everything chrome. Powdered parts are fine but I have a lot of chrome on the bike so it rather pisses me off. Laeger long travel, Protrax front end, etc. Parts I am most concerned about are the pipe and swing arm. We do not have many chrome guys here that are worth using. I am not sure as to the severity of the damage yet but I will guess re-chroming will be needed. Really kind of sucks. I know getting new chrome on pipes can be a real bitch. I have never had luck polishing chrome. Chrome is a very nonporous surface and any scratch really shows up so polished just seems to haze the finish and I have never been happy with it. If I could get a large improvement in the finish, I might just leave it for now. My race bike so it could take a tumble at any time.

I would recommend making mods to your adjuster system if possible. Half links severely reduce the capacity of a chain. Certainly is the "weak link" just by design. B

Head gasket is usually fine. Base gaskets will be your call. usually I will just replace them because it is not worth the hassle. If they have 5 min on them, that might be different. B

Be sure to inspect the bore carefully. Any Aluminum stuck to it will start this process over again. Good luck! B

I would expect to see that the rings are not floating free on the piston from localized heating from something. Keep in mind that new engines run hotter at the bore than worn engines. This causes ring heating and transfers to the piston. Al has a much lower melting point than steel so that will always show your heating problems. Double check jetting, carb balance, and timing. Shoot some pics if you like. B

Usually when the comp is that far apart after only a short amount of run time, there is a problem. Hopefully you find it. B

Leaky nuts are never good....