1980 CanAm Mx6-125 rebuild

I'm going to go to Unidilla next weekend and hopefully find some stuff there

Heres some pictures I took of my Mods to the piston, wrist pin bearing & etc. I rough assembled it today and just double checked the piston height. Everything looked awesome, and as I was hoping for. The only thing for me thats a little questionable is the wrist pin bearing. I'm sure it will be fine, and yes all modern 125's that I looked at used 16 or 15mm pis and bearings,,,,,,,,it just looks small compared to the original 18mm bearing.

76 to 82 Yamaha YZ125 stock 56mm piston - piston to cylinder clearence if .005"


Yz125 Piston with SKF HK1616 bearing with some spacers - the bearing had to be pressed in to the connecting rod, The spacers were something to make sure the bearing wasn't going to walk ut of the rod


The bearing installed in the rod.


This picture is not with piston at top dead center, flywheel magnets kept pulling it down.

No, not yet......been really busy at work. I got the cylinder reinstalled with the thicker base gaskets. Am one again having issues with the 7mm head studs. I've made up my mind that I'm going to replace them using 8mm hardware, just havent had the time yet. Also, I reset the timing. I didnt have the 8degree off-set hub to use with the stator coils that I bought this winter. I know the timing for the 125s (& I believe the 175) with no timing box should be .047" btdc. I used a TDC dial gauge and set it to .055" btdc. Haven't put a timing light to it yet but will as soon as it runs. I basically just used the dial gauge to get my measurements and removed the flywheel key and rotated it to where I wanted it t be and torqued it down. The tapered shaft will hold it in place. I have a 76Rv Sled and timed it the same way when I ditched the Bosch ignition and installed a Nippon-Denso stator & cdi unit with the Bosch flywheel. The sled was originally timed at .100" And I set it to .055" as per an old SkiDoo tech, who incidentally is still with BRP.

I was initially concerned about the possibility of failure due to lack of oil, but after looking at things i came to a conclusion, If it fails then i'll try to do something completely different, like install a different connecting rod. It should get noisy before the rod fails and I have a iron lined cylinder-very tough-I figure the worst would be con rod failure, but should give lots of signs long before it fails. But..... here are a few of my thoughts. The new bearing are not completely closed off on the side, to me it should let some oil in, though not as much as a normal wrist pin bearing, Though, that may work to my advantage. Being its somewhat closed on the side I made sure to pre-oil the bearing. So that pre oiling is somewhat trapped and cant flow out of the bearing, Would seem somewhat logical if I'm using a good quality full synthetic oil(XPS Synthetic 2stroke). I'm not an engineer but I would think that the oil that gets inside and is trapped and hopefully will have good enough film strength to keep things lubed.

As far as installing the bearing,which was a little tighter than I thought it would be. I made a puller from a 8mm bolt, nut & washers with a appropriate sized sleeve. The bearing was a little wider than the rod, I wish it were a little wider, but the 22mm wide bearing was too wide for the piston.

Well, havent posted any updates in a while so i'll post things that I've done this winter. I ran into an issue with the head bolts/studs.....they stripped....... bummer, big time. They are 7mm studs and have you ever tried to find 7mm studs that are the right length......Ive heated the cyl assembly and removed the liner and measured and recorded its dimensions and made a porting template and am going to have several liners made and then I'll cut in the ports. I also hopefully finally resolved my issue with the 6 head bolts/studs. I tapped the original 7x1.0mm holes to 8x1.0mm for studs that I'm having made. 8x1.0mm will thread into the cyl and the other end of the stud is 8x1.25mm which I'll use a tower nut on.

I actually heated the cyl & froze the sleeve and reinstalled it. I turned it about 1.5mm so as to work better with the YZ125 piston to turn the edge of a port a little farther from the ring end gap.

I ended up getting some m8x70x1.0 bolts, cut the heads off and had the tops threaded at m8x1.25(a lot easier to find appropriate nuts for). I got the new studs installed into the cylinder and used hi-temp Loctite to fasten them in. It was almost painful for me to drill the head to work with the new 8mm studs.



To get the cylinder liner out i got a tin/steel can that was deeper than the total height of the cylinder and was about 2x the diameter than the cylinder liner. With the cylinder assy upside down on the tin can(used the can to catch the liner in case it dropped out on its own.) Put it into the oven(told my wife it might sell a bit but I'd turn one the vent fan. She was ok with that.) and turned the oven up to 450f. after 30min, it didnt drop out on its own so I took it out and with it upside down still & lightly pushed with a wide flat blade screw driver where the rear transfer port is(you can see from the picture the sleeve is well exposed there as the port is just a big hollow area to the top of the port). The sleeve pushed easily pushed out about 1/2 way. I put it back in the oven for about 10 min and took it out with hot mitts and the sleeve easily pulled right out.

When I reinstalled the sleeve, I froze the liner over night in the freezer and put the cylinder in the oven at 450f again for approx 30 min. I pushed the sleeve about 90% of the way in(it would have gone all the way but i wanted it close so I could turn to line up the alignment marks that i scribed into the aluminum cylinder). I put it back into the oven for 10 min and then turned the liner to the appropriate mark and then pushed it down hard and fast(felt it "slam" and seat against the aluminum cylinder). It didnt drop out as nicely & freely as most Rotax cylinders I've done before but it didn't fight at all and is an easy job.

No, I havent really thought more of that. I'll worry more about that if this one fails...i'm actually pretty confident that the modded wrist pin bearing will do fine since I oiled it well before I assebled the top end. To me if its hard for the oil to get in....it will be equally hard to come out. :o) The power of optimistic thinking!!

Got it running again. Also I finnished setting the timing. The spec for the 125 was I believe .104" btdc but the 125 originally had the timing box. My ignition is from a 175 engine which I believe was timed at .047". So, Ive got everything marked, flywheel at tdc, and at .050", .070" & .090" btdc. thought Id add the extra marks in case I want to try things a little advanced with some higher quality fuel. So my final timing setting is .060"btdc. I also checked the compression and I'm pretty happy as it has a fairly mild 160psi. with the new Yamaha Yz piston with zero run time, and just some assembly lube on the cylinder wall.
Finally done.......almost a year and a 1/2. Im very happy with the way it turned out though I dont know what the long term durability of my modified wrist pin bearing, guess it cant do any worse than fail. I think the only thing left will be to maybe some color matching numbers(blue, orange, black....something like that). But, I guess its ready for Unidilla Rewind 2018. Its been a fun project, but theres also been some major headaches. My next project is a 94 ATK 250.......next winter project!! Thanks everyone for all the help along the way and I hope i was able to help someone else.

Just a little update on this bike guys.......took it to Unadilla Rewind 2018 and let my best friend drive it. It ran awesome. no issues at all. So far the engine has about 2 hours on it. Running Av100LL 50% & 91non-ethanol 50% & mixing Brp XPS Semi-synthetic oil at 36:1. Usually starts 1st or 2nd kick. Also very happy with the Sedona rear tire. Transmission fluid I switched to type F transmission fluid.