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Mag Side Melt Down

1406 Views 7 Replies 8 Participants Last post by  rob7374
Was out on Lake Simcoe on Saturday doing about 65 mph and she just died.When she came to a stop i went to pull it over and no go.At that point i knew my day was over.Took plugs out,pto side first looked good then mag side ,aluminum dust all over plug.Think it was a midrange lean-out.When i took it to the dealer for new needles and remapping parts were on b/o.The parts came in on Wednesday and i was going to get the work done on Monday.So im still getting it done on Monday plus new piston and new jug.When taking out wrist pin shouldn't there be a cage for the bearing.Good thing i had a rag under piston to catch all the parts
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for a time being, skidoo didn't use a cage on the wrist bearing for some of their applications. I replaced a piston on a sl 500 that didnt have one. I dont think you can reuse that, you have to order a new one, you have to slide it in and make sure you get it right the first time, steady hand helps
That sucks. The 800 piston pin bearings are cage less.
The stock wrist pin bearings on my 99 670 HO are cageless. They are re-useable but if you loose even one pin then you are going to have problems even if it doesn't drop into the crank. I think that there were 28 needles in mine.

My brother melted the mag side piston on my wifes sled this weekend too. But he toasted one of the crank bearings at the same time, cracked the engine mounting plate, killed the reeds, etc, etc. Some might have been done before.
what caused her to burn down like that? maybe a plugged pilot jet?
Looks like a lean spot to me. Are you running stock jet needle shim under the c-clip (lots of people flip it to lean a little). Once the ring fails the combustion pressure blows the oil down the side of the piston and it feeds on itself. I would put a ring on the other pistion just as a fail safe measure and check the jet needles for straightness and shims. Give the old jug a brief hone with a 180 grit flap wheel (ball hones risk chipping edge of exhaust port plating). Use a similar sized deep socket as a bearing pilot when you reinstall wrist pin.
i do understand the reasons for a cageless bearing and you can doo what you want but i always convert them over to a caged style. it cuts down on stress if the motor has to come apart again. big twin `s generally are more prone to mid range burndowns as the piston is big and it takes time to transfer the heat to the cylinder walls and out the cooling system. i try to run pretty rich in the mid range as i too have melted just cruzin along. good luck...its all part of sleddin, or is that all part of owning a doo!?
If memory serves me correct Cudney found many 800's had air leaks around the stator bolts. You may want to check them and seal them properly.
As for the cageless bearings...guess you didn't notice the sticker on the engine that said it had cageless bearings.
I always replace them with caged bearings from Yamaha. The later SRX's used the same bearing but caged and half the price...them you can also get rid of the spacers on each side of the needles as well.
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