79 Enticer 300 -Anyone rebuild the engine?

P

Paul_Aris

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Oct 6, 2004
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OK, I bought this really clean 79 Enticer 300 for the kids. Well the first snow the kids wanted to ride it bad so I got it out and away they go around the yard. After a while I had to put some gas in it. Anyway they started to ride again and I was in the garage working. Then I heard the kids outside playing but not on the snowmobile. I asked if they were done already and they say, "it keeps locking up". So I go over and grab the rope and give it a yank. It fired right up and then died. I grabbed the rope again and it was locked up.

I tore it down a couple of days later to find the pistons and cylinders were fine. So I kept going and found the PTO crank bearing to be completely shot. I sent the crank out for a rebuild and all new bearings. I figured while I am at I should hone the cylinders and install new rings on the old pistons.

HERE is where the PROBLEM IS. I get my new aftermarket rings from Als Snowmobile Warehouse. Well the bottom rings went on great. After hours of cleaning the top ring groves I could not get the top rings to close up all the way. They kept getting wedged in the ring groove. So I finally get smart and decide to try one of the old rings I pulled off back on the old piston and it fit like a charm. I really didn't want to use the old rings. Plus I destroyed 3 of the 4 to used to clean the rings groove so the old rings are not and options.

After checking the parts phish on-line I figured 1 of 2 things could be wrong.
1. These aftermarket rings were not manufactured close enough. It appears the tapper on the stock ring is steeper and narrows down more toward the inside.

2. in 1980 the piston and ring part number changed according to the Yamaha parts phish. The cylinder is the same part number so you know the diameter of the pistons and rings need to be the same but maybe the groove and taper are different.

So I decide to buy OEM Yamaha rings with the 1979 part number. I spend more money than on the aftermarket rings. I wait for them to show up and they did on Christmas eve. I run out to the garage to throw them on and same problem. I thought for sure this would be the answer. I can not get the top ring to close up enough to get the cylinder on.

So now my only option seems to be to order OEM pistons. What if these do not work? Should I get the 79 pistons or the 80-84 pistons?

Anyone run into anything like this before?
 
Are you sure the ring is on the right groove or maybe upside down. I think there maybe a difference. Did you check your ring end gap? Are you putting the ring gap so the locator pin is in between it.
 
mtnmaxman600 said:
Are you sure the ring is on the right groove or maybe upside down. I think there maybe a difference. Did you check your ring end gap? Are you putting the ring gap so the locator pin is in between it.
Click to expand...


Yes, Yes, and Yes. The pin is near the top side of the groove so and the end of the rings have a notch on the end to except the pin. Really can only go one way. I mic'd everything and both rings are the same. I've tried switching the bottom ring with the top rings and everything.
 
The only reason I asked about flipping it over because I just rebuilt my 600 twin and had the same problem just flipped the ring over installed it and it went right together I didn't think that there was any difference but must of been. Is there a burr on the ring anywhere that maybe hangin up when you put it in the groove. Maybe you could take a sheet of 400 grit sandpaper and just sand the ring a little on each side to clean up any burrs. Worth a try
 
No amount of burr removal will get these to close up far enough. I don't get it. I looked at the direction the rings were when I removed them. Plus the old stock one closes up all the way with out getting stuck in the groove. The only thing can see and measure any difference is the taper and the thickness on the very inside edge.
 
rings

Odd , Are the old rings the same style ? If so, measure the gap with the old ring and make " file " the new rings to fit without the piston in the bore. Once the rings show the same gap install on the piston, unless the rings are different, check for the same design. Iinstall them with the numbers / letters up.
 
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