Rebuilding an engine

heinzsnowmobiler · Feb 22, 2006

ok i decided to purchase an rt100 with a blown motor for 100$....when i had it torn down about a month ago i found a screwdriver bit siting on the edge of the crank case....now this bit could have been dropped in while the engine was apart at my friends so i don't know if its the culprit...but newayz it looks like the rings caught and tore the piston to hell...its scraped up and has a chunk missing...there was steel shavings inside the crankcase and i checked and one of the bearings has a light black color to it and the other one is shiny....i removed the rings and oiled it up and the engine spins freely so i don't think the crank has any issues....so now to the questions....will i just need a new piston, wrings, wrist pin, C clip, and a gasket set.along with getting the cylinder bored or honed.......i am buying a ring compressor and torque wrench from harbor freight this week to do it....the bike is a 97 RT100

if you want pics let me know as i cant figure out how to post them on this forum

chevy383cid · Feb 22, 2006

Your probably better off selling it on *bay and look at finding another bike!! For the money that you spend on this bike you could buy a nicer one thats already running!! I've been there and done that and it's jusy not worth it.Just my two cents Good Luck

xprojectstevex · Feb 22, 2006

I would say you'd be ok with what you said as long as everything is ok with the crank and there are no other problems with it.

nickyd · Feb 22, 2006

while you are in there, change the crank bearings and seals. If you plan on it lasting, you'll be glad you took the time. skip the ring compressor - you won't need it. use your fingers and take you time you will be able to get the piston up in the cylinder easier than you think.

heinzsnowmobiler · Feb 23, 2006

ok...i have found all the parts except the spark plug that is recomended for this bike...does anyone know

bleeds · Feb 23, 2006

Nah I bought one of those last fall, and rebuilt it. It is a great little bike. You can get all the parts you need for it at Wiseco, and Bikebandits.com. Shouldnt cost anymore than 300-350. Ditto on skip the ring compressor. Carefully check the crank to rod bearing play. IF all ok..then replace the crank bearings and seals, and you should be ready to rebuild the top end. YOu will have to split the case to change the bearings. Although it is kinda a time comsuming job, then end results should be good. I rebuilt mine top to bottom and it fired up on the 2nd kick, and has ran strong and smooth since. Even the carb jetting is perfect. Plug is the same one, and always chocolate brown. Get the manual, and take your time. YOu will need a steering wheel puller from autozone to split the cases or pay a shop to do it for you. Either way, as long as the other stuff on the bike is ok, it is way worth fixing. At least mine was...
Bleeds
PS I found the gasket set at Dennis Kirk...

dklink2000 · Feb 23, 2006

heinzsnowmobiler said:
ok...i have found all the parts except the spark plug that is recomended for this bike...does anyone know

I have an RT in the stable, I don't remember what spark plug it takes off the top of my head, but I'll look when I get home.

TimberPig · Feb 23, 2006

NGK BR7ES is the plug it calls for.

heinzsnowmobiler · Feb 23, 2006

ok so i tore it apart today and i am afraid to split the cases...theres all those springs and stuff and knowing me i will lose one...so i got all the steel pieces out using teh chaincase dipstick from my sled which has a magnet and then i soaked it in oil...rinsed it in mixed gas and refilled it with oil to sit until i get all the parts....it spins freely and the rod has little to no play( i can't remember)....what would happen if my bearings went bad....would the piston get hurt???

TimberPig · Feb 23, 2006

If the bearings merely seize up, your top end wouldn't likely be hurt. Normally though, the bearings come apart, throwing pieces throughout the crankcase and top end of the engine, which would destroy the top end.

In your case, given the damage you describe, I don't think I would try running it without splitting the cases and flushing any debris out of the rod bearing, and throwing in new main bearings. You could gamble and get lucky and not have it go, without any further work, but I wouldn't be willing to bet on it lasting.

heinzsnowmobiler · Feb 23, 2006

truthfully i prolly will have this one year and if it blows again i will put it on ****.....i will prolly rebuild the topend....run it for about an hour drain the oil and fill it back up....

TimberPig · Feb 23, 2006

heinzsnowmobiler said:
truthfully i prolly will have this one year and if it blows again i will put it on ****.....i will prolly rebuild the topend....run it for about an hour drain the oil and fill it back up....

If the crank or main bearings is damaged, you won't have it that long without a rebuild. It will go south very quickly, probably less than an hour at best. You do realize that the oil in the bottom end of the engine only lubes the clutch and transmission, so changing that will do nothing for the crankshaft. The crankshaft is lubed by oil injection, much like your snowmobile. It is a 2 stroke engine, not a 4 stroke.

heinzsnowmobiler · Feb 23, 2006

the oil injection had been removed and the gas was premixed

TimberPig · Feb 23, 2006

Was it done correctly so you don't have a huge air leak in the oil injection system? That would lean it out, potentially causing the seizure that started the whole thing.

heinzsnowmobiler · Feb 23, 2006

i am alomost positive it was....the gear seems to have been removed....the bike blew when it was revved all the way up...its also been sunk in a river and layed down alot....its hard a harsh life and it was rebuilt back in 2000....after i inspected it closer i think the ring grabbed the exhaust port and tore it and that took a chunk out....it seized when he was riding it...

TimberPig · Feb 23, 2006

Well if that is what caused it, you better radius that port edge so it doesn't snag again. If it's been ridden as hard as you say, then maybe the suggestion to part it out and find something else isn't a bad one? I would suggest cleaning the bottom end out by splitting the case as being a very wise decision fi you want it to last. Also, don't dump too much into this thing, it's not worth much whole, so don't invest too much, but don't try and cheap out when you know it will cause it to die right after reassembly.

heinzsnowmobiler · Feb 24, 2006

well i am not trying to sound mean timber pig but i am just gonna do the top end and see if she holds....the motor spins fine now with no troubles....so when i rebuild do i refill the crankcase with mixed gas since thats what it runs

nickyd · Feb 24, 2006

You sound like your mind is made up about what you want to. if a ring snagged and snapped, it would not cause a seizure. It would cause a mechanical failure. All of these people are giving you the RIGHT advice - not assumptions. IF the rod seized - and you free'd it up there is no telling if it will last 5 minutes or a year. IF it does give out, be prepared to junk it - there is a strong possibility its going to trash just about everything good you still have in there. Just my 2 cents.

heinzsnowmobiler · Feb 24, 2006

ok...a rod didn't seize....even when it first locked up it was moving fine...the piston was stuck....the crank was stuck earlier because a piece of metal was stuck but i have flushed the crank case about 6 times with gas and also used a magnet to get the big pieces....everything spins fine now...i am planning to junk it if it siezes again....i am heading to the junkyard tommorow to see if i can find another motor for it that fits that frame...thanx for all your help and ill keep you updated

nickyd · Feb 24, 2006

whoops was thinking of another post where the rod did seize.

heinzsnowmobiler · Feb 24, 2006

well i found a new twist to the story today....he sunk it and thats when it seized...so the friction cause the rings to expand...and it tore them

heinzsnowmobiler · Feb 24, 2006

well i finally decided....i sold it back to him....he called and said he wanted it back so i got my money back...thanks again for all your help

Rebuilding an engine

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