SPORTFIRE QUESTION

[427cobra]

Hey Guys,

I got my 84 SF out today and getting everything ready on it.

I noticed a loud rattling when it idles. But it seems to smooth out at higher RPMS. I checked for loose tins, exhaust, loose parts...etc.

I did a compression test and one side is slightly lower. I am wondering if that could cause a rattle.

It doesnt sound like a grinding or rubbing (like a bad bearing)

It seems to be running fine. But it will not idle below 2500 rpms... So I have the idle set at 2500 and it revs out nice and smooth. I took it up and down the road a few times and everything is running and working good with plenty of power.

I just need to find whats causing the rattle....??

[Sprailfire340]

Take the empties out of the glove box

[427cobra]

Ill look into that...

[tipitup]

a friend suggested clutch weights. I don't know, just passing info.

[427cobra]

Thanks!

Ill remove the clutch and see if that eliminates the noise.

[That Girl Racing]

Could be piston skirt rattle.

[wycrumb]

Something loose in the fan tower or a bad bearing?

[427cobra]

I am leaning toward the fan tower. I took the clutch off, heads are tight, I removed the tins as well...and the noise is still there!!

So I will pull the motor and see if I find anything in the fan tower....

[wycrumb]

You shouldn't have to pull the motor.

[427cobra]

I figured it might be easier to pull the motor...

I suppose I could pull the fan out fairly easy. Ill take a closer look at it.

[427cobra]

Hey guys

Removed the fan belt with no change.

Maybe thats the way these fan cooled motors run?? I dont have my Trailfire to compare anymore. Maybe a rebuild is in order...it ran fine last year just they way it is. So I am stumped.

Maybe it is piston skirt rattle...??

[johnnycyclone]

Quote "Maybe thats the way these fan cooled motors run??"

Eric,
I am by no means an expert on snowmobiles, but I have a similar situation. I have just finished a restoration (minus decals) of an 82 Sportfire. I had Jerome rebuild the crank, all new bearings. It has new pistons, rings, pins and needle bearings. It also has new fan bearings. After firing it up for the first time, my first thought was, wow it runs! My second thought was, what is that rattling noise? To me it sounds like the engine is rattling at idle, but goes away when you apply power. I just assumed this is the way it sounds when idling, so I've never looked into what was causing it. The sled runs fine, and idles fine. I too, have nothing to compare it with, so I'm not sure it is normal, but assuming it is. Not sure if this helps, but it's nice to hear from someone who has the same problem, or I'm guessing it's not a problem, just the way it runs.

Terre

[427cobra]

Thats what I was thinking as well Terre. My sportfire has also been recently rebuilt and runs good.

Good to know!

Thanks

[lwb140]

eric it sounds to me like your 84 is in bad,bad shape and you need to sell it to me immediately just kidding wade

[427cobra]

Haha....EVERYTHING is for sale for the right price Wade....