1984 Sportfire Compression

sdakotajd · Post by **sdakotajd** » Wed Dec 28, 2005 4:19 am

I purchased a 1984 Sportfire last week. The seller claimed that the sled was very reliable and was driven into the shed where it was parked (four or five years ago) and may start right up. I cleaned the gas tank and carb, replaced a bunch of brittle fuel line, cleaned out the oil reservoir, replaced spark plugs, etc. When trying to start it, it wouldn't hardly fire, even if I primed the cylinders with a little gas. The spark plugs fire well when I pull it over. I just got a compression tester and the chaincase side has 140 lbs. of compression but the clutch side only has 50 lbs. of compression. Where should I look first? Should I check that the valves are seating properly or that the timing chain is timed right (lol - a little 4 cycle humor). Is there a gasket or seal that may dry out and fail because of non-use? Is it possible that the piston rings are stuck on the weak side? What should I check first. I am new to the world of snowmobiles and any help would be appreciated. Thank you.

Sdakotajd

harleysportster · Post by **harleysportster** » Wed Dec 28, 2005 4:41 am

sdakotajd,
Something is diffenently wrong with the mag side cylinder. More than likely the piston burned a hole from a lean condition. Start by removing the cylinder head and look for a damaged piston. The cylinder jug will have to come off as well. Plan on replacing the crankshaft seals during re-essembly. Check out this link for a service manual for the liquifires, which is similair.
http://www.ryanquick.com/jd/info/
I recommend to purchase a service manual for your sled as well.

jdsledhead · Post by **jdsledhead** » Wed Dec 28, 2005 10:37 am

If you want to know if it is the rings or a hole, dump a few onces or so of oil down that cylinder and turn it over a bunch, then recheck your compression on that cylinder. If it goes up then it most likely means that (A) the cylinder walls are scored and worn out, or (B) the rings are weak/worn. If it does almost nothing than there is probably a hole in the piston. These are only things i would do and are only meant as a suggestion. It just saves a little time, but most likely you will have to tear it down anyways to get the compression back up. IE. new rings and gaskets.
Also a thought, i have seen stuck rings before, they may build pressure again, but may not. The oil may help. The reason i say this is that the other cylinder has such high compression that the rest of the engine may be in good shape, but have stuckl rings.

sorry to go on for so long, but im bored at school...

later
timk

JDFanPa · Post by **JDFanPa** » Wed Dec 28, 2005 1:44 pm

I doubt a hole with 50lbs I would bet money [if I had any] its stuck rings. It really doesnt take much rust to form on the rings themselves or the cylinder walls the stick them. You can try spraying a good amount of carb cleaner down the plug hole with the piston all the way up or at least close to the top.Let it sit an hour or so and come back and pull it over with the plug out will spit stuff out so watch. After you pull it over several times just sprsy a little liquid wrench/wd40 type stuff down the hole and pull it a few more times then check the compresion again. If this doesnt do anything you can try and let it sit over night with a bunch of liquid wrench in the cyl;inder . If you get lucky with either method and can get them free enough to get atleast 75lbs or so it should start and often they free up the rest when running if not you will be putting rings maybe a piston in it.

sdakotajd · Post by **sdakotajd** » Wed Dec 28, 2005 10:46 pm

Thanks for the help all. As a devoted follower of the KISS manual, I started by placing the piston at TDC and putting some carb cleaner in the cylinder. One hour later, it was all gone. On the upside, what can be seen of the piston looks good. I put a little WD40 in the cylinder, turned it over and retested compression. The first test showed 75 lbs., the second 60 lbs., and the third 55 lbs. I put a little more WD40 in the cylinder and tried starting it. The engine gave a couple of weak attempts to start but wouldn't. With compression dropping fast, I didn't think that it would. Next up, I plan on tearing the motor down and fixing as needed. This is the only sure way to know that the engine will be reliable. Once again, thanks for the help.

Sdakotajd

Danzig · Post by **Danzig** » Thu Dec 29, 2005 12:29 am

Get some additive called SEAFOAM and dump it in the cylinder and let it sit for a day or so, I would add about 4 tablespoons or so to the cylinder and then crank it over and repeat this process for another 24 hours before tearing this down. I had a similar problem on my X8 and this worked and this has worked also for the automotive industry.

deererunner · Post by **deererunner** » Thu Dec 29, 2005 9:58 am

I have just purchased an 80 liquifire that only had 60 psi on mag side. I used a good quality penetrating oil and kept turning it over the course of a couple of weeks. I`m know riding it at 130 psi. No tear down reqiured but i did remove carb and Y pipe to confim that everything was shiny and it was. Sled only has 843km. on it Best of luck ..