View Full Version : Need Help With Cooling Options

05-16-2016, 06:44 PM
I completely tore down my 1990 Ski Doo Safari LX 447 fan snowmobile this weekend after a buddy melted down the left piston. We are contemplating purchasing a new cylinder and piston, but don't want it to overheat again. What are any possible options for getting it to run cooler? We already want to make the mixture richer with different jets, and we want to add a temp gauge and possibly add an electric fan in addition to the crank driven one already on the motor. Any and all thoughts, comments, and help appreciated on any of this :)

05-16-2016, 08:41 PM
I am assuming 2 stroke here... back in the day when all there was was air cooled birt bikes, quads, 3 wheelers etc there wasnt much that could be done other than let it cool off every now and then. Synthetics oils will help some.

05-16-2016, 08:43 PM
Yes, two stroke. So there's nothing that can be done to help it?

Buggy Builder
05-17-2016, 02:02 AM
Oil Injection or Premix?
My first buggy was powered with a Kawasaki two stroke twin. It was intended to be an ultralight engine. Built in belt driven fan and shrouding.
On the first trip out I burned a hole through the piston just like you did.
I did 3 things.
1. Increased Jet size.
2. Switched oils from some synthetic 100:1 mix to Yamalube R at 32:1
3 Installed a cylinder head temp gage to keep an eye on things.

Car never holed a piston again.

05-17-2016, 09:10 AM
It's oil injected. So we will up the jet size and install a cylinder head temp gauge. It didn't necessarily burn a hole Through the piston, just took lots of particles from the top exhaust side and dispersed them throughout the cylinder and exhaust pipe lol not that it makes any difference. But either way, thank you for your help :) it is much appreciated

05-17-2016, 12:07 PM
But an elec fan in front of engine would help I think.

05-17-2016, 12:17 PM
One other thing you can consider Bob is the fuel. If you are just buying gas anywhere at any old gas station it will likely have ethanol in it. If it does this makes it run a lot leaner in a two stroke. If you jet it to run good on regular gas and then get some with ethanol it will automatically run leaner and hotter and can cause issues (even with a single cylinder, even liquid cooled, ethanol can suck....).

Another problem with ethanol is its never the same twice. Sometime buying it from the same pump it's more or less. Guess what. Gotta jet for it each tank.... Fun eh?

Or you can buy race gas ($$$$) but safer to jet to run hard. You can also often get gas at Marinas where boats do as it often does not have any ethanol. Some automotive street corner gas stations also sell gas with no ethanol in it. Gotta ask and do some research. I would not trust the guy or gal behind the counter to know!!!!!! Gotta check deeper than that!

I have one two stroke left with carbs and any sled two stroke I would ever use again would HAVE to be fuel injected. The F.I. systems can deal with the ethanol as they adjust on the fly. But I would still avoid ethanol if I could.

With ethanol fuel in a carbed two stroke you have to jet it so rich to survive the variances that it will not have the good old two stroke power hit but soggy old fourstroke power (old as in old days fourstroke not new power fourstroke stuff) and still need a lot of spare spark plugs as they tend to foul out. Sucks eh?

Also just to be sure you need to do a "crankcase pressure test" (both negative and positive) on both cylinders (Not a compression test but those are needed too) If you have a tiny air leak it will also lean out the cylinder and melt the piston no matter what unless you are running MEGA rich already.

I have had bad bearing seals, bad gaskets, porus metal in the cylinder passages and even a cracked phenolic (type of plastic I am spelling it wrong I think) carb spacer cause a lean condition too. Only way to find these is a good inspection but more-so a crankcase pressure test. Easy and pretty cheap to do. Should be a regular part of any two stroke maintenace and will often save you good money in return. If you do not know how to do these we have a tutorial on this site buried somewhere! :]

One thing I NEVER do is assume when a two stroke melts a piston. It may be jetting. But until you check for crankcase leaks your just guessing.

Many times I have seen guys burn down a piston. Hone or bore the cylinder and buy a new piston/rings and gaskets. Slap it together only to ruin the new piston in minutes because the leak in the crankcase "zone" is still there and its too dam lean.

05-17-2016, 12:20 PM
I will also add that I think that sled engine only had one carb. I have seen guys with twin fan air cooled with dual carbs actually run a tad richer jet on the left side away from the fan as that cylinder gets the warm air from the first nearest the fan and runs hotter due to this. Not worth worrying about if you do not already have dual carbs.

05-18-2016, 09:11 AM
It actually is a dual carb, and that makes sense but I haven't checked jet sizes yet. If someone could tell me how to do the pressure test, that would be a good thing to do it sounds like. And Carl, what were you looking for pictures of? The melted piston and cylinder? The whole engine and setup? Pics of both are on my build thread, but if you'd like I could post a few here. Again, thanks for all the help.

05-18-2016, 09:13 AM
Oh and we are also considering a whole new engine from a different snowmobile if that option proves cheaper. It will cost around $300 for two cylinders, pistons, rings and bearings, and we might be able to find a whole motor or sled for that much on Craigslist somewhere. Just keeping our options open

05-18-2016, 10:07 AM
Was thinking whole engine in car. With a fan in front pushing air across. I'll check the thread.

05-18-2016, 02:31 PM


This is what the motor in the cart looks like, except there is about a 4 gallon gas tank above it behind the black speaker box. The fan is on the right side of the motor

05-18-2016, 03:02 PM
Being your a Yooper I would bet a liquid cooled sled engine would be pretty easy to find and likely cheaper than rebuilding that one. Of course you would need to add a radiator and redo the mounts. No big but still.

I typically never tear an engine apart before I do the pressure test just so I can see if I find a leak to know if it caused or contributed to the meldown. Being you already took it apart that not a big deal as long as you do it when you reassemble. I always do it before and most definatly after a rebuild. No pass no gas! If its not dead sealed I will not reinstall it. This below I typed up a while ago and is cut and pasted.

From Bill the Troll! :]

Here yah go. This is part of a teardown and rebuild on any two stroke. It SHOULD be done before you take the worn motor apart and after you got he new motor together to check the work. Anyone who tells you its not needed is gambling.

NEVER ASSUME new seals have sealed and new gaskets are perfect. Often far from it. Especially with stuff being done cheaper and China crap being substituted in!
Any two stroke has seals in the crankcase. If these go bad you usually lean out the motor and fry a piston and can ruin a good cylinder along with that.
To pressure test a two stroke should be done BEFORE you tear it apart for a rebuild.

(If it fails then a top end rebuild alone will fail due to the bottom end is leaking. If the motor fails a crank pressure test and the pistons is bad the bottom end is usually what caused it.)

AFTER you rebuild it to check the seals (and gaskets) you just worked with. And at regular intervals (along with piston compression checks) to monitor your engines internal life.
To do a pressure check you need to remove the pipe and carb and go to a hardware store and get some stuff from the plumbing department to seal both holes. Rubber caps and a hose clamp usually work good on most exhaust pipe snouts and PVC pipe caps can normally be found easy that will fit in the carb boot. You then either need to make or get a fitting that allows you to put an air hose to either one of the caps or into the spark plug hole.

Basically you need to have a way to feed air into or out of the motor.

If you cannot find a way to use the sparkplug hole with a fitting then drill a hole in the PVC pipe cap thats in the carb manifold (Take it out of the manifold first if its already in there! I hope I didn't need to tell you that but just in case! I have seen people drill things where crap from the drill falls into the works. Not good). (My Honda Pilot had a fuel pump hose fitting on the side of the cylinder (some motors have these on the crankcase) for the pulse to make the fuel pump pump fuel. If you have that fitting you can use it (on a single cylinder. In a twin it can only be used for the cylinder its under just so you know)

Once you KNOW the pipe and carb holes are sealed tight (The spark plug too if you have you air fitting there. If the plugs in it should be fine.) make sure the piston is down in the bottom of the cylinder (You don't want it blocking the ports. The very bottom is good. Just clearing the cylinder ports will be fine.) Then you need a vacuum gauge/hand pump ($20 to $30 bucks at any auto store for the hand pump version.) Put about 6 inches of vacuum to the crankcase. If it drops to 4 inches of vacuum in under three minutes the bottom end seals are bad or at least weak. Some say less than an inch of vacuum a minute is fine but as you regularly test your motor if you see it loosing its negative pressure faster then you will know the seals are getting weaker and its a lot cheaper to fix it before it toasts everything. (This requires you to make sure the carb and pipe plugs you made are good so you are only checking motor gaskets/seals.)

Thats a negative pressure test. You can go up a little higher in vacuum pressure. The motor should be able to hold some for over five minutes or the seals are toast. One inch of vacuum a minute lost is starting to get bad.

Many also do a positive pressure test. Same deal as above. I like them better as its easier to see soap bubbles and ID the leak. Seal the motor and get a hose connected with the piston at the bottom of the cylinder like before. In the NEG test above the pump stays in the line and holds the vacuum. For the POS test you will want a little on/off valve in the line. Then once you put pressure to it you can close this valve to hold the pressure in. As long as you have a setup that holds the pressure in at the hose your fine.
HERES THE CATCH. If you put to much POSITIVE pressure to the crack case you can literally Blow the seals out! NEVER JUST PUT A AIRCOMPRESSOR HOSE TO THE SETUP YOU MADE TO PRESSURE TEST IT AND "THINK" YOU CAN HIT IT WITH A LITTLE AIR AND TEST IT THAT WAY. You make one little mistake and its gonna need to be taken apart and repaired. So do this instead. Get one of those small portable air tanks. Put about ten PSI in it with the compressor. Then bleed it down to 6 PSI or maybe 5. This way you cannot put more than that to the crankcase. Better safe than sorry. Put the 5 or 6 PSI to the crankcase and seal the valve. It should not leak more than a pound a minute. Less is better. More is questionable. I will not settle for more than 1 pound every two minutes one my stuff.

You can get a gauge at the auto parts store that reads both POS and NEG on the same gauge. (They are NOT high pressure they are more for car manifold tests) This gauge can do both tests for you. I have in the past used these (I still have mine and use it) AND used a HUGE syringe to provide both the vacuum and the positive pressure. It sometimes takes a few pumps to get the pressures I wished but it can be done.

If that did not make sense GOOGLE pressure testing a crankcase and you will get some more insight. I also test the entire motor and all the seals on my test equipment each time. I have had leaks that formed on the tube joints of my test equipment. The soapy water bubbles led me right to it. I check every seal and gasket line and even around bolt holes.
I HAVE actually discovered air leaking out a cylinder hold down nut like this due to a porous casting flaw from the intake port near the stud the to the engine. I had to go back in and seal it to stop the leak.

Doing this test while you can still see both sides of the main crank seals is best. Easiest to get to to fix too if need be. Cover the entire outside of the motor with soapy water. I have had slow leaks that make the tiniest bubbles that I could not see/locate till nearly 3 minutes into the test. But then noticed.
I won't install a motor that does not pass this test

05-18-2016, 03:12 PM
A couple other things I should add to the above (and will) When testing a cylinder/crankcase for pressure integrity you should make sure the piston is at least down past the ports. it will help get faster more accurate results. In a twin you then obviously need to rotate it 180 degrees when you do the other cylinder.

The air cooled engines I used to mess with were nearly all Cunya's. These had a mean fan but blew the air from the first cylinder right across the second making the second hotter by design.

Your engine feeds air into the front and across both kinda sorta equal. I cannot help but wonder if it has any air ducting inside that shroud to guide air more equal. Otherwise in a setup like that it may blow more air across to the farther away cylinder? Without pics or seeing it I am just thinking/wondering/guessing.

05-19-2016, 01:02 AM
Just curious, would a fan cooled or liquid cooled sled engine run better in summer...? Because to me, if a motor needs to be liquid cooled for winter, I can't see it fairing very well in summer. But that's just my thought process, I could be completely backwards. If we do decide to rebuild this engine, I'll definitely pressure test it. Thanks for the info

05-19-2016, 05:16 AM
While it is easier to cool the liquid cooled two stroke one thing you need to get right is the RPM's. A two stroke gets a butt-load of its cooling from the air it takes into itself far far more than a four stroke as the air goes thru the crankcase on the bottom of the piston and up the cylinder ports into the chamber.

Dogging a two stroke can make even a properly jetted one run hot. Especially an aircooled. By spinning it faster and moving a lot more air it helps cool it better even though its making more fire in the top end. So you gotta get the RPMs where the engine ws built to run.

Even in the summer a two stroke aircooled sled engine properly jetted in the proper RPM range the engine was built for that's not pulling some stupid oversized heavy load can run cool enough to keep itself together.

Will it make as much power in the winter when its cold? Of course not.

Liquid cooling is a better way to transfer heat of course. But either air or liquid sled engines will be fine as long as you obey the three majors. Jetting, Proper RPM's, and not oversized load.

Most liquid cooled engines make more power than thier air cooled counterparts since they can remove the unwanted heat better. There are some balsy aircooled ones out there but the liquid cooled genrally make more power for thier size.

Liquid cooling can also take a stick thur the radiator if its not protected well. Air cooling is a little more forgiving in that respect in the boonies.

In a light weight buggy like you have that motor you have now running right will be faster than the buggy should probably go. Which is just about right!!!

05-19-2016, 09:10 AM
It sure is fast haha I've wanted to gear it down a little or declutch it so it has better lower end grunt, and because it already goes way faster than anything else we have on the peninsula I dont mind sacrificing a bit of top speed of necessary lol

A buddy of mine is selling a mid 90s 440 fanner out of a Polaris sport I think it is. Do you think this would be a good option?

05-19-2016, 02:22 PM
If the price is right and it runs good and can be fit to your setup with a reasonable amount of work your cool with I see no reason it should not be OK.

05-19-2016, 03:53 PM
He said $200 (which is the same cost as a rebuild of the necessary parts, not counting ones that don't need to but could be replaced too) and he'll help us put it in and make sure it runs. It sounds like a decent option to me, the easiest and cheapest I've found so far anyway