I agree with Chunky5678 about jetting a little fat at mid throttle. All three of my machines have CVTs. The way I see it, there is no reason to jet for optimal performance over safety at anything other than full throttle. Even worse than cruising at mid throttle and the RPMs being high is a high speed run and then easing off. I toasted a piston a couple years ago 200 feet after the end of the drag strip. It gets nice and hot and then you cut the fuel and oil while still spinning near the same RPMs.

I also run additional piston to wall clearance with Wiseco pistons over stock ones.

I just had several FL350 pistons coated and will be running them that way now.

 

Paul, on the next rebuild, do yourself a favor and install an OE replacement piston. Seriously.

 

I warm it up by putting around for a few minutes and stopping for a while and going again. Right?

Paul

 

Well,if I have to put another piston in it then I want the best possible piston for durability/reliability. That coated piston sounds good. I just want the jets to be set at a place where I dont have to change them twice a year. I live in North Carolina. Its typically humid and warmer here than in some places but in the winter it can get a little cold so we see all three seasons. When the engine quit I was riding in a foot of snow. I apreciate all the information. The dealer I bought it from is in the middle of know where. All he sells is polaris but he lost 1 of 2 mechanics and I'm not too trusting anymore. Anyway, any tips are trulet apreciated.

Tx,
Paul

 

The Polaris OEM pistons have a problem with skirts breaking off so you are better off with the Wiseco. A lot of people hate Wiseco because they have had problems treating them the same as cast pistons. They expand more total and expand quicker during warm up. Just allow a little extra tolerance and a little extra warm up time and you will be fine. I have heard of, but never seen, Wiseco pistons losing a locator pin. I have actually seen an Art (OEM for Honda and others) lose a locator pin. So the problem is not limited to Wiseco. It is a rare situation regardless.

Swain Tech does the skirt and dome coating for $32.

If I am going to get on my machines hard, I let them idle for 5-10 minutes before going. An example is the entrance into Silver Lake dunes is a slow uphill climb. I won't start my machine and then hit the dunes. I start the machine and then put on my helmet, gloves, ... If there is a long line before the check point, I will putt over to that line and the engine will be warm before I have to start the climb into the dunes. My FL350 has a 4900 RPM engagement, so it is kind of hard to putt around though.

 

If you seized it, even ever so slightly, then there are just a couple of reasons why.

1. Piston is a little too tight. How I like to do it is bore the cylinder to the thinnest clearence allowed. Then hone it out to a clearence that is in the middle of the min and max accepted clearences.

2. Oil to gas ratio is off. Make sure (especially when the piston is new (less than 20 hours) you run a little more oil in the fuel. If you still have the oil injection hooked up, then don't worry unless your quad isn't jetted right then jet it a little rich. Especially on the air screw and needle position.

3. Cold siezure. Make sure (by feeling) the cyclinder is real warm to the touch before riding, but don't burn yourself.

All of the points above are not a Polaris thing. All engines are affected from the above.

If you are a little mechanically inclined, you can do the piston replacement yourself. A 2 cycle is real easy to dis-assemble and re-assemble. You take the new piston and cyclinder to a machine shop and tell them to set it up in the middle of the clearence specs. Wash the new piston and cylinder after they are back and re-install. You will need to buy a service manual for torque specs and make sure you take a rag, dip it in 2 cycle oil and wipe the cyclinder/piston with it before starting and you got it.

It sounds a little hard, but after the first time, no big deal. If you mess up the piston, shoot they are just a $100 bucks, boring maybe $50, gaskets $30 and your time.

Now 4 cycles are another beast.

Note: Here is a oxymoron - More oil in the gas makes the engine run leaner. Oil lubricates but causes a hotter burn. The absence or presence of fuel dictates the hotness of the combustion. So you only need enough oil to lubricate the cylinder wall and piston skirts. The oil helps prevent seizures if the clearences are acceptable AT ALL TEMPATURES (cold thru hot).

If there is more oil in the fuel mixture than needed, then there is less fuel per combustion stroke. So it is leaner than need be. There is only so much fuel metered into the chamber per stroke via the carb. So more oil means less fuel. Less fuel means it is leaner and has a hotter (and more powerful) combustion. If the combustion is too hot, a hole is burned in the piston. No other way can it happen. You can have an air leak causing leaness, partially clogged carb whatever. Leaness burns holes in tops of pistons, period. I won't discuss too hot of plug, but safe to say the mechanical laws above apply to this situation, too.

Seizures are either too tight of a setup, lack of oil to lubricate or improper warm up procedure where the piston warmed up quicker and expanded before the cyclinder expanded making room for the larger piston. The piston got larger from heat before the cyclinder expanded from heat and made room for the larger pistion.

I ordered an EGT so I can find the sweet spot of safe, cool (ie.. fuel rich) jetting while trying to gain the extra (free) horsepower with having the hotter combustion. You cannot feel the difference between jet settings on the last 30% of the powerband looking for that extra 2-4 horsepower. The tempature of the exhaust lets me know if I am in the zone of safe jetting vs. max hp.

Sorry for the rant, but a few concepts can help people enjoy their quads without a lot of un-necessary costs.

Finally note: Oil removes heat from the metal components. That is it's main function. Not to lubricate, but to carry the heat away to be cooled. For example, take your hands and rub them together. They are fine at first. But the more you do it, the more they get hot and want to stick together. Take a little water from the sink while still rubbing them and watch how the water removed the heat allowing you to not stick and rub easily together again. Oil removing heat is important. So pay attention and run the correct oil weight/mixture so the oil can get into the crannys to pull the heat out. But not to thin of weight where the oil breaks down and the engine components rub together getting hot (wear and seizure).

Again sorry for the rant, I know most know these mechanical laws, but reviewing them helps to proper aid in diagnosis of engine problems.

Chunky

PS Honda having a air cooled 400 is OK stock, but hopping it up you get into the oil issues I discussed above. The Hondas lose their reliabilty because of the air cool engine and they are setup real tight from the factory.

 

One of the chain saw companies did a test where they dynoed a motor as various gas to oil mixtures. Jetting was set properly at each ratio. They found that power increased with the amount of oil right up until 6:1 where the motor would not run from the plug fouling out. I would run my machines at 20:1 if that did not make them spit spooge out the exhaust. I run them at 32:1. Even the Drakart which I was recomended to run at 40:1 by the manufacturer and 50:1 by Rotax (engine manufacturer) after removing the oil injection. The oil injection is gone on mine and removed off every motor installed in Drakarts after the number of failures that have occured. My motor was one of the failures do to oil injection failure. I am not sure, but I think the oil injection was 50:1 at WOT and 100:1 at idle. If I still had oil injection, I would mix my gas at 50:1 to get a result of 25:1 at WOT and 75:1 at idle. If the oil injection goes out, I still have the minimum amount of oil.

You can't just install an EGT to check jetting. You have to get baseline temps when jetted correctly and then use those after that. Correct jetting might give you 1100 degrees or it might give you 1300 degrees. Once you know what is the right number for your motor though, all you have to do is keep it there when the weather or altitude changes. Some mods will affect what the right number is too so you should double check that your jetting is still correct after mods even if your EGT is still reading the same number.

 

Chunky,that was a good post you put on here,but I have to disagree with you about oil. You stated that oil carries heat away from metal and that is the main reason for oil, not to lubricate. Oil is the only real bearing in a engine,oil forms a micro film oil layer on metal that prevents metal to metal touching. So if you run a engine without oil it will get HOT and seize,so from that standpoint you can say oil carries heat away, but the oil LUBRICATES the parts to keep them from touching each other keeping them from getting to hot and wearing.

 

Granted oil provides a film strength for parts to "ride on". I didn't mean to imply it doesn't. It is much need. In fact film strength is needed where heat cannot be removed satisfactory.

A little research will show the oil research is greatly concentrated in heat removal. If you can get a oil that is thin (for carrying heat quickly away in all crannys) with a strong film strength, that is ideal. And yes I know about certian clearences depend on certian oil weights, so we must watch our oil weight to ensure clearences are maintained.

There is a lot to oil technology, and I don't want to bore everyone with discussing it. But I can tell you heat is the big enemy and where a lot of effort is placed in research.

The film strength, detergents, rust/corrision, evaporation, emissions, etc... are factors, but in the simple discussion above heat was the main thing for the 2 cycle seizing.



Please excuse my brief discussion above. Just wanting to review a few main concepts, but not to the point of confusion.

Chunky

 

Something else to think about. More oil in the gas mixture doesn't make it burn hotter,it makes a engine more powerful because it burns slower causing the combustion period to last longer therefore pushing the piston down further with force.Low octane gas burns hotter than high octane gas. During the combustion period using a low octane gas as soon as the gas ignites its gone very quick therefore causing a blast force on the piston.High octane gas burns slower.During the combustion period using a high octane gas as soon as the gas ignites it burns longer causing more of a pushing on the piston instead of a blast, this is why higher octane fuels seem to make some engines run hotter because the combustion time last longer.