General 4-Stroke Question

LabRat · Sep 11, 2009

I was thinking about the benefits of 2-vs-4 stroke, and one item came to mind which I can't answer. Specifically, one of the benefits of a 2-Stroke is the ability to run properly in any orientation since there is no oil pan. Hence why chainsaws, etc are likely always going to remain 2-stroke. My question is regarding a 4-Stroke snowmobile.....what happens when the sled rolls over while still running. (Yes, I tend to roll mine from time to time). Is there any cause for concern with a 4-Stroke sled that rolls over and the oil sloshes up behind the pistons? Is there an auto-shutoff or something in these sleds? How does being upsidedown while running not cause damage? Sorry for the 101 question, but it's been bugging me.

Sammy · Sep 11, 2009

Always a concern on a 4 stroke in the event of a rollover of loss of lubrication. Any 4 stroke requires either pressure lubrication or splash to ensure it will survive. Both the Apex and Nytro are dry sump pressure fed engines and will survive a typical rollover. The risk of course is when the sled is stuck upside down and cannot be shutdown in a reasonable amount of time. Even with no oil pressure being fed to the mains and rods, the bearings can survive a short interruption of oil. Oil film strength is the key here and with no load on the engine and low rpm a short interruption is possible with no damage. Lots of us have experienced rollovers(multiple) only to carry on. Hope this helps.

LabRat · Sep 11, 2009

Thanks Sammy. It's good to know I wasn't dreaming it up......and also good that it's not a huge deal.

SLY · Sep 11, 2009

Put a tether on the sled if you are concerned. That way if you come off and roll the sled the engine will cutout anyway. Real easy hookup in any brown ignition wire with a normally closed tether switch.

Lococoin · Sep 11, 2009

I agree with the tether comment. It helps with the oil that leaks out when you roll it too, less oil comes out if the engine is off.

Mountaintech · Sep 11, 2009

LabRat said:
I was thinking about the benefits of 2-vs-4 stroke, and one item came to mind which I can't answer. Specifically, one of the benefits of a 2-Stroke is the ability to run properly in any orientation since there is no oil pan. Hence why chainsaws, etc are likely always going to remain 2-stroke. My question is regarding a 4-Stroke snowmobile.....what happens when the sled rolls over while still running. (Yes, I tend to roll mine from time to time). Is there any cause for concern with a 4-Stroke sled that rolls over and the oil sloshes up behind the pistons? Is there an auto-shutoff or something in these sleds? How does being upsidedown while running not cause damage? Sorry for the 101 question, but it's been bugging me.

Your chainsaw referral is incorrect. 4 stroke trimmers have been around for several years now and they can be operated in any position. Why? Because although they are 4 stroke, they still use mixed fuel. 4 stroke sleds use a dry sump oil system which means there is little oil at the bottom of the engine should it go into a weird attitude.

Lococoin · Sep 11, 2009

RX FUN said:
Your chainsaw referral is incorrect. 4 stroke trimmers have been around for several years now and they can be operated in any position. Why? Because although they are 4 stroke, they still use mixed fuel. 4 stroke sleds use a dry sump oil system which means there is little oil at the bottom of the engine should it go into a weird attitude.

4 stroke trimmers do not use mixed fuel. Even if you did run it it would do absolutely nothing to help with saving the engine if you ran it upside down. All it would do is smoke out the exhaust

Tuesday · Sep 11, 2009

Tether for one, second once upside down the engine will sense low oil pressure and shut itself down. If you are lucky it does like to puke oil all over the place especially on the rotor and clutches.

Mountaintech · Sep 11, 2009

Lococoin said:
4 stroke trimmers do not use mixed fuel. Even if you did run it it would do absolutely nothing to help with saving the engine if you ran it upside down. All it would do is smoke out the exhaust

Stihl 4 stroke trimmers use 50:1 mix. They've been on the market since at least 2002.

Ak nitro · Sep 11, 2009

I love 4 strokes but this is there weakness, I have seen two engines fail, one Nytro and one phazer due to this. The Nytro tipped over and the throttle was pinned wide open, it blew most of the oil out of the tail pipe, it looked like a bomb went off, smoke and oil everywhere, the engine finally shut down due to the low oil pressure cutoff, it was too late a few weeks later it started knocking really bad. The dealer said it was the crank bearing. The phazer seized a crank bearing and broke a rod due to all the oil draining out of the oil filter, after a dealer had performed a half *** oil change and doubled up the gaskets, once again the low oil pressure cutoff stopped the engine but it was too late. That engine never ran right again and started knocking so bad it finally seized up. What I have seen is if the low oil pressure light comes on it is too late, the damage has been done. The Nytro engine would have been saved if it would have had a tether. I have a tether on my nytro and roll it all the time and have never had a problem. The phazer engine would have been saved if I would have changed the oil myself, at least yamaha sent a crate engine and replaced everything.

Lococoin · Sep 12, 2009

RX FUN said:
Stihl 4 stroke trimmers use 50:1 mix. They've been on the market since at least 2002.

That is because it is not a true 4 stroke engine. Ya it has intake and exhaust valves but it does not have a crank case with oil in it. A true 4 stroke engines crank cannot be lubricated through the fueling system.

Mountaintech · Sep 12, 2009

Lococoin said:
That is because it is not a true 4 stroke engine. Ya it has intake and exhaust valves but it does not have a crank case with oil in it. A true 4 stroke engines crank cannot be lubricated through the fueling system.

True 4 stroke???? If it has an intake, compression, power, and exhaust stroke it is a 4 stroke, regardless of how it is lubricated.

philsummers21 · Sep 12, 2009

RX FUN said:
True 4 stroke???? If it has an intake, compression, power, and exhaust stroke it is a 4 stroke, regardless of how it is lubricated.

have to agree here

SLY · Sep 12, 2009

The Stihl 4 mix trimmers are true 4 strokes, they just have a revolutionary, patented lubrication system. There is no crankcase so they are lighter. I sell them, they are very good machines and are very low maintenance. There is no oil to change, the oil is just mixed at 50:1 with the gas. I had a tough time getting my head around it at first but the fact that it is a 4 stroke has nothing to do with the lubrication system. Detroit Diesels are 2 strokes but you don't mix the oil in with the fuel.

Mountaintech · Sep 12, 2009

SLY said:
The Stihl 4 mix trimmers are true 4 strokes, they just have a revolutionary, patented lubrication system. There is no crankcase so they are lighter. I sell them, they are very good machines and are very low maintenance. There is no oil to change, the oil is just mixed at 50:1 with the gas. I had a tough time getting my head around it at first but the fact that it is a 4 stroke has nothing to do with the lubrication system. Detroit Diesels are 2 strokes but you don't mix the oil in with the fuel.

Sly, so true. Ran the FS110's commercially for 5 seasons straight with barely more than pull cord repairs. Awesome units to say the least.

Lococoin · Sep 12, 2009

Ok fair enough it is a 4 stroke but no crank case oil lubrication system. I will admit I have never heard about this before now. All i was trying to say was that you cannot run a traditional 4 stroke upside down like you can a 2 stroke(and a stihl trimmer) because you will not get lubrication to the crank.

I shouldnt have used true what I meant was a traditional 4 stroke.

Mountaintech · Sep 12, 2009

Lococoin said:
Ok fair enough it is a 4 stroke but no crank case oil lubrication system. I will admit I have never heard about this before now. All i was trying to say was that you cannot run a traditional 4 stroke upside down like you can a 2 stroke(and a stihl trimmer) because you will not get lubrication to the crank.

I shouldnt have used true what I meant was a traditional 4 stroke.

Totally right there. Running a 4 stroke with wet sump lube upside down is a disaster waiting to happen. Honda came up with 4 stroke trimmers in the late 90s that ran on straight fuel and had oil in the crankcase. You could run them upside down. They had a really cool lube system but I forget the details. My Nytro will be getting a tether.

Lococoin · Sep 12, 2009

I had a tether on my nytro and loved it. Then it quit working at the start of one ride. Low and behold I flipped the sled on a hill and the throttle was stuck. I was able to shut it off right away but it could have been worse. I have since upgraded to carrying a spare tether in case mine fails.

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General 4-Stroke Question

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