Why do pistons burn up? Hirth Pistons

[jayvee43]

Well well well lets see this from another view point. I am a "marine Tech" I see a lot of Hard running engines, but not like the marine outboards. WHY? you may ask. I have never seen a land operated engine work like that of an outboard. I explain: Immagine for a second you have your car pulling a medium load trailer up a 30 degree hill constantly at 5500 rpm. Yes 5500 rpm is the average for an outboard/inboard engine. with constant load. (Now lets think a little about that) constant load, constant heat, constant fresh oil fuel mixture comming in for miles on the open water. WHY does my piston not melt???

Some will say it is water cooled. Yes it is, but the exhaust manifold reach temperatures of 450F - 550F at this temp you can cook a turkey. Aluminum melts at about 1,300 degrees.
What I use, and have been using all along in my 2 cycles is CASTROL TCW Which mean Two Cycle Watercooled. (outboard blend)

If You want the best, get the best from a reliable company that develops oils for today's gasolines. You know the 50 years old sleds had oil blend recomendations for gasoline containing LED. Good luck finding Led based gasoline today. There are so many chemicals to control the burn and not detonate that we don't know about.

IF I have to choose an oil designed for temporary loads and varying temps on my pistons domes, or a oil designed for prolonged enduring flames atop my piston with high rpm's; It is no contest... Castrol all the way. They are as old as oil itself.

BTW I do mix 40:1 for my Snowbug which is a 292cc aircooled, and 30:1 for my Diablo.

[Barrie2777]

Today was hovering around tbe freezing point but with grandkids here i took two husskis (444 & 400) on a one hr ride. I was riding my 600 but decided against it due to their history of overheating.Normally i wouldnt ride too far today but though it okey. Half way through the ride we turned the machines off. Bubbles were coming from the carb and pushing the gas back to the carb. After a 20 min break both started but needed choke due to the now empty gas line. At home i pulled the plugs on both machines. The 444 plug which is always more black than brown was close to white. The 400 plug which is always brown had a lighter color. These plugs way not be a scientific trial but next warm day ill take my own advice and not ride.

[Go Go Diablo]

We should talk a little about gas too.

For years, I was not seeing an issue using regular unleaded gas with up to 10% ethanol. Honestly, I was a little worried about a premium fuel with higher octane burning hotter in my cylinders. This year after 3 to 4 years on my carb rebuilds, my gaskets were mush. I had to rebuild them all.

With that, last winter we talked about this on the forum. There were multiple opinions out there I trust more than my own on the subject matter that said higher octane premium gas actually burns cooler than regular gas especially gas with ethanol. I've been running premium ever since.

Any comments supporting or tossing that concept?

Bruce

[jayvee43]

Hi Gang

I just came back from a 3 day E.F.I. course in Toronto, where we talked in depth about the fuel system, and calculations and ECM (computer) mapping (performance and clean emission) I can assure yous, the 3 types of fuel available at the pump today, all burn the same. That is. The flame fronts are all the same.

I don't think ethanol is good. For two reasons and one is as you just said Bruce. I was testing fuel "phase separations" Google that; and saw the results myself.

the number two reason ethanol is not good for our type of engines is ambient air has moisture in it naturally. Ethanol in its gasoline form draws in this moisture from the air and turns it into water in the fuel system. (believe it or not) It wants to return to its natural state. Organic. It does that in about 6 months of storage on the shelf. So immagine our seasons. 8 plus months in storage. phase seperated fuel in the tank and voila. bad burns, bad spots on the piston domes.

I'm not trying to be smarter than anyone here guys. I'm simply sharing what we discovered first hand on our EFI course.

Jesse

Check this video: https://www.youtube.com/watch?v=Wrb4pl03xCg

[snocatpete]

This is a very interesting topic Bruce... the very first picture you posted definitely looks like serious lack of lubrication causing a lot of heat that ended up scoring the piston really badly. And like you said, 50:1 oil to gas mixture is extremely lean in my opinion as well. And I agree that the relatively cold ambient air temperature coming in to the engine will keep the intake side of the piston cool compared to the exhaust side. Bear in mind that 50:1 oil mixture is what lubricates the rest of the engine like your crankshaft bearings, connecting rod bearings, wrist pin bearings, piston skirt and cylinder wall and crankshaft seals - all these parts need lubrication so as everyone knows, the oil plays an important part in lubricating and cooling parts. So less oil you put in your fuel mixture, the less lubrication you will have on these parts, and the less cooling you will have, causing all these moving parts to generate more heat. Personally I would never run anything 50:1. That is just way too lean and a recipe for disaster. The flip side of that is using too much oil in your mixture, from what I have seen (in my experience) causes fouling of the sparkplugs, carbon build up on the piston, carbon build up on exhaust ports and muffler. I have done a lot of work on small engines and have seen this problem where exhaust ports have been almost completely choked off due to carbon build up. However, I would rather de-carbon my engine of excessive oil from over oiling vs replacing pistons and cylinders and crankshaft bearings etc from not enough oil in the mixture. Also, touching on the cooling system, it is very important that the cooling system is in good shape. I mean that the fan shroud is super clean on the inside and not built up with dirt, cylinder fins and nice and clean with no debris or oil or grease on them creating a layer of insulation on them, as well , all the fan blades are clean with no build up on them. I think I also commented once a long time ago on this topic - that I would remove my engine hood from my hus-ski on extremely warm days so it would have better air flow and better cooling for the engine. ( but that means+10 +15 C on a hot spring day). I also agree with you and Jesse on the fact that you should ONLY use good quality oil. I have always used Castrol Super 2 stroke air-cooled oil and I have never had any issues with this oil. I have never had an engine seize or bearings fail using this oil so I will continue to use only Castrol oil. As far as gasoline goes, I have heard arguments for regular and premium gasoline. I personally use regular unleaded gas and I have never had any issues so in my experience and opinion, I don't see a need to use premium gas. Those are my thoughts....I really enjoy this topic

[Go Go Diablo]

It's a year later and again, warm spring weather is upon us. I think we had less pistons burn up in the 2017 / 2018 winter although I had a few calls just this past week.

This past weekend, the Dr and I were attending the Top of the Lake Snowmobile Museum's annual trail ride and show event. Randy and I drove the trails for most of the day on a warm afternoon with temps in the upper 30's.

IMG_1229-001.JPG (45.8KiB)Viewed 13308 times

It's temperatures like these that I get a little worried about. But we richened up our carb settings and ran easy all day and had no issues.

Something I thought about while riding that day was in addition to all the things we have already talked about, another factor to how hot your engine gets is the load you are putting on it. How easy your Diablo tracks turn and how hard the sled is to pull. We have going for us a couple of good things:

- All our bogie stations have lubrication zerks in them. I inject oil into my stations and they turn free as can be. This is probably the biggest opportunity to make your Diablo roll a bit easier.
- We have wear skins on our skis. No matter the weight, they pull super easy across the snow.

If your Diablo is working hard and add to that the warm temperatures, that is another reason pistons can burn.

IMG_1234-001.JPG (39.86KiB)Viewed 13308 times

We enjoyed the weekend. Had good weather. Met some new friends and caught up to old friends. And of course, Randy was Randy.

IMG_1233-001.JPG (32.81KiB)Viewed 13308 times