I’ve been looking forward to this rebuild for 2 years. Not because I enjoy the thrash (I think we all wish engines would last forever), but because this is the first time I’ve ever gotten to do a real long term comparison of 2 stroke oil brands and ratios. While my methods and results would get laughed out of a lab they tell me what I needed to know for my engine and riding situation.
Here are the piston, ring and power valve comparisons from the 2010 rebuild
Engine One 2010
- New Wossner Piston
- Refinished nikasil cylinder
- Ring ends gapped at .013”
- Oil PJ1 Gold Mix used at recommender 32:1 ratio
- Engine was then used for approx. 160 hours of trail riding
Findings during 2012 Rebuild
- Ring gaps were between .023” and .028”
- - Signs of blow by were almost no existent
- Piston was extremely worn on the exhaust side, no vertical scratches, but there was a at least a .003” of wear on the exhaust side that started a half inch below the rings and continued down near to the bottom of the skirt. Almost exactly the same shape as the exhaust port. (more on that later)
- Power valve was extremely dirty. At least 1/8” of more of buildup. Exhaust port and pipe were also covered with thick deposits. The pipe was so plugged up I decided to replace it rather than clean it (it also had some bends and dents)
- Piston crown and head were very clean.
Piston, ring and power valve comparisons from the 2012 rebuild
Engine Two 2012:
- New Wossner Piston
- Ring ends gapped at .013”
- Motul 800 2 Stroke Oil used at recommender 50:1 ratio
- Engine was then used for approx. 180 hours of trail riding
Findings during 2014 Rebuild
- Ring gaps were between .028” and .032”
- Considerable blow by below lower piston ring
- Piston is slightly worn on the exhaust side, no vertical scratches. There are still faint factory machining lines on most of the exhaust side and even the grey coating Wossner puts on the piston was visible in many areas.
- Power valve has very little buildup on it. No more than 1/16” and barely anything other than a sticky film in some spots. Exhaust port had only a brown oily film that wiped off with a rag and brake cleaner. The pipe has deposits, but only about ½ what the PJ1 pipe had.
- Piston crown had considerably more deposits on it than the last one, but they were evenly spread and brown. Head had a slight frosting of carbon that wiped off with brake cleaner.
I should point out that a number of mods were made to the engine in 2012 including a reshaped combustion chamber (that added considerable compression), porting and some case stuffing. All these changes should have equated to greater engine wear, yet they didn’t.
The only reason I wanted to run 50:1 is so that I don’t need to bring a gallon of oil with me on my rides. I was certain the reduced oil content would cost me in reduced piston and ring life, but considering the additional 20 hours the 50:1 engine had and that the only measurable difference to the reduced oil ratio was slightly more ring wear I will never go back to 32:1.
I said I’d get back to the piston wear on the exhaust side of the first engine. I’m thinking that the carbon buildup in the 32:1 engine may have caused that as I recall smooth carbon formed around the port that was likely wearing on the piston.
It also seems that Motul deserves a shout out here. Seems they make decent oil that doesn’t cost a lot more than others. However I’m not sure if I should use it again, or try an 80:1 Amsoil oil to see what happens. On one hand 80:1 would be so easy to carry around in my backpack, but on the other hand we do a lot of high speed riding between trails and I cringe at the thought of being pinned out at 80mph for 5 minutes at that ratio. Maybe better to let someone else do that test.
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Originally Posted by Blue Viffer
