I would like to know what can be told by reading the tops of pistons. Here's two pictures of a engine that has been run maybe 5 minutes, the picture of the cylinder is so you can see the port layout. What are the carbon tracks telling me? It looks like, to me, that the two center transfer ports are flowing the most charge, the outer transfer ports don't seem to be flowing much, and neither does the boost port.

BTW, I'm using Pennzoil aircooled and the carbon is very soft.

i love to hear this all i read is spark plugs

GREAT topic for a thread!!!! Hope to see good information come into this one!
Well done!

Major contributors to carbon and if it's hard or soft on piston and cylinder are type of oil, engine temperature, how much full throttle running it has had as well as total time on the engine.

WRK

You are correct in thinking that a lot of information can be obtained from the piston top, and bottom of the piston is removed. 5 minutes is a little on the low side of the timeline to develop much information.

What you are see is not so much how much is flow but more, how it is flowing. Typically transfer ports are designed to direct incoming charge across the top of the piston and towards the back cylinder wall. Boost ports are usually directly steeply upward.

Remember, loop scavenged engines were originally designed with 2 transfer ports that directed fuel across the top of the piston that, among other things, helped cool the piston. (These ports also direct the new fuel/air charge away from the exhaust port eliminating the need for a baffle on top of the piston and reducing "short circuiting" ). The boost port was added later to help direct the main charge towards the top of the cylinder.

What you are likely seeing is the effect of how the gasses are directed out of the ports. Given that the ports are not all the same, it shouldn't be a surprise that there are also different temperatures and soot patterns.

Bill

The engine has not yet been through the wringer, so reading at this stage is of little use. A good synthetic oil should have left the piston and ring top spotlessly clean, especially at the low loads this engine has been run.
The modern high detergent oils also make piston reading very difficult. (also plug reading for that matter)
More important is the piston inside, where conclusions can be drawn on piston operating temperature, and how near to disaster you have operated your engine, by judging the colour of the oil deposits.

Maybe it's just me but I don't think that engine is going to run very well; you have a big hole in the top of that cylinder. I wouldn't be worried about the carbon trails, you have bigger troubles! [:-]

Pe

Do you have any pictures of the bottoms of pistons to show what to look for?

Rich,

You're still much too early o be obtaining any useful info from the engine. The only thing I can see right now is that you're using a lot of oil in the fuel, the mixture is on the rich side, and like Pe noted, it's a mineral oil. The bottom of the pistons will look ash grey or white if you've been running them too lean, too hard, or too hot.

Hughes500E:

?????????????????????????????????????????????????? ??????

Yes, it's Pennzoil at 32:1, after an hour or so I was going to switch to 50:1. I bought Bell-Ray, I was thinking I would try running one of my MT62s cradle to grave on it. I would have done that with my 366GT, I had ask you about oil, but Scott's the guy warranting the engine and he said start with Pennzoil. The 366GT is broken in so now it will get the Bell-Ray, it's my favorite engine period.[sm=thumbup.gif][sm=thumbup.gif]

Changing oils is not very kind on the engine. The engine will be "confused" for about an hour. Some engines will hardly show it. some others will run worse during that period. It probably depends on the kind of oil change as well.
The same phenomenon has been noticed by investigated Blair and Jennings. Blair used radioactive tracers. When the last trace of radioactivity was gone, the engine ran better again. (Yamaha racing engines under test). It took about one hour for the last tracers to disappear, showing that all old oil had been replaced.
I too noticed a notable and quite temporary reduction in engine performance when I switched from a High detergent low SAE oil to a low-detergent high SAE oil.
In Bugman's report, I also noticed this behavior with some oil changes in the oils he tested.

I'll switch now to Bell-Ray and always run it on it.

I guess the oil molecules get into the metal surface imperfections and stay there pretty well if it takes an hour to purge them.

I like playing so I took rpm readings, then did a few mods to the engine. I cut a window for the boost port, trimmed the crankcases a little, and trimmed the jug .050", who needs a warranty anyway?

Maybe my old eyes are deceiving me, but where is the ring anti -rotation pin, and what is the hole on the land above the ring?

Once you screw a plug in that hole it should be ok.

The anti rotation pin is in that hole, only about 50% of the pin in in the ring grove and it's in a ways so as to have no chance of scratching the wall.