One possibility for the piston being clean where the squish band is is because the piston is able to effectively transfer its heat to the cylinder head and carbon gets washed off the cooler parts of the piston like the spots near the trasnfer ports. There's probably other reasons but that is my educated guess as to the main contributor.
661 Oil Test 32:1 vs 40:1 vs 50:1 ?
- Thread starter redbull660
- Start date
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Trx250r180
Saw polisher
I will add the mobil is one of the least offensive smelling oils i have ran ,dumonde was a little less smell but not much ,working over my post hole drill the mobil does not make me sick like some other oils ,not that any exhaust should be breathed in ,but it happens .
I suspect you see more carbon on the milling 660 due to higher temps causing the carbon to cake up on the crown. I also suspect that's why it's cracked. I would at a minimum open up the cage, if not completely remove it. I understand you want to keep the noise down, but that heat needs to get out.
I can tell the 660 was ran at steady throttle. That glassy look is typical of that. Also all of the pics show overly rich tuning.
Trx250r180
Saw polisher
I have 2 modded mufflers for it ,i guess will have to break out the stihl ear muffs ,one of Redbulls test mufflers i need to try out ,with modded baffle and extra side port ,and the one Randy gutted when built the saw .The gutted one gave me a headache after a while is why put the stock one on with dual front cover to let some heat out .
Go with a gutted body and a single large opening.
Trx250r180
Saw polisher
I have it set to clear up ripping with a 32 inch bar ,it 4 strokes bad when back out of the cut ,as hard as the constant load is i feel safer a little rich on the mill . Loaded the engine pulls pretty smooth
Wasn't an indictment, but rather an observation. And only brought up because tuning greatly effects deposits and piston appearance.
Ron660
Addicted to ArboristSite
I personally prefer Randy's modded muffler (factory DP originally) on my 660. It breaths really well.
Ron660
Addicted to ArboristSite
I wonder why my ported 660 is really clean inside although I tune a little rich. Well 13400-13600 isn't that rich in my book if it cleans up in the cut. I took this pic today. Last several tanks were 93 non-E and using only Motul 800 off-road at 32:1.
Ron660
Addicted to ArboristSite
Ron660
Addicted to ArboristSite
800 has difficulty reaching full combustion when ran rich. Your saw is a great example.
This MS 260 has been ran since new on Motul 800. I bought it nib this summer. It's been tuned spot on and this is a good example of what the muffler should look like and what the exhaust port looks like when not washed by raw fuel.
Ron660
Addicted to ArboristSite
I would say it's the excellent detergent/cleaning additives. The current tune cleans up well under load especially noodling. It definitely sounds better noodling. That puts a good load on it.
Ron660
Addicted to ArboristSite
My ported 036 looks extremely clean also. I could lean-it-out more and see what happens. I still think higher compression ported saws benefit using racing (higher viscosity) oils.
See my pics. It's fuel washing the port and piston clean and gunking up the muffler as a result.
Four stroking is so rich the motor is drowning in its own fuel. Because it cleans up under load doesn't mean your not rich.
Racing oils are not universally higher in viscosity. They really run the range.
KG441c
Keith
Im liking hp2 so far as good as any oil Ive used
With 800 in saws that don't mill it looked like Ron660 piston and muffler. Milling with it it burns completely. Granted when I used a liter of the stuff up it was summer time and aim the 90s. The bar oil would boil and I couldn't touch any of the area around the front of the saw without gloves.
