I've had this question in my head for over 30 years.
"How is a 2-stroke piston/crank assy lubricated while going downhill with a closed throttle"?
Seems to me that should be a deadly combination....but I've never had any problems doing it. Why hasn't my bike seized??? There are times in my area that I will be going downhill with very little to no throttle for several miles...at over 5000rpm.
If you went out into the garage, popped off the jug, and turned the bike upside-down, you would be shocked on how much oil pools in the bottom and dripped out.
Bob's not kidding. I took the cyl. off of my old 1990 to check tolerances, and it looked like somebody dumped a bottle of HP2 down the case before I took it apart. And I ride in the sand all the time WOT most of the time!
40:1 here cuz i run wide open quite a bit.. I know lots of fuel = lots of oil but running at extended periods of high rpm's i want to make sure my stuff stays well lubed..
32:1 here. Conversed with the builder of my main motor (not Glen) this past weekend while I was up in the Napa Valley and he told me to spin that thing 9500rpm. At that kind of rpm theres no way I'm running any less.
Its on a kart... We'll find out what it does this weekend at 9500. I've got the gears to do it and a tach to tell me I've done it. Worst that can happen is it goes boom and I do a 10-15 minute swap and put my fresh GSS motor (pictured) on.
I've thought about having it dynoed just for shits and grins... maybe I will at some point.
[quote="fastkart"]Its on a kart... We'll find out what it does this weekend at 9500. I've got the gears to do it and a tach to tell me I've done it. Worst that can happen is it goes boom and I do a 10-15 minute swap and put my fresh GSS motor (pictured) on.
I've thought about having it dynoed just for shits and grins... maybe I will at some point.
Last edited by Skidmark on July 8th, 2008, 12:33 am, edited 1 time in total.
OK, so we've come to the conclusion that there is a bunch of oil pooling around in the bottom of the cases. That tells me nothing about what is taking place on my piston, rod, wrist pin, etc....... The air passing over said "pool of oil" in my cases is VERY unlikely to pick up much (if any) oil on it's way through to the top of my engine............or am I wrong?
More detail please.
Oh, and to add one more 2-stroke mystery. Why on decel, does the motor catch every so often with a nice "ping" then back to bogggg like it should be?
OK....Hell I'm asking for the world already so here's another. I'm on my 1974 DT250A idleing while chatting with a friend. She runs out of gas....leans out...revs to the moon (1000rpm beyond redline)...I TURN THE KEY OFF.....and she's still redlining her little brains out for about another 3 seconds until I gather myself and dump her into gear to kill the motor. WHY DID THAT HAPPEN ??? Was she dieseling?
Hey thanks guys!!! "Skiddy" here needs a little 2-stroke 101.
AlisoBob wrote:If you went out into the garage, popped off the jug, and turned the bike upside-down, you would be shocked on how much oil pools in the bottom and dripped out.
Oil is everywhere.....
So should I put to market my idea of a drain plug for the lowest part of the expansion chamber (ala trumpet spit drains)?? Theoretically, that oil is displacing a certain volume from a very acurately measured expansion chamber, technically changing the location of the "powerband" via altering the volumatric efficiency of the chamber.
The oil forms a thin film on all the moving parts and the lining of the crankcase. The oil is not pooled when the engine is running. The film is constant, but individual molecules are cycled through - added by new pre-mix and lost via the exhaust gases. Depending on the pre-mix ratio oil make take more or less time to be cycled through. At 40:1 this is nearly 2 minutes. The film would have minimal effect on the working crankcase volume and therefore the power characteristics.
Maybe if the engine continued to run at artificially high revs with the throttle closed for a long period of time, eventually it would seize. But nothing one would worry about in normal use.
redrocket190 wrote:The oil forms a thin film on all the moving parts and the lining of the crankcase. The oil is not pooled when the engine is running. The film is constant.
now, it CAN AND WILL seize if dragging too long without any additional oil. Justin (MFDB) seized his 500 doing a dyno run because he left it in gear waiting for the drum to slow down.
I engine brake down the hills at dumont (which some of you know can take a while) and haven't damaged anything in the process. I run 44:1 927.
basically to damage the motor to have to keep it turning for a long time without any extra oil, a long enough time, you will probably never run into a hill on your bike tall enough to squeek you engine braking down it.
'09 kx450f 4-Poke
Gen-4 trail bike --SOLD--
Gen-3 badass trail/mx bike --SOLD--
Gen-1 built dunes bike --SOLD--
'05 klx110 --SOLD--
'95 pw80
you shouldnt use compression braking on a 2 stroke. on a four stroke it is fine but most ring vs. exhaust port damage occours when decelerating using the motor to pull you down. its best to just pull the clutch and use your brakes.
i dont own assault rifles, i own homeland defense rifles!!!!
I know lots of fuel = lots of oil but running at extended periods of high rpm's i want to make sure my stuff stays well lubed..
