transfer ports and passages theory

Jason Luther /

so when the piston is at TDC should the transfer ports on the piston skirt line up with the transfer ports in the cylinder. and if so why? wouldnt the gases just be making loop? perhaps its to prime the transfer passage. anyone?-jason

Re: transfer ports and passages theory

transfer ports on the piston? Do you mean piston skirt's cutouts or does that piston have holes bored through it?

Sometimes they bore holes in the piston that match up with boost (additional transfer) ports .. this might be to increase flow or perhaps to cool the top of the piston crown or to help lubricate the 'little end' of the connecting rod and cool the underside of the piston crown...or.. it depends.

Re: transfer ports and passages theory

Jason Luther /

the cut-outs on the piston skirt. im thinking its just a coincidence that they kind-of line up with the transer ports in the cylinder-jason

Re: transfer ports and passages theory

Don Pflueger /

tomos a35 engines have the transfer ports in the piston. they line up with the cylinder port at tdc because a vacuum is created in the crankcase at tdc and this vacuum draws the fuel in. as the piston moves back down the fuel is pushed up thru the tranfer port into the cylinder.

Re: transfer ports and passages theory

If the sides of the cutouts are narrow, they can and should be enlarged if they block a portion of the transfers passage.. the limit is the exhaust port which the skirt must always cover with a few millimeters to spare.

But on a stock bike the strength of the piston is at stake and the cutouts are probably OK the way they were made.. smoothing everything over can't hurt..

I guess cutouts do have a purpose or two.. they make the piston lighter, provide easier transfer flow up the side of the piston especially when near BDC.. maybe some other things.

Re: transfer ports and passages theory

if i understand you correctly, that's a new one on me.. i never heard of a piston with transfer grooves cut into the side of the piston.

Re: transfer ports and passages theory

Jason Luther /

okay, but the transfer takes place as the piston is moving from tdc to bdc. so if at tdc the cutouts in the piston line up with the transfer ports in the cylinder, the air is just making a loop. the only reason i can think of is, like joe said, and easier way for the top end to get lubricated, and/or priming the transfer passages.. i only ask because i think the piston that came with a morini engine i got wasnt the correct piston, ive sense cut away alot of the piston to get much better performance. and the cutouts in the piston didnt even come close to matching with the transfer ports in the cylinder.-jason

Re: transfer ports and passages theory

Jason Luther /

or its just a coincidence, and it serves no function

Re: transfer ports and passages theory

Don Pflueger /

not grooves. ports. it has openings in the side wall. i'll take pics later today to show everyone who's never seen them.

Re: transfer ports and passages theory

Don Pflueger /

ive never seen a morini engine that had a piston with cut outs on its side. i doubt its the right piston.

Re: transfer ports and passages theory

See Ya Moped Army /

Don, here is a Morini piston that has what looks like cutouts, but they do not actually go through the piston walls.

1104757351_morinipiston.jpg

Re: transfer ports and passages theory

Don Pflueger /

i have seen those, but they are not on the port side of the piston. i dont think those holes will cross a port at all.

Re: transfer ports and passages theory

Don Pflueger /

here is a pic of the side ported piston used in an a35. the bottom of the port measures 28mm from the edge of the crown. the top of the transfer port measures 34mm from the top of the cylinder. so the port in the piston travels up past the transfer port therefore sealing it by 8mm at tdc, not lining up with it as i thought it did. so at bdc must be when they are lined up, but i dont have the measurment of the stroke to confirm this. for some reason i thought they opened up on the upstroke which created a vacuum, then as the piston moved downward it pushed the fuel up into the cylinder thru the side transfer ports which are located in the cylinder at the wristpin side of the piston. i was off in my thinking the first time so i hope this clears things up some.

1104766823_dcp_1811.jpg

Re: transfer ports and passages theory

Steamboat Aka J. R. Stevens /

Being a 4-stroke man< I have had problems understanding the term transfer ports. I just think of them as fuel intake ports that transfer fuel from the crankcase to the cylinder. Am I wrong? some drawings I have seen show more than one transfer port.

Re: transfer ports and passages theory

Don Pflueger /

most two strokes have two transfer ports. i guess this is to allow maximum use of all the fuel that is pumped into the crankcase. i'm more of a four stroke man myself since i do more lawn and garden repair work than anything. but two strokes are simpler and very easy to understand if you have a basic knowledge. i like more complex engines with lots of moving parts and things that need to be timed. and growing up around cars really quelmed my interest in that manner.

Re: transfer ports and passages theory

i saw the pix posted down there... and it's much clearer now.

it looks like the purpose of the holes is cooling and lubricating the underside of the piston.

Re: transfer ports and passages theory

Don Pflueger /

no. they allow the fuel to enter the crankcase first. they line up perfectly with the intake port. and the transfer ports are 90 degrees off from these holes, so its the only way for fuel to enter the engine. maybe they do help in cooling some, i dont know. but they are clearly for the transfer of the fuel/air/oil mix into the engine.

Re: transfer ports and passages theory

ok.. we're talking about intake, not transfer. Now it fits. It's hard to picture it without having the parts in front of me.

I do believe they did it that way primarily to lube the little end of the connecting rod which, using normal intake/transfer methods, is lacking since the rod end and piston pin are in a spot where mix is not circulating well.. Circulation is relatively stagnant up inside the piston.

Re: transfer ports and passages theory

Don Pflueger /

could be. like you said, to lube the rod bearing. or for cooling. i dont know. they call it a transfer port too so it is confusing.

Re: transfer ports and passages theory

Maybe i am missing something, but if the piston is at bdc when the holes are lined up then there is no fuel going into the holes, rather the fuel is being sucked in through the intake port which is currently exposed and the exhaust is currently sealed at bdc. PLUS, if the gas went through the side holes then it would drop into the crankcase and not do anything, leaving the engine dry. All fuel reactions must take place ontop of the piston. I'm almost certain that the holes and cutouts are to both lighten the piston and to insure good cooling. What im really interested in is how you "lightened" the piston without messing up its balance creating it to grind one side of the cylinder, or create excessive heat.

Re: transfer ports and passages theory

Jason Luther /

is this what all morini pistons look like? if so i definatly dont have the correct piston. but it runs great now that i cut it all up to work.

Re: transfer ports and passages theory

Jason Luther /

non of the pistons on any of my peds have the side transfer cut-outs like an A35. im talking about the cut-outs in the skirt that are on either side. i understand their function at the bottom of the stroke, but not at the top. i can see why everyone is getting confussed now.

Re: transfer ports and passages theory

according to this A35 repair manual: Page 35 and 36

http://www.mopedriders.org/article_view.php?faq=2&fldAuto=21

the engine uses reed valves.. It is not a piston-ported intake engine.

So, in this case, the piston can open or uncover the intake port for 360 degrees of rotation if desired. The reeds control intake according to piston pumping action. Intake duration is not controlled by uncovering a port.

On many reed engines the reed block is right on the crankcase so you do have technically have 360 degrees of "intake" .. but in this case, on the A35, reed block communicates with the cylinder. Since it is on the cylinder, intake fuel mix can go straight into and through the piston hole and lube the little end directly.

Re: transfer ports and passages theory

Don Pflueger /

the holes in the piston ar the only way for fuel to enter the engine thru the intake port. the transfer ports are located 90 degrees from the intake. so the charge enters the crankcase, then gets pushed up thru the transfer ports into the cylinder top. i didnt measure to see if its exactly bdc, but it is close. whatever point they line up at is when crankcase vacuum is just about at its peak.

Re: transfer ports and passages theory

Don Pflueger /

most of the ones ive seen were solid.

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