magyarbacsi

I have an article (Homelite mods)that stated that to measure transfer port timing, line up top of piston with top of transfer prts, viewed through exhaust port, and measure the degrees it taks as piston travels upwards till the piston closes the xhaust port. I get generally 24-30 degrees, depending on what motor. I read several posts that state 120-130 degreesis desirable. Obviously the higher numbers are obtained using a different method. If I understand correctly, the numbers are obtained in measuring the length of time in degrees the exhaust is open before the intake transfers open. Carlos, on shark racing site mentions 24-30 degrees, then gives an overall measurement of a much higher degree.
So what is the correct way and what numbers to seek on a not so wild modification and retain a good idle. This is a 260 in a 20# Thundercat look alike.

BajaBob-delete

The numbers quoted are generally duration numbers,not the relation to one another unless so stated.If you don't understand these numbers maybe you need a refresher on the operation of two stroke engines.

magyarbacsi

Thanks for the advice , Bob, but I was hoping for information. And if you are willing to provide such, I will listen. Actually read.I understand that such measurement are in degrees of the crank rotation between the time the exhaust port opening and the transfer port opening to lower the pressure in the chamber to that below the transfer port. Thus the entering charge forcing the burnt gas out of the chamber and allowing fresh charge to enter. In one instructional page it said to line up top of piston to top of transfer port and measure in degrees how long it takes to close the exhaust port, in degrees. As I said, depending on what motor, this is usually between 24-30 degrees. I have seen articles where, e.g. on a 230 rc motor, 130 degrees is desirable. It is obvious that different reference points are used.

OLD_SLOW and in the WAY

there are two schools of thought here. with a degree wheel mounted and a pointer on the engine rotate the degree wheel to zero then count the degrees the port is open so its either gonna be a big number like 120+ or a small number like the 24 to 30 degrees it all depends how you look at it.
here is a degree wheel you can print out and back it with a carboard or plastic then make a pointer that will fasten to the engine. there are lots of sites that deal with using the wheel.

good luck

magyarbacsi

Thanks Larry. I have a degree wheel and used it to change intake and exhaust timing, but have not messed with the transfers yet as I was not clear on points of reference, i.e. measure between what two points. So if I line top of piston with top of transfer port and use this as zero degree, rotate crank and move piston down. This opens up the port. Then continue the rotation, piston to BDC then keep rotating until it moves up again and stop at the top of transfer port, my starting point, is this my duration time in degrees?

OLD_SLOW and in the WAY

its the total amount of degrees the transfer port is open to scavenge the burnt gas out of the cylinder

BajaBob-delete

Heres a link for you with a ton of of info,

[link=http://www.macdizzy.com/index.htm]Macdizzy[/link]

magyarbacsi

Thanks Bob. interesting board. I understand now that the large numbers refer to the time from the piston on its downward travel, after opening the exhst. prt, exposess the transfers and as the piston reciprcates and begins to move up, eventuaty coses the transfers and this is the larger numbers, i.e. duration.
Thanks again.