Rm 250 T / Pe 250 X barrel difference

[oldfart]

Just spent the last hour measuring and comparing the 2 barrels and there seems to be no difference .
Ports sizes and positions are within .5 mm of each other
Or is there one and I have over looked it .

[LWC82PE]

with the PE's its the barrel fining and rubbers that are the main differences, but also look at HP figures. 81 and 82 PE have suposedly got more HP than the T. im yet to be able to view/print my 250 z microfiche card but i would like to see the barrel part number on that one.

i think your onto something here. i reckon the X and Z PE 250 could use the T model RM barrel. that would explain the HP difference maybe? hmmm but the MX porting wouldnt be right for a enduro bike?

[oldfart]

Lieth    you have read me well, trying to suss out why the Pe have that little extra gain over Rm set up , disregarding the fly wheel 
I have traced the ports on both barrels and done an over lay , there's nothing in it.

[Lozza]

The timing is of more importance, then ports were all pretty crap back then anyway. An easy way to look at Time/Areas is to do a rubbing on graph paper and count the squares.

[LWC82PE]

ive got port maps for PE 175 T/X and RM 125 T and possibly N as well as RM 250 B and PE 250 B, but i dont think i have any on RM 250 N/T or PE 250 T/X/Z

there are higher compression ratios amongst all this too. i was looking at this the other week. They bumped the compression up on later PE 250's. i think the 80 was a little lower ghan X/Z, this was just done by different head gasket thickness.

[oldfart]

timing , as in stator base plate  adjustment or CDI unit  

[LWC82PE]

i think he means port timing, (and not port size) and when the piston opens and closes the ports

[LWC82PE]

have you measured the PE -X barrel and compared to measurements of PE-T barrel?

[oldfart]

I have about 10 barrels on the bench  Rm 250 N-T  Pe  T-X  and there is SFA difference
Rods and Pistons are the same .

Getting back to the Institute  - Just measured stroke centres and there appears to be 3mm difference

 

[Marc.com]

never under estimate the difference 0.5mm makes in a 2 stroke port. Of course there is the pipe to consider. Tuning is always a combination of ports/ pipe/jetting and how you hold your mouth.

[LWC82PE]

how the hell do you port a engine with a porting tool and get into those tight, difficult to reach spots to tollerances .5mm or less i will never know. must be an art to it. how do you get in there and measure with calipers/ruler etc and measure this accuratly?

[oldfart]

I used a piece of cardboard rolled up to form a cylinder , dropped it in one bore and rubbed it so as it left an outline of ports. Spent half an hour to cut the holes so they matched up perfectly with the one I had traced , then tried it on all the others with pretty much the same results 
I'm stuffed if i know how you would get a die grinder into those reed tranfers .
Not one of my barrels has had any port work done . Most of the work has been on the intake and base ports ( what ever they are called ) 

[Lozza]

That's like sealing the shocks ,a trade secret Leith, and why I command the big $$$   . Half a mm is production tolerances nothing more and any affects (if at all) depend on rod and stroke length. A thing to look for on ported cylinders is a knife edge on the transfer dividing fin which indicates the hands of an amature at work.I always work in mm from top of the barrel and use the sine rule to calculate degrees from that.

[LWC82PE]

why does a knife edge at the edge of fin between the transfers indicate amature work?

was boost ports the term you were looking for oldfart?

[Lozza]

Because it shows that whoever did it has NO understanding of gas dynamics.Show me a pic of a LEADING surface/edge of a chopper rotor, plane wing, open wheel race car wing, push bike helmet or anything else that goes fast(besides a boat bow) that is sharpened to a point.