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Author Topic: RM250 Rebuild  (Read 16877 times)

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Offline TMKIWI

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RM250 Rebuild
« Reply #15 on: March 08, 2013, 10:51:25 PM »
Quote from: evo550 on March 08, 2013, 03:22:26 PM
What's your DC plastics like?

Had no problems with the set on the 125.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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« Reply #16 on: March 08, 2013, 10:52:31 PM »
Quote from: opfermanmotors on March 08, 2013, 10:42:02 PM
2 Stroke ports are "chamfered", i.e. rounding off the ports so they aren't sharp edges.  This prevents wear and tear on the piston and rings as they pass over the ports (i.e., like going past a gillotine every stroke!).  4 Strokes have valves at the top so they don't have to worry about that :)

Yep know all that.
Was talking about the 'ramp' in the inlet tract.
« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline TMKIWI

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« Reply #17 on: March 08, 2013, 10:54:52 PM »
2T Instutute.
Do you know Peter Sales. Was thinking of sending the cylinder to him for some work.
Or there is Wobbly.
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Offline 2T Institute

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« Reply #18 on: March 08, 2013, 11:54:22 PM »
Never heard of Peter Sales and he's never heard of me I suppose  :D Post a pic of the inside and the bottom of the cylinder, check for +ve or -ve deck height and give me the rod length, stoke and measurements from the cylinder top and I'll give you some pointers.
Truth is you can buy the stuff and do it yourself
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Offline TMKIWI

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« Reply #19 on: March 09, 2013, 01:42:26 AM »
Will do.
Cylinder getting bored this week.
Will check deak heights etc and let you know.
I have a die grinder and have done abit myself just thought if it was worth paying someone with abit more experience.
Cheers.
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Offline 2T Institute

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« Reply #20 on: March 09, 2013, 05:49:47 AM »
NO DIE GRINDERS.
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Offline TMKIWI

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« Reply #21 on: March 09, 2013, 06:38:21 AM »
Well a dremel then.
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Offline 2T Institute

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« Reply #22 on: March 09, 2013, 07:44:59 AM »
Much more like it  :D
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Offline opfermanmotors

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« Reply #23 on: March 09, 2013, 05:37:49 PM »
Quote from: TMKIWI on March 09, 2013, 06:52:31 AM
Quote from: opfermanmotors on March 08, 2013, 10:42:02 PM
2 Stroke ports are "chamfered", i.e. rounding off the ports so they aren't sharp edges.  This prevents wear and tear on the piston and rings as they pass over the ports (i.e., like going past a gillotine every stroke!).  4 Strokes have valves at the top so they don't have to worry about that :)

Yep know all that.
Was talking about the 'ramp' in the inlet tract.

Ah ok, I misunderstood since the last picture of the ports was the one shown by the question and I skim read so I just saw Ports, the last picture and assumed it was the chamfering lol

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Offline _X_

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« Reply #24 on: March 09, 2013, 06:15:26 PM »
my A$$ is chamfering from sitting on it all winter.
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Offline TMKIWI

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« Reply #25 on: March 10, 2013, 06:14:24 AM »
Problem.
The rod I ordered which the online fisch said was the superseded part number is too long.
Standard length 122mm. This rod 128mm.

Question. Should I make this a long rod motor.?
What negatives would there be , if any.?

I have access to a water jet to make the 6mm base plate.
Bore 72mm stroke 64mm.
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Offline 2T Institute

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« Reply #26 on: March 10, 2013, 08:31:47 AM »
1. a)YES b)NO
Looks for a piston with 6mm less comp height  ;) or cut the spacer plate.
What is the comp height, gudgeon pin size ,  length of your piston bottom of skirt to timing egde and distance to bottom of exhaust port.
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Offline TMKIWI

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« Reply #27 on: March 10, 2013, 09:58:00 AM »
I'll do a measure up tommorrow.
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Offline TMKIWI

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« Reply #28 on: March 11, 2013, 07:19:23 AM »
Current specs.

Bore 71.5mm   Stroke 64mm
Rod length 120mm ( Not 122 ) .
18mm gudgeon pin.
Centre of gudgeon to piston edge 33mm
Piston skirt length 69mm.

FPV      25cc
HGV     6cc
DHV   +2cc or 0.5mm
PCDV   11.7cc

Porting.
From top of cylinder.
Exhaust 33mm-65.8mm
Inlet       52mm-64mm

Will post some pictures shortly.
Cheers 2T.



« Last Edit: December 31, 1969, 04:00:00 PM by ' »
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Offline 2T Institute

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« Reply #29 on: March 11, 2013, 09:00:03 AM »
Sure it'a 22mm gudgeon not a 18mm? Height to top of A,B and C ports What is the distance from top of pin bore to timing edge? Positive or negative deck height?

Quote
FPV      25cc
HGV     6cc
DHV   +2cc or 0.5mm
PCDV   11.7cc

flat plate volume 25cc
dome is 6c
What are the others?
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