Rm125 cylinder swap help

travo375
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travo375
So I know a 05 cylinder will work on a 04 but will an 06 also work on 04? Also will a 05 head work on a 06 cylinder? I have so many random year parts laying around an I’m running a sleeved cylinder on my 04 an it’s time to upgrade so I’m trying to make something work.
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40acres
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40acres 7/31/2019 11:17am
7/31/2019 11:17am
2004 has a longer stroke, so you would have to change the connecting rod as well. The head/cylinder on a 2005/2006 rm125 are exactly the same.
travo375
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travo375 7/31/2019 11:25am
7/31/2019 11:25am
40acres wrote:
2004 has a longer stroke, so you would have to change the connecting rod as well. The head/cylinder on a 2005/2006 rm125 are exactly the same.
Are you 100% on that because when you buy a crank assembly it’s the same part number from 04 to 07? Plus I no 100% a 05 is a direct bolt on just have to use the 05 powervalve as well.
40acres
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40acres 7/31/2019 11:30am
7/31/2019 11:30am
I'm not 100%, I'd say 98%. I don't know where you're looking up parts, but 02/03 use the same crank assembly and 04-06 are all different part numbers.

Looking at specs for those year ranges the stroke on a 2004 is 55 and the stroke on a 05/06 is 54.5.

I had this same issue on an 04 that had an 03 cylinder on it. Had to rebuild crank with the 03 con rod. I know it's a different direction in respect to year models, but I learned the hard way buying an entire crank for what I thought was an 04 cylinder.
slipdog
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slipdog 7/31/2019 11:44am
7/31/2019 11:44am
'04 to '07 cranks are the same. They went from a 102mm rod('03) to 110mm in '04.They also changed from domed piston('03) to flat top in '04 but '04 through '07 should all interchange. Stroke is 54.5mm an all 125s back well into the '90s
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travo375
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travo375 7/31/2019 12:15pm
7/31/2019 12:15pm
slipdog wrote:
'04 to '07 cranks are the same. They went from a 102mm rod('03) to 110mm in '04.They also changed from domed piston('03) to flat top in...
'04 to '07 cranks are the same. They went from a 102mm rod('03) to 110mm in '04.They also changed from domed piston('03) to flat top in '04 but '04 through '07 should all interchange. Stroke is 54.5mm an all 125s back well into the '90s
Thanks that what I thought. I have an 05 head an pv with an 06 cylinder an going to put it on an 04 so I hope it all works out. I also have an 05 pv governor I’m told I need to use.
travo375
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travo375 7/31/2019 12:32pm
7/31/2019 12:32pm
40acres wrote:
I'm not 100%, I'd say 98%. I don't know where you're looking up parts, but 02/03 use the same crank assembly and 04-06 are all different...
I'm not 100%, I'd say 98%. I don't know where you're looking up parts, but 02/03 use the same crank assembly and 04-06 are all different part numbers.

Looking at specs for those year ranges the stroke on a 2004 is 55 and the stroke on a 05/06 is 54.5.

I had this same issue on an 04 that had an 03 cylinder on it. Had to rebuild crank with the 03 con rod. I know it's a different direction in respect to year models, but I learned the hard way buying an entire crank for what I thought was an 04 cylinder.
Sorry part numbers off aftermarket cranks not oem. Anyway your issue was the 03 cylinder. Like slipdog said they changed the piston shape in 04 to a flat top piston which required a longer rod I believe but I’m no expert. I know from 05 an up the cylinder an head are way better as well as pv timing.
slipdog
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slipdog 7/31/2019 2:29pm
7/31/2019 2:29pm
40acres wrote:
I'm not 100%, I'd say 98%. I don't know where you're looking up parts, but 02/03 use the same crank assembly and 04-06 are all different...
I'm not 100%, I'd say 98%. I don't know where you're looking up parts, but 02/03 use the same crank assembly and 04-06 are all different part numbers.

Looking at specs for those year ranges the stroke on a 2004 is 55 and the stroke on a 05/06 is 54.5.

I had this same issue on an 04 that had an 03 cylinder on it. Had to rebuild crank with the 03 con rod. I know it's a different direction in respect to year models, but I learned the hard way buying an entire crank for what I thought was an 04 cylinder.
travo375 wrote:
Sorry part numbers off aftermarket cranks not oem. Anyway your issue was the 03 cylinder. Like slipdog said they changed the piston shape in 04 to...
Sorry part numbers off aftermarket cranks not oem. Anyway your issue was the 03 cylinder. Like slipdog said they changed the piston shape in 04 to a flat top piston which required a longer rod I believe but I’m no expert. I know from 05 an up the cylinder an head are way better as well as pv timing.
I believe the cylinders of the '04+ are taller for the longer rod and flat top piston is designed to work with the '04+ toroidal head design
Bruce372
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Bruce372 7/31/2019 3:40pm
7/31/2019 3:40pm
I ran a 2005 cylinder on my 2004.

You have to use the 2005 power valves in the 2005 cylinder since they won't interchange. Its also advisable to use the 2005 powervalave governor since it opens at the right time.

The 2004 and 2005 heads will interchange, but the 2005head has a much better profile
Falcon
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Falcon 8/5/2019 2:30pm
8/5/2019 2:30pm
Also remember guys, the length of the rod does not change the stroke length; only where the stroke operates in relation to the crank center. Clearly, a different length rod requires a different cylinder or a spacer at the base, but it will not change the displacement of the engine.
travo375
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travo375 8/6/2019 4:43pm
8/6/2019 4:43pm
Bruce372 wrote:
I ran a 2005 cylinder on my 2004. You have to use the 2005 power valves in the 2005 cylinder since they won't interchange. Its also...
I ran a 2005 cylinder on my 2004.

You have to use the 2005 power valves in the 2005 cylinder since they won't interchange. Its also advisable to use the 2005 powervalave governor since it opens at the right time.

The 2004 and 2005 heads will interchange, but the 2005head has a much better profile
Do you know if a 05 power valve gov. Would be beneficial to use if I kept using the 04 cylinder. Also are you saying I can use the 05 head on the 04 cylinder? Sorry for all the questions I’m still learning.
Bruce372
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Bruce372 8/6/2019 5:10pm
8/6/2019 5:10pm
Yes and yes.

I ran a 2005 governor on my 2004, it was later on that I went to the full 2005 cylinder setup.

The 2005 head should work because it's the same piston and cylinder height, the head is a better design but indont know if it will compliment the 2004 cylinder... notnsure it will make much difference.

No matter what, take lots of measurements and make sure nothing is setup stupid before running it. Nothing worse than Frankenstein engines....

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