RM180??? Errricccc any chance?

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#1
So if we can easily make an RM125 into a 144cc bike with piston alone...

Is the new RM125 rod on the 2004, actually 8mm longer as the mags are saying, or is it repositioned to give 8mm of stroke or ???

I could see 8mm more, an aluminum plate with two base gaskets (not the best I know) and 180cc's of retro rocket! NOW THAT, would be cool...

Any chance it would work Eric? Rich?

Mike
 

bclapham

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#3
Mikey:

the 2004 rm125 has a longer rod, but it still has the same 54.5mm stroke and 54mm piston, i am yet to see a 04 but i am not sure how the cylinders will interchange easily with the older bikes. as you know, the 58mm big more makes 144cc. what year is the bike??? Last time i spoke with eric, he was building himself a 2002 rm155- 58mm piston with an extra 2mm stroke- its easy to do since the older rm125 (97-99 i think) rod is 2mm shorter so no spacer place is needed. I beleive Eric is getting into doing the stroker kits since the wiseco cranks are available and another company is doing the stroked versions on a kind of off the shelf deal, so the kits are going to be much cheaper than the elaborate work done by a certain shop located not far from glen helen raceway.

from what i understand, if you go any further than 2mm stroke, you run into serious issues with port and ignition timing and your pipe and ignition wont match up with that much increased stroke, and you will also have to wonder how the bike will rev since i am a bit sceptical of some of the 167 dyno curves that i have seen on the net. and then you have to put all of that power through the RM gearbox, asking for trouble IMO.

if Eric reads this, sorry for taking the liberty of answering on your behalf and please make any corrections. there has been a few threads on this before, so do a search on stroking since Eric did an article on this very topic and the rm case study. it is somehting i will consider when by engine gets its overhaul next season if the stroker kit isnt much more than a replacement crank.

and if Rich reads this, come on mate, spill the beans, i am sure you have had your hands on this 155 somewhere down the line:) give us the full scoop.

cheers, Bruce
 

MikeS

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#4
Bruce, Mikeeep

Eric will be doing 2 motors with overbores/long rod and stroking combinations.

I am not sure on specifics on the RM125s.

One thing Eric mentioned is that with the overbores some bikes loose their ability to rev this is do to the port timing. Alot of cylinders get lowered with that piston kit. They become great stump pullers and enduro machines. Just by chance if the 58mm kit has the same pin height as your stocker then a 4 mm stroke and a 2mm longer rod should allow the stock cylinder to go in place without a spacer or cutting the base. I think the longer rod when used with the overbore enhances the ability to rev out more.

I guess that software and all the trial and error Eric has done can only tell the true effects of all this.
 
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#5
That was just a little "made ya look" kinda fun thing. Actually what we're talking about right now (Eric and I) is the 155cc kitted engine.

Eric is already working on his, me - we'll be doing that next. They're going to be monsters even at 155cc verse some of the larger engines that are out there. Hopefull they'll retain some of the 125cc flexibility.

Here is the way I understand it... the longer rod, actually passes top dead center at a slower speed than the shorter rods... this allows a more complete combustion of the gases and thus more power to literally expand/expell the piston back downward ie: more freakin' horsepower mates!

So the idea is to go out there, make the engine run better and we'll use a spacer plate with two gaskets one on either site (we meaning ERIC as I'm just a moto junky just like you guys) and when we're done Eric is claiming that he thinks he can get a pretty substantial number.

What kind of number does he think he can coax with a race porting, and 155cc kitted engine... over 40. He's aiming at 43 stinking horsepower!!!

Think about that for a minute! His is nearly ready to go, so we'll see if the new 250cc killer needs a bit more development or of it's ready to march... hopefully the later, I'm ready to build mine now! LOL

When Eric told me he thought he could get 43hp out of his engine tonight, I sat there silent for a moment to see if he'd giggle or laugh to let me know he was joking... he didn't (giggle or laugh) and suddenly I felt a sick feeling in my stomach... yeah. I'm a power junky. TOO MUCH IS NEVER ENOUGH! haha

Mikeee P
BTW, I'm curious what would happen to one of these engines if you ran the KTM125SX's PWK39.5mm carb on it?!!!
 
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#6
Speaking of RICH...

Hey Rich, I didn't have the chance to ask Eric, is that number he's hoping for on race gas, or on a Rich Rohrich concotion?

Mike
 
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#7
Regular old garden variety race gas ;)
 

bclapham

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#8
Originally posted by MikeeeP
BTW, I'm curious what would happen to one of these engines if you ran the KTM125SX's PWK39.5mm carb on it?!!!
you will fire up the bike, wack open the throttle and hear a big bwwwwwaaaaaahhhhhh and not even make it out of the pits!

for some reason, these bikes run kinda strange with the pwk carbs- i met a guy running a essentially stock rm 125 (02 i think) at the track last weekend, he could get it running well with 48p, 1468 needle and a 6 slide with 170 main with the keihin carb- for some reason, my 144 likes a really rich slide, i had to use a 5 with a 1465 needle just to get it running reasonable, but it still bogs a bit in corners and i have a 4 slide coming but its on back order:(

i first tried a 39.5mm pwk with a 36mm sleeve in the front, and again, i think the opening is just too much to enable the bike to suck fuel through the main/needle circuit and it just bogs when you wind it open.

totally ironic since the stock mikuni tmx38mm was just too lean everywhere no matter what jetting/needles/slides i played with.

that said, i wonder that if even with 43 hp wether i still would have come last on sunday, LOL- maybe i should call eric to see if he can bore and stroke my rm to 450 and stick a few valves in as well :)
 
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#9
Hi guys. Whats the point of stroking and boring your 125 puddle jumpers to 144 or 155 or what ever. What gains do you get from this apart from a little extra HP.

Why not just go out and buy a 250 if you are after that extra grunt, or am I missing out on something here, so come guys spill the beans.
 

MikeS

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#10
Curley

Some of us just want mo-power in small packages. :p Others are fascinated by just doing these projects. Nothing like a CRF50 with a 120cc kit... :scream:

In my case I am in between fascination and reality. We run the 0-200 class offroad. Unless we run a KTM, Gas Gas or old KDX we are out classed to a point. Yes the 125 rips and with the correct rider you can win.  ;)  Junior likes the extra HP over the entire rpm range when you get in trouble and I like tinkering.

Mike