View Full Version : Interesting engine swaps?

11-11-2008, 12:28 PM
Already had an eye on the KTM 690/625 series...They're excellent road-going machines, and obviously make a lot of power.

Question was size, I don't know if that motor would even begin to fit under the petrol tank.

what other right-side-chain motors are out and about? husaberg stuff?

11-12-2008, 08:12 AM
Rotax make a 250cc 2 stroke single that goes in, thats been done a few times. Rotax 257 its called. would be no good for you street guys as it wouldnt pass regs? but for track would be good. there are 2 versions with different gear ratios etc

11-12-2008, 08:51 AM

11-12-2008, 11:23 AM
Also, i think the old 90's Aprilia Pegaso has everything on the right side etc

11-17-2008, 02:45 PM
Rotax make a 250cc 2 stroke single that goes in, thats been done a few times. Rotax 257 its called. would be no good for you street guys as it wouldnt pass regs? but for track would be good. there are 2 versions with different gear ratios etc

Regs mean nothing in my state. much reason why I tagged mine right away.

So whats the price on the 257cc motor? shipping from the UK is cheap for me (thankfully) so I don't have the pay the inflated prices of the shops importing stuff for the bike.

11-17-2008, 03:57 PM
If I'm not mistaken 257 is the engine designation not the displacement. It's only 250cc. Much like our 125cc motors are 123/122 models.

Here's the swap on an older bike.


11-02-2010, 08:16 AM
Hey guys been researching the RS125 to see if it is something I would want on the track.
I would like something that would go about 130 to 135mph. I doubt I can do that on the RS125 as I weight 190lbs.

What top speeds have some of you seen with out swapping the engine? (If you are about my weight)

Also what engine swaps easy into the RS125? I was hoping for a CR250 as I can get them cheap here and know how to work on them. I would have to find out what speed I can get it up to though.

11-02-2010, 09:45 AM
going to have to go euro to get the chain on the correct side. CR won;t do it.

there are a few KTM 540 D/XC's around for sale......certainly would make a 125 frame move about with ease....prob a pretty easy fit too

11-02-2010, 09:59 AM
KTM 540 swap? Is that still a 2 stroke?

I will ask my buddy about his RS125 as he has a CR80 engine in it. Not sure what side the chain is on but that is a good point. I take it the suspension will handle the extra weight and the brakes will still handle the extra power of the 540 fine?

11-02-2010, 07:24 PM
we got the 125 over 100 with my big ass on it.

the 540 dxc is a 2 stroke.....really developed for sidecar racing as I understand it.

not a whole lot around...and no idea what the parts avail is like.

I figure with a lighter rider ( real light) the ape 125 is good for maybe 110 without getting inside the engine

my light pilot was unavail as he was busy riding his 250 nitrous bike this past weekend.

Brakes.... fine at 100.....I'd do the GSXR front end swap if putting a dxc motor in.

mines for sale...sorted out with all the cool bolt on stuff already:banana:

11-03-2010, 09:29 AM
Thanks for the info! I heard the newer 125 frames are not good for the 540 swap?
I was told from a friend the RS50 and RS125 is basically the same frame but the older RS50's have stronger frames and would be better for a larger engine swap. Is this true?

Also they sell Athena Kits for the 125cc dirt bikes over here making them 180cc's.
Does anyone sell anything like that for the RS125? How fast would that raise it in power/speed and what are the pros vs cons?

11-03-2010, 06:41 PM
The 125 frame is much stouter than the 50 frame....not sure what your buddy is smoking but have him send me some.

the 540 is not really a good choice...makes alot of power but vibrates a bit ( alot)

Polini makes a big bore kit.....154 I think. no top end but adds mid and low range as I understand it.

not sure if the rotax 124 can go much bigger

12-08-2010, 12:52 AM
KTM made some really awesome 125cc 2 stroke dirt bikes in the 90's that have the chain on the "wrong" side like this bike. If I had kept mine I planned to put one in as the compression and power and better than the US RS Rotax motor.

12-18-2010, 02:45 PM
Why not a husaberg motor ?

12-20-2010, 11:16 AM
This is my project it is a 2000 rs 125,
I'm busy with putting a Ktm lc4 engine in and 2007 model bodyparts.
And a 2000 gsxr 1000 frontfork.

12-21-2010, 12:06 PM
Take a look here:
mate of mine put a ktm 500 in his old superteen bike, interesting read and pretty sweet engineering.

Micah / AF1 Racing
12-23-2010, 09:57 AM
The Pegaso 650/ BMW F650 engine should be a pretty easy swap if you have mad fabrication skills. I have always wanted to so this, clothe it in the old school roundy bodywork and have my own personal Aprilia-Supermono.

12-29-2010, 11:56 PM
I'm doing the KTM500 swap. Bought a couple of motors on ebay...waiting for delivery!

Was gonna do the KX500 swap, but the LH chain was alot of work to make work. Will start work ASAESU (as soon as engines show up) lol

04-28-2011, 10:52 AM
is there much difference for the 257 swap into the newer 123 chassis than the 122 chassis? I love the new ones and they can be had fairly cheap. Want to know before taking the plunge though.