Four stroke options

[FourstrokeForever]

At 104KG Im at my lightest,anything under 100kg and I feel like I lose some strength,so my poor bikes have to lag me around the track.
Im having a different idea with the RM chassis now,I have a fast little XT250 engine here,would this be a better choice?
Im happy to leave the SP in relatively standard form and fit the best suited forks and best shocks I can get on it and mod or fit a longer swing arm.
That way I can use the RM and end up with 2 bikes instead of one.
I have the shed to myself this weekend so will test fit some parts and see what I come up with.
GMC do you make extended bolt on swing arms for the SP?

I'm with you in the weight department James.....My bikes have to work to carry my considerable body around 

If it were me with a fast XT250 motor lying around, I would put it in the RM frame. The XT motor is lighter and has smaller external dimensions than the SP and will probably fit in without too much drama.
Failing that, If you decide not use the XT motor, I'd be interested in buying it from you to fit into my restored KLX250 frame rather than trying to extract some more neddies from the fragile KLX motor!

[evo550]

Its interesting that people spend a fortune to try and get acfourstroke 10 kg lighter, when the rider is the one contributing to the load, imaging how well the four stroke would handle and the suspension would work if the rider lost 30 kg.....just sayin'

It's all about reducing the unsprung weight...

Dead right Pete!

What about lowering the center of gravity.....

[James Lee]

I probably over exaggerated on the XT engine I have,its stock apart from a good exhaust with alloy muffler,I have 5 running XTs and this one is way faster that the rest,I hated XTs till I got this one.
Anyway the xt engine wont fit unless I cut away the mount tube closest to the airbox and the coil tube and may have to lean the front main tube forward or,
Cut the lower rails out and make the engine part of the structure like an XT.,would that mean the engine would bottom out before full suspension compression and cause some mischief?
Im having a hard time cutting into the RM frame,its a really nice bike for whats there.I trial fitted a late DT175 to it and looked good until I saw it was a center port and wouldnt be able to get an exhaust on it.
Would love the XT engine in it,just scared to dive in with the cutting disk.

[HeavenVMX]

What about an RM engine it will probably an easy fit

[James Lee]

If you had or knew of one at a reasonable price Id prefer to go that way,Id need electrics and pipe.Im just trying to build stuff with what I have here.

[Tomas]

Agree HavenVMX. 79 RM 125 are great looking bikes.One of the best Suzuki's rm 125 ever made. Here is motor for your RM 125 frame http://forum.ozvmx.com/index.php?topic=40442.0  I just dont understand why would you want to waste time on puting 4 stroke engine in it that is heavier, does not fit, does not have that much horsepower and is not a Suzuki engine after all. You can probably sell the rolling frame to someone who will apreciated it as it is rather than butcher it with angle grinder.

[James Lee]

At the end of the day this thread is called 4 stroke options,some sort of contribution would be more appreciated than hard opinions of wrong and right of other peoples property,usually 2 stroke biased.But thankyou,you have given me the motivation to go back to the shed and build something out of my $200 rolling frame purchase.will be a 4 stroke too sorry.

[FourstrokeForever]

Go for it James. It is yours after all, and you will have something that no one else has.

Why not remove the front and rear springs and bottom the bike out to find out how much, if any ground clearance you have to play with?
I'd be very reluctant to mess with the front downtube and would rather keep the motor as far back in the frame as possible.
In saying that, I'd still be tempted to use the SP main frame and give it the MX treatment by narrowing the rear loop to fit a MX seat and fuel tank.
Anything is possible with a whole heap of parts and some imagination mixed with determination.

Funny thing about how hybrids divide opinions. When oldfart on here built a hybrid out of an RM, no one whinged and moaned about what is the supposed right and wrong thing to do with an old bike. The build even made the cover of VMX magazine!

[TT5 Matt]

ive seen a xr200 motor in a rm125n or maybe t model which no cutting and shutting of the std rm engine mounts/engine cradle, it was mocked up to be a HL. the only bad thing i could see about it was the engine was tilted back to get the countershaft spocket in the right position and youd have to run the oil level on the drip stick higher and youd have the rejig the inlet manifold for the correct factory angle

[LWC82PE]

Yeah i have seen that bike too. Not sure what forum it was on though. Maybe Thumper Talk?

[oz555ktm]

photos taken of Bikes at  Vinduro

I dont have the Photo of the Yamaha TT250cc in a 1980  Husky frame

and a there bloke in the process of  is putting a Honda XR 200cc in a KTM 1984 125 frame now I think He is Bloody MAD why Cut up a KTM 
But I can understand  wants something that Handles . and lite ..

[Sorelegs11]

I had an RM S with ahonda 123 with all the bells and whistles that were availiable in 1979, regoed and all.
From memory I paid 500 and rode it for a year and got the cash back, great little rig.
 Put together by a bloke by the name of Paul Burns from Hamilton South.

[James Lee]

The Rm with the alloy wheels looks really good,I really like it apart from the head light.

[TT5 Matt]

brentj had the xr200 powered ktm, all dump shop finds

[oz555ktm]

Want to see this Bike and hear it Click on the Youtube link  you will see it and Hear it in the bush at the start
and that the End it will Roar past .


 
                      https://youtu.be/aceGGj3M6xs