270° 953cc Sidecarcross engine build

[270YAM]

I bought the crank from a friend who knows the guy who built GRM motors back in the early '80s in Europe. Still wrapped up in the original wax paper, brand new!
Stamped in the side of it is
84 (stroke)
81 (I am guessing year of manufacture)
S (Staschel, the guy who made it)

 

[270YAM]

What have you done to the head to get it to flow sufficiently for 953cc?

I sent my head over there to Mike Morse, it had the full CNC and valve job. Looking forward to seeing how it performs.
Sounds too small when you consider that my motor is 27% larger than the 750 that the head was designed for, but bottom end grunt and strong midrange is essential for this kind of racing.
If it doesn't work on the 950 I'm sure it would go great on my 850!

 

[650performance]

A number of XS racers in OZ have purchased the CNC heads and are enjoying good success. I hope it works for the larger engine as well. I have some stock vs. CNC flow curves and other performance info that I can send you if you'll give me your email address.
Craig @ ctweeks@aol.com

 

[BigJimmyW13]

subscribed

 

[blackbetty]

 

[270YAM]

Thanks out of curiosity what do those pistons weight?

Jack, sorry I haven't had a chance to weigh them yet, (weighed them about a year ago and forgot) ill weigh them over the weekend an let you know.
They were within a few grams of an 85mm SP370 OEM cast Suzuki piston, the ROSS piston itself is a bit heavier but the assembled weight is almost the same due to the lighter wrist pin ans rings

 

[270YAM]

4 speed gearbox arrived today, Photos later!

 

[270YAM]

Here is a few photos of the new 4 speed box.
it has 5 pairs of gears as per the original gearbox, but 'first' gear does not actually engage, it is just there so the kick starter can work. It also came with a spacer to go in place of first driven gear if I wanted to remove the kick start gear.
New gearbox will only require 2 out of the original 3 gear selector forks.

I will need to file some clearance in the crank case where first driven gear sits, because it is closer to the Right hand side of the motor.

Countershaft old and new:

Clutch shaft old and new:

Old cluster, New cluster:

 

[racerdave]

1st gear is not needed because of the extra torque, or no standing starts, or??

 

[270YAM]

1st gear is not needed because of the extra torque, or no standing starts, or??

I would normally take off in 2nd from a standing start, and ride most of the race in 3rd.
Having first gear not engaging has also freed up a bit more space to make all the other gears wider/stronger,

 

[hotdog]

they look nice & fat - should handle the extra power OK & prevent box failures...

 

[270YAM]

The new gearbox has turned out to be a bit more of a mission than I first thought! Had to remove material from both side walls of the crank case, all scraped out by hand, man I wish I had a milling machine!

I used a sharp 1/4" pin punch to scrape out a radius in in the corners, and ground up the end of an old file to do the flat parts.

 

[270YAM]

Here is a shot of all the gears off the clutch shaft placed next to their equivalent OEM gears:

Yamaha 3rd gear on the left (prone to breaking dogs) New 3rd gear on right:

Don't want any of these floating around in there...

 

[scabber]

Looks good. It would be nice to see a picture of the head. Just to see what you get for the cost of the work. I think more people might buy one if they could see one first. Hope you can get it to hook up with the power that motor will put out. It should throw some dirt.

 

[h3llb3nt1]

subscribed

 

[270YAM]

Thanks out of curiosity what do those pistons weight?

Hey Jack,
Finally got around to weighing the pistons:
Bare piston on weighs 297.6 grams,
Piston with rings, pins and clips weighs 381.5 grams.

 

[Anthrax0505]

Where could I get my hands on a 4speed gear set like that

 

[GreasyC]

We need updates! Where you at with this beast?

 

[rebel542]

subscribed

 

[270YAM]

Sorry I've been a bit slack on the updates!

Below is a photo of the new gearbox bearing, I bought a blank one and cut the circlip groove in the spot. As mentioned above, the gear assembly is wider, so the standard bearing no longer fits.
Cutting the groove accurately without any machine tools was a bit of a challenge, it involved 2 vices, a 5" grinder with a 1mm cutting disc, dial indicator, gearbox shaft, G clamp, patience and beer.
It turned out surprisingly well, and the offset it within .002" of where I wanted it.