The Service Dept

THE SERVICE DEPT

Barry Watkins

MONOSHOCK UPDATE, PART II

Last month we showed you how to improve both the handling and performance of any 250cc Monoshock, YZ or production. The handling information also applies to big-bore models, and since they’ve already got plenty of power, you should be all set in that department.

For recreational riding or low-key racing, your 250 YZ doesn’t really need more in the way of modification, but for serious competition, the improvements suggested so far are not enough. The reason is weight and chassis geometry that is close, but not perfect. (The following mods are also appropriate for pre-Monoshock YZ owners wishing to update their machines).

THE C&J MONOSHOCK FRAME

The solution is to replace the frame with a 21-lb. unit manufactured by C&J Precision Products. The chrome-moly frame saves you 8 lb. Add the C&J swinging arm and you save an additional 3.5 lb. The reduction in swinging arm weight is particularly beneficial because it means a reduction in unsprung weight. Less unsprung weight allows the wheel to react more quickly to ground irregularities.

Handling will improve, as well, because the C&J frame has one degree less steering head angle. No more front wheel wash-out. No more relying on berms. With the new frame you can take the inside line if it’s faster. And, with the Maico forks we recommended last month, high-speed stability remains good.

As far as quality goes, you won’t find a frame anywhere that is better designed and built, so forget any fear of breakage. Price is $525.

BITS AND PIECES

For cosmetic purposes, we took our stock aluminum tank to a local paint stripper and had him dunk it. The cost was $5. Then we sanded it for a couple of hours with number 600 wet/dry paper and buffed it on a big buffing wheel.

Stock fenders can be used, but we chose some ultra-light plastic ones. They’re milky white and give our machine the look of a factory prototype.

The modified Monoshock assembly suggested last month was bolted in place with no additional modifications, as were the Metzeler tires.

Our final touch was a genuine Yamaha leakproof petcock. This will fit any Yamaha MX since 1972 and will cure a lot of headaches. Part number is 322-24500-02, cost $4.

SUMMARY

As we indicated earlier, our C&Jequipped machine steers a lot better than stock without sacrificing stability. With the modified suspension, both ride and control are excellent. Weight reduction is significant, too, so you don’t get as tired.

We were happy with the machine but wanted to get another opinion; and we wanted to get that opinion under racing conditions. To accomplish this, we asked a local CMC expert, Jack Hazard, to take the bike out the next time he raced.

Jack took us up on the offer and won overall 250 Expert by taking two lsts and a 3rd in three races. In the race that he finished 3rd, he was knocked down in the first turn.

Jack said that our Yamaha either pulled or stayed even with the newest machinery. Steering was perfect and he loved the soft suspension.

Whether you go all the way with your Yamaha or modify it according to a budget, we’re confident you’ll be pleased with the results. If you run into any trouble, drop CYCLE WORLD a line. We’ll be glad to help.

PARTS PRICING APPROX. COST

K&N filters ................... $12

14T countershaft sprocket...................... $5

38mm Mikuni carb.............. $52

3.00-21 Metzeler................ $30

4.60-18 Yokohama ............. $30

Maico front end with Wheelsmith kit.............. $350

Terry Industries or Number One Products kit ....................... $50-60

Fairway or Orange County Cycle modification................... $30

C&J frame .................. $525

LIST OF SUPPLIERS

Wheelsmith Engineering 3625 W. McFadden Santa Ana, CA 92704 (714) 839-0150 K&N Engineering P.O. Box 1329 Riverside, CA 92502 (714) 682-8813 C&J Precision Products 3873 S. Main St.

Santa Ana, CA 92707 (714) 540-7350 Terry Industries P.O. Box 1321 Hesperia, CA 92345 (714) 244-3139 Orange County Cycle 1 3666 Harbor Blvd.

Garden Grove, CA 92640 (714) 530-7340 Fairway Racing Products 1350 E. Yorba Linda Blvd.

Placentia, CA 92670 (714) 524-1205