Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126012
ASK • • By E. C. Birt CZnake! I have a 1975 CZ 250 MX·desert. red fram e with a two pound Motoplat flywhe el elec tronic ignition, 34mm Mikuni, and a Dean Maro "pipeline " pipe. My problem is th e down pipe is alwa ys getting s mashed. I was wondering if you co uld build me an up pipe that w ould be out of th e way, or a snake pipe lik e th e fa ctory Can-A m s were using earlie r this year. 1 know that MX Fox has an up pip e; but I k no w so me one who has one of their pip es and it seems to stick o ut too much to su it m e. I w ould also like to kn ow wha t you d o to really mak e th em go. Keith Opeka Beltsville, Md. I co uld build you a sn ake pipe except for one little problem . T o do so I would have to have your comp le te motorcycle mailed to me, and th at would b e a lot of st amp lic king. But I know some one that might handle your problem. South Bay CZ, 200 1 Artesia Blvd., Redondo Beach , Cali fornia has a craftsman working for them by the name of Chris Allen. There is nothing that he can't do with sheet metal and he can build you a snake pipe if it's possible to do. Cost to build a pipe lik e this 1 won't even try and guess, but I would be ready to spend $100. As far as the rest of your engine is concerned it looks like you have it. You co uld bore your carb out to 36mm. CZs like 36mm carbs. After you h ave filled out the layout sheet that 1 have sent you we may come up with some improvement in the porting. • has gas kits that will fit . Now back to the engine. From what 1 gather from so me of my other readers a lot of the government b ases have very well-equipped hobby shops. With this thought in mind let's start from the top and work our way to the end. . First, there is no reed made for the Sachs engine that will just bolt on because of the way the in take port is des igned. To install the reed to your engine takes some welding and mac!.ining. Is it worth it ? As far as I'm co n cern ed , yes. The reed engine will not give y ou any more horsepower on the top end but it will double the torque down on the bottom end an d in the midrange. Sure will m ake the b ike a lot easier to ride. Let's assu me that you want to build it as a reed engine. Now here is a warning. If you are the complete "gassit" type rider and you know t hat you will have the engine working most of t he time at the high end of t he rev range, then you better pull the engine, split the cases and replace the rod with a rod from a KTM 17 5. Note the pictures of the two different rods and you can see how much bigger the I 75 r od is compared to that of the 125. T he tw o rods are the same as far as top pin bearing and length, an d there is no problem as far as deck heigh t. However, the 1 75 rod is wider at t he bottom and your crank I nI 9Z.Omm fI T 4Z.0JMl 41. 0mrn IIII • ~ E Now this porting diagram may be old hat to all you Sachs fiends out there, but 01' E. C. felt like it ought to be exposed to all those virgins who still aren't going fast enough. Right, E. C.? Now the crank is ready to put back togethe r. Note: Be sure that yo u use t he pin fro m your crank and not the pin fro m the 175 rod assembly. The 17 5 crank pin is straight. The crank pin for the Sachs is tapered. Since you have the case s apart, set each case half (one at a time) on t he cylinder and match the case half to the bo ttom of the cylinder transfer opening. on the cylinder. Now to machine the cylinder for th e reed. First step: go to the local Hodaka dealer and pu rc hase a D.H . reed for the Wombat. Set the cy lin der up in the end mill with the bore 90 degree to the mill table. Machine the lower three fins back ' to the base gasket surface. (Note picture.] After you have t he fins cut back remove the cylinder and weld up Five steps toward the definitive Sachs six speed 1) Machining the intake flange for the reed body. 2) D.H. Reed pieces bolted up to the modified jug. 5) Boost ports for the reed go in at 30 degrees. Piston will be cut to match. bi~nd clearance on your crank wheel to accept the 175 rod. . I've just purchased a ne w Tyran 125 MX and n ow alon g with thousands of others own a Sachs 12 5cc six speed engin e. First I plan to use th e bik e f or desert racing and trail riding. Where can I purchase an "up pipe" with a silencer and spark arrestor for th is bike? Secondly, what are th e dimension changes for moderately porting this engine? Thirdly, is th ere a reed-valve system on th e market for this engine? Fourth, what is th e trick set-up for the Tyran front forks ? Capt. Ray Harris Edwards AFB, Calif Welcome aboard, Cap tai n , and the next time you dro p in at the Ponderosa Inn say ~'HiH to everyone for me. A high pip e for y our bike will have to be custom built for your bike. In the L.A . area there are three shops that can do the job right for you . (1) Flying Mach ine Factory (213l 53 0·465 6 (2) Lee's Pipes (714 879-1393 ' (3) Precision Cycle (213) 370-8822. On e thing, though, you . will find the high-pi pe a li ttle uncomfortable because there is just no place for it b ut up the side of the bike. Let's skip for t he momen t to the forks . The forks on your bike are American Profile and the wo rst part abou t them is the fork springs are on the soft side. That problem can be handled by converting th em to air. Ottows Werks, 15156 Downey Aven ue, Paramo un t , California (213) 531-880 1 Z9. Omm TR~S 41 Machining extra Sachs and the single cylinder T wheels have to be machin ed to ex cep t the wider rod. First step is to mi ke th e th ickn ess of the stock rod (lower end) t hen mike th e 175 rod. Divide the differe nce by tw o and this is t he amoun t th at you take fro m each crank h alf. The bes t w ay to , rem ove th is me tal from the crank wheel is set the crank half up in a mill and with a fly cutter remove the needed me tal. The crank wheels are harder than the hubs of he ll and your cutter will have to be carbide. Tool steel won't even touch it. After the crank wheels are machined to the right thickness, p olish the surface till it is very smooth (no burrs) . While you are in t he botto m end of t he motor check all the shi mming and be sure that it .is shimmed 'righ t and . hing t urns free, eo no te the Sachs engine is a little o n the heavy side. You can rem o ve ab o ut five pounds from it by cutting o ff all the extra fu fu. Along the whole bottom of the engine there is a bunch of fins that are no t needed . Cu t th em all off and grind the cases smooth. These fins hurt more than they help because they hold dirt and mud . A lso the cylinder and head can be cut down three-quarter inch on a side. This not only gets rid of some weight but will help keep yo u from b:mging yo ur knees 3 ) For super reliability, KTM 175 rod at right has more meat at both ends the little low spots that you have left. Pu t the cylinder back in the mill and now machine this surface on three degrees inclination. Take the reed housing and set it on the cy linder surface, placing it so the top of the reed ju st touches the fourth fin fron: the bottom. Mark the four stud holes o n th e new surface, then drill and tap 6 mm holes. Back to the Hodaka sh op, get fo ur intake studs and nuts for the Super Rat intake m an ifold . Install these studs in the cylin der and now y o u can bolt the reed cage to the cylinder. If you wish to u se yo ur stock Bing or one of the new V84 Bings you wil l want to use a 10 degree man ifol d. If you want to use a 30mm Mikuni use a five degree adap to r for the Honda reed. If y~u have any pro blem in finding the parts that you need fo r th e reed then call Dale Herbranson at D.H. Enterprises (213) 679·3402. Two boost ports are then machined from the bac k of the cylin der in to the intake po rt (see 'pho to ]. These ports have to be mach in ed in at 30 degree and are a must for good performance. Be sure that they are not so wide they let the ring pi ns ru n over t he p orts. If you wo uld ra ther take the easy way ou t, I can do all the mach ining and p o rting for you for $140. Since you are usin g the engi ne for desert racing and a p lay b ike" th en 1 wo uld not mo ve any of the ports around. Just clean the m up an d go ride it . If you feel that you wan t to lose so me low end torque th e enclosed po rting diagram wil l give y o u so me more mid ran ge and to p end. • ; 31