Ktm 250 Mc-5
KTM 250 MC-5
CYCLE WORLD TEST
A Dual-Purpose Bike for the Competition Rider
KTMs are made in Austria by Kronreif and Trunkenpolz Motor-Fahrzeugbau KG.
With a corporate name like that it's no wonder they are marketed simply as KTM (formerly Penton on the east coast).
KTMs are common in the winner's circle at both enduros and motocross. In fact, you seldom see a KTM rider who does poorly, but more than just machine ability is represented by that statement. A person has to be a true hard core dirt rider before he forks over $2100 plus tax, freight, setup, etc. for a 250 dirt bike. And by the time he becomes hard core he has usually gained quite a bit of experience. Few beginners are going to walk into their local dealer and buy a KTM, Husky or Maico for their first dirt bike. Most work up to a European bike. By the time a rider feels the need for the little bit extra these bikes sometimes offer he has also acquired the necessary skills to properly set it up and maintain it.
The MC5 has several improvements for 1978. The forks are now 38mm Marzocchi leading-axle units that allow 10 in. of wheel movement. At the rear non-reservoir gas Bilstein shocks have replaced last year's Marzocchis. The Bilsteins are mounted farther forward on the swing arm in an effort to maintain a more constant rising rate throughout the rear wheel's 10in. of travel. The new arm has also been lengthened some. KTM was one of the first companies to use a curved swing arm on their motocrossers. The curvature allows the use of a longer shock without an equal increase in seat height.
In the past KTM used different frames for the motocross and enduro models. The enduro utilized a frame known as a High Breather—basically the same as the MX with the addition of a rear frame loop and a large backbone tunnel that connected to the air cleaner top. This allowed air to enter under the gas tank, where water splash and dust was less likely to contaminate it. For '78 a common frame is used for both the MX and enduro. The High Breather frame has been dropped.
This makes it simple for the local dealer to have a bike in stock that appeals to a wider market. The bikes are available as a MX. like our test bike, or the MX with a large tank and skid plate for desert, or as a fully prepared enduro mount with large tank, VDO speedo and drive, Petty headlight, Petty IT rear fender, aluminum skid plate and spark arrester. The enduro option is available as a separate package or already installed.
This approach makes it possible to tailor a machine that matches a person's local riding area and personal demands. Also, by buying a MX model and a complete enduro package the bike can be used competitively for both MX and enduros. What KTM has actually done is invent a new type of dual-purpose machine for the competition rider.
The new frame is a redesign of last year's MX frame. It is made from chrome-moly tubing and heavily gusseted. The rake has been steepened half a degree and now' measures 28‘/2 deg. The frame has also been narrowed in the area under the seat. This makes it much easier to move around on. Although KTM frames are based on a double front down tube design, they look like no one else's.
Every frame gusset has one or more holes punched through it. The termination of the seat rails is tied together by gusseting that looks like a Swiss cheese replica.
The double down tubes roll under the engine and loop upward to form the upper mounting point for the shocks. From here the tubes continue back to the lower part of the steering head. A large tube forms the backbone but only runs from the top of the steering head to a point just in front of the seat. Two short tubes run from this point down and rearward to just behind the swing arm pivot. The seat rail tubing runs back and has short tubes that triangulate it back to the area at the shock's upper mount.
The swing arm pivots on needle bearings. The axle for this arm is a plain shaft held in place by a pinch bolt, a different but efficient method.
The engine's rear attaching bolt is directly under this shaft, which .makes us wonder why a single large bolt isn't used to perform both chores. The new Maico Magnums and Husky automatics use only one bolt to hold swing arm and engine and it works quite well.
The air box has been redesigned to fit the narrower frame. To help retain KTMs reputation for fording deep water, the air box draws its air from under the seat. To keep water splash out, it has a thin plastic guard that covers its top and three sides.
This guard is spaced about Vi in. away from the top and sides, allowing air to be drawn under it and from the top left. This opening is further protected by the form-fitting plastic side number plate. Filter maintenance is performed by removing the foam filter through a large opening in the lower left side of the air box. If the machine is going to be used in water a plastic cover for the opening is supplied and held in place
with a large rubber band. If the bike is going to be ridden mostly in desert terrain the owner has the option of leaving it off to improve breathing.
It is basically a nice design but it does have a couple of flaws. First, the Twin Air foam filter is on the small side, which means the operator will have to clean it often to keep the engine running cleanly. Second, it is a hassle to remove. It is secured to the air box with two nylock nuts. Access to the nuts is limited and a wrench is required down to the last turn. This makes a distasteful filter cleaning job even more so. Although a hassle to clean, this system offers tin exceptionally good leakproof seal.
The full width front hub and conical rear are cast from magnesium. Both brake backing plates are also magnesium and help keep unsprung weight to a minimum. Adequately sized spokes and nipples are used to lace the hubs to American made Sun rims. These Sun rims have every MXer's favorite tire mounted on them Metzelers.
Plastic is used for the side number plates and fenders. The side plates are secured to the frame bv aluminum screws.
The rear fender looks a little short and is. The front fender looks much like ¿1 Preston Petty Mudder but is made in Austria.
The slim gas tank is fiberglass. Two petcocks are employed, both at the front part of the tank. A rather strange placement. until vou take a close look. The frame tubes prohibit a sanitary rear installation. The front placement also makes it impossible to shut them off' with your knees when riding. The tank's shape and size are fine but the choice of material is poor. Fiberglass is much less flexible than plastic and easy tv) hole in a crash. The gas cap is made from aluminum and vers light. To ensure against loss and droppage it has a safety chain attached tv) it. a trick off-road racers have been using for mans years. Too bad the cap or metal spout leaks gas. This leakage soon causes the decals to fall off and expose an ugls seam down the center of the tank.
The KTM's seat and tank junction is nice and narrow. The seat blends into the tank and makes movement eass. It has a quality cover and boasts a firm foam. In fact ours was hard. But once a hard seat breaks in it becomes perfect and won't sack out for a long time.
All of the correct pieces are on the KTM. The footpegs are spring-loaded and well-cleated.
1 he shift lever has a spring return end tv) avoid breakage and bending and all hand controls are the latest from Magura.
Clutch and throttle cables are good items but for some reason the front brake cable is a small wimps thing that should be replaced.
KTM engines have a distinct look, with their large tins and squarish side covers. The fins measure an incredible 1 1 in. across. Under the giant finning is a cast -steel liner, so reboring is possible. Bore and stroke remain the same as last sear (7 1 mm \ 62mm) but the porting and combustion chamber are ness. This change, combined ssith vi new pipe and silencer, has broadened the poss'er considerabis.
The center cases vire also lavishly finned. These cases and the side covers are pressure die cast magnesium.
Naturally, the rod rides on needle bearings and a dual ring forged Mahle piston is furnished.
Primary drive is by straight-cut gear. A multi-plate wet clutch is employed. A 6speed transmission is standard on the American models, a 5-speed is stock on European models.
Since the MX and Enduro utilize the same gearbox. 1st is quite low. just right for crawling out of a slipperv creek bed. Low will never be used on a MX course but the track racer has five more eloselv-spaced gears tes choose from. The gear choice will work well for both the MX and enduro enth usiast.
The drive sprocket sets fairlv close to the swing arm pivot and the giant 530 chain is nicely routed first over a roller and then through a large nylon block just forward of the retir sprocket.
The clutch release arm is precariously placed on the engine's right side, between the mag cover and drive sprocket. A case saver is furnished and fits close to the chain and drive sprocket to help prevent damage tes the clutch arm and cases in case of chain derailment.
A 36mm Bing carburetor supplies the necessary gasoline and a Motoplat CDI ignition with lighting coils furnishes the spark.
The KTM's kick starter is mounted on the left side and does an efficient job of turning the engine over. Most starts are accomplished with one kick.
The clutch pull is moderately strong but once under way isn't needed anvwav. Shifting is smooth and positive but all of the test riders accidentally bumped it out of gear on rough ground. It happened a couple of times leaving jumps and the subsequent dead stick landings caused instant fear. We moved the lever up one notch but still had a problem with it. The cause is a throw that is verv short.
The bike has to be ridden to reallv appreciate the wide powerband. KTMs have always had adequate power but it was mostly found at high rpm. The new porting and pipe have changed all that. It has a wider, more usable powerband than anv 250MX we have tested. And without the use of reeds or rotary valves!
The power is even fully usable when exiting a slipperv. hard packed, off-camber turn. We drag raced it against an RM250C and concluded they were virtually equal on a surface that offered good traction. But when the ground is slipperv or muddy, the KTM's power doesn't go up in wheel spin and it quickly pulls away. Our test bike had a hard seat and this, combined with verv little suspension sag. projects a tall clumsy feel, especially in corners. After a few laps this feeling disappears as the rider adapts and begins to enjoy.
The 38mm forks and strong chromemoly frame allow the rider to pick the lines he wants, but it takes several hours before most riders become fully comfortable on the machine. >
Part of this is due to the brakes. They stop well but both require more pressure than necessary. The front requires the use of all fingers. A few fast laps on a MX course cause the right forearm muscles to ache. Part of this forearm fatigue is caused by the forks. They work well on small and large bumps' as long as the bumps are rounded. Square edged ones cause a hydraulic lock that transfers a shock back to the rider. They also lock when landing
from high-speed jumps if the rider slaps the front end down hard. This is a common fault with the large Marzocehis. They can be effectively modified by drilling another compression hole V2 in. above the existing one. Make the new hole the same size and position it 90 degrees from the existing one. (The compression hole is the lowest one on the damper rod. just above the hydraulic stop cone.) This mod makes the new Marzocehis comparable to anything
on the market. (Can-Ams have this mod done at the factory in Canada.)
The same can't be said about the new Bilstein shocks that are delivered with the bike. The first criticism is the lack of reservoirs. Not a big problem if finned. But. they don't have fins either. A hard rider can fade them quickly on a rough course and their action is marginal. A fast pace is possible but constant attention and correction is required by the rider.
The bike lands with an audible thud whenjumping. a result of the fork lock and marginal shock action. We suggest the fork modification for any owner and a shock swap if the bike is going to be used in MX or high-speed desert. The trail rider and enduro enthusiast will probably be happy
with them as is. Our KTM proved stone reliable during our long test. We didn't even have to change a spark plug. Gil Vaillancourt. owner of Works Per formance Shocks, has two KTMs that he
uses for shock development. One of them has over 10.000 hard, whooped desert miles on the VDO and it hasn't had a major overhaul yet! That kind of reliability almost justifies the initial price.
KTM 250 MC-5
These magnesium Marzocchis are Urn ited by excessive compression damping in high-speed situations. When en countering square-shouldered obsta cles and the like, the forks tend to lock hydraulically, giving the rider quite a jolt. Drill an additional hole in the bot tom of the damper rod, adjacent to and the same size as the original. This will reduce the compression damping by about half, and improve fork action con siderably.
Slow-speed and enduro riders may be happy with the stock rear suspension, but more aggressive riders will find it a definite liability. Spring and compres sion damping rates are high, causing the rear to be slightly stiff; rebound damping is excessive, and allows the suspension to pack down. To correct the situation, install a set of 14-141/2-in. shocks with medium to firm damping; units with 41/2-in. travel would be ideal, yielding 10-in, of wheel travel. Progres sive springs with a 100-lb./in. initial rate should then be installed.
