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PENTON / KTM motorcycle
Technical Information Page
Identification / Owner Manuals / Piston Specs / Motor Tips
Re-sleeving Cylinders / LC clutch covers / setting piston Deck Heights
Year, Size, Model Identification
Every work day I receive calls from someone looking for parts to restore
or repair one of the many models of Penton and KTM motorcycles that were
sold from 1968 thru 1982. I am pretty good at knowing what some of the
parts many people are calling about, especially if I know what year,
model, and size of motor the bike is. It
saves a lot of time if the caller knows this information before calling.
It also helps if the caller has a part number to identify exactly what
part that they are looking for.
Penton/ KTM Frame Identification
1976 MC-5 1978 GS-6 frame
KTM Motor Identification
1976- 400 1982- 420 1988- 350
The KTM motor serial number
also contain a code that identifies what year and what size the motor
is. On the 1972-80 motors these numbers can be found on the ignition
side - just below the cylinder fins. On 1978+ motors the number can be
found on the clutch side - on the bottom front. The first three numbers
are the code. The first number is the year, the next two are the code
for the motor size. The following is a list of the different codes used
from 1972 thru 2003:
51 = 125 1976-81 52 = 175 363 = 50cc
450= 50 SXR/ S5-E/T/GS 1997 490 = 80cc LC 1986
510 = 125 1976-81 520 = 175 503 = 125 1998-2001
= 250 1973-80 55 = 400
523 = 200cc 1998-2001
500 = 125/II RV or II LC 501 = 125 MX/MXC/GS (LC)
502 = 125 LC 1987-1992
541 = 250II GS(RV) 542 = 250 MC 565-30-005 = 500 LC 1990
543 = 250 LC 546 = 250/300/380 1996 547= 250/300/380 2000
555 = 350 LC 1986 565-30-205 = 540 LC 1990
560 = 420 1979-84 561 = 350 1980 580-30-005 = 500 (90mm) 1988
562 = 390 GS 1980 563 = 495 1980-83 580-30-605 = 600 (95mm) 1988
583= 400/620SX,EGS LC4 1996 584= 400/620 LC4 1997 584= 625 LC4 2003
590 = 400/520 LC4 2000
590 = 250/450/525 2003
770 = 250 LC4 SX-F 2005
Date Codes (clocks)
There is a date code cast into every motor case around the drive sprocket area towards the lower rear part of the motor. It looks like a small clock with a triangular arrow in the center. The arrow points to a number on the clock indicating the month. There are two numbers under the arrow which indicate the year.
There are also part numbers cast into the outside of the center cases. The first two or three numbers are a way of identifying what size the motor is.
It is important for everyone to be able to identify what year and size bike that they have. Most used bikes have the original motors still in the frames, however I have run across situations where the motors have been replaced with a dissimilar year. (e.g.. a 1979 frame with a 1976 motor). Although many of the early KTM motor parts are the same and are interchangeable (1974 thru 1979) there are differences in some of the parts especially the clutches, push rods, and bearing plates.
Parts lists are available showing every part on the bike and motors and
identify everything with a part number. The illustrations help in
determining if something is missing, what order the parts go in
assembly, and how many there should be. The part numbers help you to
obtain the exact part that you need.
KTM Motor Tips
Do not remove the stop bolt for the kick starter, on the bottom of the motor, to drain the oil. Follow the directions in the owners manual to do oil changes. When doing an overhaul of the motor, remove the stop bolt after removing the kick starter shaft. Check the bolt for wear. If it is worn flat, replace it.
On the black motors, check for cracks around the hole in the case for the kick-start stop bolt. Cracks and breaks can be welded. ALL KTM MOTORS ARE MADE OF MAGNESIUM. Take it to a certified welder with experience. They use magnesium welding rods. Small cracks can be repaired with JB Weld or any high temp. epoxy to seal oil leaks.
On 250, 400, 420, and 495 motors, check and tighten any loose nuts and bolts after every race day. Pay attention to the motor mounting bolts on all big bore bikes. Loose bolts will allow the vibration of the motors to wear away the magnesium mounting areas.
Casting mark under exhaust port
250 casting mark above intake
400 casting mark above intake
KTM Cylinder Re-sleeving
All KTM cylinders can be re-sleeved, however in some cases there are more than one style of sleeve for a size of cylinder - in particular the 250 and 400 cylinders.
The 250 cylinders could use a sleeve with a standard bore size of 71 or 72mm. Look for casting mark "ELKO EZ 71" or "ELKO EZ 72"
The 400 cylinders could use a sleeve with a standard bore size of 81 or 82mm. Look for casting mark "ELKO EZ 81" or "ELKO EZ 82"
Double check the casting marks on your cylinder (see above photos for locations) to determine what size cylinder that you have before calling to order a new sleeve.
The 1972-75 175 cylinders were throw-a-way cylinders that did not have replacement sleeves. The cylinder must be over-bored to install a sleeve.
Do not take your cylinder to just any shop for re-sleeving or boring. Make sure that they have the experience of working on vintage 2-stoke cylinders. Shops doing work on the new motors can screw up your cylinder because there is a difference in setting them up.
KTM Liquid Cooled Engines - clutch case covers
Almost all KTM engines are made of magnesium. Water and magnesium do not get along with each other. Water (and moisture) will cause magnesium to corrode. This is a big problem with the Liquid Cooled KTM engines. The pump areas become corroded, eating holes into the case. Unless they are shown on this web site, replacement clutch cases are not available from me and as far as I know are not available anywhere in the USA. If the corrosion is not severe (metal around the seal eaten away), it will need to be cleaned up and repaired.
Repairs can be made by first cleaning out all the corrosion. This can be done by bead blasting it (bead blasting can cause more damage to area if you are not careful) or vapor blasting (a recommended method that will not tear up metal). Repairing the damage can be accomplished by the most common method of using "JB Weld" epoxy. Another method is to reweld the area with a magnesium rod by someone who has experience with welding magnesium.
If the corrosion damage is severe, you will have to find another engine with a clutch case that is not damaged.
As a preventative measure, if your pump area is not damaged, it is recommended that you paint the inside pump area or coat it with "JB Weld" epoxy.
Setting KTM deck heights
All KTM engines require setting the deck height of the cylinder to establish the proper amount of compression.
The gaskets sets come with an assortment of different thicknesses of base gaskets. Use the proper thickness of base gasket or gaskets to set the deck height "x". NOTE: check the spec sheets for your engine. There is generally 2 specs - one for MC and one for GS. It is recommended that the GS specs be used on 400 engines to make them easier to start.
For clutch slippage and sticking the following steps should be followed in order:
Left photo shows a new clutch arm (right) and a used clutch arm (left)
Right photo is an enlargement of the used arm, showing the wear on the top of the pin shown in the center.
2. The clutch actuator and arm must be within specifications before dis-assembling the clutch. A loose or worn arm assembly will not allow enough pull against the clutch pressure plate to allow the plates to release.
NOTE: Clutch plates can stick together if the motor has been sitting unused for a length of time (more than 1 month). Although I have not been able to prove it, it is my theory that the type of oil (gear lube) used in the bottom end has an effect on the clutch plates causing them to bond together. Sometimes the plates can be broken loose by starting the engine, pulling the clutch lever in and putting the bike in gear. Or while the bike is moving (at low speed) pull the clutch lever in and apply the brakes.
In worst cases, when a motor has been sitting for 10-20 years, it is best to open the clutch assembly and pry the clutch plates apart.