1975 KTM 250 MX - 1st Project Bike/Newbie

[KTMTOM]

Thought I'd post a few updated pix from my current build. Thanks to Paul Hudy over at Speedynamics for taking the time to find all the parts and do a complete overhaul on my shocks to get them current and allowing me to keep the originals in lieu of something aftermarket. Turned out AWESOME! Bought an old side stand on E-Bay and had a buddy fab one up for me using some stronger steel which also turned out great! It's good to have friends who are handy!

[Big Mac]

It seems like the West-Coast "KTM" badged machines that went the new distributor route starting in '75 followed more closely with the Euro-styled KTMs of the day. The '76-'77 MC-5s with "KTM" on the tank out west were red tanks unlike the orange "Penton" badged MC5s, while the '77 GS-6 out west was Blue and the Turtle-back style frame instead of Penton Orange.

May simply have been that the KTM factory had a Penton-style bike coming off one line and a KTM-style bike for Europe off another, and when the West Coast change took place, they just sent Euro-style "KTM" badged bike that direction. Don't believe they sold a lot out west, no where near as many as went through Lorain OH during the '75-'80 period. I was on the west coast the whole time and never saw a KTM of this era anywhere but in magazines until the vintage mx revival kicked in....still very very few out this way being raced and run.

Jon McLean
Lake Grove, OR

[KTMTOM]

Great little bit of history and information, thank you! Keep it comin!

[dirtbike]

Really great looking resto as far. Clean looking engine. Looks just like mine. Have you done anything to the engines internals?

[KTMTOM]

No, I didn't do anything to the motor. The gentalman I got it from had made some updated mods to the clutch, and from what I can see through the ports, the piston looks good. Not to mention, it runs great! Grant it, I'm sure it could use a ring job, but I don't forsee putting many, if any real time on the bike. It's going to be more for my show that for my go! Very good chance I won't even put gas in it when I get the tank all done. Still up in the air on that one. Like to keep it, but we'll see what happens when she's all done and I'm itchin for another project. Hope to have it rolling by the end of the weekend. Just waiting on my tank & side panels to get back from the painter, and my pipe to come back from my buddy's place. Had to put an end cap on the muffler. What was on there was a joke someone cobbled together. It won't be OEM, but it'll look pretty close to what was of that time frame. Outside of the silencer, the pipes in fantastic shape. Seemed like a shame to not try to fix it up.

[KTMTOM]

I just have the shocks temp. mounted up in these pix, but decided to put the nut on the inside, along with a shorter bolt for the top mount. Anyone know how they came? Nut on the inside of the wheel well or on the outside as would be the case in the pix I posted?

1975 KTM 250 MX
2009 KTM 250 XC-W (e)

[Big Mac]

Every old original "barn" bike I've seen had the nuts on the inside of swingarm and frame.

An unexplained shock mounting trend I've noticed: The US bikes of this era all seemed to have their Marzocchi piggy-backs mounted with the reservoir on top, while the Euro bikes seems to be set up with the reservoirs on the bottom...or upside-down in my view.

Check out the KTM-badged early '74 Euro bikes at http://web.tiscali.it/ktm70pages/

[454MRW]

I'm not sure of the validity of it, but upon arriving at Mid-Ohio this past year with a 76 MC5 250 on my trailer for sale, I was approached by someone that purposed to know that if the reservoirs were not positioned at the top, which it clearly shows in the MC5 chassis manual, the shock vavling would not work correctly. I have seen them both ways on other models, an even pictured the opposite way in the GS-6 chassis manuals, so I am not sure that this information is correct. Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S

[Steve Minor]

I have a 77 sales brochure that shows the GS6 with the reservoir on the bottom and the MC5 with the reservoir on top....Go figure. Maybe Tom or Dane can comment.

Steve Minor
Wilmington, NC

[brian kirby]

Having rebuilt them I can tell you it makes no difference which way they are installed, they will function the same. That is the purpose of having a bladder separating the gas/air from the fluid just like modern single shocks, it allows you to mount the shock in any position you want.

Brian

[454MRW]

The person who approached me said there are shims in the valving that gravity has an effect on and that they would not work correctly upside down and claimed that he was a reputable rebuilder with a lot of experience in this design. So his story goes...Mike

Michael R. Winter
I enjoy rebuilding and appreciating Pentons!
1974 250 HS Pentons-1980 KTM 175-400'S

[KTMTOM]

Well I wasn't sure if they were suppose to be mounted up top or down below, but the "majority" of the bikes I see pix of have them mounted on the bottom. I've heard all kinds of reasons for mounting the reservoirs up top from guys not wanting to dry out the seals to the "gravity" shim comment. Personally, I like the look of them being on the bottom, as it's just "different". I've seen pix from the way back when with them mounted on the bottom so I tend to believe that's the way they came from Austria. Good info though guys, appreciate all the feedback. Got the wheels on today and hope to have the rear fender and a few other misc items on by days end tomorrow. Got wind my tank/side panels are in primer, so should be seeing them in a couple weeks. Can't wait! Discovered I don't have the right rubber boot for the OEM Magura throttle, so contemplating putting a side pull throttle on. I'll sleep on it, but wondered if they were available back in 1975, or did they come later in life? Trying to keep it as close to period correct as possible.



1975 KTM 250 MX
2009 KTM 250 XC-W (e)

[Big Mac]

Have you tried to fit your airbox in there? I always reassembled with box going in before engine, or at least before carb and intake. Recall it was super tight to get box back in, sort of like getting pipe out...a KTM design thing.

[KTMTOM]

Airbox is still at the painters, but shouldn't be an issue in terms of the motor being in. For sure though, I'll hold off on mounting up the pipe/carb until it's in, but the air box is pretty well out of the way of the motor on this one.

1975 KTM 250 MX
2009 KTM 250 XC-W (e)

[marsattacks]

Your bike is looking great.  Thank you for posting your progress.  

Insofar as direction of shock mounting, Dane Leimbach (see the link below) has previously provided an explanation that appears to be highly sensible -- USD position will act to reduce unsprung weight on the swingarm.  Not being a scientist or a particularly knowledgeable rider, the weight differential would appear to be negligible but perhaps the effective weight differential increases dramatically under working loads (sort of like how they tell mothers that it is impossible to hold their 30 pound baby in their arms in the event of a crash because it now weighs 150 pounds or whatever).  Like Brian, Dane dispels the notion of gravity-induced problems but adds a mud consideration.  Both of my bikes with Marzocchis are mounted in the way you have mounted yours and I like them that way too.

Good luck!  John

http://pentonusa.org/forum/topic.asp?TOPIC_ID=6152&SearchTerms=shocks,down,sprung,weight

Mars Attacks!