Suzuki RM 400 Vintage Race Bike Build

Discussion in '2 smokers' started by Racer111v, Dec 22, 2013.

  1. Racer111v

    Racer111v Been here awhile

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    First off I blame all of you FF's on this forum for getting me off the couch and actually doing something....:huh

    After successfully avoiding vintage racing for years, I've giving in and building a bike.

    A little personal background first. In novice class I rode a Yamaha mx250, a cr250, and then a Bultaco 360 Pursang. Then in 1977 I got a new YZ400D and made armature on it. I got some wins on it and kept it for years after racing it. I got a new Honda cr250 , then in 1980 I got another new Honda cr250 and put a Mugen 360 kit on the older side port cr250.I raced the 250 and open class that year. The Mugen kit cost $299 plus $12.50 shipping. That included a cylinder, piston set, rings&gaskets, pipe, and some transmission gears. That's a bike I wish I had kept, but I needed the money for the next bikes.
    I bought a new 1981 Honda cr250 & cr450. Those bikes were awful and repeatedly tried to kill me. If you held the clutch in too long in the gate the clutch bushing would seize and take off with the clutch lever pulled in. The shock shaft broke several times (including the Fox Shock several times) and threw me over the bars.
    In 1982 I bought a barely ridden Husky CR250. I loved the bike, but I wasn't very fast on it. I kept it for maybe ten years, until the tranny blew up. I tore my ACL in 1982 and quit MX just a few points of getting my Expert plates.

    With all that said, I figured I would look for a late 70's EVO open class bike. I missed a few deals, and decided a few were to far away. I actually started looking for a RM 400 as they are pretty easy to still get parts for, and a good all around bike. I had good friends racing them back then, but never owned one. So I found one on CL about 70 miles away. He listed it with the atv's and snowmobiles so no one scooped it right up. He finally posted some picks, and it looked pretty good, except for a missing air box. He listed it as a 1980. I looked on EBAY and there is a 1979 complete air box. I bought it thinking It should work on an '80 even though the changed it during those years. The 1979 & 80 are very similar. It worked out for me that the bike is really a 1979 according to the serial numbers.

    So here's some pictures.


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    A lot of cheap satin black spray paint and new mismatched plastic. But the basic parts were mostly there.

    [​IMG]
    #1
  2. bykpimp

    bykpimp Live and let ride

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    I swallowed a mouthful of spit reading the cost of the Mugen 360 kit!!! Neat backgorund story. I don't believe I've ever ridden the 400 but the 370? rings a bell. Can't remember if that was a TM or RM? Any who neat looking bike!!! Looks like someone did a lap in the snow on her.
    #2
  3. Racer111v

    Racer111v Been here awhile

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    It took a while to get the shed cleaned up, but the weather was pretty mild, so there was no better time than now. I know that it always takes twice as much as twice as much as I think it will to get these projects done. So it's time to get the bad news. It took about as much time to completely disassemble to a frame as it takes to do an oil change on the 950....

    The first thing I realize is this is not a RM400 rear wheel. At first I thought the rim looked narrow because of the 4.10/18 tire. Then I see no floating brake and a brake cable instead of a rod. They did a nice job on the conversion. Add a hub and backing plate to the list. It was getting spokes and rims anyway.

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    The carb to cylinder tube was installed porely and is junk. These are still available new for short money. Put it on the list.

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    This is the custom front engine mount. Looks like some sheet metal from a lawn mower fan shroud. Only two of the four bolts installed.


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    This is probably the result of the custom mount.

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    Nothing my tig welder can't fix easily. That is nearly free, no part required. My welds won't look any worst than Suzuki did.
    #3
  4. Racer111v

    Racer111v Been here awhile

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    The RM370 was '76 and '77 if I remember right. A big step forward from the TM 400 Cyclone. The Cyclone ended a lot of racing careers. The tracks were from pushing not riding. I really hate to ride a bike I haven't worked on. It's not an ego thing, I've just see it go wrong to many times.

    A year earlier the Mugen kit was around $1500, but when Honda went to the center exhaust port they just blew out the old kits. I was lucky to be riding out of a shop with a race interested general manager.
    #4
  5. FJ_Kevin

    FJ_Kevin Been here awhile

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    Welcome to the club! And great bike you have chosen to rebuild. I had a '79 RM250 purchase brand new. Raced it extensively... this was my favorite, handled fantastically, thought I was on a factory bike.

    My racing buddy had one too. We both ran Ohlin$ $hocks on them. Tony D front fenders too. The motors were mostly stock, just some port/case matching. They were very competitive. We broke the frames and cracked swingarms on the drive side. But we broke frames on other bikes (Maicos, KTMs, Yamahas) even more so we thought the Suzuki's were still very good in this respect.

    About a year or two ago I tried to find a twin shock '79-80 RM 250 or 400 in my area without success. Gave up and settled for some twin shock Huskys instead.

    I am really pleased to see your project and will be watching closely.

    Here is a couple of photos from the old days. First my buddy Paul on his RM250.

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    And a nice side shot of my RM250. I really loved that bike!

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    Good luck!
    Kevin
    #5
  6. Rot Box

    Rot Box Been here awhile

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    Nice. Looking forward to updates :thumb
    #6
  7. buls4evr

    buls4evr No Marks....

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    I will say the rear wheel is wrong AND a 4.10 is not close to enough tire for that explosive 400 engine. Watch the bottom of the frame just ahead of the footpeg area for cracks. The tubing on the frame was as junky as the welds were. The rear suspension really hooked up well but the forks were at best so-so flexys. The engines in the later ones had more flywheel and a little better torque off the bottom.
    #7
  8. buls4evr

    buls4evr No Marks....

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    Another thing that comes back to me is that the bike was really hard on 3rd gear when we ran it in Hare Scrambles. The dogs for engagement seemed to round off pretty easily. Might want to make sure it "holds" 3rd gear under power as it is one that you use a lot. Can't remember if it was the driving gear or the driven gear most often, but if it jumps out of gear this is the culprit. They didn't chip....they just rounded off.
    #8
  9. Racer111v

    Racer111v Been here awhile

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    Thank you for the info. I've decided to tear the engine down. I have the time now and I hate to haul all the way to an event and have some simple thing keep me from riding.
    I have to clear some space in the cellar to pull the engine apart.
    #9
  10. Racer111v

    Racer111v Been here awhile

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    After doing some more research it seems this thing got a PE400 (1980) s/arm and wheel assembly swapped on it. I have some conflicting info on the differences of the two. The pe uses a chain rub pad instead of a wheel. This is no big issue and could be fitted if I really cared. There is some info saying the axle end opening is slightly different. Once again it shouldn't be a big issue. The s/arm pivot parts are the same, except for two spacers. The pe ones are available oem.

    These are some of the things that make restoring an adventure.................

    I'm off to make room in the cellar to pull the engine apart. :1drink
    #10
  11. Racer111v

    Racer111v Been here awhile

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    I have cleared a spot to work, so here we go.

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    The clutch cover had some signs of the clutch bolt or bolts backing off at on time or another. The primary gear bolt (crank) is only finger tight. The fact that it is a left handed thread is the only reason it is still there. After removing the clutch pressure plate, I can see that some of the friction plates are broken, actually the first two. The clutch nut is also finger tight, the tab washer is barely holding it on.


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    The piston is at it's last OEM oversize, .5mm. I am chasing down some 1.00mm that were made. If that doesn't pan out, Maico 440 pistons will work. Those start at +2.00mm and go up to +4.00mm. These have a thick liner.

    The rod is loose and no longer available OEM. I have a lead on someone making them in NZ. The crank pin and bearings are still available.

    The shift shaft was slightly bent. The drive gears in the tranny look good, but the driven have some rounding on the dogs. I have seen some on ebay , or I will just square them up a little. Two shift forks show a little rubbing, and one is in perfect shape. I still need a puller for the mag.

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    #11
  12. Kevin K

    Kevin K Adventurer

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    My 79 RM125 had a roller for the chain leading to the countershaft. my 1980 had a wear block instead. I'm just mentioning it because you noted the same difference between the RM400 and PE400.
    #12
  13. Racer111v

    Racer111v Been here awhile

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    I just looked up the 1980 rm400 and it went to a pad also.
    #13
  14. Racer111v

    Racer111v Been here awhile

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    I've been busy checking out the online oem dealers. Some are showing parts being available that others are showing obsolete. I have ordered a total of nearly $800 from several Suzuki dealers. I'm expecting to actually receive about $600 of those if I'm lucky.
    I will summarize the dealers that had parts after I actually receive them. I was able to locate a small company selling +.75mm, +1.00mm, and +1.50mm piston kits. Gaskets are mostly obsolete from the oem, but I have located some people with some decent quantities at a realistic price and some people that have had some made from the aftermarket.
    I have ordered a few more used parts. I am going to wait on some of the easy parts like tubes, tires, cables and controls.
    My first thought on shocks was to just buy a new set of Works Performance, but after visiting all these sites in the last few days, there are a lot of great options out there. If a few thing go right, I may spend a little more on shocks.
    #14
  15. D.T.

    D.T. Difficult but useful

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    Nice build!

    I was at the SX at the Metrodome this past April and have some nice pics of Donny Schmidts RM 400 if you want to see it I can post it...
    #15
  16. Racer111v

    Racer111v Been here awhile

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    Put it up, it would be nice to see. :clap
    #16
  17. Scootern29

    Scootern29 Been here awhile

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    Buy a big bottle of locktite. My experience with RM's is that they spit bolts off the bikes faster than you can install them.
    #17
  18. D.T.

    D.T. Difficult but useful

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    [​IMG]
    #18
  19. MotoChris521

    MotoChris521 Been here awhile

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    SWEET ! :clap
    #19
  20. Racer111v

    Racer111v Been here awhile

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    Nice pic D.T. , Thanks

    As expected, the rod that Midwest Action Cycles showed as available, isn't. The only other part was a counter shaft sprocket that is back ordered from another dealer.

    After a lot of searching , I found a company in Spain that makes two stroke rod kits. A lot of older road race bikes deal with lack of replacement rods. Those bikes will go through several in a busy season. They don't have one specifically listed for a RM400, but will make one with not big problem. I just need to give them a sample of some key dimensions.
    The company is F.SAMARIN CO.LTD. They replied right away to my Email. I did find a non oem rod and I am in the middle of closing the deal. I will update how that goes as soon as the deal is done.

    Now for some great news. I did my daily ebay ckeck and there is a 1980 RM400 bottom end for sale, with a buy it now option. The seller has a good reputation, and says the crank is in good shape. I hope that is true. He also had a pro ported cylinder with a fresh Wiseco piston, for sale. I bought them both. I wouldn't mind having two good engines when the dust settles. :D

    I have a rear wheel on it's way. I still need a rear brake backing plate. I bought a DG pipe and silencer, they will be here Friday. I would still like a RM swingarm, but the PE one will work fine in the mean time.

    I got in touch with RK Tech and as soon as I can give them some dimensions, I will send them the head to rework the chamber. This is something these big bikes really respond to.

    Later :clap
    #20