RM100 Restoration

[Fallenleopard]

Just thought i would wack a post up to get some advice on my latest project.
It's an RM100 1980 model, got it pretty cheap knowing the engine wasn't going and frame needed a patch up.

First problem i came to was a crack in the frame that went all the way around the tubing. Got a friend in the welding industry to weld that up and also fix one of the engine mounts that had cracked.

As for the engine, the piston had shattered (which means that i will have to split the case)

I went to the local Suzuki dealer and got a quote of $1100! I know there is less than $500 in parts even for OEM!
So i have decided to do the rebuild myself.

They also said if i replace the top end i will also need to replace the whole bottom end crankshaft and all, is this really necessary?

Can i just get away with piston, cylinder, rings and maybe a new rod?

Also for anyone who has done this before can i change the rod without any special tools? i know i will have to pay for the cylinder to be bored out, but i want to know if i can do the rest myself.


Do they sell manuals on rebuilding the engine itself? all i can find is the overall service manual for the bike.


Thanks

 

[Kaptain Krunch]

Any play in the big end rod bearing? The only thing you wont be able to do with some basic tools, and creativity, is replace the rod. The crank is pressed together, and balanced, impossible to do without the correct tools, and knowledge.

If there is no play in the big end rod bearing, your safe and can simply split the case, replace crank bearings and seals, and new piston/rings.

To split the cases, you can either buy a $50 tool, or you can make one out of a harmonic balancer puller. If your lucky, when you split the cases the bearings will stay in the case, and can be pressed out carefully with a socket. However, if they stay on the crank you'll have to get creative, or get one of those bearing pullers from the auto parts store. Again be careful with the crank, no hammering, no impacts to take out the flywheel nuts, etc they are easy to throw off balance.

When putting the cases back together, again you can buy a tool, i think they are about 50-75 bucks or so. It grabs the end of the crank, and pushes on the cases to seat the bearing onto the crank. Do not try to tap the cases together with a mallet, or anything like that. no longer case bolts to pull it together, because the crank is 3 piece and pressed together and balanced, so if you go putting uneven force on it you could damage it and have a motor that shakes like a bastard or worse.

I made the tool, out of an old bike peg and some threaded rod. works fine for me.

Only other special tools you may need would be a flywheel puller, but depending on the style that can often be done with a small harmonic balancer puller.


a few tips that might make simple things even easier.

- Freeze your new crank bearings overnight, and slightly heat the cases before you press the bearing it, should pop right in with a rubber mallet no problem.

- Let the bearings come to room temp, and freeze your crank. Again just makes it easier going together.

- USE LOTS OF ASSEMBLY LUBE. I just use 2 stroke oil, you can buy actual assembly lube which is tachy, either is fine. Make sure you lube the inner lip of the crank seals, along with all bearings, and lots of oil in the cylinder too.

- MAKE SURE ALL GASKET SURFACES ARE CLEAN! nothing worse than an air leak for a two stroke, case gaskets, base gaskets, intake gaskets, etc very very critical.

- Tear it all apart and figure out what you need before you order a bunch of parts, as you may find its not worth it once u really get into it.


EDIT: obvious, but may be overlooked. MAKE SURE YOU GET ALL THE PISTON FRAGMENTS OUT! there are oil passages that lead down to your crank bearings and seals, take out old bearings and blow out all passages with air.

 

[Fallenleopard]

I don't quite know what you mean about the play in the bearing, but there is play in the rod sideways...don't know if that's right or not.

Because I can't replace the rod then I don't want to open the case...but I know I will have to because of the metal filings will just eat away at he engine

I have got some flywheel pullers that I have used on bearings before. I would mind spending the money on the tools so make sure it all goes back together well.

So you think if I just do the bearings, seals and the top end it should run fine? (if it's done properly)

I know it's an old bike but unless there is some major damage I can't see yet I think I will go ahead with it. It will be my first bike and I need the engine experience

 

[OzFab]

Sooo many times I've seen top ends rebuilt only for the bottom end to fall apart within months. The main reason is because the new top end exerts pressure on the bottom end that it's just not used to.

If the piston is broken (which I can see it is) then, chances are, the engine was pushed hard so there will be damage in the bottom end too

 

[FatCat]

You should able to buy a crank/rod thats pre assembled.

 

[Fallenleopard]

Sooo many times I've seen top ends rebuilt only for the bottom end to fall apart within months. The main reason is because the new top end exerts pressure on the bottom end that it's just not used to.

If the piston is broken (which I can see it is) then, chances are, the engine was pushed hard so there will be damage in the bottom end too

Yeah I know what you mean but it apparently was only just rebuilt before I bought it. The owner said he did bottom and top end. I know why the piston broke, too much movement in the cylinder it looks as though he just bought a new piston and neglected to bore the cylinder.

 

[Fallenleopard]

You should able to buy a crank/rod thats pre assembled.

If I can then great, I will replace it! I'm just trying to do most of the work myself to save a bit of cash.

EDIT: can't find a crankshaft for mine

Because I will be buying most of the parts from America can any of you guys recommend any good after market brands that you have used before?

 

[FatCat]

I recommend tring to find NOS Suzuki parts.

 

[Kaptain Krunch]

By play in the rod bearing, i mean up and down play. should be none. hold the crank from spinning, grab the rod and pull it up and down carefully and feel for play. If theres a bunch of aluminum from the piston gummed in the bearings its done too. if not you could just spray it out with some brakeleen.

 

[Fallenleopard]

By play in the rod bearing, i mean up and down play. should be none. .

yeah there is slight movement but its hard to tell because it moves sideways.
I have emailed a bunch of places to see if they have the crank assembly, hopefully someone does.

 

[Fallenleopard]

So i have good news

My local wrecker that i bought some parts from said that she can get her mechanics to rebuild my engine for me for only the cost of labor if i wish to supply the parts. Alternatively they will use aftermarket parts and it will still cost only about half of what the Suzuki dealer quoted me.

Today i patched up some holes in the swing arm and began sanding the frame.

If you can see in the photos the rear mounts for the side panels, one is damaged do you think just a little stick of flat bar with the nut welded on will do the job? or should i attempt to re create what is on the other side?

 

[karl]

I had a 1980 rm100, good times. I gave it to my freinds dad so he can restore it mint.

 

[OzFab]

My local wrecker that i bought some parts from said that she can get her mechanics to rebuild my engine for me for only the cost of labor

That could still be very pricey, be careful...

If you can see in the photos the rear mounts for the side panels, one is damaged do you think just a little stick of flat bar with the nut welded on will do the job? or should i attempt to re create what is on the other side?

Trying to recreate it would look good but, it couold be a bit tedious. If you're not worried about looks then your idea will be ok. Otherwise, cut 'em both off & start again

 

[Fallenleopard]

That could still be very pricey, be careful...

Yeah I'm going to get a quote on Wednesday but they said under $500, I was going to do it myself if it costs anymore then that.

Only things i will be doing to the bike will be cosmetic, I painted the swing arm Aluminum colour which might looks funny now but i found when i add the clear coat. It turns into a very lovely grey.

I also painted the engine mounts and fuel tanks mounts just to add a bit of colour to what will mostly be a black bike.

Currently saving my money from the engine rebuild and probably new rear springs, sprocket cover, new brake pedal and the rear wheel repairs.

Also a photo here of the weld i had done on my frame, He recons the rest of the frame will break before that weld....I might have to test that haha