200 MachIII crank rebuild

[anotheroldtrailrider]

Hi Folks - I'm finally back on my Bridgestone racer replica project and actually making progress - the chassis is complete other than lacing up the new rims, and I made a one-piece carbon fiber tank/seat/tailpiece that's almost ready for paint.  This finally let me start on the engine, and as the title implies, I need to replace the rods - I've read the 1977 RM100 rods/brgs/shafts will fit right in, can anyone confirm that?  They're in stock a couple places I checked, so would be an easy choice if correct.  The other choice I've read about is the Suzuki X7, but it requires skimming a mm off each crank wheel for the wider rod - this seems like it would be an undesireable increase in case volume??  Last, since I'm doing crank work, it seems silly not  to do the 20mm center pin while I'm at it - does anyone have these pins or do I need to have my machine shop make one, and does anyone have an updated parts list or part numbers, etc for the larger bearing setup?

Thanks, Art Astle

[anotheroldtrailrider]

Oops, just noticed the MachIII typo, sorry.

[bsracer]

Hi Art,
Karl Swartout sent me a mssg that you were looking for info on some crank modifications. I think you are referring to some of the mods that Vince Gunning had done with his racers? Sadly, Vince passed away last year. I would have to go back and find Vince's notes but I believe the Suzuki may use the same 19mm big end bearing as the Bridgestone however I thought the big end pin was wider. I have a sample Suzuki rod for an A100 and this crosses to the other rods you mention but you would have to narrow the crank cheeks. I have modified my crank with a 20mm "center shaft" using a hardened industrial pin. This is done by removing the original shaft of the Bridgestone web then making a new hole and opening the other from 16mm to 20mm. I have used Yamaha KT100 kart rods which are the same dimension as the Bridgestone stock rod except they have a 20mm big end pin. This allows the use of silver cage bearings which stand up to some higher revs.

There is a lot of machine work involved in the modification I had done. All the big end holes are opened from 19mm to 20mm (these are just for arbitrary reference, the actual size would be whatever gets the proper fit). I have the angled edges of the left and right outer cheeks cut to match the intake port window to smooth the flow. The center pin modification to 20mm straight pin. I have the area of each cheek "pocketed" for rod shim/spacers which are used on the KT100 cranks. The center pin is an industrial hardened pin from Grainger (80mm by 20mm). They have to be shortened and centers added. The Bridgestone big end pin is 48mm wide. If I remember the Yamaha big end pins are 48.8 and need to be shortened.

I have another modification that would require the pin holes for the rotary valve drive pins be opened to take 4mm pins instead of the 3mm Bridgestone stock pins. This would be to convert to a steel rotary valve but I haven't  got the final version of the rotary valve cover done yet. Karl 3D printed me some from a modified file but they need some tweaking to fit.  I got some outrageous quotes to perform the all the mods I have done and I couldn't justify the cost at the time. I've been running this "test" crank for far too long and need to figure out what I'm going to do pretty soon.

paul

p.s. are you planning on racing your bike?

[anotheroldtrailrider]

Hi Paul - thank you for the trove of info - as you commented, there's a significant amount of complex machining, so I have some decisions to make before I can really start on the motor.  I suppose if the RM100 rod was wider and needed slight relief on the crank halves, that would be easier than boring the big end pins oversize?  I expect to use single ring coated-skirt KX100 pistons - is the crown height lower than the original?   (I'm a big fan of ceramic coating on piston tops - any reason to avoid it here?)  I haven't decided between ceramic bores and nikasil - my KTM's have survived extreme abuse for years with nickasil.  For the state of tune, it won't be raced but will be used hard on spectacular Ozark back roads - I want upper mid-range and some top end is nice but I don't want to constantly wring it's neck.  I'm spoiled, 15 minutes away there are a couple hundred miles of various loops with no tourist traffic and very little local traffic. 

For the chassis, I re-did the shock mounts and back of the frame and built a swing arm with a slightly larger pivot bolt and bearings instead of the rubber bushings that's slightly longer and stronger than the original to accommodate (rebuilt) adjustable integral-reservoir Marzocchi's from that period.  The forks are 300 Ninja units with cartridge emulators.  I haven't laced them up yet but have slightly wider 18" rims that will be sealed with bicycle rim tape to run tubeless on the original hubs.  (I've done half a dozen sets of wheels with this tape and zero problems, it's available in several widths and very easy to use.)  Obviously, weight reduction is a major goal, and I just finished a one-piece carbon fiber tank/seat/tailpiece.  I'm still on the fence for carb's but since it'll be hidden inside the fairing there's more choices on intake, etc and since I'm not racing it rules aren't an issue.  For the electrics, I have sensors mounted on the original plate to trigger modern coils and a lithium-specific regulator/rectifier for the little lithium battery, and I'll do a LED lighting wiring harness to be truly street legal.  As a Suzuki/Can Am/Vespa dealer in the 70's I loved 2-strokes, but it's been 30 years since I built anything other than 4-strokes so I have a lot to learn.  Once I figure out for sure what I want, I still need to find a machine shop of that caliber - any suggestions there? 

[bsracer]

Wow Art,

that all sounds pretty interesting. I have the cylinders Nikasil plated. I'd think the ceramic would be fine but I've never tried it. Just relieving the webs might be an option. I'll have to look at the sample Suzuki rod and see why I strayed from using it. Might have been because I wanted to use the shims and that would have taken more out of the web than I wanted.  I had one Kawasaki (not sure which one) piston for a sample but remember the crown heights were quite different. I think the Kawasaki was much taller. May have had the ring pegs in the wrong position too. Not sure how the KX100 pistons compare. The Wiseco Suzuki RM85 pistons are just a hair shorter if I remember and I use shims under the cylinder anyway. A lot of things can be done especially if you don't have any restrictions. Racing in AHRMA has plenty. If you want to give me a ring I'd be happy to go over some of the stuff. Undercut stock trans helps with keeping it from jumping out of gear or false neutrals. The standard 5 speed isn't the greatest for racing but has got me along for almost 20 years. I've also modified the cam on the shift drum to help this. After seeing a few other bikes over the years I may change the way I do a few things. I attached a photo of the sample Suzuki rod kit.

cheers paul
619.675.4060

[bsracer]

These are the center pins I have modified for the center of the crank. They were pretty inexpensive from Grainger.

[bsracer]

Undercut transmission, I have a couple of sets but they need a minor adjustment to be used. That little step that isn't finished to the teeth is the problem.

[bsracer]

Modified cam gear for the shift drum. I stumbled across two shift drums that the gear is a separate piece. Have never found any reference part# wise or anyone who has seen one. I got a cam from a Kawasaki ZX-10 from a wrecking yard and had the profile copied and redrawn to the 5 seed Bridgestone pattern. I had several profile done and water jet cut. I went with the "tallest" profile that cleared.

[bsracer]

ZX-10 vs stock Bridgestone.

[bsracer]

Rotary valve covers. The first set I ran for a long time were done on manual mill and lathe by Rob North. After first couple of races I noticed aluminum bits in the bottom end. The stock rotary valves are too abrasive of the raw aluminum. I then had to repair them and have them hard anodized. The discs still wear thru the hard anodizing after several races. I've had them re-plated once but went back to run the SR cast covers until I decide how I will proceed. I had the ones Rob made copied into CAD so I could have more made (long story of trying to build motors for someone else). They didn't work out and in trying to save some of the samples I modified one set to adapt Kawasaki KE100 steel discs which are considerably thinner. This meant adding material to the face of the inner side of the disc. I was close but again the attempt failed and put aside for now. 

Image 1- rotary valve covers made by Rob North
Image 2- rough CNC version
Image 3- added "slice' to make the face deeper
Image 4-5 again redrawn with thicker face for the Kawasaki thinner discs and 3D printed by Karl Swartout. Still need some modifications to fit.