Diff'rent Strokers

[Tuckerbag]

Over at NSR-World user SiLikesGuiness looks like he is getting into manufacturing NSR250 (MC21?) cranks.
See Si's post at NSR-World

Unknowingly and simultaneously I have been slowly looking into the MC18 R5k / R6k crankshaft.

I am currently getting a quote on making the inner two crank wheels for the MC18 5/6k. By “inner crank wheels” I am referring to items 2 and 3 in this diagram. It takes a little while to load.

The poll above is just to get some sort of gauge of how much interest there are in the parts. I have estimated €600 for a single pair of items 2 & 3 but this is just a wild guess. Again,.. A WILD GUESS! If members treat the poll seriously, it could spur others into action as well as myself. The conrod price is for real and is for one conrod (GP 250 spec!), and has a lead time of 5-6 weeks for a batch of 12.

The two outer crank wheels (items 1 and 4 in the above diagram) are generally re-useable, so I see no need to manufacture these.
I believe that all other parts of the MC18 crankshaft can be sourced.
Main bearings
Big end bearings
Thrust washers
Seals x 3
Conrods
I suspect that the supplies of main bearings and seals may be finite. I find it very hard to get good information on this. If anyone has info on where to get main bearings and seals I would love to know. RGVspares.com and the guy in Greece (mixalisen at NSR-World) must get them from somewhere. I am not meaning to be negative here as mixalisen gets them from his local Koyo dealer and supposedly sells them on at no profit. Good on him!

I intend to get the two inner crank wheels made to match the production version:
28mm main pins
25mm big end pins
54.5mm stroke
They will differ slightly from the production units:
1) I intend to provide some flat surfaces to make pressing them together a bit easier.
2) I will modify the shape slightly to make machining simpler and therefore cheaper.

For the steel, I am using case hardening steel EN39B (or possibly EN36 if EN39B is not available).

It will probably be about 2 months (plus or minus about 18 months, yep that’s product development for ya) before I get a complete crankshaft assembled using newly manufactured inner crank wheels. Then I will want to run it in a bike for about 1000 miles or so. After that, if all is well, I may offer the items up for sale if anyone is interested. Of course, I have absolutely no idea on price at the moment. Give me another 2 – 20 months. By which time SiLikesGuiness may hopefully have better options.

I see the process as having five steps:
1) CNC machined - slightly oversized in places
2) Stress relieved
3) Re-machined in critical areas that were initially oversize
4) Hardened in critical areas
5) Pins ground to correct size.
Some jigging will also be required for the final grind.

The idea of making the big end pins 22mm in diameter is tempting as it allows for cheaper MX conrods to be used. This will be weaker and is a risk that I am not going to take.
In terms of a “rebuildable” crank; having crank pins that are not an integral part of the crank wheel, but are pressed in, is not an option. This is because the two holes that would then be required in item 3 of the diagram would be too close together and would give serious problems when the pins were pressed into them. Also the big end hole would have to be a blind hole so as not to interfere with the centre-main-bearing-seal sealing face.

Stroking the crank is also tempting, especially in the case of a 300. Maybe in a few years time I may look into that.

I will post again in a few months time with a progress report.
If anyone can see any problems with what I am doing here please let me know.
_________________
Yes,.. I too know how to waste Time and Money!
See here

[si.likes.guiness]

stick with it mate