Identifying donor crankshaft

[Michael CheckleyParticipant @michaelcheckley34085]

Evening!

I`m trying to identify a crankshaft that was used in a friends model aero engine project as I would like to build a similar engine. Sadly he has passed away so I cant ask him where he got it from but I have been told it came from a chainsaw. I`m not having much luck identifying a crankshaft long enough to take 2 bearings. I have attached some photos and a drawing, if anyone has any experience in engines from chainsaws, cut off saws or similar sized engines any help or direction would be much appreciated.

[Michael CheckleyParticipant @michaelcheckley34085]

[RJWParticipant @rjw]

Michael, does that rectangular stub on the end of the crankpin screw out by any chance?

It looks very much like a Velo-Solex crankshaft, the big end on those is held in place by a bolt screwed into the end of the crankpin,
The con-rod is a one piece alloy casting with pressed in needle roller bearings for both the big and small ends, the big end needle roller has an inner race which is a polished steel tube and a light push fit on the crankpin, this is then locked by a bolt and washer. 

If it is a Solex, the centre waisted section carries the driving hub which rubs on the tyre and has another bearing near the taper which is located in the other half of the crankcase,

I've got one of those engines stripped down but it's in France, so can't offer any photo's unfortunately.
Solex engines are French and fitted to bikes mounted to drive the front wheel, there's also an active web forum for them.

John.

 

Edited By RJW on 03/08/2016 13:55:13

[Michael CheckleyParticipant @michaelcheckley34085]

Hi John,

Thankyou for the info, I will check out Solex engines and see if I can see a match. The flats on the end of the crank pin were ground on to accept a 'new' section for the crankshaft, the old one being 3 pieces pressed together. I`m thinking the half of the crankshaft I have must be screwed or pressed together as I cant see how they can press the bearing over a ~1mm step.

The plan at the moment is to find something similar rather than an exact replacement which is still proving difficult and the technical departments of the major manufacturers don't seem interested in helping. A repair shop may be more helpful which is this weekends challenge.

[clogsParticipant @clogs]

HI Michael, u will find the same style crankshart on most petrol engined strimmer/brush cutter's…..

there quite a few different sizes…….most engine range from 20-50cc………the cranks seem to last for ages, it's usually the carb or the electric's that stop em running………..

I live too far away but my barn has at least 10 junker's (kept just for spares, hahaha)

a good place to look is the local tip, it seem's that they r now cheap enough to throw away when they stop running….

good luck…..Clogs…….

[Ian S CParticipant @iansc]

I'v got a number of small engines from 15 cc to 40 cc, the ones with two crank cheeks are pressed together, some have plain bearings, others either needle rollers, roller, or ball bearings. The bearing on your crank should be on a step the same or larger diameter as the bit to the left by the taper.

Ian S C

[RJWParticipant @rjw]

Michael, I've taken a look at a few images of the Solex crank, and although the web is similar, the mainshaft is much longer than that on yours,
The style of the crank is definitely vintage, modern stuff tends to have machined full disk webs, and often pressed construction, may be worth thinking along the lines of old moped engines, I had a shuftie at Lambretta, Vespa, Villiers and JAP cranks, but nothing that looks like yours, not checked out the NSU Quickly and similar types yet, or 4 stroke singles.

John.

[Michael CheckleyParticipant @michaelcheckley34085]

I have had a look at scooter crankshafts and although it looked quite positive at first I think the one I have has come from a chainsaw, albeit an old one. My only requirement now it to find one with a similar diameter shaft and length (before the taper), if that search fails then I`m going to investigate making one, materials and heat treatment e.t.c

I called in to my local lawnmower/chainsaw repair shop and he looked at me in horror and basically refused to help me without a specific code to order an equivalent replacement. He was not prepared to help and show me anything similar incase anything came back on him in the event of the part failing. How ridiculous, no wonder this country is being left behind when it comes to innovation.

[Ian S CParticipant @iansc]

A model aircraft engine with a crank that size is going to be quite large. There is a fair bit on the net about using weed whacker motors for model aircraft, maybe one of those sites might help.

Ian S C

[Tim StevensParticipant @timstevens64731]

The GN motor car had a similar design of crank, but that was in the early 1920s. And if you find a spare one, some GN owner will bite your arm off for it.

Cheers, Tim

[Author]

Posts