Recycled lawn mower crankshafts

[Putt-Rite]

I've got some lawn mower crankshafts. I've read here that crankshafts are bad to machine at home. How about I anneal what I have, will they then be machinable?:fan:

 

[MachineTom]

Most small engine crankshafts are made of the cheapest metal available. A kind of cast steel based on machining I have done on them. Not one had any hardness to it, bandsaw slices it up easy enough.

What are you wanting to make out of them.

 

[wackyvorlon]

You can certainly give it a shot. It's hard to ensure that you don't distort the crankshaft during annealing.

 

[chucketn]

I have 'Freecycled' many dead lawnmowers for aluminum for casting. The cranks I have used to turn pistons for some of my model engines. Turns fine for me. Like good cast iron.
Chuck

 

[Putt-Rite]

I'm wanting a built-up crank for a v-twin.

 

[mcostello]

I have recently seen it commented on the 'net that China is sending over Nylon crankshafts. No personal experience yet.

 

[wackyvorlon]

The consensus here seems to be that the author said comment was very confused:

http://www.yesterdaystractors.com/cgi-bin/viewit.cgi?bd=ttalk&th=340951%3E

 

[Putt-Rite]

I've noticed quite a few plastic gears inside lawn mower engines. I think there is a decompression release gizmo with flyweights that is turned with a plastic gear. Or it's an oil pump with a plastic gear. Not sure which, or both.

 

[MachineTom]

Re: I have seen plastic camshaft on Briggs small engines. Not a crankshaft ever.

 

[wildun]

The crankshafts on small Briggs engines (flathead lawnmower type ) have been made of nodular cast iron (SG Iron) since Adam was a boy.
This is bendable material (but it is cast iron nonetheless) and quite often people try to straighten the crank using a gas torch - this is a no no, and like all other CI stuff, if cooled too quickly will become brittle, - then they can't understand why they break!
I am not sure if the actual crank journal is surface hardened, but I don't think so.
I should imagine that the material is quite good quality SG Iron. I've never machined any of these cranks, however I have made quite a lot of stuff from SG Iron billets - it is beautiful stuff to machine but as with all cast iron it is messy because of all the free carbon it contains!

SG Iron (spheriodal graphite) is a cast iron containining its free graphite in little spherical or ball shaped "nodules" as opposed to flaky graphite as you would find in ordinary CI. This then makes it much stronger and is the reason it can bend.

Having said all this, the cranks on most two strokes will be made of case hardened steel and if you want to machine them, it is best to anneal them first.
You can machine them as they are of course, but you will be cutting through the case hardening here and there and the results will be a little inconsistent (unless you want to cut a lot of material off.).
Nylon cranks? - Yeah right!
Thanks for listening to the sermon, -
I haven't Googled SG Iron or Nodular Iron as yet but you no doubt will and I hope I'm right!