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MG Midget and Sprite General - Another Ebay Novelty (A-series content)

This has been for sale for a while. The description is a bit limited!

http://www.ebay.co.uk/itm/120771795163
Dave O'Neill2

Yes I did see that and did wonder if then new downsize supercharge craze might have early origins
Onno K

I can't see a crankshaft and that would be a problem to fabricate.
Chris H (1970 Midget 1275)

Dave. I think it will be for sale for quite a bit longer too.
I wonder what the three offers were for, a door stop?

Bernie.
b higginson

Chris,

It wouldn't be difficult to machine one but you would have to decide whether you wanted even firing pulses with each piston rising at the same time or odd firing pulses with the big ends 180 degrees out. I was discussing this with a mate over Christmas, for a reason I can't remember likely too much beer, and the former is not great due to crankcase pressurisation as the pistons rise and fall together leading to breathing and leak issues and the latter leads to uneven firing pulses as the firing is 180 degrees apart then a 540 degree pause for the next firing.

The FIAT 500 used both rising and falling at the same time and that seemed to work. Never driven one myself but the engine looked like it would make a good paint shaker on the engines I've seen running at least at idle or near it.
David Billington

You could also make a 'big bang' engine, with both cylinders firing together.
Dave O'Neill2

Might make a good lawn mower engine

Prop
Prop and the Blackhole Midget

Dave What would you machine it out of? I would imagine that the original would have been forged to allow the grain flow through the journals and then the journals case hardened. You would then have to heat treat to stress re-leave, harden and temper after rough machining and then grind the journals. And don't forget the balancing. Any stress points would be a disaster, not that easy.
P Ottewell

making a crank, and a cam would not be difficult, it just costs money ":oD

Machined from a giant dowel of steel (rather than forged) is called a billet crank.

By the way, did you all notice that the intake/exhaust ports and the spark plugs are put on the opposite sides of the head from where they are on the 4 - cyl A series?


Norm
Norm Kerr

here is a link with some photos of billet crankshafts (scroll half way down):

http://amccars.net/cgi/yabb2/YaBB.pl?num=1293734066

in this case, an AMC V8 crank, from a 360 lb piece of bar stock machined down to a 59 lb finished crank!


Money for a good machinist = fun on tap.


Norm
Norm Kerr

whoops!

My bad, the ports and the plugs are where they "belong", it is just that the thermostat is on the "back" of the engine!


Norm
Norm Kerr

Yes easy with 40 years experience, copying an existing crank with all the design and stress engineering done. As it says in the thread he's focusing on balancing these days "the best in the business". Things like the placement of oil ways are calculated and engineered not just guessed. Not just the cost of material, the engineering expertise and skill should not be under estimated, it is not easy. Hey what do I know, I've only been in engineering for 34 years, anyone can do it.
P Ottewell

Chris,

It wouldn't be difficult to machine one but you would have to decide whether you wanted even firing pulses with each piston rising at the same time or odd firing pulses with the big ends 180 degrees out. I was discussing this with a mate over Christmas, for a reason I can't remember likely too much beer, and the former is not great due to crankcase pressurisation as the pistons rise and fall together leading to breathing and leak issues and the latter leads to uneven firing pulses as the firing is 180 degrees apart then a 540 degree pause for the next firing.

The FIAT 500 used both rising and falling at the same time and that seemed to work. Never driven one myself but the engine looked like it would make a good paint shaker on the engines I've seen running.
David Billington

This thread was discussed between 01/01/2012 and 02/01/2012

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