Question for the 2-stroke gurus

The Other PaulG

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• Jun 6, 2010

• #1

Here's one of those questions I have wondered about for ages and never really been able to figure out an answer.

Why do 2-strokes need their cranks to be re-built every now and then, whereas 4-strokes almost never do???

It seems to me the cranks are doing very similar jobs, with similar stresses and similar implications if they go out of true..... so why do strokers' cranks need so much more attention?

Paul G

 

(RIP) Kaister

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• Jun 6, 2010

• #2

Cos 2 stroke cranks have needle roller bearing bottom end and are lubed by the oil from either the petrol or by seperate pump not directly fed to the big ends under pressure like a 4 stroke

2 stroke cranks are built up and pressed together to aid dissasembly

 

DrFarkoff

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• Jun 6, 2010

• #3

BEcause they are usually needle roller bearings and they are vapour lubricated not pressure fed

the oil in suspension via the fuel mist eventually gets to where it's needed

Sometimes the rollers pit and can damage the crank

Lots of small reasons BUT I think Mainly If your crank is rebuilt you know your bearings are fine and that i ain't gonna lock up there so you run it in and then go doo lally on it!

 

The Other PaulG

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• Jun 6, 2010

• #4

Thanks guys - yep that makes perfect sense.

Aaaah brings back happy memories of the little end needle roller bearing imploding on my X5 many years ago... I had forgotten about that!

PG