Bigger bottom end....

[scotsjohn]

You can alter the stroke of a crank by re-sizing the journals.
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You really can't...
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Regrind the journal giving it a smaller diameter with a centreline further from the centreline of the crank. Conrod is sleeved and smaller bearing shells fitted..Conrod now has increased travel up and down cylinder. Or reverse.

[Yoof]

I understand completely what you're talking about- but the stroke is still the same, no matter what journal diameter you have.

The only way what you're talking about will work is to offset the journal, but it's pointless and a highly expensive task for any machine shop, and you've built a compromised crank as it willbe far weaker.

[dub-disaster]

Just out of intrest are 1w cranked 77mm bore engines less "rev happy" because of the increased stroke ? Or is it not increased by enough to make a difference?

[polo classic]

I understand completely what you're talking about- but the stroke is still the same, no matter what journal diameter you have.

The only way what you're talking about will work is to offset the journal, but it's pointless and a highly expensive task for any machine shop, and you've built a compromised crank as it willbe far weaker.

Offset grind has been fairly usual in drag racing circles, but normally they have found standard size rods with smaller journal that can be used, eg using Chevy BB rods in stroked Ford BB's

[scotsjohn]

Thats what I was talking about Pete, I said a reground journal with a centreline further from the centreline of the crank. I assumed you knew what I was talking about, the description was aimed at Rich who seemed oblivious to the idea. As stated, I didn't have the dimensions to see if it was possible.

[Yoof]

I'd be surprised if there was enough meat in the crank to make it viable on a Polo- main thing is cost, machine shop time is by no means cheap, especially for custom tooling and one off jobs.

I'm only aware of this being done to get within capacity regs for specific motorsport applications, I'm still unsure why you'd bother with it cost wise, when a custom set of pistons is circa £600/set.

[Insight G40]

I will be selling a complete 1473cc engine very soon.

[dub-disaster]

Isn't it already sold?

[Richg40]

It's not the modification of the crank that increases the stroke, it's offset of the sleeved conrod that would alter the swept distance. Totally fucking pointless in the grand scheme of things. Lets get some perspective here, this is a polo engine (!) not a 10000 horse drag machine burning an oil drum of alchohol every 50 yards. Fucks sake.

[Insight G40]

Isn't it already sold?

No, I have two, one in bits that is sold, and one built that I haven't listed yet.

[dani1326]

would it be easyer to bore mine out to 77mm (1341.11cc) then slap in some Wössner 77mm pistons??