Opinions on removing crank counterweights

[ELS]

So I read in this tuning book on a small NA inline 4 engine where it said to mill off the balancing counterweights, knife edge all the edges, and then turn down the main bearing points to accept a roller bearing instead.
this all seemed like it was a lot to ask for a stock cast crankshaft to handle when you intend to spin it up past 7k rpms

what do you think?

[Walter R. Malik]

WoW ... A flathead 4 cyl Model T.

Rotational balance is not the only criteria to balance. "Radial" and "Axial" need those counterweights just as much.

[englertracing]

Don't do that

[Schurkey]

So I read in this tuning book on a small NA inline 4 engine where it said to mill off the balancing counterweights, knife edge all the edges, and then turn down the main bearing points to accept a roller bearing instead.

What book? How "small" are these 4-poppers?

Do you see a lot of 4-cylinder motorcycle engines with no counterweights and roller bearings?

[mag2555]

To me doing such would be akin to stpitity on parade!

[ELS]

So I read in this tuning book on a small NA inline 4 engine where it said to mill off the balancing counterweights, knife edge all the edges, and then turn down the main bearing points to accept a roller bearing instead.

What book? How "small" are these 4-poppers?

Do you see a lot of 4-cylinder motorcycle engines with no counterweights and roller bearings?

80mm bore and 79mm stroke, 96cui or 1.6L all together

ris24.gif

this is how it was shown in the book

but I wonder now... how do they get the middle bearing on? did they like cut and weld it?

[englertracing]

You want the opposite

13310-F20-400.jpg

[dannobee]

Just don't. Talk to any bearing engineer, a pressure lubricated plain insert bearing will have less friction and be MUCH cheaper and more reliable. The only caveat is that you need to give it a steady supply of quality oil. And I can't imagine balancing a roller bearing crank that lacks counterweights. SPG used to make roller bearing cranks for things like VW engines and the counterweights were HUGE. I haven't seen one running in at least 30 years. And if it detonates at all, the roller bearings will take the brunt of it and get hammered out (or hammer out the crank, since it's softer than the rollers). There are other drawbacks too.

Running roller bearings on a shaft, like a cam, transmission, or turbine engine is one thing, but on a 4 stroke reciprocating engine, you'd be better off with plain bearings and decent oil pressure.

They usually assemble the cranks with a press. Sometimes they're splined. And they'd often be pinned or welded to keep them from twisting up when drag racing.

[Dan Timberlake]

I think a light flywheel and small or dual disk clutch would rev just as quick, cost less and survive FAR longer.

Was that a Datsun 510 performance "book" ?

[ELS]

it's not about the inertia, it's about less windage losses.
if roller bearings are so bad for 4 stroke engines, why are many bike engines running roller bearings on their cranks?

[dannobee]

Which 4 stroke motorcycles still use roller or ball bearings?

[ELS]

Which 4 stroke motorcycles still use roller or ball bearings?

well I should've said many bike engines did use roller bearings, can't say I know any modern ones.
but those that did use roller bearings weren't unreliable, so why would it be brittle as glass as you say it is.

[Schurkey]

Back when I cared, Suzuki and Kawasaki were using roller bearings on pressed-together cranks on their 4-stroke "Literbikes", circa 1982--83. Both had problems with the press-fit slipping which caused engine vibration, and--I'd expect--severe case damage. Seems to me one or both eventually pressed the crank together, then spot-welded it so it was less-likely to shift in use. Both used counterweights. Kawasaki, in particular, seemed to have overall good results on the track with those engines.

(I bought a plain-bearing Honda.)

Shaving counterweights and converting to roller bearings seems NUTS to me...which is why I asked what book was recommending this.

[englertracing]

Roller and ball bearings are common on singles and twins as it doesn't add much complexity to the crank.
The reason they are used is to allow some intermittent lubrication. Like a mx bike, backflips wheelies, stoppies, being crashed....
And If you don't believe me about intermittent oil supply, think in terms of a 2 stroke..... just a bit of oil in the fuel is all those bearings get!
On a 4t that's bound to be dropped (now the efi bikes stay running on their side) it's a great idea.

But they do not last like plain bearings in your toyota.

[gunt]

no to the roller bearing , the film of oil takes shock much better ,

but cutting down the crank like in the pic ,, very dependant on the build and spec , so my guy [ passed away since ] pulled 3lb weight out of a 1.6 4cyl crank , while also basically guaranteeing it , balance for 10500rpm [ enough to safely miss a gear ]

on his race engine [ bikes ] there were 1000cc , he had 2 riders , rode completely differently and not only power bands but the weight of the cranks were completely different ,

wish he let me work under him for free ,,,