Triumphrat

shrugger

I likely misread something some where. But to be sure...
Crank was ballanced to 50% Should that be correct?

__________________
"Thanks to denial, I'm immortal" -Phillip J. Fry

Webby

Hi Shrugger,
The static balance factor for the 650s according to the book is 85%. I have no idea how this is calculated or if the balance factors are different for dymamic and static balancing. The balance weights (Z138) used on the crank journals weigh 689 grams each.

Webby

shrugger

Yeh, I thought 85% as well. That may be static ballance?
The ballance weight would be differant from factory due to the
750 pistons from the Morgo I'm using
Jeff said he checked various referances, as well as a couple guy's
experianced with Triumph's. Seems they all agree with 50%.
First I'd heard though.

__________________
"Thanks to denial, I'm immortal" -Phillip J. Fry

Coroja

Shrugger - crank balance bob weight is 100 percent of the rotating weight plus 50 percent of the reciprocating weight. In your case, reciprocating weight is the weight of the piston + pin + rings + locks + small end of the rod = 461 gm. Half of that (i.e. 50%) is the 230.5 gm figure on the balance sheet. Even though the engine is dry sump, I might have added a couple of grams (or more) for oil attached to the crank (windage).

A 50% balance factor is standard for vertical twins. Effectively, that means that half of the vertical (up-and-down) imbalance caused by piston movement is being "converted" to horizontal (i.e. fore-and-aft) motion, which is less easily felt. Engines operated primarily at higher RPMs (e.g. race engines) are often balanced to a higher factor (percentage). Current NASCAR practice is to overbalance to about 85%, because it seems to increase the life of the main bearings. However, that is being done with V8's that regularly are turning 9000 RPM.

__________________
The people who talk the most generally have the smallest results. Results speak for themselves. - Matt Mladin

shrugger

Newer referance than my 40 year old reprint.
Now that you've explained it. It makes sense.
It should run smooth as hell now. (Well, for a British twin at any rate.)

__________________
"Thanks to denial, I'm immortal" -Phillip J. Fry

jimmy bush

For 50% I come up with 586.5 grams. The way I read the data sheet gives me 314.5 for the big end of the rod plus 41.5 for the bearing = 356 grams of rotating weight (not 360 as shown. Maybe the machinist added some to compensate for the oil in the sludge trap cavity). This is added to 50% of the reciprocating mass consisting of piston, pin, rings, clips, & small end of rod. (461 X 50% = 230.5). 356 rotating + 230.5 reciprocating =586.5 for a 50% balance factor. The static balance and dynamic balance factors should be the same. The dynamic works better because it balances the crank from side to side eliminating some of the horizontal coupling. The machinest I talked to when I had my 68 crank balanced said he used the 50% figure for multi cylinder engines where the pistons were staggered in their rotation but didn't think 50% would work for a vertical twin. I had mine done to 75% and am pleased with the results.

Coroja

Jimmy - I agree with your computation of the rotating mass and suspect you are correct about the source of the extra few grams. I didn't focus on the rotating mass because the original question appeared to be about the balance factor. However, it could just as easily been about the discrepancy that you have pointed out. Thanks for the clarification.

__________________
The people who talk the most generally have the smallest results. Results speak for themselves. - Matt Mladin

jimmy bush

Coroja, I wasn't trying to correct anybody, I just type too slow. When I started my post, Webby's was the last post. While I was typing my post, Shrugger posted twice and you once. I didn't know until I submitted mine with what observations you saw.

shrugger

For those not following my restro thread. Here's what was removed
to ballance. They ran outta places to drill so the counter 'ears'
were also shaved. This thing must have been right out from the factory

and 2 more on the other side.

__________________
"Thanks to denial, I'm immortal" -Phillip J. Fry

EddyJ.

"Back in the day" ['63-'64] The Bonneville I rode for Johnson Motors was balanced at 65% FWIW. I was 26 at the time and as long as it went fast, why would I notice "Smooth" ? :-)
Ed J.