Rod balance jig tool for Zero $

[RichHawk]

I'm going to use a chemists scale today from the local high school chemistry lab for balancing my rods and pistons. I know the chemistry teacher.

The digital scales they have are impressive. They have resolution to .001 grams (Uh, I think that's a bit overkill), and I've been told cost $3000 each, and get calibrated every semester.

So I had to make up a jig or tool for holding the rods steady and parallel in the scale while allowing me to weigh the big end and small end quickly without having to worry about side loads affecting the scale.

Last night the teacher called me and said it has to be late this afternoon if I want to weigh my stuff. I couldn't fine even one reference on the pelican board for a "make your own" Jig. But the internet had one from the corvair guys.
So credit where it is due, I blatantly copied my concept from here:

http://www.angelfire.com/ca4/CorvAIRCRAFT/RodBalance.html

So at 10:00 on a Sunday night I went to my garage to see what I had that I could make a jig up with. It wasn't pretty. I just threw out all my scrap lumber. The only thing I had were a couple 2x4 that I've used to spread the force when jacking a car up..

So excuse he crudeness. This was a "1 hour and what do you have lying around" project. If I had a full machine shop at my disposal it would be billet AL, with adjustable hand wheels, and roller bearings.

Curtain brackets, Shoe strings, Zip ties and 2x4s. It sound like and looks like a Rube Goldberg machine. But it will work just fine. Note the adjust-ability of the scale end. Ohhhh... Fancy slot and flat head screw!

Richard

[RichHawk]

And I got about Zero dollars of usability from it....

After fussing around with it for a couple hours, I concluded that it's really really easy to get inaccurate measurements by not having the correct diameter ends on the jig.

As it turns out it's real easy to get either end off just a smidge from resting centered in the bore, and that affects the scale reading by as much as 5 grams with the most minor of adjustments.

My recommendation, make the diameter inserts to match the rod end and crank end like what the Corvair guy shows.

But the good news is that my rods all weighed in statically within 1.4 grams of each other. I was able to mix and match rods, pistons, and pins to get 0.6 grams variance from heaviest set to lightest set.

Richard

[sc_rufctr]

Good effort... Sounds like you learnt a lot so it was well worth the time to build your jig.

I enjoy making my own versions of "P" tools for my car.
The first thing I do when planning a major project is seek out the measurements of the required Porches tools and go from there.

I own a Mill/Dill and a rotary table so it's relatively easy for me to make these.

My next project it to make a wheel alignment jig based on a "Starrett" No 99 Surveyors level I bought of E Bay for $40.
I'll post some pics in the 911 engine forum when it's complete.

[Raceboy]

Thanks for the info, I'm going to fabricate a jig for Porsche rods soon to balance mine.

[gearheadgreg]

Nice job Rich. I made centering pieces from using fiberglass resin (with no fiberglass) using an old rod. Drilling the centering hole was harder for me to do.

[kenikh]

Man this is a good "how to" video on balancing rods:

[haycait911]

interesting video. goes to show the build quality of our cars. all six of my SC rods were within 2 grams overall weight, stock.

[jbell959]

I've been to John's shop (Costa Mesa R&D) a few times and he does really nice work. He does a lot of 911 machine work for local shops.