Coats 1250 2D Balancer Accuracy Problems

[cavalry]

Well my $77 auction balancer apparently has issues. Everything at its face works as it should with no errors. I have a couple (probably) known good balanced wheels that when balanced will say they need weight. I can then rotate the wheel on the shaft 180* and it will say a different amount of weight in a different spot. I need to pick up a dedicated test wheel but dont have anything appropriate on hand. I guess first need to go to my buddies shop and verify that the known good ones are spot on but since I can rotate them on the shaft and get different readings I am thinking its not the wheels.
There is no water or anything in or on the tires, the correct cone is being used, the wheel face is clean as is the hub. I have not run a calibration as my understanding is the calibration procedure is to align the machine to actual, I do not think it will help since I can't get repeatable readings in the first place?
I can find no technical manuals for any coats balancer, I am sure they exist somewhere. Anyone have any insight on troubleshooting these? Hiring a tech is probably not going to happen, a service call and parts is likely to exceed the value of the machine.

 

[39CAMC]

I don't know if it will fix it, but you absolutely need to do the calibration as the next step. And at least on Hunter machines, calibration is designed to fix this *exact* issue - it even has you move the test weight 180 degrees during the process.

Not doing it is the equivalent of an engine having a dead miss and not replacing the 10 year old spark plugs and wires and pulling the head instead.

Even on a properly working machine, any tire that has been driven on is likely to show at least .25 oz change on 1 out of 4. It's one of those rounding type things, initial spin that showed OK was .12 oz and showed as OK. When you bring it back, the bead is seated better, or there is a pebble and it reads .13 so the machine shows .25 oz needed.

DaveW

 

[cavalry]

This has been an educating experience and a bit of a saga. I was able to find a service manual for a similar machine which seemed to have enough similarities that I could take a stab at diagnosing rather than just WAG. Sidenote- this machine keeps track of how many "spins" it has on it during its life, this one is super low hours, 187424 spins lol. Thats a lot of tires!
Everything I have read states that the calibration tire should be at least 16" but should be a small hole, width wasn't really mentioned. This presents issues for me as I primarily own light trucks, no cars. I had a spare tire for a RX8 that was a 17" so I balanced it at a friends shop, figuring a wheel was a wheel. When put on my balancer it pretty much was saying that all the weight should come off and it would be nearly there without any. I am not for sure but I think the narrow width had something to do with it, either throwing off the machine I used or mine...no clue.
Back to the beginning of this. I borrowed a couple tires off my buddies Audi, they didn't have a lot of miles on them so I figured they would be at least close in balance. They were all over the place 2-3oz off and would not consistently give the same numbers. This was again my folly, thinking that they were being run and 2oz should have shook like a *******. I should have just stopped when I noticed that on both wheels the tape on weights were outboard only, nothing inboard. More time wasting bad decisions.
I finally had enough screwing around and not getting anywhere and drove an hour to the u-pull it to find a suitable tire. Living in the salt belt steel wheels are going to be rusty and I didn't want to pay for an alloy thats never going to be used. Ideally it would be awesome to have something that I didn't have to break down to check for water and then balance. This left me with the ultra rare full size spare. Apparently full size spares are a prize at the u-pull it. I assume because they are low to no miles and people sell them as new even though they are dated out. 2 hours of searching and I found a Volvo with a 16" steel full size spare, still with the ****, factory balanced, perfect as the day it was placed there in 2012 in Torslanda.
I got home with my $22 tire and threw it on the $77 balancer, 00-00, .21 total imbalance. Thats good enough for the girls I go with. I guess I will balance some stuff for real and see where I end up.