With Wings As Eagles: Craig P. Steffen's Blog

lightening the load

2009 May 23 09:09

I balanced the new pistons for my VW yesterday. They came with a spread of a little over 3 grams across the set. I spent some time grinding and weighing yesterday, and reduced the spread to .4 grams, and it would have been better if I hadn't overshot on one of them. The VW factory tolerance for new pistons is 5 grams, so even the original set was within spec. My inspiration for doing more was this post by Bob Hoover.

Here's my setup, fairly shortly after noon, with my supervisor looking on

Here's what I was doing. Pistons are cast with "balancing pads"; sections of metal that are specifically designed to remove to reduce weight. Here's the piston that started out as the lightest; I haven't removed anything from its pads. They are marked with green dots so they're easy to see.

And here's what started out as the heaviest one, which I basically ground the pad down to the base metal. With the pads the size they are, I don't think you can safely remove much more than 3 grams to balance it.

To do the grinding, I went out and bought a bunch of the cylindrical grinding sleeves for my rotary grinder. I used up quite a few of them.

When you're sanding metal or wood, typically the coarser the sandpaper, the faster material is removed. This isn't necessarily the case with rotary grinding tools. I found that the 120 grid rotary sleeves were much better at removing Aluminum than the 60 grit. While the 60 is more abrasive than the 120, I guess the 120 has more material in contact with the target metal?

I took yesterday off work to get a running start on the weekend. It just turned 10 am here, and in many respects how I do today will be a measurement of how much I've actually gotten better at working on stuff this spring. I am a serial procrastinator, but I've gotten slowly better this spring. More instances of going on trips and unpacking immediately when I return, rather than unpacking a suitcase when it's time to pack in it again. More leaving for trips on time. The summer gets busy in not too many weeks, and this weekend will provide the best chance for me to work on this engine for the next couple of months.

I don't realistically think that I'll get it done and in the car this weekend (although that'd be great), but if I get it far enough along that I can just continue to work on it in the evenings, then that will be a great accomplishment. However, that's going to require me to dig in and really work on it today. None of this lounge around on vacation and sort of putter; I need to dig in and work. Yesterday was a good start, but I need to do 8 or 10 hours of good work today.

And I just realized that I never checked the head chamber volume on the second new head that I have. Argh.