SeanMurphy - the car was running, but was severely "disabled" on power output.

DaveO - that's indeed it's an old ironing board, stripped of its fabric cover. It's worked very well for me for many years doing the bulk of my small oxy-acetylene welding jobs, and many general torch heating duties, etc. When it's not needed, it easily folds up and stores out of the way, taking up almost no space.

I've used hand files to surface things flat as well. Really works well when you can clamp what you're working on in a vice, (or clamp the flat file in vice) and stroke the piece across the file (or file across piece) consistently. You need to be attentive, don't want the edge of the file "digging in". On aluminum, stroke backwards with some pressure as well, to help clear the shavings/chips out of the file teeth. Sometimes how you orient the piece and file, can allow gravity to help clear the shavings as well. Alternating directions of filing can be helpful as well. For example if you file or sand for a while with strokes in a "/" direction, change and do it in an orthogonal "\" direction for a while.

You can get a pretty reasonably accurate assessment of flatness of a long surface by simply viewing down the surface and observing if ends are sticking up beyond the middle, or if middle is sticking up beyond the end.

For more precision, you can do ti with a precision straightedge, using the same procedure you use to measure engine block or cylinder head flatness. Lay the straightedge across the surface, and slips various thicknesses of feeler gauges underneath the gage the flatness. (You can also observe how much light shines underneath the straightedge.)

I had to put some spacers under the granite piece, and clamp it down to bend it completely flat. (Maybe because the table I had it setting on was not completely flat.) But I know there are pieces of thick rock that are pretty flat out there. It does help to have a flat table to set them on (if they are not extremely thick.) Big pieces of metal, surfaced flat on the one large surface, work well for surfacing things flat also. The ideal scenario is to have your "flattening tool" be of larger dimensions than the piece you are trying to flatten. I've heard of some people using spray-mounting adhesive to bond sandpaper to the flat surface. That would definitely keep it from slipping around.

You can either move the flat, abrasive tool against a stationary workpiece, or move the workpiece against a stationary, flat abrasive tool.

I've actually straightened surfaces that were milled warped by careless machinists. If a machinist pre-stresses a part excessively, they can easily machine the surface flat as long as it' stays bolted/fixtured to the milling table... but if they do it wrong, as soon as they release the bolts, the work can spring into a different shape and the freshly machined surfaces may not longer be flat.

sportbike - I'm planning on removing the EGR in this VW TDI. I have an innovative method in mind for it. Stay tuned...