Surfacing Cylinder Heads with Sandpaper - Quick and Easy

[bulletpruf]

So, I learned something new over the weekend. You can actually surface cylinder heads quickly and accurately with some 60 and 80 grit ceramic sandpaper (Don't use box store sandpaper! Get Hercules ceramic sandpaper from Harbor Freight), a feeler gauge, an OEM Tools 2' machinist straightedge, and an inexpensive granite surface plate.

I used a 12 x 9 x 2 granite surface plate that was about $80 from Amazon, and after I cleaned the machined surface on both heads, I found that one was .0025" warped and the other was .003" warped. Both were within spec of .001" per cylinder (max of .004" per head) but I've been wanting to try this process for a while and I also wanted to give the mating surface a bit more texture to grip the gasket (not using MLS gaskets).

I used 3M's 77 spray adhesive to secure the sandpaper to the block and I used the surface block like a sanding block. I used my straightedge and a black sharpie to draw a grid of diagonal lines to give me a better idea of where I was removing material.

I started with 60 grit, and after a few minutes, when I checked my progress, and I had already taken it down about .001". At that point, I switched to 80 grit to finish it up. I was able to get both heads straight within .0015"; that's the thinnest feeler gauge that I have and it wouldn't go under the straightedge anywhere.

I realize 99% of the folks get this done at the machine shop, but if your machine shop is an hour away, you don't have time to wait in the queue, and/or you just want an excuse to buy more tools and learn a new process, this is worth trying. I was surprised at how easy it was.

I shot a video of the process in case anyone is interested. Mods - please feel free to delete the link if not allowed.

 

[ntsqd]

At the Vintage Race & Touring Car shop we used to "scoot" parts like that semi-regularly. Usually they were much smaller parts. MISF's remote oil filter adapter for his Pontiac Gran Prix's engine was made from a broken truck leaf spring that we draw-filed and then scooted flat. It has never leaked.

Rather than a micro-flat for a budget flat surface I've used a thick piece of glass from McMaster.

 

[bulletpruf]

At the Vintage Race & Touring Car shop we used to "scoot" parts like that semi-regularly. Usually they were much smaller parts. MISF's remote oil filter adapter for his Pontiac Gran Prix's engine was made from a broken truck leaf spring that we draw-filed and then scooted flat. It has never leaked.

Rather than a micro-flat for a budget flat surface I've used a thick piece of glass from McMaster.

I've tried to use glass for this application, but it's typically not flat enough.

Thanks

 

[ntsqd]

Thin glass rarely is. It needs to be 3/4" thick or thicker, and even then it is not as flat as a microflat, but it is flat enough for most uses.

Ideally what you're scooting never reaches an edge of the abrasive and should not hang over the edge. Not uncommon for the edge of an abrasive sheet to be ever so slightly thicker than in the middle of the sheet.

I'm not convinced that it matters so long as care is taken, but I was taught to use a figure-8 motion in the scooting. The idea is to not dwell in any one spot.

 

[bulletpruf]

Thin glass rarely is. It needs to be 3/4" thick or thicker, and even then it is not as flat as a microflat, but it is flat enough for most uses.

Ideally what you're scooting never reaches an edge of the abrasive and should not hang over the edge. Not uncommon for the edge of an abrasive sheet to be ever so slightly thicker than in the middle of the sheet.

I'm not convinced that it matters so long as care is taken, but I was taught to use a figure-8 motion in the scooting. The idea is to not dwell in any one spot.

The stuff I bought was 3/4" or close to it, but believe it was .004" or so warped, so I didn't end up using it. Probably would have worked fine, but I didn't want to take the chance.

Interesting point in the edge of the sheet; wasn't aware of that.

Anyway, I'm not sure I would use this method on the Space Shuttle, but it works well enough for my junk.

Thanks