Another Technique for Piston Notching.

Good article - well written, good technique. Nice work!

Any feel for how long the belt sanding paper will last, how many notches before it needs replaced? Obviously, your mileage may vary.

I used 2 disks. The first wasn't worn, but I tried to speed things up on the 4th piston by bearing down fairly hard and it lost a disk. The 2nd disk finished that piston and all the remainder. Both were a little worn, but still usable.

I used 50 grit because it was free and would expect that 36-40 grit would cut faster and last longer. It would also leave deeper grooves. The 50 grit never clogged.

As a side note, I first tried to eliminate the 50 grit scratches by following up with an 80 grit (belt sanding roll) disk but it quickly clogged--that is when I reverted to the Dremel.

Does anyone know of a way to notch the pistons while they are out of the block? I suppose if you take an initial measurement from one cylinder you could rig up something on a drill press. Notching in the block is too risky for me but I don't ride roller coasters either!

Awesome work Dennis!! This is the method I use as well...with only a few differences. I do use 36 grit, simply for the ease of cutting and the larger particles it seems to leave (not a lot of dust). Another difference is I leave the paper about 1/8" larger than the valve. This helps make a nice blend at the base instead of a sharp cut. The final real difference is that I use a 3m scuffing disc (picture green scrubby, only round and 1.8" larger than the valve head) glued to the valve head to 'polish' the cut. This takes the scratches out from the 36 grit, and leaves a VERY nice, very smooth, lightly turned appearance. Smaller differences are I used an old 1.78" SBF intake valve I had laying around from some 289 heads for the exhaust, and a 2.24" 351c 4v valve for the intake. I, like you...feel that radial clearance is JUST as critical as depth clearance.

Here's a picture of how mine turned out. Note, I didn't need to do the exhaust on this one...only trim up the intake for radial:



The roughly circled area is the area I cut.

Anyhow, again...awesome write up, and thank you for taking the time to let everyone know how this stuff works in such a clear, and concise manner =D.

Cris

Not to make a fuss, but what in the world does the appearance of the valve notch have to do with the performance of the engine?

You both made yours pretty after the notching for clearance, but why?

Carbon can more easily stick to a rough surface and sharp edges can heat up and cause preignition.

Originally Posted by bmcd66250

Carbon can more easily stick to a rough surface and sharp edges can heat up and cause preignition.

Exactly...it's an anti-detonation/preignition tactic! It's the same reason that, before you assemble a motor you put a light bevel on the edges of all the reliefs to round them off a bit. Just one more step towards the safe running of these motors when they're going to be abused with either compression, rpm, load...or any combination of the above.

Cris

Excellent knowledge to have! Thanks!

Very good article. This is why I am now a paying member for this site.
Thanks.