In-Frame Piston Mods

While I had the head removed on my daily driver for some upgrades over the winter break and holidays, I performed some in-frame piston bowl modifications. This is my true daily driver so I stayed conservative on the de-lipping in hopes of keeping the compression ratio reasonable.

A die grinder with a carbide burr was the main roughing tool and blue painter's tape was used to cover passages and openings on the motor to try to keep the aluminum shavings out of the oil system.









After some finish cuts with a dremel tool and sandpaper roll, it cleaned up ok... LOL good enough for my 300K mile motor. With 57mm diameter bowl openings, I calculated that I dropped compression from 17.5:1 down to 16.5:1.







It was tight back on cylinders 5 & 6 so I had to use a right angle air-powered die grinder.



I put the motor back together with a .010" over headgasket so the final compression ratio should be really close to 16:1. A good compromise between daily driver and performance.

wow! I was cringing until i saw the finished pics. looks like it turned out ok.

Finished product looks good.

jlibert said:

wow! I was cringing until i saw the finished pics. looks like it turned out ok.

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Same here. I'd still be worried about all those shavings.

Will, you are crazy!!! I would like to have seen you layed up there working on 5 & 6. Looks good though.

Never in a million year did I figure I'd see someone do that and do it so well.

Ummm. How'd you prevent the shavings from going between the piston and cylinder wall?

I seen people flycut pistons with motor in truck with a router

Thinking about doing the samething to mine while i have the head off. Are there any concerns about the difference each piston weighs now since you weren't able measure exactly how much was taken off? I know in your junker thread you balnced your pistons just curious.

Balanced to +/- 1g. No problemo.

You sir are a man with more time and kahones than phucks to give.

INTHERED said:

I seen people flycut pistons with motor in truck with a router

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yes a router, with a pieces of plate steel with a hole in it for a pattern would do awesome.

oldestof11 said:

Ummm. How'd you prevent the shavings from going between the piston and cylinder wall?

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You should be able to roll to TDC and blow most of the shavings out.

I've never really heard of wider bowls making a substantial increase in power on a moderate build though. It's hard to tell from the pics, did you cut them to the edge of the bowl?

You should be able to roll to TDC and blow most of the shavings out.

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There's still quite a bit of room before the top ring where pieces could get lodged.

Atleast it's aluminum. Think about all the little chips from bottom tapping for head studs people probably let fall in.

Me and will had joked about this a while back when I visited, didn't think he'd actually go for it!! LOL

I had to do something similar to get my Pistons to not hit the valves.

TheBigNasty said:

You sir are a man with more time and kahones than phucks to give.

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Couldn't agree more with this statement..

To keep the bowls somewhat round, I took measurements across the bowl in multiple directions as I roughed them in. By the time I got to the 3rd piston, I was pretty good and keeping even pressure as I made rounds in the bowl cutting away layer after layer.

As far as aluminum chips, some do get trapped in the area between the top ring and side of the piston, after a combination of WD-40, carb cleaner, compressed air, and rotating the motor over twice, I removed 100% of what I could see and the cylinder bores were clean after (2) revolutions of pushing the chips up and spraying with compressed air.

As far as balance for weight/piston bowl volume, you could use a piece of plexi-glass with a small hole to fill the bowls with water from a metered syringe. Lots of YouTube videos demonstrating how to "cc" the combustion chambers on race heads that use the same process. For this high mileage daily driver, I just used my calipers to make them close and called it a day.

I did not fully de-lip the bowls, there would be too much compressor drop for what I want to do with a daily driver as far as cold high mountain hunting/camping trips where I need a reliable cold weather starting rig.

I cut the pistons so I could continue to run 26* timing where I'm getting excellent fuel mileage without the bad side effect of spraying fuel right on the lip where it will eventually cause cracks and piston damage.

Considering diesel needs more compression to ignite at colder temps, you think this'll still start up great past 0deg F? Just curious. Even at 21deg and a stock short block, mine does not like it. I'd probably take a gasser on a hunting excursion instead just for assurance.

You sir, are a very ballzy man though! I was totally expecting to see that you rigged your lathe up on top of the engine or something like that. Good work!

They do have mag drills out there that could do the job, find the right size hole saw and go to town! LOL

will, my 16:1 motor does okay at around 25* at lower elevations, up at 7000ft I do have a hard time starting just on grid heater alone, A little sniff of ether takes care of that.

YOUNG GUNS15 said:

A little sniff of ether takes care of that.

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A breath of summer air in a can.