Use a table ban saw to hack off the 340 piston crown .

-
I say go for it. You seem hell bent, so why even ask for opinions? Use a bastard file to get the crank journals undersized, too.
 
Now at home Depot, all the tools needed for your home carpentry project AND your engine machining projects...IN ONE KIT!
 
Chuck em up in a wood lathe, use a sharp tool.
If ya really want to get the job over with, clamp em up in a electric miter box, with a triple chip blade, rrrrrrrowe done, :lol:
 
Haha, that’s right up there with my coat hanger coil spring compressor…….
 
340 piston in 360 block : take off bout 0.10" from piston crown if it's thick enough, add a 0.080"head shim on the engine side with a standard 0.038" thick head gasket gets you 0.118" to work with. Subtract from the 0.27" sticking out....you need to shoot for the perfect 0.030 squish/ quench @tdc for the turbulence it creates in your combustion chambers...measure carefully and take in to account your rpm, stroke, stretch at the high end...
What you need is a set of custom rods or destroke the crank.
 
Now at home Depot, all the tools needed for your home carpentry project AND your engine machining projects...IN ONE KIT!

The way American shops keep ditching good quality machines and buying the next cheapest thing on the market, that ain't far off the mark.
 
I've always wondered if you took the doors off a jeep and then drove down the road hanging out the door opening with pencil in hand, how long of a line could you draw with said pencil before the graphite ran out.

A similar method could be used to remove the excess material from the 340 pistons without the risks of cutting round material in a band saw. That's generally a bad idea.
 
I've always wondered if you took the doors off a jeep and then drove down the road hanging out the door opening with pencil in hand, how long of a line could you draw with said pencil before the graphite ran out.

A similar method could be used to remove the excess material from the 340 pistons without the risks of cutting round material in a band saw. That's generally a bad idea.
That reminds me of this.....

 
Another thing to consider when removing a lot of metal from the crown: the top ring is exposed to more heat, & could soften it such that it loses tension. It will also need a larger gap, being exposed to more heat.
 
OP is keeping awfully quiet :poke:Probably enjoying the results of a successful trolling.

:p

I will have to visit the smallblock forum more often, we rarely get entertaining threads like this in the bigblock forum...
 
kind of action necessary if you have an obsolete engine with no or little support...
or the nearest spares are 13,000 miles away.

but a lathe or milling machine is what you need.....not any kind of saw

i run magnum pistons in a Australian hemi 6 maninly becasue i couldn't stomach the cost of custom pistons for what was a pretty standard build (carbs, headers, cam and CR changed) $200 for 8 magnum speed pros from the mexican equivelent of summit :) (i.e 2 for experiments) or $200+ per piston as a custom job from Jaycee.. nice pistons but champaign taste didn't fit my beer budget

Put head on reach down bore and scribe the bore shape into the head
put piston on rod and rod and crank in motor see how far piston sticks up out of the bore
scribe round it at deck height

30 thou in my case

check head/chamber shape inside your scribe line. does the head need work with a flycutter to accomodate your piston ??
decide on angle to cut piston based on the angle you could cut the head chamber perimeter
45* might be good for a quench ring

all looked too hard to me...maybe next time, so didn't bother and just took the edge off the piston, flat

open chamber head on mine and bore and edge of chamber matched pretty good but the piston would have hit head without surgery

So i cut 30 off the edge of the piston crown in a band of about 1/8 inch all round
i put head on motor with no gasket and torqued it up
then checked clearances with platiguage strands glued to the new edge at 12 and 6 o'clock
i.e more clearance than zero but still bloody close at the very outer edge
all good.. i will be running a gasket with an appropriate bore.
i then checked distance from my new edge of piston down to the top ring
found it no worse than a many others
then used this as a model for the 6 i would eventually use

gave me static cr of 12.5:1 with nail head valves as apposed to dished and a standard monotorque gasket. 30+ thou
carbs x3 cam and gearing chosen to suit

been running it like that for 10 years

some luck involved i'm sure, but when i did the build i was perfectly happy in my ignornace of many things... i would not run so fast and loose, these days and would be a little more careful, piston rock with hypers is small due to tight clerance. but i was working with the crapest core in the world, that had been converted to run chevy pistons with a massive deck cut and an odd overbore on a New house new familiy constrained budget i own 50% of all of these engines in the whole of the UK and apart from my spare the rest are in cars I had to use what i had.

as it turns out the special versions i.e race versions of the motor i had, used a similar set up from the factory...

so i lucked into doing something similar to what the factory did

short answer as said by many above
if you can get the correct pistons get them
if you want to modify pistons a lathe is a better bet
this kinda things is dpendent on chamber shape

can you get it all to work effectivly when saddled with a perfect new set of too tall or indeed the wrong pistons?
...... yes i did, and so did chrysler Australia.

easier to do with open chamber head
would not be possible with a near flat heart shaped chamber
never had a wedge head so don't know about them

don't use a saw

Dave
 
Last edited:
Hello fella just find an old guy with a mill in his garage and get the tops milled down...I'm having an old set of 12.5 trw's done now!!!
 
-
Back
Top