View Full Version : skimming piston tops
jimbob-mcgrew
26-09-14, 12:48 AM
is there anything bad about skimming the tops of pistons ?
i was thinking about taking off the outer raised circumference, just enough to make the tops flat, taking as little as poss from the centre.
https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-frc3/1506869_10152470309439447_1594872705_n.jpg
Peredur
26-09-14, 08:04 AM
So long as you've got about 6mm of crown thickness left it should be fine. I'm going to heavily modify a set of 1.2 pistons and that's the rule of thumb I've found out
I take it your doing this in a lathe?
jimbob-mcgrew
26-09-14, 10:29 AM
I take it your doing this in a lathe?
yeah, i'd be getting a machinist to do it.
i dont think i could get it quite true doing it myself. even if i measured the hell out of it continually as i went.
Flap disc FTW
hehe, its tempting to cowboy it, with an angle grinder, and emery cloth. lol
why?
im planning something a bit un-orthadox, and experimental, and need to free up approx 20cc for a 10.5:1 CR
jimbob-mcgrew
26-09-14, 10:35 AM
So long as you've got about 6mm of crown thickness left it should be fine. I'm going to heavily modify a set of 1.2 pistons and that's the rule of thumb I've found out
it would be less than 6mm on these pistons. :cry:
the 1.2's have more meat on them to play with.
are you doing a hi-comp 1.3, bored out with 1.2 pistons ?
http://img.photobucket.com/albums/v305/NovaSport/DSCF2194.jpg
the old fashioned way (as in how PMC did them & I copied their pic from CCC mag) of doing this was to machine out where the dish is, and go in approx. 5mm (depending on your final cc requirement) this then looks a lot like the original 1.3 low comp piston crown. mine did high 5 figure miles reliably with it done
20CC!!!!! WOW thats a lot! Or do you mean 5CC per piston?
I'm guessing your doing somthing with forced induction, what will the controller be for the fuelling and spark?
Peredur
26-09-14, 12:01 PM
Yeah, mine's gonna be a variation on the high comp 1.2/1.3 combination. Loads of meat on the 12ST pistons.
jimbob-mcgrew
26-09-14, 12:52 PM
the old fashioned way (as in how PMC did them & I copied their pic from CCC mag) of doing this was to machine out where the dish is, and go in approx. 5mm (depending on your final cc requirement) this then looks a lot like the original 1.3 low comp piston crown. mine did high 5 figure miles reliably with it done
these are 16se pistons, with less meat. im scared lol
20CC!!!!! WOW thats a lot! Or do you mean 5CC per piston?
I'm guessing your doing somthing with forced induction, what will the controller be for the fuelling and spark?
yeah sorry, 20 - 21cc total, so roughly 5 - 5.25 cubic per piston, which to me, looks maybe not quite do-able on the 16se pistons. looking at it, id take a wild guess and say theres maybe 4cc available per piston ? .. i might have to take the final 1 - 1.25cc out of the head chamber. i dont really wanna touch the head tho.
spark and fuel wise, itll be a basic single choke carb and 8v breakerless ignition.
Yeah, mine's gonna be a variation on the high comp 1.2/1.3 combination. Loads of meat on the 12ST pistons.
works nice i hear. 1297cc upto roughly 1400 with the 77.8mm pistons heads. and the compression ratio at a custom figure, depending how much meat you slice off the 1.2 pistons.
mowgli took approx 5mm off his, for a 10:1 CR. i think 10:1 is as far as you can go with regular unleaded. anything higher will probably need super unleaded to combust properly.
Novasport
26-09-14, 01:39 PM
it would be less than 6mm on these pistons. :cry:
the 1.2's have more meat on them to play with.
are you doing a hi-comp 1.3, bored out with 1.2 pistons ?
http://img.photobucket.com/albums/v305/NovaSport/DSCF2194.jpg
Pic thief lol
Mowgli, when you say you machined into the piston, was that 5mm from the total piston height or 5mm down from the base of the valve cut outs?
jimbob-mcgrew
26-09-14, 01:47 PM
Pic thief lol
Mowgli, when you say you machined into the piston, was that 5mm from the total piston height or 5mm down from the base of the valve cut outs?
was that yours was it ? .. hehe, yeah, i thieve from everywhere. dirty bugger i am :)
pretty sure he meant 5 mill from the top, just enough to give them a flat profile
if you get it running I will be impressed, if it runs for more than 1K Miles I'll be even more impressed lol.
I refer you to Edd's Sig quote from me... "cheap turbo builds end up in expensive tears" lol
jimbob-mcgrew
26-09-14, 08:57 PM
i wasnt planning on a turbo, but what i have in mind is more than likely a silly idea, that will result in doom lol
jimbob-mcgrew
26-09-14, 09:10 PM
c16se bottom end, with a 1.2 head.
skim the pistons down to move away from the harsh 12.3:1 CR
i calculated roughly 22cc out, would bring it down to 10.5:1
with the 1.2mm larger diameter of the 1.6 head gasket, id guess the chamber side will already get 1cc, which leaves 21 to be removed from the pistons (if poss).
taking the pistons down should help avoid valve contact from higher cam lift too.
it might work ?
i was tempted to go to town on the head as well, and dremel the valve guides out the way, for better flow.
the only downside is the tiny sized valves of the head. its not the best head to start with, but im not after a rocket ship really, just something a bit more fun.
Pic thief lol
Mowgli, when you say you machined into the piston, was that 5mm from the total piston height or 5mm down from the base of the valve cut outs?
from the top, and the bloke who did the work never billed me for it. he was certain it would blow up
Novasport
26-09-14, 10:01 PM
Did you leave the crown and just have the dish machined out?
the outer flat bit remained, and part of the valve cutouts, and the centre dish was machined with a flat bottom & a radiiused edge.
Hmmm, 1600 with a 1200 head and carb...... I can see where this is going lol
jimbob-mcgrew
27-09-14, 09:21 AM
Hmmm, 1600 with a 1200 head and carb...... I can see where this is going lol
whats gonna happen, it go b00m ?!?
https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcS9YI4nBeqHJmPSQKnex25iJgxR7AY4s OeKX-0VhLu53O8PtcgkiQ
lol
jimbob-mcgrew
27-09-14, 10:01 AM
http://preaprez.files.wordpress.com/2010/09/exploding_car475b9884-1ef2-49b3-898cc91da79ad0d1large.jpg
http://2.bp.blogspot.com/-IyoxVWh6Bvw/UnnJU6PaNKI/AAAAAAAAG58/HUMYGyAEYpU/s1600/transit+car+crash+exploding+hay.jpg
http://www.amazingfunnypictures.com/albums/userpics/10002/exploding_car_04.jpg
http://img1.wikia.nocookie.net/__cb20100611172635/althistory/images/8/8b/Castle-bravo-atomic-nuclear-bomb-test.jpg
http://www.worldculturepictorial.com/images/content/bomb_crater_in_city.jpg
http://www.bjwinslow.com/albums/rottedskeletons/Burnt_Riley_Skeleton_114.sized.jpg
n0o0o0oooooooooooooooo0o0o0o !!!!!!!!!
nova_niek
27-09-14, 11:52 AM
Oh dear... lol
jimbob-mcgrew
27-09-14, 07:15 PM
ok, i guess it'll explode ?
ill scrap that idea
Not what I was thinking lol its either to cheat at Motorsport or for another reason :p
jimbob-mcgrew
27-09-14, 10:23 PM
nah, no cheating going down. it was just gonna be a fun daily, and fancied giving it a go, something different.
honestly tho, what problems might i run into ?
i know the 1b carb will probably run lean.
can the delco remy ignition keep up with a 1.6 ?
compression should be ok @ 10.5:1 shouldnt it ?
jimbob-mcgrew
27-09-14, 10:29 PM
all the piston heads ive examined, i know id have a much higher chance of success with a 1.4 bottom end, but this particular 1.6 is good and strong, and doesnt need rebuilding
Novasport
27-09-14, 10:30 PM
If it did work I would use a 1.3SR inlet manifold with a Sierra 1.8 Pierburg twin choke carb. That is assuming you would be using a 12ST cathedral port head.
jimbob-mcgrew
27-09-14, 10:46 PM
i thought about that myself, as a later date option, a 13s manifold could always go on.
not sure if id want another 2e tho. there ok, and i know them well, but fancied something else. a single downdraft 40, made to fit the inlet, would be interesting. expensive tho, you could probably buy a nova for the price of one of those webers.
the inlet runs on the 12st manifold are horrible too. after the carb drops the fuel, it heads 90 degrees left and right, and i bet it bumps the wall at the end, before entering the port channels. the design doesnt have much fluidity.
why not use a thicker headgasket u can get them made and I would use a weber DMTL carb.
meritlover
28-09-14, 11:57 AM
The 1.6 efi manifold has enough meat on it to be port matched to the 1.2 head. Get the CR right up and management it. No more wobbly distributors or dodgy carbs to worry about.
nova_niek
28-09-14, 12:10 PM
i thought about that myself, as a later date option, a 13s manifold could always go on.
not sure if id want another 2e tho. there ok, and i know them well, but fancied something else. a single downdraft 40, made to fit the inlet, would be interesting. expensive tho, you could probably buy a nova for the price of one of those webers.
the inlet runs on the 12st manifold are horrible too. after the carb drops the fuel, it heads 90 degrees left and right, and i bet it bumps the wall at the end, before entering the port channels. the design doesnt have much fluidity.
The 1.6 efi manifold has enough meat on it to be port matched to the 1.2 head. Get the CR right up and management it. No more wobbly distributors or dodgy carbs to worry about.
Something tells me this is a shoestring experiment so any form of engine management will be unlikely. lol
Why oh why a 1.2 head I don't get it? If it's to run a 1.2 inlet and carb then the is enough metal to remove from the 1.6 head to match the inlet. Not that the carb and Inlet can flow enough to satisfy a 1.6 anyway. So all irrelevant and stupid
It'll be like the 16SV engine lol
Peredur
29-09-14, 12:41 PM
Not wanting to hijack but, does anyone know the chamber volume of a 14SE head?
Thanks
It's smaller than the 1.6
jimbob-mcgrew
29-09-14, 05:42 PM
Why oh why a 1.2 head I don't get it? If it's to run a 1.2 inlet and carb then the is enough metal to remove from the 1.6 head to match the inlet. Not that the carb and Inlet can flow enough to satisfy a 1.6 anyway. So all irrelevant and stupid
cant afford to do anything else.
was hoping to sell some, keep some, and use what bits i have.
but cant afford to keep any of the engine anymore, so will have to sell the c16se complete, and give up on any idea.
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