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BIKELAND > FORUMS > DRAGBIKE ZONE.com > Thread: Head Milling vs. Thin Gasket vs. Pistons (Raising Compression)? NEW TOPIC NEW POLL POST REPLY
Shane661


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posted October 17, 2009 02:13 PM        Edited By: Shane661 on 17 Oct 2009 22:14
Head Milling vs. Thin Gasket vs. Pistons (Raising Compression)?

There are a few different means of raising compression (that I am aware of). I was wondering if it really matters which you use? One difference I see with milling is that it affects combustion chamber volume. And it would seem that milling or a thin head gasket would also affect ptv clearance, and I have read, cam timing.

But strictly from a performance standpoint, which would be the best choice?

1) Milling
2) Thin Gasket
3) High Compression Piston

Remember, I am new to this stuff. So if I am missing the obvious, forgive me.

Shane

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BrooklynNYZX12


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posted October 17, 2009 03:09 PM        
Shane,what exactly are you looking for? Are you looking to raise the c.r a little ? A thin head gasket would probably be the way to go,the other options milling and or pistons you may as well go through the entire motor then...A head gasket will be a 1/2 tear down,new gasket ,put it back together the other 2 are more work in my opinion....if you are gonna mill the head I would assume Jim would do it,may as well have him do a valve job too maybe a clean up too...it just snow balls so you have a nice dilemma but what exactly are you looking for,I mean I know your bike is an 8 second bike you are just a big guy. i remember when the 14's first came out 2 guys at E-Town had them and they couldnt get them in the 8's well the track manager was Eddie Krawieck at the time and he hopped on both of them and cranked out 8:80's on 2 different 14's. We were all slack jawed ask Rick Mazzola we were all there.
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Shane661


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posted October 17, 2009 03:19 PM        
I don't have any specific goal right now...just looking for some theory, really.

Of course you never know what could happen over the winter.

Oh yeah, I'm no jockey...that's for sure. Still, I'm not too worried about getting in the 8's really, I know it will happen soon.

Shane

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KZScott


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posted October 17, 2009 03:27 PM        
Pistons usually have deeper valve pockets to allow for big cams
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01 ZX-12R 8.84 @ 156.3 no bars, DOT rubber, Pump Gas NA..... turbo 8.47 @ 164
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot... turbo 8.32 @173
00 ZX-12R NA 1: 222.04 1.5: 226.39 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB

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almost_les


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posted October 17, 2009 03:44 PM        
if you just want a little extra CR, the thin head gasket isnt a bad choice. i did it. along with adjustable cam sprockets. good performance gains if you're on a tight budget like me. IMO pistons don't seem like they are worth it unles you are going with a big bore, or big nitrous/turbo. i can't see why it would be justified buying high CR pistons for the stock displacement.
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Y2KZX12R


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posted October 17, 2009 03:57 PM        
quote:
There are a few different means of raising compression (that I am aware of). I was wondering if it really matters which you use? One difference I see with milling is that it affects combustion chamber volume. And it would seem that milling or a thin head gasket would also affect ptv clearance, and I have read, cam timing.

But strictly from a performance standpoint, which would be the best choice?

1) Milling
2) Thin Gasket
3) High Compression Piston

Remember, I am new to this stuff. So if I am missing the obvious, forgive me.

Shane



Set the squish to .036"-.038" and then mill the head to the desired CR.

Both milling and the head gasket can change the CR but milling cant change squish.

Both milling and head gasket change the Piston to Valve clearances.


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Shane661


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posted October 18, 2009 05:57 AM        Edited By: Shane661 on 18 Oct 2009 13:58
quote:

Both milling and the head gasket can change the CR but milling cant change squish.



How is it that milling does not affect squish? It would seem to bring everything closer together:



How can it not affect squish?

Shane

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Y2KZX12R


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posted October 18, 2009 09:14 AM        
Because that diagram is a 2 stroke cycle engine. The squish is totally different in that example.

Look at another example and picture milling the deck surface.
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Shane661


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posted October 18, 2009 09:15 AM        Edited By: Shane661 on 18 Oct 2009 17:37
quote:
Because that diagram is a 2 stroke cycle engine. The squish is totally different in that example.

Look at another example and picture milling the deck surface.


I found that diagram on a Harley oriented site (NHRS), sorry.

http://www.nrhsperformance.com/tech_squish.shtml

Apparently certain harley cylinder heads have an angled squish band.

I'll see what else I can find...

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Shane661


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posted October 18, 2009 09:21 AM        Edited By: Shane661 on 18 Oct 2009 17:35
edit
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Shane661


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posted October 18, 2009 09:27 AM        Edited By: Shane661 on 18 Oct 2009 17:32
Another image:



If this picture is accurate, I think I see it now...

Shane

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Y2KZX12R


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posted October 18, 2009 09:38 AM        
Yep. I knew it was just because of that 2 stroke picture you didnt understand.
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Shane661


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posted October 18, 2009 09:41 AM        Edited By: Shane661 on 18 Oct 2009 17:59
Harley head with angled squish band:



http://www.nrhsperformance.com/tech_squish.shtml

It figures that I would find something oddball.

Shane

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TRNorBRN6001


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posted October 18, 2009 06:35 PM        
Hey don't forget us fellas that have a base gasket, lol.
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whitehendrix


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posted October 18, 2009 07:30 PM        
all of them within reaon affect PTV. using an offset piston ( as far as the crown thickness) would if the valve pockets aren't cut to compensate.. ( assuming you'd change another PTV vraiable.

base gasket and head gasket are beneficial from a cost standpoint. if you're dealing with stock internal values you KNOW will clear .00X-.0XX" difference in gasket thicknesses, then you can esentially instal la thinner head or base gasket and be done with it.. tho i'd surmise you won't gain a hell of a whole lot with just that. pistons are pricey, but add a bit of "insurance" to your rotating assembly, and have (usually) an added benefit of being lighter and stronger. milling is usually between the price ranges of gaskets and a piston set, and at least wit our head designs, squish isn't affected for a "normal" amount of material removed from the head. if one were to go apeshit crazy with the shellmill, then squish would be affected, but then again, the head would be ruined at that point as you'd be cutting into the valveseats.

if price isn't an issue, i think a combo of pistons and gaskets would be the ticket.. now, i'm not on a pro level like our resident gurus, but i've built enough off-road race engines to know that combo is usually for the win.

any time you move the head (axially or radially.. whatever way) you'll affect timing.. i wish i could tel lyou it's only going to account for exactly 1 dgree for ever .005" or something, but i really have no idea. Jim or doug probably know.. but yes.. it will be affected, even if it's on a sub-degree level.




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Y2KZX12R


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posted October 19, 2009 04:15 AM        
quote:
at least wit our head designs, squish isn't affected for a "normal" amount of material removed from the head


Actually Jim squish doesn't change AT ALL when you mill the head no matter how much you mill it.
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almost_les


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posted October 19, 2009 07:27 AM        Edited By: almost_les on 19 Oct 2009 15:27
+1 with these head designs, the "squish shelf" is on the same plane as the head gasket seating surface. you mill the head and you're milling the squish shelf too.


picture jacked from kzscott

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KZScott


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posted October 19, 2009 12:44 PM        
Shane, some info about measuring squish in this thread http://www.bikeland.org/board/viewthread.php?FID=13&TID=44211&pagenumber=1
pics from dads motor(more in the thread):




____________
01 ZX-12R 8.84 @ 156.3 no bars, DOT rubber, Pump Gas NA..... turbo 8.47 @ 164
00 ZX-12R 8.62 @ 165.2 no bars, slicks, Pump Gas, 55 shot... turbo 8.32 @173
00 ZX-12R NA 1: 222.04 1.5: 226.39 Loring AFB
00 ZX-12R street turbo 1: 227.9 1.5: 234.1 Loring AFB

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Shane661


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posted October 19, 2009 01:03 PM        
Thanks for the pics, guys.
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whitehendrix


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posted October 19, 2009 07:20 PM        
you're right ( as always) Jim.
i dunno what i was thinkin.. i was thinkin that.. well, i don't really know.

i see where i messed up. i apologize for misinformation.
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weapon. The black is for formal
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ill never own a busa unless
someone gives me one.... and then
ill sell it -KZScott





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Shane661


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posted November 01, 2009 07:12 AM        Edited By: Shane661 on 1 Nov 2009 15:13
So, as far as setting the squish....

This is done via base and/or head gasket thickness, and/or machining the tops of the pistons?

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entropy


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posted November 01, 2009 08:44 AM        
quote:
So, as far as setting the squish....

This is done via base and/or head gasket thickness, and/or machining the tops of the pistons?


Shane,
yup, but machining pistons is a PITA,.
Base gasket is best option bc you can get thicknesses down to .005 (copper)

In KZ's pic above, he'd prob get more consistent results if he cut the solder into equal lengths (i use 1/4"), and place the solder very near the edge of the piston so the entire piece gets "squarshed".

Measure the thickness of all pieces, then average the 2 which were on opposite sides = repeatable to .001"
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dougmeyer


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posted November 01, 2009 04:06 PM        
I do it a little differently. Don't like all the monkey motion with the head on/off etc. Icky grease and all. Use tools. You all might remember my pics of Brenda's engine going together. It seems to work.
D.
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chavcat


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posted November 01, 2009 05:11 PM        
Doug - what was this post titled?
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dougmeyer


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posted November 01, 2009 06:31 PM        Edited By: dougmeyer on 2 Nov 2009 02:34
I just looked at it and there was only one pic- SO here are some more.

First bolt the assembly you want to check together


Then measure the piston height above or the depthe below the deck with a dial caliper of dial indicator. Measure just above the pin to negate rock.


Measure the thickness of all the spacers and gaskets you'll be using in the assembly.
Do the math - add all the spacer thicknesses and determine the net effect on the piston deck height or depth.
If you are doing an assembly that employs a composite gasket (not solid) you have to measure a used one that has been squeezed down.



This is a very accurate process if you are careful. I've checked it against the solder method when in doubt and found errors generally less than .002"
Questions?

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BIKELAND > FORUMS > DRAGBIKE ZONE.com > Thread: Head Milling vs. Thin Gasket vs. Pistons (Raising Compression)? NEW TOPIC NEW POLL POST REPLY

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