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Old 11-14-2012, 03:18 PM   #1 (permalink)
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Cometic head gasket for 120?

Anyone have a part number for a .030" Cometic head gasket for a 120? Just want to bump the compression a bit and want to be sure I order the right one. Any suggestions for a good vendor?
Thanks,
Joe
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Old 11-14-2012, 06:38 PM   #2 (permalink)
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If it's a 120R with a standard 4.060 bore...the .030 Cometic head gasket part# is:
C9070-030
Listed $44.99 a set.
Cometic is right below you in Ohio...and will sell direct.
Their phone number is:
(800)752-9850

.030 milled off them MVA heads and a .030 Cometic gasket will wake that 120R up!!!

Just my 2 cents...from No Cents


Last edited by No Cents; 11-14-2012 at 06:41 PM.
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Old 11-14-2012, 07:12 PM   #3 (permalink)
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Cents, With .030 being milled and the .030 head gasket what kind of increase in compression could be had. I must be reading to much since it get the brain rolling in warp speed.

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Old 11-14-2012, 08:22 PM   #4 (permalink)
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thats perfect. Thanks brother.
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Old 11-15-2012, 04:43 AM   #5 (permalink)
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It puts the static compression right at 11.0:1 with a .030 cut on the heads and a .030 head gasket. Gives the 120R a lot better bottom end pull...the stock 266 cams love the added compression.
It produces pretty much the same results as running the domed piston that GMR offers for the 120R.

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Old 11-15-2012, 03:35 PM   #6 (permalink)
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When I call Cometic for my 120, I ask for a .027 Head Gasket at 4.090 and a week later it is on my porch.
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Old 11-16-2012, 07:57 AM   #7 (permalink)
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While you have the heads off, check piston height. You can fine tune deck height with a thinner or thicker base gasket. From memory Cometic base gaskets are $20.00. If front to rear cylinder height is not the same, get one thickness for the rear cylinder, and a different thickness for the front.
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Old 11-16-2012, 08:01 AM   #8 (permalink)
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Is there a tutorial on how to check the deck height? I'd like to be certain I'm doing it properly.
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Old 11-16-2012, 08:10 AM   #9 (permalink)
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At one of the site sponsors, Big Boyz. Here's the link.

http://www.bigboyzcycles.com/showthread.php?t=92
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Old 11-16-2012, 12:35 PM   #10 (permalink)
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I find that the solder method is the easier way to check squish, as you can do it before disassembly - here's one example:

http://hammerperf.com/ttcheckingsquish.shtml

I prefer to just leave the motor assembled and use a long peice of solder with a 90 degree bend in it inserted through the spark plug hole and held against the cylinder wall directly above the piston pin.

I check it on each side of the piston, and shoot for .030-.035 squish -- and if it's higher, get a thinner base gasket to correct.

If your squish is set nice and tight you'll notice a snappier midrange and less pinging (my compression is much higher than stock, running the same cam, but getting less pinging than before -- and I attribute it to having the squish set correctly)
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Old 11-16-2012, 02:32 PM   #11 (permalink)
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Use this bridge and a dial travel indicator
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Old 11-17-2012, 06:56 PM   #12 (permalink)
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Quote:
Originally Posted by nw_guy4_fun View Post
Use this bridge and a dial travel indicator
This device measures squish clearance?
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Old 11-18-2012, 10:16 AM   #13 (permalink)
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Add a travel indicator and then read the actual TDC piston depth, then an intelligent head gasket decision can be made. I know typical on the 120r but you never know for sure until it is measured and straight edges and a feeler gauge is a recipe for problems in the hands of most.
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Old 11-18-2012, 10:50 PM   #14 (permalink)
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Randy's vid. will walk you through the measurements.
Watch the vid. at the top of the page.

http://kingofcubes.com/?page_id=148
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