cometic head gaskets - Page 4

BillK · 06-21-2017, 10:02 PM

Quote:

Originally Posted by Jeff Stout

On my sbc I didn't spray coating as I was informed by many not to. If you had good luck spraying then I will on next rebuild for piece of mind as I run alot of nitrous and feel leary of not coating them. Thanks for the info.

You have to be careful with this as most MLS gaskets have a coating on them from the manufacturer that is there to help them seal. Putting another coating on them might actually make it worse. I prefer to go with whatever the gasket manufacturer recommends.

carl hinkson · 06-21-2017, 10:23 PM

Quote:

Originally Posted by Jeff Stout

On my sbc I didn't spray coating as I was informed by many not to. If you had good luck spraying then I will on next rebuild for piece of mind as I run alot of nitrous and feel leary of not coating them. Thanks for the info.

Jeff
I have always sprayed my Cometic head gaskets with Copper head gasket spray with no problems to date.

I have seen quite a few old Cup engines that have used cometic gaskets that were sprayed with Copper head gasket spray. If they are using it that's good enough for me.

terry1 · 06-22-2017, 08:08 AM

Rick, are you going to be ready for the Miramichi NHRA races???
Terry K

RonP · 06-22-2017, 01:04 PM

OEM head gaskets require a "smoother" surface finish to seal coolant and oil passages. The "rubbery paint" is there to provide a micro-seal against leaks. OEM head gaskets are beaded to provide an effective sealing load around these passages and the chamber.

A torque wrench measures torque, not friction as someone stated earlier.

Torque = friction coefficient x tension x thread diameter (for elastic region bolts).
Friction coefficient is generally 0.1 ~ 0.3.

Adding oil or other lubricant will increase the bolt tension over a dry or unlubricated condition. Something a friend and I did at work years ago with a strain gauged bolt to see for ourselves.

SSDiv6 · 06-22-2017, 03:25 PM

In lieu of the Copper head gasket spray I would recommend Hylomar spray.
Do not use the Permatex/Loctite Hylomar sold at most auto stores; it's a watered down version of Hylomar.
The best Hylomar is the Yellow can industrial version.

BillK · 06-22-2017, 03:42 PM

Quote:

Originally Posted by RonP

A torque wrench measures torque, not friction as someone stated earlier.

Ron,
That is correct and what I was trying to get at was the fact that the friction will significantly affect the preload on the fastener for a given torque. My choice of words were not the best

Rich Biebel · 06-22-2017, 08:22 PM

I have used Cometics with zero issues for at least 5 years. I have reused the same gaskets 3 times with no additional coatings and also another set 2 times with copper coat spray. This is a 15-1 compression engine and with or without the copper coat there was no leaks. Pretty smooth finished block and heads. I generally block sand the heads if they are off with wet 400 paper in a wash tank. Cometics work very well for me.

RICK W · 06-22-2017, 10:18 PM

Thanks for all your comments guys, the block is just machined too rough for those gaskets

Ed Wright · 06-23-2017, 02:18 PM

Listen to Rich.

Greg West · 07-05-2017, 08:29 PM

Something else to consider on a SBC is the size of the dowel pins. The OE dowel pins are .309" diameter. If .3125" (5/16") pins are used the head can bind on the pins. This will prevent the head from clamping properly to the block in the lower corners. Several companies sell SB dowel pins that are actually 5/16" roll pins.

06-22-2017, 08:08 AM	#33
terry1 Member Join Date: Sep 2006 Location: Moncton, N.B. Posts: 276 Likes: 24 Liked 24 Times in 13 Posts	Re: cometic head gaskets Rick, are you going to be ready for the Miramichi NHRA races??? Terry K

06-22-2017, 01:04 PM	#34
RonP Junior Member Join Date: Mar 2003 Location: Detroit,MI Posts: 75 Likes: 25 Liked 24 Times in 11 Posts	Re: cometic head gaskets OEM head gaskets require a "smoother" surface finish to seal coolant and oil passages. The "rubbery paint" is there to provide a micro-seal against leaks. OEM head gaskets are beaded to provide an effective sealing load around these passages and the chamber. A torque wrench measures torque, not friction as someone stated earlier. Torque = friction coefficient x tension x thread diameter (for elastic region bolts). Friction coefficient is generally 0.1 ~ 0.3. Adding oil or other lubricant will increase the bolt tension over a dry or unlubricated condition. Something a friend and I did at work years ago with a strain gauged bolt to see for ourselves. Last edited by RonP; 06-26-2017 at 11:08 AM.

06-22-2017, 03:25 PM	#35
SSDiv6 VIP Member Join Date: Feb 2003 Location: Glendale, Arizona Posts: 2,991 Likes: 693 Liked 1,457 Times in 543 Posts	Re: cometic head gaskets In lieu of the Copper head gasket spray I would recommend Hylomar spray. Do not use the Permatex/Loctite Hylomar sold at most auto stores; it's a watered down version of Hylomar. The best Hylomar is the Yellow can industrial version.

06-22-2017, 08:22 PM	#37
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,275 Likes: 25 Liked 510 Times in 200 Posts	Re: cometic head gaskets I have used Cometics with zero issues for at least 5 years. I have reused the same gaskets 3 times with no additional coatings and also another set 2 times with copper coat spray. This is a 15-1 compression engine and with or without the copper coat there was no leaks. Pretty smooth finished block and heads. I generally block sand the heads if they are off with wet 400 paper in a wash tank. Cometics work very well for me. __________________ Rich Biebel S/C 1479

06-22-2017, 10:18 PM	#38
RICK W Junior Member Join Date: Jun 2007 Posts: 64 Likes: 0 Liked 0 Times in 0 Posts	Re: cometic head gaskets Thanks for all your comments guys, the block is just machined too rough for those gaskets

06-23-2017, 02:18 PM	#39
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 389 Times in 168 Posts	Re: cometic head gaskets Listen to Rich. __________________ Ed Wright 4156 SS/JA

07-05-2017, 08:29 PM	#40
Greg West Junior Member Join Date: Jul 2016 Posts: 55 Likes: 11 Liked 46 Times in 19 Posts	Re: cometic head gaskets Something else to consider on a SBC is the size of the dowel pins. The OE dowel pins are .309" diameter. If .3125" (5/16") pins are used the head can bind on the pins. This will prevent the head from clamping properly to the block in the lower corners. Several companies sell SB dowel pins that are actually 5/16" roll pins.