Head Gasket Trimming Idea

robs ss

robs ss

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I noticed an article in the April edition of Real Classic on head gaskets (pp 106 - 108).
The gist suggested was to trim the gasket to leave behind only "essential" areas, hence maximising contact pressure in these critical areas - not completely unlike, in effect, Jim Schmidt's idea of glueing 0.005" wire to both sides of the gasket.
The picture below shows before and after shots of a Royal Enfield Super Meteor gasket.
Has anyone tried this with Norton twins copper head gaskets?
If so - any comments on results?
Cheers
Rob
Head Gasket Trimming Idea
 
It seems like a reasonable thing to do.

With Norton head gaskets, the problem is ..... there is hardly any non-essential area on the gasket, especially with spigotted barrels. I am not saying this idea has no merit, only that the application in a Norton is not as straight forward as that given above.

Regarding the gluing of 0.005" dia wire. I just fitted my Atlas head. I glued the wire only to the barrel side of the head gasket. I was concerned the copper wire might indent the aluminum head if done to both sides. I have not yet cranked up, so cannot report yet on results.

This is a good topic. I hope good data comes forth.

Slick
 
texasSlick said:
With Norton head gaskets, the problem is ..... there is hardly any non-essential area on the gasket, especially with spigotted barrels.
Slick
Click to expand...

Well Robert... and I'm not saying I'm sold on this idea...
Below is a picture of my first pass at how you might trim my non-spigotted gasket - using the model in the article.
Not sure of the science of the width of the annular rings around the bores/pushrod tunnels/oil gallery.
Worth a thought though!
Cheers
Rob
Head Gasket Trimming Idea
 
With spigoted barrels, at least on singles so i assume also on twins, the spigot provides the gas seal so no great advantage trimming the gasket in that case.
 
Yes, Rob, it is worth a thought and a try.

As far as science is concerned ..... avoid sharp corners such as your diagram has near the pushrod tunnels. They create stress risers.

Next, physics dictates contact pressure increases in direct proportion to area decrease. However, in an essential area, intuition dictates both pressure and area are necessary. I know of no engineering studies that attempt to define the relationship of pressure vs area to sealing.... not saying there are none .... just dunno any. So, in lieu of any engineering or science, we are all in experimental mode.

In my graduate studies, we touched on labyrinth seals. These work to reduce seepage to acceptable levels because the labyrinth progressively reduces the pressure gradient pushing the fluid. This concept can be applied to a typical gasket as follows:

Consider that a gasket surface at the microscopic level, is not flat, but bumpy. The pathway around the bumps results in a labyrinth that reduces the driving pressure as the pathway lengthens. This pathway length is the area function necessary for sealing (think long pipe vs short pipe).

Increased contact pressure pushes gasket material into the microscopic depressions between the surface bumps, reducing the cross-sectional area of the microscopic labyrinth channels. The area reduction reduces the driving pressure of the fluid (think small dia pipe vs large dia pipe). This is the contact pressure function necessary for sealing.

I believe the wire technique creates a very high local contact pressure that presses wire into the the microscopic voids, fully closing the channel.

As far as spigots.... Norton singles sealed on the lip of the spigot, but in the twins, there is clearance between the lip and head. I am not sure if the spigots in the twins provides any benefit at all. The subsequent elimination of the spigot suggests they did not.

I do think Rob is on to something here .....

Slick
 
texasSlick said:
As far as spigots.... Norton singles sealed on the lip of the spigot, but in the twins, there is clearance between the lip and head. I am not sure if the spigots in the twins provides any benefit at all. The subsequent elimination of the spigot suggests they did not.
Click to expand...
Thanks, i've learnt something today. : )
 
I'll do a bit more work then invite comment here before taking dremel in hand.
I agree on risks from sharp corners - you will have noted there are no less than 14 (per cylinder) in the magazine article.
I think I would use a smallish drill (2-3mm) at each "corner" then join the dots with a dremel and finish with fine emery cloth.
BTW - I feel certain that this style of gasket will benefit from waisting all 3/8" studs/bolts to 5/16" - as put forward by others here (notably comnoz & jseng).

Rob
 
Well here's a bit more... comments welcome!
The crosshatched area is material to be removed from the gasket (standard copper).
I have used a 5mm annular ring around the bores and pushrod tunnels. The minimum is 3mm adjacent to bolt holes 3 & 6.
I settled on 3mm around stud/bolt holes as they are only there to locate the "sealing rings" in the correct position.
I've used 3mm drill dia. at all 30 intersections.
It looks like a reduction in area of around 50% - will confirm when cut as stock copper gasket weighs 62g so final weight will confirm area reduction.
So it looks like around 100% increase in clamping pressure should be achieved.
Head Gasket Trimming Idea

Cheers
Rob
 
Last edited:
Rob, it is still uncertain how much of the gasket is "non-essential". I am particularly concerned about the annular rings, and the area around fixing bolt #1.

My concern is that you may create a situation like that posted by Comnoz (reply #18, Commando Head Stud, Commando Forum).

As I posted above, it is not straightforward to determine the minimum width of the annular rings to prevent a blowout.

This is not to discourage you .... just be careful, go slow, and be alert for signs of gasket failure.

Slick
 
Stress risers are only a problem where flexing occurs. A head gasket is usually trapped between two surfaces.
 
Yes Alan but copper work hardens (hence the need to anneal) so avoiding sharp "inside" corners is probably wise - and costs nothing.

I may even try the process, discussed the the Real Classic article (first post), of etching away the "hatched" area so that it is thinner and doesn't come under compression.
May make the whole thing a bit more robust.
 
acotrel said:
Stress risers are only a problem where flexing occurs. A head gasket is usually trapped between two surfaces.
Click to expand...

True Alan, but thermal cycling can also induce a crack to propagate from a sharp corner.

As Rob says, it is cheap insurance to avoid sharp corners.

Slick
 
Okay - my latest thinking (thanks for the comments Slick) is...
(the drawing is a bit rough - but I think you'll get the idea)
If I'm going to etch the hatched area down from 0.036" to say 0.025" then the whole gasket will be more robust (than the trimmed/cut version).
So I won't need the "rings" around each bolt/stud hole.
Therefore the only areas needing full thickness (read full pressure) are the 5 annular rings around the bores/pushrod tunnels/oil gallery.
I've investigated the etching/masking process and looks do-able - so my latest mark-up is...
Head Gasket Trimming Idea

This should yield four to five times the clamping pressure at the critical areas - worth going for!
Comments welcome!
Cheers
Rob
 
Last edited:
Wonder if anyone has tried tinning the copper head gaskets with solder (instead of using the .005" wire) in the pushrods area? I'd bet the solder coating would be thin enough and slightly compressible.
 
batrider said:
Wonder if anyone has tried tinning the copper head gaskets with solder (instead of using the .005" wire) in the pushrods area? I'd bet the solder coating would be thin enough and slightly compressible.
Click to expand...
It may be difficult to get a consistent thickness.
 
batrider said:
Wonder if anyone has tried tinning the copper head gaskets with solder (instead of using the .005" wire) in the pushrods area? I'd bet the solder coating would be thin enough and slightly compressible.
Click to expand...

Don't do solder!!!. Solder flows with time, temperature, and pressure. For the same reason, never tin a wire, then crimp on a terminal. Crimp, then solder is OK.

Slick
 
Danno said:
It may be difficult to get a consistent thickness.
Click to expand...
Danno
Within reason, I don't think it's important to get consistency - just thinner than the areas you want clamping pressure
 
robs ss said:
Okay - my latest thinking (thanks for the comments Slick) is...
(the drawing is a bit rough - but I think you'll get the idea)
If I'm going to etch the hatched area down from 0.036" to say 0.025" then the whole gasket will be more robust (than the trimmed/cut version).
So I won't need the "rings" around each bolt/stud hole.
Therefore the only areas needing full thickness (read full pressure) are the 5 annular rings around the bores/pushrod tunnels/oil gallery.
I've investigated the etching/masking process and looks do-able - so my latest mark-up is...
View attachment 4923
This should yield four to five times the clamping pressure at the critical areas - worth going for!
Comments welcome!
Cheers
Rob
Click to expand...


The problem I would worry about with this approach is that torqueing the fasteners to normal specs might distort the head, since there is nothing to compress at the fastener location. We don't have that problem with things like the copper O-rings some use around the bores, or the .005" copper wire around the pushrod tunnels, because the wires will compress enough to give a high unit pressure, but the total gasket thickness after tightening will still be the same at the sealing areas and around the fastener holes.

Ken
 
Ken's comment (#19 above), crossed my mind as well. I dismissed my concern knowing about the copper rings around the bores which I assumed resulted in no warpage problem. I confess however, that I do not understand Ken's explanation why using copper rings does not leave the fastener area unsupported.

Slick
 
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