Head Gasket Trimming Idea

Thanks for the comments Ken, Slick
If I etched as per post #13 the amount of copper removed would be about 0.010" - is that sufficient to warp a head?
I'm not arguing a point here - just interested.
On Norton (and other makes) singles, with alloy heads, the head was torqued down on a spigot, which is essentially what the effect of the annular ring gasket is.
I'm not aware of singles' heads being damaged from this practice.

Again thanks for your thoughts!
Rob
 
I would be uncomfortable with a 10 thou gap and would be worried this could cause issues with distortion.

If I understand correctly, Maney barrels liners protrude 4 thou above the barrel. And this 4 thou is ‘taken up’ by the soft copper head gasket.

So, perhaps 4 thou is a better number?

I got to thinking that trial and error might be the only way to establish this figure.

Then it occurred to me that a really easy trail might be to use a pair of JS 3 thou thick head gasket ‘rings’ along with a standard copper gasket.

This would simulate 3 thou etching. One either side would simulate 6 thou etching...

Just a thought.
 
Thanks Nigel
I would like to avoid, as far as possible the increase in the number of joints associated with the "rings".
I'll post another version soon - with logic - for comment.
I'm sure you're right about trial and error being the ultimate test - although careful thought beforehand should reduce the amount of error!
As I was doing this I had a thought that the "etched" surface should face downwards (against the barrel) - the smooth upper surface may be easier on the head?
I think all this stuff fits in the "use it or lose it" category - and you never know, something valuable may come of it!
Cheers
Rob
 
Rob, why not leave a 3 to 4 mm wide annular ring around each bolt hole and stop the worry?

Aside from possible warpage, I do not think the reduced clamp area will hurt the head, but I am hesitant to put 0.005" wire on the head side.

Slick
 
Last edited:
But the 5 mil copper wire doesn't pose that much of a gap because it flattens out under pressure.
JD
 
@jaydee75

I am concerned the 0.005" copper wire will indent the aluminum head. Not sure of this, but chicken to try and see.
If anyone has experience with the copper wire on the aluminum head, please let us know.

Slick
 
Rob, why not leave a 3 to 4 mm wide annular ring around each bolt hole and stop the worry?

Aside from possible warpage, I do not think the reduced clamp area will hurt the head, but I am hesitant to put 0.005" wire on the head side.

Slick
I agree with your concern about the wire damaging the head - in part driving my interest in this style.
My hesitation for putting rings around bolts/studs is to minimise them robbing pressure from where its really needed.
The picture below, from the article, shows the 700cc RE acid etched gasket - you'll note it doesn't have the rings around fasteners and it apparently was running this way for many years.
The previous owner etched his own gasket as, apparently, these machines are notorious for head gasket leaks (unlike Norton twins - hey?).
The current owner (article author) made the cut gasket but doesn't explain his rationale for adding the fastener rings to the original design.
Head Gasket Trimming Idea

I have thought on your concerns however and offer the following revision for comment:
Head Gasket Trimming Idea

Some thoughts on this are:
1. Fasteners 3, 4, 5, 6, 9 & 10 all grip the head alloy and are now about 50% supported by the wider 7mm rings.
2. Studs 2, 7 & 8 all grip the cast iron barrel so should not see fluctuations in tension due to thermal effects. Are the proximity of the rings good enough? Especially for #2!
3. Bolt #1 is a quandary for me - to some extent this one does the most sealing work of any fastener (see shaded area) other than maybe #2. I have added a "bridge" between pushrod tunnels but is that enough?
The head alloy is 25mm thick here with finning and pushrod tunnels quite close-by. You'll note I haven't hatched all the way to the hole here - demonstrating my uncertainty!
4. When I have some masking agent (awaiting postage) I will experiment to see how much control I have over etching - can I etch to 0.005"?
The etching fluid I intend to use is 2 parts hydrogen peroxide (3%) and 1 part pool acid.
5. When I have settled on a design and completed etching I'll the assess risk of using it - 650ss heads are pretty rare these days! (opening Ken??)

I'll keep you guys informed
Cheers
Rob
 
Last edited:
@ROB: Reply #27

Comments on your points:

1. Agree.
2. It is not thermal effects I was concerned might warp the head, but the moment due to a force a distance from the support area. The distance for fasteners 7 & 8 seems small enough, but why not eliminate the concern by extending the non-etched area to touch and enclose the area around #7 from the 3:00 position to the 6:00 point. Similarly do #8 from 9:00 to 6:00. This will give the 50% support the fasteners of point #1 have. Stud #2 is a concern. I would feel more comfortable if it has some support around the hole .... 3 mm?
3. I am more comfortable with bolt #1 having no annular ring than #2 since it is supported nearly 360 deg. around it with only a short distance for non-supported gap. I think the bridge between the tunnels is good but could be removed. If it were eliminated, bolt #1 becomes more like, but not as unsupported, as stud #2. Like bolt #2, putting a 3 mm annular ring around #1 would remove the worry.
4. Etching can be controlled to very small (+/- 0.002") tolerances, but the etchant must be fresh and consistant composition. It is controlled by timing the dip. Obviously, you will have to experiment to determine the time rate of metal removal. And it should be obvious, the rate of metal removal decreases as the etchant becomes contaminated.
5. "650ss heads are pretty rare these days!" Yes! .... that is why you (we, who might follow) should error on the safe side.

Slick
 
Thanks for your thoughts Slick.
I'll do another iteration an post here before etching.
It'll be a few weeks before I will get around to etching as I have a bit on at the moment.
 
Here is a digitally enhanced photo of the head gasket I recently removed from my Atlas. It was on the bike for about 50K miles, always had a slight weep ... just enough to keep the area near the right pushrod tunnel oily.

Note the blackened (carbonized) area where the combustion gasses invaded the gasket surface. This is a view of the gasket looking down from the head side. This is a spigotted gasket.

Head Gasket Trimming Idea


In the weep area, it appears gasses have blown thru the entire width of sealing area where the bolt/stud holes are. I think many Norton owners report seepage near the bolt holes.

FWIW .... Comnoz had to mill the head to make it flat. That may explain why so much area is carbonized. OTOH, this pic may indicate every bit of gasket area is essential.

I am not trying to discourage Rob. Just presenting what evidence I have to help him decide how much area to etch. The rear part of the cylinders appears to have been well sealed. It suggests, that with a flat head and more clamp pressure, Rob's proposed sealing area may be adequate. OTOH, the left cylinder has gas invading as deep as Rob intends to leave non-etched. The barrel side of the gasket had minimal gas invasion. The truth still eludes us.

I would dearly love to see Rob seal this deal (pun intended).

Slick
 
Last edited:
OTOH, the left cylinder has gas invading as deep as Rob intends to leave non-etched. The barrel side of the gasket had minimal gas invasion. The truth still eludes us.
Slick

Slick - regarding that area outside the left hand cylinder...
It could be hypothesised that the area circled in blue (below) could have had higher clamping pressure and therefore robbing pressure from the area immediately beside the bore - leading to the gas invasion.
Head Gasket Trimming Idea

Lack of flatness of the head probably casts doubt on any hypothesis though.
I have checked my head and it appears good - can't get a 0.002" feeler under the straight edge anywhere.
I'll post the latest (last?) gasket proposal soon.

BTW - is that an Atlas gasket? I thought pre-Commando gaskets were "angular" like mine - matches the gasket surface of the barrel rather than the head (see my head and barrel below)
Cheers
Rob
Head Gasket Trimming Idea
 
@ROB: reply #31

It is an Atlas gasket.

I agree, since the head was not flat, no conclusions can be certain. I also have no clue why the head was not flat ..... I know the history of the bike, I am the original owner.

I agree, your hypotheses of the area circled in blue may be correct, but again nothing is certain.

Do not let my gasket dissuade you ...... I encourage you to pursue this idea.

Cheers,

Slick
 
I have had my commando from new.. whenevr the head has been off .. only 3or 4 times it has needed truing on a surface plate ... I could only assume that this was a consequence of heat distortion probably through specification of composite gasket. Yes I can see that reducing the gasket
will increase the surface pressure but it also presumably reduces the area of metal tometal contact through which the head can get rid of heat. Wonder if this might induce distortion in the head similar towhat use of composite gasket seems to do?
 
You may be right there oldmikew however I'm only going to etch about 0.005" from the shaded areas so any distortion should be minimal.
This etched gasket should be better, in that respect, than a composite gasket in that it will have full thickness copper around (or very close) to all studs/bolts whereas the composite only has crushable material.
Cheers
Rob
 
They are the norm on many engines guys. Or at least, many standard production engines.

They work well, and they seal well.

But, probably perhaps for the very same reasons that you’re thinking about, solid copper seems to be the norm in the tuning / racing Norton world?
 
I’ve been thinking about the topic of heat transfer twixt head and barrel via the gasket face...

Why are we so sure that MORE heat transfer is a good idea?

I’ve been thinking the opposite may be true...

My hypothesis is thus:

Heat is generated primarily in the head. Letting that transfer to the barrels is allowing the heat to ‘soak’ into the engine, whereas ‘isolating’ it in the head is going to encourage it to be expelled via the exhaust ports and dissipated via the head cooling fins.

Encouraging heat into the barrels seems counterintuitive to me, and I’mwondering if it could lead to bore distortion etc?

I have zero evidence for any of the above. Please feel free to point out that I’m talking nonesense. I’m OK with that. I’m used to it...
 
Nigel

Am increasingly mindful of one of those classic ' development' foibles of the 60s . Lets improve the oxcart lashed up out of bits of wood with heavy scarcely round wheels. so light weight all metaI carts with suspension but which proved to be a total failure they could not cope with the hammering metered out by unmade roads .Improve and strengthen one item then another fails . Project was abandoned.

It seems to be thus with the Norton engine.. It started out lest we forget as an iron head motor with bolt spacings presumably for iron and using copper gaskets.. Get rid of the heat , so alloy heads but the bolt spacings quite adequate for iron , not for alloy which is presumably why the heads distort (slightly) And then composite gaskets.. True never had one blow or as much as a leak , but it still seems a good idea to me to lose heat. The effective radiator area of the barrels surely can cope with dissipation of a little more heat. But in extremis who knows..
 
Last edited:
Ludwig
It's not really clear to me what you've done there - could you please spell it out for my thick head?

And I tend to agree with Nigel that potentially reducing heat flow from the head to barrels is not necessarily a bad thing

Cheers
Rob
 
Last edited:
Back
Top