Author Topic: Gaskets  (Read 1204 times)

Offline rowan.bradley

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Gaskets
« on: 23.11. 2017 17:11 »
At risk of stirring up another hornet's nest, may I ask about the best approach to gaskets? Nowadays can or should one dispense with paper gaskets, and JUST use a silicone compound like Hylomar? If so, which joints in the engine can one do this with? Presumably not the head gasket? Rocker covers? Crankcase halves? Block to crankcase? Timing covers? Oil pump? Primary chain case? And what is the best technique - just squeeze a small bead of hylomar along one surface of the joint (having cleaned and degreased it, presumably), and then do it up, presumably not too tight, so there is a film of silicone all the way round, not metal to metal contact? Maybe do it up a bit tighter when it's cured? And which silicone compounds prove to be best for this purpose?

Can or should or should one not use paper gaskets PLUS silicone? If I am to use gaskets, which type (i.e. which material) works best? Who supplies the best ones?

Re the head gasket, my instinct is to fit a solid copper one. Is this the best approach (even if the bike originally had a copper asbestos sandwich gasket)? I have memories of copper asbestos gaskets, because my M21 used frequently to blow out (with a big bang) a 1 inch piece of gasket near the exhaust valve while riding along. I became quite adept at changing the head gasket by the roadside. I can still remember some of the spots on the road where this happened  ;).

And if using a solid copper gasket, when annealing it, should one quench it in cold water, or not? This seems a bit strange to me, because when you quench steel, it makes it harder, not softer. But maybe copper is different...

Thanks - Rowan


Current bike: 1958 A10 Super Rocket (in bits), purchased in 1967.
Previous bikes: M21

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Re: Gaskets
« Reply #1 on: 23.11. 2017 17:28 »
Quote
if using a solid copper gasket, when annealing it, should one quench it in cold water, or not?

this has come up before and the consensus was I believe that it matters not either way.
I use paper gasket smeared (very very lightly) with silicon and left for it set before using the gasket, now it has struck me that the paper the gaskets are made of could be made with some sort of coating that did the same job and no doubt someone here might inform me (and you) that this is already available but possible not on ready cut gasket *sad2*
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online mikeb

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Re: Gaskets
« Reply #2 on: 24.11. 2017 03:28 »
+1 to solid copper head gasket (not layered type). annealed one way or other.

i don't think the surfaces on our old bikes are flat or machined enough to get away with no gasket.  like everything else BSA related, gaskets appears to vary a lot in quality. some I've found are too small... like they've been shrunk by 5% just to be annoying - recently I found this on the rocker box. some appear to look like thin paper. not surprisingly cheaper ones are more likely to be trouble. I recently bought a SRM gasket set and while I'm yet to use them they look well made - thicker and a bit squishy (sorry for the complex technical terms).

For anything likely to be removed I've tended to put silicone on one surface and hylomar on the other so they come off in one piece. (hylomar is not silicone - it does not set). don't overdo the silicone or hylomar as  both can block an oilway. some people say they get away with grease on the gasket faces but i prefer to avoid the risks of oil leaks. for case halves (and other joints that won't get separated) silicone both sides.

i think you have a super rocket so a later model primary case. good - that avoids the whole sorry topic of the older pressed tin primary cases

some people like copper gaskets on the rocker box but a mate has reported they still leaked for him.
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Offline worntorn

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Re: Gaskets
« Reply #3 on: 24.11. 2017 05:13 »
This Company http://www.cometic.com now has  almost all of SR gasket shapes on file. I sent them a new paper set last summer and they made me a set of their special gaskets from the paper gaskets. Cometic  gaskets are nitrile rubber sprayed on both sides of an aluminium core. I've used this type of gasket on other bikes and am sold on the product. The gaskets are nearly impossible to break and can be used over and over again, always seem to seal perfectly.
That reminds me, I broke an old brittle paper gasket tonight when setting tappets on the Norton. Ill have to make a new one tomorrow. Not the end of the world but this doesn't  happen with the Cometic gaskets.
The unbreakable and reusable qualities are especially nice when you have to dismantle things while out on tour.
I haven't installed the Cometic set in the A10 yet, so I cannot vouch for fit. I expect it will be fine if the paper set was right, that has been my past experience with these gaskets.
The nitrile and Al is not suitable for the head gasket, but is good as a replacement for all of the paper gaskets in the bike.



Glen

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Re: Gaskets
« Reply #4 on: 24.11. 2017 06:38 »
I always use normal paper gaskets with Hylomar on one side and grease on the other. That way there is a chance of them not ripping when you remove covers etc. for a spot of maintenance. Silicone has its uses - Velocette primary chaincases being a particular case - but I wouldn't replace a normal gasket with silicone.
As for head gaskets, solid copper can be prone to oil seepage. The one on my alloy head A10 is fine, but on the Norton I have had to revert to the regular composite one.
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Online JulianS

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Re: Gaskets
« Reply #5 on: 24.11. 2017 09:20 »
Be cautious with the thick rocker box gaskets which come in the currently sold new production. They are not quite the right shape for the light alloy head at the front of the inlet rocker giving only a small width of material there. They tend to settle quickly giving rise to the need to retighten and re adjust valve clearances.

Always offer up a new gasket to the joint to check the fit. They dont always fit well which is poor given the price asked.

Iron head I use homemade ones cut from gasket paper which is much cheaper and light alloy head now using copper with a smear of Threebond sealant.

One advantage of copper being that it does not settle like a composite material gasket.

I use silicone on inner and outer timing covers no gasket- modern gaskets seem too wide and the inner not quite the right shape and usually needs trimming around the breather hole. Just a thin bead of silicone to avoid it squeezing inside the engine.

Offline duTch

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Re: Gaskets
« Reply #6 on: 24.11. 2017 09:29 »
 
 Julian rounded me up this time;-.....

I've been making my own for as long as I've owned a Beeza (since '70's), and plenty of mention of that on here, but will add that a while ago I bought a pre-made one for my Gutzzi Gearbox, but only because of uncertainty of the relationship to end-floats. It was a bit small so had a whinge to Tom I bought it from, and he said soak it in water and slap it on.... it fitted staraight on and I think it did the job, or maybe I let it sit to dry and then pulled it out and did my usual of 3Bond on both sides and silicon grease on the inner surface so it comes off easy, and to be reused- either way, it's still in there.

 The only place I'm aware of that doesn't need a gasket is the crank-case halves, because it will affect end float, and the gasket that goes in the gearbox between casing and biscuit (inner cover), also needs to not affect the end-float adversely...

  I took a bunch of time to flatten my outer timing cover mating face, but even having done that it seems to have an inherent warp, but I've just adopted the method of 'screw it up and screw it ', and doesn't seem to leak  *eek*

** With my above lax methods I don't have many leaks  *eek* ** , but had an issue with the rocker feed banjos leaking, I couldn't find fibre washers the right size, and what I could find fell apart, so made custom ones of nitrile from the local rubber shop, and seems to work ok after a couple of nip-ups



Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Re: Gaskets
« Reply #7 on: 24.11. 2017 09:35 »
Quote
it seems to have an inherent warp

yes I've noticed this on several covers ( I have a few spare ones but think Ebay prices will get me polishing them up soon)
Quite surprising how they screw up into correct shape
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online Greybeard

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Re: Gaskets
« Reply #8 on: 24.11. 2017 09:46 »
Quenching copper in cold water has the benefit of shocking most of the oxide off. You'll still need to clean the copper with wire-wool though.


I put my head gasket on one of the kitchen hob gas rings and used my plumbers torch to add extra heat. When It's rippling cherry red to clean copper I quickly dunk it in a bowl of cold water.

Online KiwiGF

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Re: Gaskets
« Reply #9 on: 24.11. 2017 10:01 »
In answer to one of the questions, There is no way I would use silicon in place of a gasket where there is the possibility of bits of excess silicon squeezing into the engine and breaking off (eg timing cover).

There are better alternatives to silicon that do not “set” like loctite 515 or 518 ( I use those with paper). The theory is these will not block oilways.

I just tried sealing a pressed steel chaincase on my b31 with silicon and no gasket, it’s safe to use there, but it’s been a dismal failure and leaks badly  *problem* *problem* so I’m note sure what it’s good for.

I’ve not tried the technique of coating a gasket with silicon anD letting it harden but that sounds promising.
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Offline rowan.bradley

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Re: Gaskets
« Reply #10 on: 24.11. 2017 11:41 »
I've been making my own for as long as I've owned a Beeza (since '70's)
What material do you use to make them from?
What technique do you use for cutting them, and in particular for making the screw/bolt holes?

Thanks - Rowan


Current bike: 1958 A10 Super Rocket (in bits), purchased in 1967.
Previous bikes: M21

Offline BSA_54A10

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Re: Gaskets
« Reply #11 on: 24.11. 2017 12:02 »
What a lot of questions, so we will need to start from first principles.
1) what is the purpose of a gasket in the first place?
There are 2 reasons for fitting a gasket.
To make a fluid tight seal between surfaces that are not 100 % flat:- gearbox or primary chain case is a perfect example
To allow for differential expansion Head gaskets are the easiest example of this.

Thus some times you can substitute a gasket for a sealant and some times you can't
And hear , gear box gaskets also set the end float so they can not be substituted. primary chain case gaskets  just hold the oil in so they can.

Hylomar is not a silicone it is a non setting joining paste designed to fill in the hollows in a surface.
There are several different kinds of jointing compounds
Some are anerobic so go hard when dennied access to oxygen locktit thread sealant is this type
Some are self hardening, silicons are like this and will go off and become solid regardless of where they are.
Some never harden fully and Blue Hylomar & loktite flange sealant are this type.
And some are strait glue and go hard when the solvent evaporates,

Putting silicone on a paper gasket simply sticks to the paper to the silicone

I generally put Hylomar on one side and High temp ( bentonite ) axel grease on the other.

Now Annealing copper gaskets.
In copper, the gasket goes hard because the crystals slip on all the 1:1:1 slip planes.
When the slipped bit intersects the crystal next door they lock together in a process called "twinning" ( google it ).
When you heat copper to dull red ( or better ) the lump of one crystal that is pegged into it's neighbour either becomes part of the crystal it hit or a crystal unto itself thus it then becomes soft and the rate of cooling will have no effect.
In steel when you quench from a red heat, you trap a high temperature crystal and prevent it becoming the cold temperature variation of itself.
We call these phase changes just the same as Ice to water is a phase change.
If cooled slowly all the high temperature phase will convert to the low temperature phase, Google Time Temperature transformation curves
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Trevor

Offline BSA_54A10

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Re: Gaskets
« Reply #12 on: 24.11. 2017 12:08 »
I've been making my own for as long as I've owned a Beeza (since '70's)
What material do you use to make them from?
What technique do you use for cutting them, and in particular for making the screw/bolt holes?

Thanks - Rowan

Traditionally you use a 2oz ( very small ) ball pane hammer.
Tapping on the edges will cut the gasket paper start with the holes then use a bolt as a punch to knock the little circle out.
leave the bolts in the holes to hold the gasket in position the do the inside followed by the outside.
The other way is to smear the surface with some old dirty oil ( bearing blue if you are anal ) then press the cover into the gasket material.
Knock out the holes with a wad punch then cut the gasket around the image with a scapel or pair of scissors
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Trevor

Offline cyclobutch

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Re: Gaskets
« Reply #13 on: 24.11. 2017 12:25 »
Quote
if using a solid copper gasket, when annealing it, should one quench it in cold water, or not?

this has come up before and the consensus was I believe that it matters not either way.
I use paper gasket smeared (very very lightly) with silicon and left for it set before using the gasket, now it has struck me that the paper the gaskets are made of could be made with some sort of coating that did the same job and no doubt someone here might inform me (and you) that this is already available but possible not on ready cut gasket *sad2*

Primary gasket I bought for my XLH1200 had a bead of something all the way around one side - so not just treated 'paper' from which it was cut but applied as a post process. It was not cheap, but works very well. As in, sadly I have had to go in and out of there several times and the gasket has borne reuse most successfully.
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Offline Angus

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Re: Gaskets
« Reply #14 on: 24.11. 2017 13:11 »
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