rocker box gaskets again

[Dynamo Regulators Mike]

Hi all

As I have the head off the A10 I am looking to cure the rocker box leak one more time. I have used different types of gaskets over the years, but always they come to leak again in the end, a few thousand completely dry miles is about all I have come to expect. So I too was thinking of investing in a copper set. But the fact that John 'a101960' has found that these were not solution for him (see 'a bit of bodgery' post) and other considerations has led to further head scratching.

Now I just happen to have a piece of 0.5 mm thick Viton sheet to hand and have got to wondering if gaskets cut from this might be just the job. should be good for the high temperature and oil resistance and low creep. After all a key use of fluoropolymers like Viton is in difficult sealing applications. So my question is has anybody tried using Viton gaskets? Or any comments as to whether it is a good candidate or not for a difficult job. I don't really want to reassemble again only to find I have overlooked something obvious.

Cheers
Mike

[Beezageezauk]

Hi Mike,

As you know I've been running A10's for a few years now and, like you, travel 1000's of miles on them to camping weekends and bike rallies.  However, I've never had a problem with leaky rocker box gaskets.  Maybe because I don't use them.

Ok, some guys are going to cringe at this but I use a "Bike Instant Gasket".  It's a heat resistant silicon based sealant that replaces conventional gaskets.  It comes in a toothpaste type tube so it can be carried in the toolbox of the bike and has many applications.

It works well for me and has done so for over 10 years now.  It might be worth a try but if you do, use it sparingly and be careful near oilways.

Beezageezauk.

[Dynamo Regulators Mike]

Thanks for your suggestion, Ray.

A mutual BSAOC acquaintance (hi John of Twin Town fame) uses instant gasket as well, but I would prefer to keep a 'real' gasket on mine. If only because the valve adjusters are screwed well out, and a little more they might not clear the covers. I am thinking the Viton offers the prospect of a long term, even re-useable method without the mess of sealants.

Mike

[muskrat]

The problem with our rocker box's is the stress that joint is under from the valve operation and the head steady. John (chaterlea25) has designed a head steady to help http://www.a7a10.net/forum/index.php?topic=2912.msg19633#msg19633
I believe a solid fixing like the copper gaskets or none at all like Beezageezauk is the better way. I use the copper gaskets with a light spray of copper spray a gasket. It's not 100% successful 100% of the time but the best I've used.
Cheers

[morris]

Keep the ideas coming lads. Could us 'em. Just cured a leak at the oil tank connection, now my rocker box base started to leak at exactly the same spot as John's

[Briz]

Putting a breather in the rocker box helps.
Loctite do a good gasket silicone product. Ford use it on all their engines now; no paper gaskets at all.

[a101960]

In my opinion the rocker cover joints are a real nightmare. As I mentioned in my previous post it was the back joint that was leaking originally and that is what prompted me to get a set of copper gaskets. The irony in all of this is that the back joint is now bone dry as is the timing side joint. Previously both front joints were leak free. As far as I can tell I did all the correct preparation. I used Copper Spray and applied it exactly as the instructions directed, and just as a precaution, I also put the rocker cover on a flat piece of glass and ground it to make sure that all the joint faces were true and free from any surface imperfections. I have to say that I am quite impressed by silicone sealants but I am also very paranoid about bits of it breaking off and getting into places where it is not wanted. A big part of the problem with getting an adequate seal is that both the rocker cover and the cylinder head joint surfaces are irregular the face width varies quite a lot. This is especially true of the two front joints. I suspect that this causes the gaskets to spread unevenly because the compression I would guess is probably  not equal across all the face surfaces. The other major contributory factor to poor sealing I think emanates from the awkwardness of the whole installation procedure. The cover is as you all know difficult to get into place. Even if it all goes together properly at the first attempt (and this especially applies if you use the push rod comb) it is difficult not to damage any sealant by scraping it off one or other of the surfaces. I am not sure about the merits of a rocker cover breather. I can see that it might well help. I suppose that it is logical that some pressure  might well be generated in the rocker cover from the crankcase via the push rod tunnel, and the oil drain holes. Indeed I believe that is how the early A10s top end was designed to be lubricated. All I know is, that as I said in my previous post, it is a rotten design.

John

[bikerboy]

Well my latest build has done just over 4000 miles now and I have had no sign of any leak whatsoever from the rockerbox. Luckily for me the damned sump is more than making up for it cos I cant stop that leaking no matter what I seem to do

[Dynamo Regulators Mike]

Some interesting discussion here. No specific comments re the Viton sheet gasket idea sadly. I will try it one day but with a big trip coming up Spring next year don't want to chance it (California here I come!).

Meanwhile I intend to cut a set from 0.5mm Tesnit BA203, good for 200 C continuous although I have little idea of what temperature it will actually see in action. This sheet tends to adhere to clean surfaces quite readily so may be less inclined to wander.

One issue is that ready made gaskets are often too thick and too soft. So they work out after a time. I understand the originals were paper? I don't believe pressure build up is an issue in my engine though have not measure crankcase pressure (vacuum due to standard cork shimmed breather) for a long time now.

Not too sure about the rubberised head steady even if it appears to improve leakage empirically. Would love to hear the original thinking behind the steady explained. Which plane or planes of vibration is it intended to restrain and indeed which one(s) does it  effective against? That's another thread.

Eagerly anticipating refitting the rocker box, and the exercise it gives the fingers. Although a bit on the stubby side still find it easier to get them right in there than to use one of those damn comb things.

All the best
Mike

[bsa-bill]

ready made gaskets are often too thick and too soft

and nearly always the wrong shape, being too thin in cross section at places on the front of the rear rocker as in the photo below, so if making your own with Viton or anything else mark it out on the head not on an existing gasket.
PS since I made my own gaskets and fitted them it been oil tight

[Dynamo Regulators Mike]

Hello Bill
You're right about poor shape of some gaskets of course. Rotten quality pattern parts.

I ensure the correct shape using a printed scan image of the rocker box.  Accuracy is very good with half decent reasonably modern gear, and scale adjustment is easy anyway. Head face shape is a slight variation on the rocker box so that needs to be taken into account.

Just looked at a spare rocker box and they both show the same narrowing on the curvy section to the inside of the RHS front section in the casting. Reckon that apparent slip in the mould may account for some of the mess from the top of a lot of our engines.

Cheers

[Stephen Foster]

Im not an engineer & expect to get shot down in flames !
Wonder if a small groove could be cut all around the joint faces on the rocker box with a router , etc ,  o ring type material being next
carefully fed into this ?
Only an idea & Im certain the experts will explain the flaws in this scheme ?

Im only a retired welder !

[Briz]

It could be done on a CNC mill with appropriate programming. I'd like to see someone try with a router! Or maybe I wouldn't.
Trouble is that the mating surfaces are narrow and dont always line up that well with each other. I saw one once with less than 2mm actually meeting up.
The O-rings could be made with one of the make-your-own type kits. But I've noticed that these tend to be a bit hard at the glued joint. The O-rings would have to be very well made to stay in the groove during assembly. I bet you'd have the devils own job assembling it without some part of one of them popping out.

[WozzA]

Im not an engineer & expect to get shot down in flames !
Wonder if a small groove could be cut all around the joint faces on the rocker box with a router , etc ,  o ring type material being next
carefully fed into this ?
Only an idea & Im certain the experts will explain the flaws in this scheme ?

Im only a retired welder !

We did that to all the covers on a Honda Formula 3 motor, & it never leaked..

[alanp]

Just a thought to add to this topic, don't be tempted to tighten down the rocker box at the first sign of an oil leak unless you are prepared to reset your tappet clearances. Any extra squashing of the now soggy gasket will alter your clearances. BSA mounted the rockers as part of the head on the later A65s etc so the clearances weren't affected by whatever you did to the rocker cover.