The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Dynamo Regulators Mike on 31.10. 2013 16:29
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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
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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.
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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
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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
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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 *pull hair out*
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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.
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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
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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 :(
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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
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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
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Hello Bill
You're right about poor shape of some gaskets of course. Rotten quality pattern parts. *problem*
I ensure the correct shape using a printed scan image of the rocker box. *idea* 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. *sad2*
Cheers
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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 !
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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. *eek*
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.
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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..
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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.
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I had realised that some rocker box faces seem narrow but was considering putting extra material in the narrow areas by aluminium welding (T.I.G) , dressing
back then cutting a suitable groove ..not sure which tool would work here ?
Wondering if a Dremel type affair with suitable bit might work ?
Interested in any input as Id been mulling over this for a few years as this is the main oil leak om My "Flash" .
Steve ...
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G'day Stephen. The ones that look narrow in places are probably the SR type. The casting # is overstamped with 1142.
Cheers
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When I made mine, from paper(~.4mm?), I allowed for the mis-matched facing thickness, and made them over big inside and out with a view to trimming them back (some time)after tightening down and a bit of use- looked a bit funny, but doesn't leak (much)- maybe only if I look at it..?
Also used 3 Bond both sides,and silicon grease head side so R.box comes off easy, and have removed it a couple of times and literally thrown it back on with just a wipe of mating surface. I'm happy.
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I still think the head steady on the s/a models contribute a lot to the r/b leaks. The earlier ones don't seem to leak as badly with the steady mounted under the front r/b studs.
Cheers
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"Muskrat" ,
Assuming the cast head / rocker box faces on My "Flash" are reasonably meaty (they are) what tool would You
reccomend I try for cutting a groove ?
Steve ..
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G'day Steve.
If I were to try it (don't think I will) I'd start with a 1/32" circular burr or diamond encrusted Dremel bit, then go to a 1/16". I'd also mark out the shape on a sheet of alloy and practice at least 50 times, no beer or sex for three days prior. *cry*. There is a formula for the size of the groove for the size of the O ring, can't remember right now. Find an old stuffed r/b to try on before the good one.
If money was no object a CNC mill and a map programed in would be great, then you could do all of ours. You'd need to do 1000 units @ $50 to cover the mill and set up. *eek*
Cheers
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my 1951 G.F. was built completely out of stray parts and leftovers...so..i did every " flat "with sandpaper and a thick glass plate
all the rocker boxes i had were quite lumpy..esp in the areas of where the bolts came thru....the head surface?? dunno as I had the head guy surface both sides... I would find it hard to believe that after 60 some years it would still be flat..
the gasket thing?? once i stopped using paper gaskets.. I stopped having problems with oil leaks.....Loctite 515 517 or?? I cant see any difference...seems to work the same...
only problem with curing all oil leaks...is chasing the rust... I live about 15 minutes from a surf beach....but I have worked out how to stop the rust...I have a spray bottle with light oil...and a regular spray seem to do the trick...and makes it smell like a BSA...
if you haven't surfaced the mating parts...might be in for a surprise... after a few strokes...start wondering how in the world did that thing even hold oil..."?? some of mine were only hitting on three corners
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I still think the head steady on the s/a models contribute a lot to the r/b leaks. The earlier ones don't seem to leak as badly with the steady mounted under the front r/b studs.
Cheers
I agree with that view, having the rocker box anchored to the frame is problematic for any engine that works hard. *sad2*
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Hi guys, the head steady is the obvious problem so what would be the effect if it was not used,cheers
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Shake, rattle and roll!
A lot more vibration without the head steady.
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potentially the front engine to frame brackets would fail (break *sad2* )
Head steadies are useful things, just a matter of attaching them to something that is suitably solid on the head, rather than the rocker box.
Norton heads have a solid casting to mount to, but are even worse to assemble pushrod wise.
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"Norton heads have a solid casting to mount to, but are even worse to assemble pushrod wise"
Ain't that the truth RR. First time I had to take the top off the Atlas engine in my P11, I swore I'd rather do 100 Beesas, in the dark. In fact, on those sorts of hybrids, it's a close call whether to take the engine out to get the head off, it's all so tight.
As for head steadies and rocker boxes . . . the "just a matter of etc" can be a poser, on most marques. But have to say, on my A, only a little oil mist around the edges on the rare occasions I actually get around to cleaning it. Not enough to stop the cast iron bits from going rusty. As Manormike knows, who started this discussion, mine is a million miles from being a vision of loveliness. But despite the odd glitch she has worked, does work and I hope will keep working, with less time spent on keeping it that way than on pretty much any other old bike I have ever had. (Except a B31 - but of course.)
Having had the opportunity thrust upon me recently to rebuild the oily bits of a quite pretty sprung-hub Triumph, I know which I prefer. And it doesn't begin with T.
Cheers
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Finally had a look at removing my race engine after its last 3 day race meeting, broken head steady and damage to the cases at the top rear engine mount *sad2*
Yes these engines need all the support they can if being given a hard work out.
So it'll need repairs to the crankcases before it goes out again as well as reviewing/replacing the head steady.
The good news is there was no evidence the rocker boxes weeped *eek*
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Yeah; dont delete the head steady! Bad idea.
Think of it this way, that engine is thumping away making - what?- 50 ft-lbs torque? So whilst applying that torque its trying to turn itself in the opposite direction to the engine sprocket.
That top mount helps contain that torque. All the other mounts are much closer to the crank, so theres more force acting on them. Leave the top one off & all the others will come loose a lot faster.
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I replaced the std bracket with two pieces of steel tube squashed at both ends (at 90 deg) and drilled. Just using the rear bolts. No probs for the last 5 years.
Cheers
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Has anyone tried using thin paper gaskets with a thin coating of silicon sealant on both sides? I've used this technique on other places and will try it on my rebuild. Essentially, make a thin paper gasket, get some silicon sealant and smear it on "evenly" on both sides by pulling it through finger and thumb, let the silicon dry and then fit it. Should minimise the silicon sealant getting in to the engine oil ways but fill the gaps with a resilient sealant. ATB Keith
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Ive not tried silicon but do make my own gaskets in 0.8mm "Flexoid" paper, I use Loctite "Master Gasket" and have no leaks. When making the gaskets I make them wider than standard on purpose, so maybe as much as 3 mm sticks out into the inside of the box, and ouside, and I cut the visible paper off the ouside with a knife, as per prior post by dutch.
I dont think the paper would drop off the inside and cause problems....
I use the same technique on the primary case and timing cases, but loctite on the bottom half of the faces (saves mess and money!). Its a bit of an art getting the primary case on without disturbing the loctite. I use 2 old bolts with heads removed as "guides". I make the primary case gasket about 15mm wide, with no "dip" around bolt holes etc so theres a fair bit of paper sticking inside of the case.
Making yr own gaskets is tedious but makes sure you get the full width of paper between mating faces, like the pics in above posts I found some gaskets were pretty much the exact width of the mating faces and because they were not exactly the right shape this resulted in a relatively thin width piece of paper stopping the oil getting out.
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you get the full width of paper between mating faces
Spot on KiwiGF. I found this to be the answer also, and yes the silicon thing is good also
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Ive not tried silicon but do make my own gaskets in 0.8mm "Flexoid" paper, I use Loctite "Master Gasket" and have no leaks. When making the gaskets I make them wider than standard on purpose, so maybe as much as 3 mm sticks out into the inside of the box, and ouside, and I cut the visible paper off the ouside with a knife, as per prior post by dutch.
I dont think the paper would drop off the inside and cause problems....
I use the same technique on the primary case and timing cases, but loctite on the bottom half of the faces (saves mess and money!). Its a bit of an art getting the primary case on without disturbing the loctite. I use 2 old bolts with heads removed as "guides". I make the primary case gasket about 15mm wide, with no "dip" around bolt holes etc so theres a fair bit of paper sticking inside of the case.
Making yr own gaskets is tedious but makes sure you get the full width of paper between mating faces, like the pics in above posts I found some gaskets were pretty much the exact width of the mating faces and because they were not exactly the right shape this resulted in a relatively thin width piece of paper stopping the oil getting out.
Why use gaskets?
The Master Gasket 518 is shown used on its own.
Would the 510 be a better bet as it has a higher max temp although gap fill is not quite as good?
Perhaps it's a colour thing?
Loctite 510
Technical Data
Colour: Pink
Service temperature range: -50°C - +200°C
Tensile shear strength: 5N/mm²
Max. gap: 0.25mm
Fixture time steel: 25 min.
Fixture time aluminium: 45 min.
Strength: Medium
Cure method: Anaerobic
Pack sizes: 10ml, 250ml
Loctite 518
Technical Data
Colour: Red
Service temperature range: -50°C - +150°C
Tensile shear strength: 7.5N/mm²
Max. gap: 0.3mm
Fixture time steel: 25 min.
Fixture time aluminium: 20 min.
Strength: Medium
Cure method: Anaerobic
Pack sizes: 25ml, 50ml, 65ml, 80ml, 300ml
ATB Keith
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gasket preferences are like choosing oil, everyone has their own golden rules. Our bikes also put up with a variety of treatment and environments.
I was chatting over the weekend to a guy with an oil tight road going A10 ;) . For my race engine I'm happy if I can keep losses down to weaps and the rocker boxes do a lot of work on the swingarm bikes when the engines are worked hard.
Personally on the rocker boxes I doubt I could assemble solely with goo without disturbing it, but I could be wrong and as the rocker box comes off regularly do keep trying alternative options.
I use three bond grey in general, but havent had sucess on my rocker boxes solely with goo only options.
On my road engine i suspect I will do better with oil tightness, but am not going to lose sleep over needing to wipe it down once in a while
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Hi KeithJ, I use the Loctite 518 variant. I tried a "no gasket" approach on the primary cases as that gasket is a pain to make and it seemed I would be forever finding reasons to remove the cover *problem* but it leaked badly without a gasket so I went back to using the thin gasket approach.
Just a theory but using a gasket effectively means you get 2 thicknesses of gasket goo, so more chances of sealing a gap?
On my primary case I can fit a 10 tho feeler guage between screw holes so there is a fair gap to fill, due to the cases being distorted.
I have tried using thin (ish) gaskets with just grease. then Loctite 518 one side and grease the other so the (thin) gaskets would come off cleanly and could be re-used, but I got leaks, so for me I have to comprehensively clean gaskets faces and use new gaskets and the loctite both sides....every time.
I've not gone as far as using a glass plate and wet and dry paper to flatten gasket surfaces, as I have found what works for me to stop leaks. When rebuilding my engine I did carefully file the cases where needed, around the bolt holes, to remove the "obvious" raised areas, just to reduce the gaps a bit.
At least the Loctite is fairly easy to remove compared to some sealants, and as far as I can tell it does not have the same tendency to clog oil ways as silicon, at least I've never found any on the various gauze filters.
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Hi guys, the head steady is the obvious problem so what would be the effect if it was not used,cheers
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Not only will it increase vibration but its very likely that the barrel will crack around the skirt, even the thick flange ones can do this if you run without a head steady.
Please dont ask me how I found this out many years ago *sad2*