The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Andreas Larsen on 02.12. 2014 14:34

Title: Head gasket leak
Post by: Andreas Larsen on 02.12. 2014 14:34
Right, another case of a leaky head..

I took it apart to get a look at how everything was doing. It's my first time doing so, so I've taken a bunch of pics of how everything looked..

The gasket itself looked alright I think (see pic) but all surfaces; gasket, head and engine block surfaces was smeared in silicone it seems.. I don't know if you guys can spot any problems on the pictures as to why it would start leaking alot? The leak itself was at the back of the right cylinder (the corner nearest the ATD unit if that makes sense) and after a ride the magneto, timing cover and my right leg and boot would be quite oily..

Another thing is that the exhaust vales seemed to be recessed a little but as it's my first time inspecting I don't know if it's correct?

Pardon the long post and thanks for reading through, those who managed.  *smiley4*

Andreas
Title: Re: Head gasket leak
Post by: bsa-bill on 02.12. 2014 14:50
I can't see too much wrong here Andreas, more experienced eyes might detect something tho.
I don't use anything on a copper gasket other than maybe a light smear of grease to help it spread/bed.
If possible maybe check head and barrels for levelness and unless someone suggests otherwise I'd anneal and clean up the gasket (heat to cherry red) or use a new gasket, clean off all the old silicon and reassemble, torque to around 30lbs
Ride and see if it still leaks
Title: Re: Head gasket leak
Post by: Andreas Larsen on 02.12. 2014 15:00
I forgot to mention that I checked everything for straightness and it seems perfectly level.. I'll try and anneal the gasket and get everything together again and see how it goes.

My manual mentions that when the head is off it's a good idea to remove carbon from the piston crowns, but it doesn't seem too bad to my eyes, but would it be worth doing anyway?
Title: Re: Head gasket leak
Post by: bsa-bill on 02.12. 2014 15:34
they don't look too encrusted, the left one looks a bit damper  but I took that to be the angle of the camera shot.
I'd leave them as they are for now (always the risk of getting carbon bits in the rings when cleaning in situ)
Title: Re: Head gasket leak
Post by: Topdad on 02.12. 2014 15:46
Andreas, doesn't look to bad from need but has you've stripped it down you may has well do it, not sure if it's still the same with modern oils but I was always told to leave a ring of carbon closest to the piston edge to aid sealing . Leak must have been like like that  for some time and then left for a while ? The gasket does show more heat around the pushrod tunnel if my eyes don't deceive me so if solid anneal,, and lastly after first run out whizz the rocker box off and retighten the bolts to a similar torque bill mentioned ,can't remember exactly what it should be but within a few mins someone will post. You'll sort it and you'll already have had your first experience of BSA's . It's abit of a pain getting the pushrods back in there cups ,you can buy a special tool for about £3 but others use various tools fingers etc to engage them, don't be put off you'll soon master it ,regards BobH.
Title: Re: Head gasket leak
Post by: cyclobutch on 02.12. 2014 16:51
I'm sure there was a cunning trick for holding the push rods in position using an old piece of garden hose posted in Classic Bike Guide (I think) some time back. Maybe by an Andrew Wilson - used to have a page on A10 musings most months back then.

Does anyone have the detail on that - or did I dream the whole thing?
Title: Re: Head gasket leak
Post by: Andreas Larsen on 02.12. 2014 17:36
That sounds pretty cool! I've already acquired one of those push rod combs, but have yet to try how well I can get it to work.

Leak must have been like like that  for some time and then left for a while ?
It has indeed been leaking for a while, but for some time it was so little that I felt it would be more work than the trouble it caused, perhaps my faulty logic there... but it got progressively worse to the point as described..
Also, the bike has been standing still a couple of months because I had trouble with rust in the (dented) petrol tank, which has now been sorted out with the help of a couple handfuls of old nuts and a swig of soapy water followed by clean petrol and a little two stroke oil..
Title: Re: Head gasket leak
Post by: muskrat on 02.12. 2014 19:44
G'day Andreas.
The exhaust must have been a bit smokey on that side *ex*. Leads to the question "where was the oil coming from?". I can see hone marks but the bore looks glazed, so could be rings. Oil could be from the inlet valve or guide also. Pop the valves out to check, look for colour on the stem.
Ex valves are recessed a bit but shouldn't bother.
Cheers
Title: Re: Head gasket leak
Post by: beezermacc on 02.12. 2014 19:51
The silicone might be the problem as this is a flexible compound, totally unsuitable for head gasket sealing. It will create a soft layer which the gas can burst. I assemble cylinder heads absolutely dry or with a proper cylinder head gasket sealant (green / brown Hermetite in the old days). My advice would be to clean and flat the surfaces and reassemble, making sure all the bolts are torqued down equally.
Title: Re: Head gasket leak
Post by: Andreas Larsen on 02.12. 2014 20:31
The exhaust must have been a bit smokey on that side

The exhaust wasn't smokey, nothing noteworthy at least when I last fired it, a tiny bit of smoke perhaps  *dunno* I'l try having a look at the valves and guides next time I'm at the garage. Again referring to my old manual; it says to put a small wood block under the head for the valves rest on, but it fails to mention how to go about compressing the springs without hurting hands or fingers. Is there any ninja trick for doing this, or should I order a valve spring compressor to add to the toolbox?
Title: Re: Head gasket leak
Post by: bsa-bill on 02.12. 2014 21:10
Quote
or should I order a valve spring compressor to add to the toolbox?

yes - a good idea, apart from hands and fingers you save hours of hunting around your workshop for collets *smiley4*
Title: Re: Head gasket leak
Post by: Andreas Larsen on 02.12. 2014 21:59
It's amazing how stuff can disappear... I lost one of the head bolt washers and spent ten minutes looking for it.. turned out to be lying on the tool box mounting bracket.. A real heureka moment  *smile*
Title: Re: Head gasket leak
Post by: RichardL on 02.12. 2014 22:14
I could almost make a case for oil leakage around the return hole in front of the right cylinder (which is the oily and encrusted one; Bill, stop looking at A10s over your left shoulder with a mirror *smile*). There is some discoloration around that hole, but we can't see the other side of the gasket for additional information. Also, I wonder if the silicone got lumpy and uncompressible before the head went together. Regardless, it doesn't seem enough to be causing your bigger problem. I believe either valve guides or rings (or both) are more likely the problem, as Muskrat has said with actual respectable knowledge. I would de-coke that piston top and the combustion chamber to reduce chances for pre-ignition. Even if you get a new gasket, it needs to be annealed.


Richard L.
Title: Re: Head gasket leak
Post by: jachenbach on 03.12. 2014 00:01
You mention silicone sealer. On the head gasket? Personally, I only use the stuff in an emergency with nothing else available. I've never found it to be a particularly effective oil seal even in non-pressurized areas. On a copper head gasket, I use nothing at all, or if the gasket has been used/annealed several times and I'm feeling insecure, I'll give it a light dose of copper coat (spray can from Permatex). My money is on silicone sealer being the cause of the leak.
Title: Re: Head gasket leak
Post by: RichardL on 03.12. 2014 02:10
Jachenbach,

In case it was not clear (no pun intended), I was not suggesting the use of silicone, only pointing out that the PO who put it there might have doubled-up by doing it wrong and with the wrong stuff.

Richard
Title: Re: Head gasket leak
Post by: muskrat on 03.12. 2014 07:37
Still the ? remains. Where is the oil getting in to blow out. The piston is oil crusted, the only way in is from rings or valve/guide. You could deck the head and barrels and use superglue at the joint to seal it but the oil will still make its way to the wrong side of the piston. For a few £ a quick hone and new rings (bed in correctly) will eliminate one possibility. Worn guides/valves can be lived with but loose guides can't. I always use the copper spray on head gaskets (habit from running 14:1 on the racer).
Cheers
Title: Re: Head gasket leak
Post by: Andreas Larsen on 03.12. 2014 09:04
Copper spray is sadly not legal i the EU I htink, at least I've trawled the www for it and can only find north american or australian supplies that state they only ship nationally..

Edit: I've found some guides to make your own but I don't know if that is wise?  *eek*
Title: Re: Head gasket leak
Post by: a101960 on 03.12. 2014 09:56
Quote
Copper spray is sadly not legal i the EU I htink, at least I've trawled the www for it and can only find north american or australian supplies that state they only ship nationally..
Available in the UK from: http://www.ebay.co.uk/itm/VHT-SP21A-COPPER-GASKET-CEMENT-CORK-PAPER-METAL-GASKETS-/380614635400?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item589e666f88 I bought some from this place. They do ship to addresses outside the UK, but check by emailing here  ebay@partsorama.com for shipping cost because it can only be shipped via a courier. They cannot send via post.
John
Title: Re: Head gasket leak
Post by: Rocket Racer on 03.01. 2015 22:44
A mates '55 flash showed some evidence of a weeping head gasket so we lifted the head on New Years day. Both the front oil drains showed blow out and that was only enough to wet the fins, not leak back beyond the barrel. So not the same as your problem

It'll go back on with some copper spray on the annealed gasket, once the valves go back in.
Exhaust clearances were tight and the exhaust valves both leaking and corroded on the seat, one quite badly. Not wishing to highjack the thread, all the valves are just outside clearance but as the owner has only just bought the bike I think a bit more bonding/riding time over the summer is in order before the head gets refreshed properly. I found a decent spare exhaust valve to replace the pitted one and all the seats have lapped in nicely with a fine paste, Certainly plenty of clearances presently.

My FIL's Benelli twin had a bad oiling problem out an exhaust and it turned out to be a failed guide, the bottom half of the guide had broken up and vanished. So oil was getting down the guide remnant and that cylinder didnt run reliably, kept chiming in but not at idle.