Author Topic: Rocker box oil leak - Is a breather the solution?  (Read 849 times)

Offline owain

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It's been a while since I've last posted in the forum. Since then the A10 has finally been running nicely.

Although recently, it's been leaking oil alot from the inlet side of the rocket box. So I replaced the paper gaskets with copper gaskets with a layer of wellseal on each side. Took it for a ride but it doesn't seem to leak between the rocker box/engine head join. It is still leaking from the oil feed pipe and the nut that fastens onto the other side of a rocker. So I replaced the fiber washers with dowty washers, which reduced the amount of oil leaking but there is still plenty of oil leaking from the nut on the other side of the rocker. I'm reasonably confident that my rockerbox is as well sealed as possible and it's only the inlet side leaking...
 
Could a breather in the inlet inspection cover help solve this problem?
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Online RDfella

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #1 on: 02.05. 2020 17:56 »
Are you leaving the oil feed pipe loose when tightening the spindle nut, then tightening the oil feed after? If not, the spindle will probably be moving.
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Offline Klaus

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #2 on: 02.05. 2020 18:22 »
Have a close look at the Oilfeed and watch for cracks.

cheers Klaus


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Offline owain

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #3 on: 02.05. 2020 18:54 »
Ah that might be a fair point there RDfella. I didn't know it was important to tighten the spindle nut first and then the oil feed pipe. I'll give that a try tomorrow.

The oil is leaking primarily from the spindle nut side but inspecting the oil feed pipe seems like a reasonable and easy thing to inspect. Will do that tomorrow as well.

Can the pressure in the rocker box build up alot, I'm wondering whether there is a tremendous amount of pressure building in there that might explain the leaks?
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Offline owain

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #4 on: 03.05. 2020 14:40 »
Found the issue. The spindle nuts thread was completely stripped! A simple fix thankfully :)
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Offline owain

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #5 on: 07.05. 2020 22:29 »
UPDATE:
Or so I thought...I replaced the rocker spindle nuts today. Took it for a short 10 minute ride through town and the top of cylinder head is still covered in oil. I wiped a clean cloth between the rocker spindle/oil feed pipe and the bottom of the rocker box and there was no oil (so that's a plus) but there is still plenty of oil covering the cylinder head, almost entirely on the inlet side.

So the only sources to explain this oil that I can think of is a poor seal between the surfaces of the cylinder head and rocker box with the copper gaskets (even though both sides of the gaskets were given generous amounts of Wellseal aswell. Or perhaps oil is travelling up the threads of the cylinder head bolts (if possible?). Although I wouldn't expect them to leak oil at such a rate that the top of the cylinder head is gettings soaked in oil after  a 10 minute ride.

Assuming that it is the surfaces of the cylinder head/rocker box to each other. My grand idea is to do a diy resurfacing of these parts on a mirror with some high grade sandpaper. Like all good ideas, I have youtube to thank for this inspiration, has anyone else tried something similar?
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Online ironhead

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #6 on: 08.05. 2020 00:55 »
This subject has been discussed recently here, maybe checkout the previous discussions.
SA

Offline Scott and Jay

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #7 on: 08.05. 2020 04:55 »
Hi owain,
As regards your original question, about a breather - if the standard, timed breather is blocked or not functioning right - this causes pressure build up. This can add to rocker leaks. The corks pressing on the breather valve have to be thick enough, make it function right. I went through putting a vent in the inlet tappet inspection cover, myself. Quite a few people do, but I think this might be a bit misinformed. With the timed breather, knowledgeable people on this forum commented, and I can now see - this could be expected to suck in more air and increase the pressure....

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #8 on: 08.05. 2020 08:18 »
There are a few problems with rocker box design and the quality of gaskets and fibre washers etc. There are two main problems , the first is that the rocker box is also the component which takes the valve spring strain which is transmitted through the rockers, back to the spindles and into the rocker box, causing it to attempt to lift off its seat - this is obviously a design issue which BSA resolved on the A65 by mounting the spindles in the cylinder head. The second problem is that the rocker box is also the mounting for the head steady so engine vibration is 'jiggling' the rocker box all the time. I have heard of a rubber mount being substituted for the head steady, but obviously the softer the rubber mount the less effective it is as a steady, but it is an effective compromise. Gaskets vary in quality but generally a gasket which is quite thick will provide a cushioning effect which is undesirable in this application as it exacerbates the 'jiggling' problem. The holes in the rocker box where the bolts fit are often sloppy so any attempt by the rocker box to 'creep' are unhindered by the sloppy bolt fixings. So, this aspect of the problem is best solved with good mating surfaces and a thin but strong gasket or, dare I say, no gasket at all. The other issues with the rocker spindles should be quite easy to fix. First of all it is important to use a copper or aluminium washer under the dome head spindle nuts and to tighten them first. The banjos should be sealed with a suitable fibre or dowty washer which allows sufficient tightening to achieve a seal between the banjo and the rocker box and the banjo bolt and the banjo itself. Provided the existing engine breather is working OK there should be no need to fit an additional breather though it won't do any harm.

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #9 on: 08.05. 2020 09:04 »
 owain.  It's remarkable these gaskets seal at all, considering the narrow width of the contact areas.  First check is that rear tappet cover and proper identification of the source. A good clean, a short run, a looky look.

 Have a good look at where the leak is worse, see if a feeler gauge can be worked in to identify any area where the clamping force is less, on both sides of the gasket.

 Worth checking the two rear nuts are doing their job, and not bottoming on the plain central part of the studs, rather than clamping, or worse, that the internal threads in the rockerbox are about to let go. The single  bolt inside the rear cover also needs a check....is it clamping or bottoming on some old gasket sealer?

 If you take off the rockerbox, see if there are areas of gasket which are less compressed, indicating a low spot. Removing the studs, cleaning the mating face and seeing if it rocks on a sheet of glass is worth a go, feeler under the face for low spots.

 Replace the rockerbox without studs, gaskets or pushrods and feeler gauge between the two, looking for low spots and rock on the head.
   Providing the mating surfaces are true, a thinner gasket as suggested by Beezermac is perhaps a better choice to achieve a higher and more consistent clamping force over time.

 If it comes down to a reface, plenty of how to do it tips. Raised areas around the studs need to be flatted back. Sticking the gaskets to the rockerbox with silicone, and leaving to harden on a flat surface before trimming away the excess is also another trick, but has an obvious risk.
  From you description this is a definite leak, rather than a "weep", so something that's definitely amiss should not be too hard to find.

  Swarfy.   

 

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #10 on: 08.05. 2020 14:35 »
As per many other replies, it is an art sealing these things, even ones that have been oil tight for a number of years can without any provocation suddenly develop a weep/seep/leak as the A10 appears to have just done damik  *sad2*
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Offline paulmbsa

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #11 on: 08.05. 2020 23:18 »
There is no problem with the rockerbox sealing, ensure the mating surfaces are flat, no need for copper gaskets, assemble with a small amount of sealent and gasket and thats it. I have 8 A10 / 7 as well as building many more for people and never had a Problem in over 35 years, fitting breathers is a bodge the A10 breather working correctly is very capable of dealing with crankcase presure even in a worn engine

Offline stev60

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #12 on: 08.05. 2020 23:29 »
This is a problem I had for some time, had it off a few times, as mentioned in an earlier post check the box is level, by sitting on flat surface and remove high spots, overtightening in an endeavour to stop leaking must distort things, I used a thinner gasket and hylomar blue sealant. Banjo ive just used copper which works, let it warm up retighten. Overtightening is not good.

Offline ianbsa

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #13 on: 31.05. 2020 12:11 »
Just posted about my flippin engine rattle but apart from that! no oil leaks at all after 1000 miles.

Grt advice re levelling etc, did it myself, but this is something I've often thght is overlooked - make sure to tighten from the centre of the casing outwards, applies to all cases, as  it pushes the edges outwards keeping the surfaces dead flat, prevents bunching of the metal.


Offline Butch (cb)

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Re: Rocker box oil leak - Is a breather the solution?
« Reply #14 on: 01.06. 2020 11:11 »
Mine had a breather in the rear valve inspection cover which we sealed during the rebuild. All was good for 3k miles when it started leaking gently. Replaced with an SRM gasket and all good again. I guess it was just the usual A10 issues taking their toll - rockers trying to lever the box off and the head steady strains.
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