A7 Rocker Box Oil Leak - fixed. Possibly.

[Felters]

When I got my bike it had silicon all over the rocker box joints - however the leaks got progressively worse. So the rocker boxes were removed, cleaned up, new gaskets fitted, Hylomar smeared around, oil still pouring out...

Tightened everything up (including the nut hidden in the rear box). Made little if any difference.

So this evening I decided sterner measures were required. I know that rocker breathers get a mixed reception on here but I took off the rear tappet cover. Drilled a hole in the middle of it. Screwed a 1/4" BSP Air Coupler into the hole and attached a couple of feet of rubber compressor hose. Ran it under the seat and cable tied it to the rear mudguard stay and took it out for about a 20 mile ride. Difficult to say that there are no leaks as I hadn't cleared all the oil up between the fins etc. but I am certain that there is a lot less leakage than there was. The whole thing took about 90 minutes including the test ride and as I had the air coupler/hose anyway it cost me nothing. The aircoupler's are about £1 on ebay - http://www.ebay.co.uk/itm/1-4-BSP-Male-Air-Line-Fitting-Airline-Compressor-/110838599082?pt=UK_Air_Tools_and_Compressors&hash=item19ce7ecdaa#ht_537wt_1398

I'll let you know how it goes.

[BSA_54A10]

Rex Bunn did a lot of work on breathing ( and still is ).
Every one who has fitted one of his systems has reported zero oil leaks period.
Not many A 10 owners have bothered since the A7/10 breather works the beast of any that BSA ever fitted to a bike but a lot of B series riders now swear by them.

[Rich]

Felters
I do not wish to spread doom and gloom, but I did the rear rocker cover breather mod the same as yourself, except I used an old inner tube for the valve stem, however although things improved slightly, the gaskets still blew out, the problem as far as I can see is the mismatch between the rocker box and the alloy head on the face surfaces, I tried to match up 3 different rocker boxes. I have as my other post fitted copper gaskets and still have oil coming from somewhere onto the top left hand fin
all the best
R

[Felters]

Rich - I'm sure you right about the faces not being good matches and I'd be amazed if the were no more leaks but it has to be worth a try...

Trevor - I'm interested in the Rex Bunn stuff but couldn't find a source here in the UK. And saying that the A7 breather was the best they fitted is akin to being the world's tallest midget in my humble opinion... 

Cheers
Mike

[cosmikdebriis]

I did much the same conversion on my Dommie and was amazed at just how efficient at pumping/breathing oil that thing was/is. I used half a mile of piping with a fuel filter in the middle to catch the oil  then (cleverly I thought) directed it up under the seat and down to the rear chain...

Certainly lubricates the chain but you don't want to look over your shoulder at the cars behind you skidding of the road on the ensuing oil slick

By the way. Sealing the rocker box isn't going to cure the problem, only transfer it elsewhere

[muskrat]

 G'day all,
             I have a bunn kit on the cafe. In at the top (front valve cover) out through the original breather hole with the timing top hat crippled (always open) then into the oil tank then from there to outlet valve. It helps but won't cure bad mating surfaces.
 I had moderate success with the copper gaskets. Recently I have tried the siliconized glass mat that Steve.Carter sent me (Thanks mate). It would be the first time that I have got the box to seal first time. I used double thickness sgm and very thin hylomar.
Cheers

[chaterlea25]

Hi All,
If  someones A7/10 regularly destroys the rocker box gaskets,
The first thing to check is that all the main engine to frame bolts are tightened correctly
All the sealer in the world will not work if the engine is doing a rumba  ????

If the standard breather is correctly set up there should be no problems (unless of course the rings/bores are in trouble)
I have previously posted details of my modified head steady, and can only say no leaks after 10 years and lots of miles

To my way of thinking an open breather just leads to lots of pushing and pulling air  ???? ????

Cosmic,I have had lots of problems as well with a dommie, finally kinda sorted crankcase breathing into oiltank and a oneway valve on another pipe from the tank to atmosphere

Has anyone heard of how a Bunn system works on an AJ/Matchy big twin??
These suffer from pumping engine oil into the primary case 

Cheers
John O R

[wilko]

It's just a wetsump issue with the AMC twins.

[MG]

John, a 52x40x7mm oil seal is a good press fit in the AMC twin crankcase. You can turn the original oil thrower down to 40mm or make a new spacer of the same width. This cures the oil-in-primary-case problem (which is caused by either wet-sumping, as wilko said, or wear/too much play between oil flinger and crankcase).

Wet sumping can be (almost) cured by means of an additional end plate on the backside of the feed pump and an oil seal on its drive side, running on the (turned down) exhaust camshaft nut. I can send you some pics of the (simple) conversion if you PM me your email addy. Oil level in the tank drops by only an inch or so during the winter lay-up on my CSR, while maintaining better oil pressure at idle since the leakage paths through the pump gear axles are eliminated. Imho a much neater solution than additional o-rings on the pump gears, which will reduce the bearing width on the axles, leading to more wear.

Ooops, wrong forum...
 
Cheers, Markus

[chaterlea25]

Cheers Markus,
The AMC twin belongs to a customer, it gradually fills the primary case over a few hundred miles
Googling this issue brings forth lots of different thoughts
Your suggestions are about the only positive mods sounding I've heard 
I'll send you a pm, the details would be a great help
Cheers
John O R

[BSA_54A10]

Rex went back to NZ for good a while ago but I think that this email address is still current <rexbunn@bigpond.com>.
Otherwise he has an extensive blog so you can google it.
I am fairly sure he has an agent in the UK I know he has one in the USA.