Author Topic: Oil leak - Breather on Rocker box cover help?  (Read 1195 times)

Offline nigeldtr

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Oil leak - Breather on Rocker box cover help?
« on: 25.07. 2011 20:09 »
Why do people fit a breather on the rocker box covers? Is it to lower the pressure in the top end and hopefully keep the oil inside rather than coming out past the gaskets? I recently had to change the oil in my plunger A10 as my float decided to split and flood the engine so much that the oil was rather thin and highly flammable. After the oil change, the engine decided to start leaking oil for the top end possibly the rear rockerbox/head gasket. Can't really see where it?s coming from but gathers around the carb manifold and drips down the back of the barrels - any ideas?

Regards

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Online bsa-bill

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Re: Oil leak - Breather on Rocker box cover help?
« Reply #1 on: 25.07. 2011 20:54 »
Hi Nigel
rocker breathers are fitted because the rider blames oil leaks up there on excess pressure, divided opinion on this, myself I think the blame lies elsewhere but who knows I don't flog the motor as much as our racer friends may do so could be a difference of usage applies.
I had your problem for some time on my latest project, difficult to see where the leak was coming from, has to be said the surfaces on the head were less than ideal.
I cured it by fitting two layers of gasket, applied Loctite 5910 to both the head and the rocker box and stuck gaskets to both, left in between the gasket dry (rocker box will need to be removed to re-torque the head).
This worked, I have since had to remove the head for another reason and the gasket parted just fine
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline nigeldtr

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Re: Oil leak - Breather on Rocker box cover help?
« Reply #2 on: 25.07. 2011 21:25 »
Hello Bill,

Thanks for the quick reply. I will double up on the gaskets as you mentioned. I rebuilt the engine over last winter done about 600 miles now, will tighten the head at the same time. Engine is running sweet as anything now gets smoother as the miles are clocked up, love the old girl but she gives plenty to do *smile*
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!