Britbike forum Forums Thread Like Summary - A10 oil leak from hell

My A10 build from a pile of unrelated parts has been on the road for a few months. It has a persistent rocker box oil leak, later alloy head. Rocker boxes have been on an off many times. Two different heads and two rocker boxes.All parts have been checked for fit using machinist straight edge and .001 feeler gauge between the joints. Paper type gaskets, sealer only and .028 thick soft copper gaskets...All leaked from the same areas.
Then on the A10 website a few suggested the top mount secured to the rocker hold down bolts can cause fretting between the head and box causing leaks. I leave off the top mount, annealed copper gaskets....No Leaks!!.....
But....this is a smooth running engine for a 650 twin.... leaving off the mount has made a noticeable increase in engine vibration....
So...any suggestions on how to fix this problem..?

Hi Tony— nothing very helpful to add I am afraid but—-
Back in the day I had two A10s— both with sidecars and both had a hard life.
Now I have a A7 Shooting Star— same basic design as the A10.
Getting a good seal at that point is difficult as you have to make sure that the tops of the pushrods are properly engaged in the rockers.
BSA made a special tool— a comb— to do this but I have never had much success with this.
I have long fingers and could put a finger in the rocker box while standing astride the bike and feel the pushrod tops into position as I lowered the rocker box into position.
IME it is easy to disturb the rocker box gasket sealant and the gasket itself while getting the pushrods into the rocker ends.
I have always used paper gaskets with a smear of Hylomar and achieved good oil tight joints.
HTH

Ok I will, the sample gaskets and cover note is in the mail box

I got the Yamaha bonded swingarm bushing mentioned above , gonna go that route. I have thought about and agree the stock top mount is a flimsy piece of crap and not intended to be a secure rigid mount... Took a ride yesterday and ran the engine hard ...Seemed to leak less oil than usual, bike must be scared of a beating...lol

this is breather on the bike….5/8 ID hose…lots of air but no oil blows out. I bought NOS rocker box fasteners….the bike shows no respect…

Attached Images

Don't be tempted to do many miles with the head steady removed. The down tubes will crack just above the top front forged lugs. Don't ask me how I know this

Have you thought about doing something completely "out of the box"? for example making some cylinder head, head steady mountings using the two outer cylinder head bolts? then your head steady is working at the head and not the rocker box. Just a thought?