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Gearbox oil level rising/Primary falling

tim welsh

Well Known and Active Forum Website User
Non-VOC Member
Hello All,
Just got back from an excellent French Rally, and doing a service on the Rapide found a strange fault. Gearbox oil level at top of dipstick ( I always run it at the bottom), and primary drive almost empty. I use ep90 in the gbox and atf in the primary, and what I drained out of the gearbox had a reddish tinge, so probably the atf. Nothing else seems wrong, engine oil ok, cant find anything loose, but haven't stripped primary yet. I remember a thread by Hugo Myatt about this, so checked the engine breather (modified series d cap with a reed valve built in) and the sealing of the Alton (allows primary to breathe) , both ok. I haven't changed anything recently, and bike was running fine all the way. I run a multiplate clutch , in same atf as primary(small hole drilled through) What "connects" the primary with the gearbox? I can only think of the seal in the gearbox cover plate. Any ideas anyone before I take too much apart? Many thanks for any help . Tim
 

Howard

Well Known and Active Forum Website User
VOC Member
Not many connections between chaincase and gearbox. ATF sounds very thin, maybe passing through clutch centre between G3 and G84 (worn PD22?), only other I can think of is cover plate screw loose/missing.
I'd think there must be pressure in the chaincase to push the oil through.
I use 20/50 in all three compartments, I don't like the thought of oil contamination, even if they should be separated.
H
 

Albervin

Well Known and Active Forum Website User
VOC Member
The top of the dipstick is way above all the seals and kickstart tunnel so there must a a fair bit of pressure (-ve or +ve) to force the oils from one compartment to another. In my case there was a breakdown in the seal at the kickstart tunnel area causing oil to migrate from gearbox to engine. The oil level in the gearbox indicated the area of seal breakdown and this was confirmed when the crankcases were split. All your ATF must have been pushed into the clutch and then pushed or sucked into gearbox. At the very least I think you are going to have to dismantle your primary side. Like Howard I use the same oil in all compartments, if for no other reason than it helps if I need to top up any of them on a trip I only have to carry one small (500ml) bottle.
 

Albervin

Well Known and Active Forum Website User
VOC Member
That and vertically split crankcases. Although, my 1938 New Imperial has both and no problem. Then again it has a helical primary drive.
 

Chris Launders

Well Known and Active Forum Website User
VOC Member
On my black motor I have an piece of 1/8 copper pipe entering the edge of the dynamo sprocket cover below the footrest mount, the inner end is in the area of the centre of the cover, the outer end goes down behind the L/H rear footrest plate, invisible.
Chris.
 

Hugo Myatt

Well Known and Active Forum Website User
VOC Member
I had better put in my penny's worth although I am not sure how relevant it will be. This was some years ago after I had had the engine professionally rebuilt. I suddenly discovered the oil in the gearbox had risen considerably and the chaincase was completely empty of oil. Now I had gone to great lengths to seal the dynamo drive housing and had been completely successful. I suspected that somehow the gearbox was pressurising. I removed the filler cap and dip stick and fitted a condom over the filler neck then took the bike for a run aound the block. The expansion of the condom had to be seen to be believed! The gearbox was definitely pressurising and some.

After many travails and investigations this was the explanation. The engine rebuilder had fitted a sealed bearing to the drive side main shaft. He had removed the inner side membrane to allow for lubrication but had left the outer membrane, i. e. the primary chain side, intact. Unfortunately this acted as a very efficient flap valve. As the pistons descended pressure was forced into the primary chaincase but as they ascended the flap valve neatly closed trapping the pressure. Thus with every downward stroke of the pistons the pressure in the primary case was increased exponentially. This combined with my total sealing of the primary case caused this pressure to force the chaincase oil out of the primary by any means it could and into the gearbox. The solution was to remove the offending seal, a.k.a flap valve, and equilibrium was restored.
 
Last edited by a moderator:

tim welsh

Well Known and Active Forum Website User
Non-VOC Member
I was hoping you'd see this thread Hugo, as I had enjoyed reading your original write up on your "device" in my copy of "another 10 years"; thank you for replying. I wont rule anything out but I don't think this is happening on my bike. I have a crank seal fitted by Maughans several years ago which has been very successful, and I have not changed it recently. Also, I'm careful NOT to seal my Alton to the chaincase , to allow it to breathe(blowing into the inspection cap, it easily vents out by the Alton). I also checked the 4 small holes in the Gearbox filler cap, which were clear, so that's not pressurising.
I've got the primary drive apart and will report further!!
 
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