Author Topic: By-pass valve  (Read 458 times)

0 Members and 1 Guest are viewing this topic.

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
By-pass valve
« on: 08 December, 2020, 18:07:19 »
Just browsing through the instruction manual for my 1965 B40F. In the section headed "Lubrication system" it says:  " A by-pass valve (D) ensures a constant pressure in the system. Surplus quantities of oil are discharged into the crankcase. In no circumstances should the cap if this valve be removed by the private owner." Crikey. What's that about, I wonder. The manual appears to trust the owner to have a go at other tasks such as decarbonising,  tappet adjustment, etc, so I wonder why the owner is advised not to touch this by-pass valve. Any thoughts?    Phil

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: By-pass valve
« Reply #1 on: 08 December, 2020, 18:16:57 »
Btw, I made a typo: "if" should of course be "of". Just in case it didn't make sense!   Phil

LightningAndStarfire

  • Royal Star
  • ***
  • Posts: 106
    • View Profile
Re: By-pass valve
« Reply #2 on: 08 December, 2020, 18:58:24 »
It doesnt make sense. Perhaps in BSA factory experience many owners had been tempted to tamper with the spring in an attempt to raise system pressure.

Pete C

  • Royal Star
  • ***
  • Posts: 236
    • View Profile
Re: By-pass valve
« Reply #3 on: 08 December, 2020, 20:29:38 »
They probably just didn't want owners messing about with a critical component. Get the tappets wrong and you burn out a valve or go deaf from the clatter. Mess up the oil flow and you could sieze the engine.

Calum

  • Royal Star
  • ***
  • Posts: 121
    • View Profile
Re: By-pass valve
« Reply #4 on: 09 December, 2020, 09:45:20 »
I wonder if it is adjustable. My guess would be them being worried that someone messing with it might accidentally lower the relief pressure and potentially starve portions of the engine of oil. Pressure relief valves on any car engine I have worked on are usually non adjustable and rely on the set length and rate of a new spring. Obviously not great as springs tire over time but pretty fool proof.

JulianS

  • Empire Star
  • *****
  • Posts: 2417
  • A10
    • View Profile
Re: By-pass valve
« Reply #5 on: 09 December, 2020, 13:09:27 »
I suspect BSA were concerned that owners would assemble the spring the wrong way around. See first service bulletin.

Then they changed the spring so it would fit either way around. See second service bulletin.

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: By-pass valve
« Reply #6 on: 09 December, 2020, 13:44:58 »
As ever, Julian, many thanks. And of course to others who responded with their thoughts.   Phil.

JulianS

  • Empire Star
  • *****
  • Posts: 2417
  • A10
    • View Profile
Re: By-pass valve
« Reply #7 on: 12 December, 2020, 15:18:05 »
Looks like some  though it was the gearbox level plug................see below from BSA.
« Last Edit: 12 December, 2020, 15:48:47 by JulianS »

Phil C

  • Golden Flash
  • *****
  • Posts: 1916
    • View Profile
Re: By-pass valve
« Reply #8 on: 15 December, 2020, 16:16:45 »
Interesting article. Thanks again.  Phil