The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Swarfcut on 02.06. 2019 08:05

Title: Barn Find Bikes and Engine Problems
Post by: Swarfcut on 02.06. 2019 08:05
  A few  things to check before attempting to start a bike which has not been run for a long time. This is concerned with the engine unit, not the ignition or fuel systems as these are already covered under their own sections on the Forum.

These notes apply to all A series engines, A7 Longstroke, Plunger and Swing Arm, A7/A10.

 It is written in simple terms and assumes a basic skill level and limited knowledge of the A10 engine.

  So a few thing peculiar to the A10 engine compared to more modern designs.

 This engine has what is known as a "dry sump".   Oil from the oil tank feeds down into the oil pump, gets pumped around the engine and collects in the sump.  From the sump another pump returns it to the tank. The two pumps are side by side in a single body and are referred to as the "Pressure pump" sending oil to the bearings, and the "Scavenge pump"returning oil to the tank.

  When the bike is left to stand for more than a few days, a common event is that all the oil in the tank drains into the engine sump. So a barn find bike has a good chance the bottom of the engine has been protected by this oil. The oil pump, on the other hand, has a tendency to seize through lack of use.

  Any attempt to rotate the stored engine could result in  damage to the pump, as the drive forces are strong, but the pump body relatively weak.

 So, you need to be very gentle.  Start by taking out the plugs, note which plug lead goes where, oil the bores and see if there is any movement.  Slight movement, try rocking each way, but if you feel resistance or hear nasty noises, stop for now. No movement, seized solid, then we need to think the next move.

 Let's consider a little bit of movement. Drain off the oil in the sump. This will give an idea of the state of the engine. Nice and black, no bits, a good sign. Water, rust not so good. Clean the gauze filter, and check that the little ball valve is free and not blocked. This is the pick up pipe back to the scavenge side of the pump.
   Now decide about the pump. Would you risk it or take it off? It all depends if you can get the engine to turn without any signs of binding, nasty noises, locking up, tight spots.

 I would check the pump. There is plenty of information on the Forum about removing the pump, which will need to be checked to see if it will turn, and if not, dismantled, cleaned and reassembled with the gears in exactly the same place as they were to start with. The pump face has four holes. These are flow from the oil tank through the pump gears and out for the pressure feed, and from the pick up pipe, through the pump for the oil to return to the tank.  The crankcase has four matching holes, one of them, top right, has a spring loaded ball valve. Gently push a matchstick down the hole, you will feel the ball move. Force oil down this hole with a pressure oil can to prime the main bearing bush and the big end bearings. This oilway also leads to the pressure relief valve (PRV). See later.
 When replacing the pump, prime it first and make sure the gasket does not block any holes, and the front mounting stud has a thin washer to match the gasket thickness.

 With the pump off,  remove the rear tappet cover and pour oil down onto the cam followers. Now you can use a bit more force to turn the engine.

 With a seized engine, make a start with the pump as before, but decide if you are going to just look for the cause or dismantle the engine completely. Start with the gearbox and work back through the primary drive looking for anything preventing movement.

 If you are very lucky, the engine will turn and have compression. Check the oil lines are not blocked, take off the oil tank, wash it out, and with the engine re-assembled, refill with some cheap oil. These engines do not need the latest expensive stuff.

 There is a pressure relief valve( PRV ) on the front of the engine. Get a proper socket spanner to fit the biggest hexagon and remove  the valve.  When you kick the bike over a few times, the clean oil will flow out, showing the pump is working. The PRV can now be dismantled and cleaned. It just unscrews apart, inside is a ball and a spring. Both are readily available if replacements are needed.

 So we now have an engine that should run, but the ignition and fuel systems will need attention. On these machines, a magneto gives the sparks, no battery is required for ignition.

 Once ignition and fuel systems  are in working order, it should run.  Oil will go into the engine and be pumped back to the tank. It is always a good thing to check this oil return every time you start up first time in the day.

 That's the basics, written simply, but I would recommend getting a  good over view from the forum sections, lots of information available there, including parts lists. The Draganfly website has lots of information and exploded diagrams.  A Haynes Manual or even YouTube will help explain things. BSA Service sheets are online on numerous sites. If you are unsure, just ask, rather than pressing ahead and causing damage.




Title: Re: Barn Find Bikes and Engine Problems
Post by: Greybeard on 02.06. 2019 08:33
Good start Swarfy! Next chapter; Sludge Traps  *smile*
Title: Re: Barn Find Bikes and Engine Problems
Post by: Swarfcut on 02.06. 2019 08:54
GB,  I am sure many otherwise sound motors have been wrecked by the urgency to "just kick it over, see if it'll go"  The poor old oil pump never gets a thought. Very few pumps I have seen have been free after storage and for the sake of a clean, I would say well worth the effort for the peace of mind that it works.

 Let's see what new member fearie decides to do, but I agree that with the experience we now have with these engines, the item now closely associated with the GB Logo is a priority.

 Nice day today, off to Woolpit Steam Fair, Stowmarket, Suffolk.


 Additional...Looks like fearie knows a thing or two. He should have no problem, as we say "a dark horse"

Title: Re: Barn Find Bikes and Engine Problems
Post by: KiwiGF on 02.06. 2019 12:32
Very timely thread for me, albeit not for an a10, I’ve just bought a couple of bsa’s on a whim at a local auction (a rarity where I live) the C11 might run but I’ve no idea when it last ran so needs the checks suggested. I’m pretty sure the potential buyers will have kicked it over so if the oil pump was seized..... *eek*.

 The B21 is a challenge......beyond me I think, lots missing, so I’ll have to try to find someone else to take it on.
Title: Re: Barn Find Bikes and Engine Problems
Post by: chaterlea25 on 02.06. 2019 23:12
Hi Kiwi,
I’m pretty sure the potential buyers will have kicked it over so if the oil pump was seized..... *eek*.

Yes, they will break the oil pump drive worm if kicked over without checking the pump

Lots of info here,

Title: Re: Barn Find Bikes and Engine Problems
Post by: Black Sheep on 03.06. 2019 15:05
A splendid and well thought out list of all the things I didn't do when I attacked an A10 that had been standing for 17 years...
Title: Re: Barn Find Bikes and Engine Problems
Post by: Swarfcut on 03.06. 2019 16:57
Back in the day, neither did I. But in the light of experience and knowing now of the curious shape shifting properties of Mazac, just jumping on it could prove expensive. I guess in this world some folks are born lucky.