Author Topic: gearbox to engine  (Read 223 times)

Offline Russ

  • A's Best Friend
  • ***
  • Join Date: Aug 2009
  • Posts: 197
  • Karma: 1
gearbox to engine
« on: 20.05. 2019 08:09 »
At some point I will need to bolt my gearbox to my engine on my 51 A10 Plunger.  As per original specifications I have 2 upper bolts and 2 lower studs to secure the gearbox.
I understand some owners replace the studs with bolts however, as the holes in my gearbox mounting plate are flogged out I have two studs with a slightly larger diameter to position the gearbox correctly and align the shaft with the hole in the primary cover. Now it seems that fitting the gearbox over the 2 studs while pushing the shaft through the seal in the Primary cover will be difficult.
I have found one post on this but would like more input please. So, how hard is this task.  What are the tricks or preferred methods.?
Thanks Russ
1951 A10 Plunger.
Australia

Online Greybeard

  • Jack of all trades; master of none.
  • Wise & Enlightened
  • *
  • Join Date: Feb 2011
  • Posts: 5557
  • Karma: 29
Re: gearbox to engine
« Reply #1 on: 20.05. 2019 08:53 »
I have two studs at the bottom and two bolts at the top. I double up the nuts to lock them to remove/replace the studs. To protect the seal I wrap the end of the shaft with a polythene bag which can be pulled out afterwards. The job is much easier with the mag off the engine.

Offline morris

  • Wise & Enlightened
  • *
  • Join Date: Aug 2012
  • Posts: 1505
  • Karma: 22
  • Antwerp, Belgium
Re: gearbox to engine
« Reply #2 on: 20.05. 2019 08:58 »
For as far as I know there’s 2 possible methods.
1) My prefered method; take out the mainshaft, mount the box, and slide the mainshaft back in.
2) A bit more fiddly; unscrew the studs, position the box and screw the studs back in.
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
The world looks better from a motorbike
Belgium

Online Swarfcut

  • Resident Legend
  • *****
  • Join Date: Oct 2018
  • Posts: 713
  • Karma: 10
Re: gearbox to engine
« Reply #3 on: 20.05. 2019 09:06 »
Russ.   Four bolts would make this easy, just slide the box sideways, locate, bolt up. Studs are traditionally used in soft castings to alleviate wear on the soft threads in situations which require fastenings to be released from time to time, so why BSA used a mix of studs and bolts here is a conundrum. This is what I reckon.
   With bolts, there is always the danger of bottoming, so they will err on the side of caution and be short, this does not matter for the top fixings, in that the gearbox flange is compressed against the crankcase under load. The bottom fixings are in tension under load and will require the maximum purchase and full utilisation of the crankcase threads, hence the use of studs, which can be gently bottomed to use all the available thread.

  The easy way to assemble is to make sure the threads are free running and nice and clean, then tape wrap the input shaft  splines to protect the seal. Grease the seal and position the box loosely with the bolts, and add the studs through the mounting flange.  Finally fit the stud nuts. Check all is positioned correctly and nip them up. Cheats like me slot the stud ends, and use Loctite on all threads. Plus the usual washers.

 Fitting the studs first is OK, but risks damaging the seal as the box has to be skewed and manipulated to clear the studs. As Morris says, without the mainshaft it is dead easy, gives a bit more choice, but a pain if the box is already assembled and has to be stripped just to pull the shaft.

 Swarfy.

Online duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4444
  • Karma: 40
Re: gearbox to engine
« Reply #4 on: 20.05. 2019 09:39 »

 The above ideas have merit-especially the stud reasoning, but I made it easy by carving a great big hole in my inner case to use a seal carrier from Unit models which makes checking or removing the sprocket/seal easy without the need to remove the whole lump.....may upset the rivet counters but my sanity is worth more (and debatable *conf*)
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Russ

  • A's Best Friend
  • ***
  • Join Date: Aug 2009
  • Posts: 197
  • Karma: 1
Re: gearbox to engine
« Reply #5 on: 20.05. 2019 09:44 »
Thanks guys for your very prompt and helpful replies. As suggested I will cover the shaft to protect the seal and remove the studs then refit when box is in place.
Cheers Russ
1951 A10 Plunger.
Australia

Offline ironhead

  • A's Best Friend
  • ***
  • Join Date: Feb 2019
  • Posts: 121
  • Karma: 0
Re: gearbox to engine
« Reply #6 on: 20.05. 2019 11:30 »

 The above ideas have merit-especially the stud reasoning, but I made it easy by carving a great big hole in my inner case to use a seal carrier from Unit models which makes checking or removing the sprocket/seal easy without the need to remove the whole lump.....may upset the rivet counters but my sanity is worth more (and debatable *conf*)

me to , excellent bit of re-engineering *work* *yeah*
SA

Offline Rex

  • Valued Contributor
  • ****
  • Join Date: Apr 2017
  • Posts: 452
  • Karma: 1
Re: gearbox to engine
« Reply #7 on: 20.05. 2019 12:33 »
Mine had four bolts fitted. I never thought about it at the time, but it must have been a better way to do it (rather than studs) for ease of gearbox mounting.
After all, although bolts into ally castings isn't ideal, the threads have lasted 68 years...so far...and it's not like the engine/box disassembly would be a regular occurrence anyway.