Author Topic: Engine to gear box bolt size?  (Read 166 times)

Offline Minto

  • A's Best Friend
  • ***
  • Join Date: Mar 2019
  • Posts: 249
  • Karma: 2
Engine to gear box bolt size?
« on: 30.04. 2020 10:56 »
Good morning all
Massive thanks to everyone for Sharing their wisdom and experience. I'm at the stage now where I can start to rebuild the engine, but while separating the Gbox from the engine, one of the bolts was completely seized and needed drilling out. I've looked on all of the parts book pages and catalogues but had no luck finding a part number for them. I've managed to find the part number for the other upper Gbox to frame mounting nut and washer, which were missing!!!
Any help here would be greatly appreciated.
52 A10 plunger
Aprilia RSVR

Offline Minto

  • A's Best Friend
  • ***
  • Join Date: Mar 2019
  • Posts: 249
  • Karma: 2
Re: Engine to gear box bolt size?
« Reply #1 on: 30.04. 2020 11:17 »
Never mind, just put stronger glasses on and found another parts catalogue... got it.
52 A10 plunger
Aprilia RSVR

Online AdrianJ

  • A's Best Friend
  • ***
  • Join Date: Oct 2018
  • Posts: 202
  • Karma: 3
Re: Engine to gear box bolt size?
« Reply #2 on: 30.04. 2020 11:24 »
3/8 x 1 Whitworth?
I think the lower two bolts are supposed to be studs, which just makes fitting the gearbox difficult. Replaced by bolts on mine.
Adrian
'53 Plunger Flash, Steib S500.


Online Ted_Flash

  • A's Best Friend
  • ***
  • Join Date: Oct 2011
  • Posts: 87
  • Karma: 4
Re: Engine to gear box bolt size?
« Reply #3 on: 30.04. 2020 11:27 »
The lower two 3/8"studs are part no 35-4005.  The upper two 3/8" bolts are part no 67-1467.
Ted Wilkinson, Ramsbottom, Lancashire
1950 Golden Flash

Offline Minto

  • A's Best Friend
  • ***
  • Join Date: Mar 2019
  • Posts: 249
  • Karma: 2
Re: Engine to gear box bolt size?
« Reply #4 on: 30.04. 2020 11:58 »
Cheers guys.
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

  • Wise & Enlightened
  • *
  • Join Date: Oct 2018
  • Posts: 1370
  • Karma: 22
Re: Engine to gear box bolt size?
« Reply #5 on: 30.04. 2020 14:46 »
Minto.  Draganfly's excellent online exploded diagrams and parts list would have saved the effort of searching the parts book, and in addition this very Forum has a Nut and Bolt Chart, which will identify the size and thread  of most of the fasteners from their BSA Part No.   Have a look in the Literature section, it's near the top entries.

  This chart can be downloaded from a link, published by Musky on 5 April 2018. Good job he did, the original has gone into Cyberspace.

 Some folks attach the bare gearbox casting to the motor, then reassemble the box. This means the mainshaft can be slid across with less chance of damage to the primary case oilseal behind the clutch. I would wrap the shaft splines anyway, as protection for the seal.

 Why BSA used studs on the bottom is debatable.....my guess is that perhaps because a stud has less chance of being removed when routine dismantling takes place, with consequent less wear or damage to the alloy thread. These two fasteners are under tension big time when you give it some stick, and a correct size (lengthwise) stud offers the most support available from the weaker alloy thread, rather than shorter "that'll do bolts" used on the top, which don't have to deal with the same applied forces.

 Swarfy.

Offline Minto

  • A's Best Friend
  • ***
  • Join Date: Mar 2019
  • Posts: 249
  • Karma: 2
Re: Engine to gear box bolt size?
« Reply #6 on: 30.04. 2020 15:50 »
Hi swarfy
I did look at the Draganfly lists but just couldn't find what I was looking at, wrong glasses on I think.
Just after I posted the request I went back and had another search through and found some really useful stuff in the scans in the lit section on here. I think it's partly getting used to the way these things are listed and catalogued.
52 A10 plunger
Aprilia RSVR