BMC diesel/ Parsons gearbox.

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David Hiley

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I own a 60 year old motorsailer that was originally powered by a BMC Commodore 65hp motor coupled to a parsons gearbox. Subsequently some genius swapped out the motor for what I think is a Leyland 4/98 , 4 cylinder 70hp?motor. Unfortunately the bellhousing motor interface is a shambles with only 4 bolts holding the whole thing together. Had a real stuggle getting it apart, which is not surprising as when dialed up the shaft was 25 thou out . The side loading on the bearing must have been substantial. I'm now in the position of not knowing exactly what gearbox I've got and whether anybody marinized a 4/98 so I might possibly locate the corrct bellhousing. Mathway marine indicated that they thought the gearbox was a morris vedette. As far as I'm aware BMC never made a marine gearbox. Could it possibly be a rebadged Parsons?
Any help much appreciated.
 
David Hiley said:
I own a 60 year old motorsailer that was originally powered by a BMC Commodore 65hp motor coupled to a parsons gearbox. Subsequently some genius swapped out the motor for what I think is a Leyland 4/98 , 4 cylinder 70hp?motor. Unfortunately the bellhousing motor interface is a shambles with only 4 bolts holding the whole thing together. Had a real stuggle getting it apart, which is not surprising as when dialed up the shaft was 25 thou out . The side loading on the bearing must have been substantial. I'm now in the position of not knowing exactly what gearbox I've got and whether anybody marinized a 4/98 so I might possibly locate the corrct bellhousing. Mathway marine indicated that they thought the gearbox was a morris vedette. As far as I'm aware BMC never made a marine gearbox. Could it possibly be a rebadged Parsons?
Any help much appreciated.
Click to expand...
Any chance of photo as a starter

Jim
 
mathway as I understand evolved from Parsons so if they don’t think it’s one then I would accept that

morris did make gearboxes i believe including a weird hydraulic operated from the Austin princess limo
lots of badge engineering went on and many weird combinations appeared
 
David Hiley said:
Looks like the server doesn't like my phone photos. Although they are only 1mb each it says the files are to large.
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Post the pics on thumbsnap or one of the other free hosts, then put them up here; because you're a new member of the forum there's some rule about not being able to post pictures, use PMs etc.
 
David Hiley said:
I own a 60 year old motorsailer that was originally powered by a BMC Commodore 65hp motor coupled to a parsons gearbox. Subsequently some genius swapped out the motor for what I think is a Leyland 4/98 , 4 cylinder 70hp?motor. Unfortunately the bellhousing motor interface is a shambles with only 4 bolts holding the whole thing together. Had a real stuggle getting it apart, which is not surprising as when dialed up the shaft was 25 thou out . The side loading on the bearing must have been substantial. I'm now in the position of not knowing exactly what gearbox I've got and whether anybody marinized a 4/98 so I might possibly locate the corrct bellhousing. Mathway marine indicated that they thought the gearbox was a morris vedette. As far as I'm aware BMC never made a marine gearbox. Could it possibly be a rebadged Parsons?
Any help much appreciated.
Click to expand...
Tried to send pm but the system says no - I think we are being defeated by your newness - I do have a bellhousing which was on a 3.8 marine unit,there is no basic difference in a 4.98 & 3.8 - is the Parsons box mechanical ? are you wanting to upgrade to a "modern" box?.
Jim
 
I had the Austin gearbox that Scotty referred to on a BMC Captain diesel. One mechanic said that it was a modified Ambassador box. It was not hydraulic as such but the gear change system was hydraulic. And was a pain to operate. When I had that engine, in the 1990s, the main source of original spares was a company called Tempest Diesels. I don't know if they are still in existence.
 
bristoljim said:
Tried to send pm but the system says no - I think we are being defeated by your newness - I do have a bellhousing which was on a 3.8 marine unit,there is no basic difference in a 4.98 & 3.8 - is the Parsons box mechanical ? are you wanting to upgrade to a "modern" box?.
Jim
Click to expand...
bristoljim said:
Tried to send pm but the system says no - I think we are being defeated by your newness - I do have a bellhousing which was on a 3.8 marine unit,there is no basic difference in a 4.98 & 3.8 - is the Parsons box mechanical ? are you wanting to upgrade to a "modern" box?.
Jim
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Hi Jim. Sorry for the delay in replying. I did what Penfold suggested and put the pics in an album on thumbsnap. Now I can't move them. I've contacted them for a 'how to' but so far have had no reply. Meanwhile I'll have another attempt at removing the flyeheel which should allow access to the backing plate which will show more exactly what the size and bolt pattern is. If possible will also photograph it which should make identification easier.
 
David Hiley said:
Hi Jim. Sorry for the delay in replying. I did what Penfold suggested and put the pics in an album on thumbsnap. Now I can't move them. I've contacted them for a 'how to' but so far have had no reply. Meanwhile I'll have another attempt at removing the flyeheel which should allow access to the backing plate which will show more exactly what the size and bolt pattern is. If possible will also photograph it which should make identification easier.
Click to expand...
If its a flat plate about 8mm thick I would leave it alone for the time being ,that will probably the standard vehicle & later marine one.I may be out off action for a short while so do not despair.
Jim
 
Thankyou everyone. Ihave contacted Lancing Marine and Thornycroft , who apparently, put out a marinized version of the 4/98. Meanwhile I have created an album of 8 pics , with the title: SB motor & gearbox, on: Google Photos, Flkr and Thumbsnap that anyone registered to one of these accounts should be able to access.
 
Hi Jim. It's taken me a while to come to grips with posting the images. Lancing Marine suggested it was a Newage, the likes of which he hasn't seen for 40 years. Not encouraging. It is a mechanical box but I may have to replace it. We have yet to be able to fully dismantle it, it's fighting us every step of the way but already the carnage list is increasing. So far all of the bushes in side the brake drum need replacing, as do the bushes supporting the shafts they sit on, and one of the gears has a broken tooth. To be expected after 60 years. It doesn't look like the box has ever been apart in that time so who knows what else we will find. It's a pity, because it is a lovely classic I was hoping to keep it original but the cost may be prohibitive. If as we suspect the motor is a Leyland 4/98 it must have been out of a tractor. The cast iron sump has tangs that must have been part of the front axle sssembly and there is every poosibility that the back of the block is different from the automotive application. Now I know what I'm doing with the pics I can post a pic of the back of the block if that would be helpful.
 
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Hi.Scottie.pics you requested.. on reflection the damaged gear is missing about 1/3 or less of operating face of 1 tooth. At a pinch it may be still useable . Bushing on 2 gears nonexistent. Others all need rebushing. Not a biggie but bronze is becoming increasingly ex pensive. That's dependent on being able to dismantle it for full inspection.
 
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