Pre unit box sprocket play

[Wickedwill]

Rebuilding my old flathead that runs a pre unit trumpy box ( you see it in vid)
Got a bit of play at the gear box sprocket.
Is this acceptable ?
If not what parts might I need to replace ?
Cheers Will

https://youtu.be/8IAjKfiwo3w

[Guest]

I believe manual has specs for fit. I’d say you need a new hi gear bush and to inspect your mainshaft. In my experience replacements will be just as bad. Have one made.

[TriNortchopz]

Do you know which year or model the gearbox is?

This site has part numbers (look at gearbox shell , outer shell and inner shell numbers) which should help identify it;

Gearbox spares & parts for Triumph 1937-62 Twin Models

The mainshaft bush (ref. no. 20) is listed for: '46-'49 (2), '50-'56, '57-'61 years.
The gearbox main bearing behind the circlip, seal and sprocket is common to all.

https://www.draganfly.co.uk/index.php/triumph-shop/1937-1962-pre-unit-twins/category/1289-gearbox-tpu

[Wickedwill]

Do you know which year or model the gearbox is?

This site has part numbers (look at gearbox shell , outer shell and inner shell numbers) which should help identify it;

Gearbox spares & parts for Triumph 1937-62 Twin Models

The mainshaft bush (ref. no. 20) is listed for: '46-'49 (2), '50-'56, '57-'61 years.
The gearbox main bearing behind the circlip, seal and sprocket is common to all.

https://www.draganfly.co.uk/index.ph...89-gearbox-tpu

Not sure of the year
Cases have these numbers

[TriNortchopz]

A few pics of the complete gearbox may help to identify it. Read that numbers are difficult to determine year, may need to check with the VMCC.

Found this:

Re: Pre unit gearbox numbers?
"Another way to determine the year is by dismantling the gearbox. Starting with the inner cover, there will be (or should be) a two digit number inside a circle cast onto the aluminum. That number in there represents the year of manufacture. It could be in the same model year as the original bike it came with, or it could have been made from around September on up for the next model year.

So, if you took this apart, and found those two numbers and they were 57 for example, that's when it was cast and was destined for a 1958 model. We know this, since it is a 1958 on up gearbox. In most cases the circle has small lines around the perimeter of the circle pointing inward which indicate month of manufacture ( if familiar with a military map, it looks like a symbol for a depression in the ground). The inner gearbox cover and the gearbox shell will both have these 2 digit cast numbers on the inside.Hope this helps a little bit!"

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=104829

[Dougtheinternetannoyance123]

Up and down or a wobble is not good* but front to back across the tranny (Primary side to kicker side) is normal within a degree.
Its hard to tell from the video, all you can see is there is play. Now shot from above, it might be better.
There is limited places for wear and slop. 3 actually. There is a bushing on the mainshaft gear and those wear, You can kinda see it in the video. They lead a hard life, dont get a lot of lube so normal for some slop and I have seen some run for years with wear there, Not saying its good to do,, but the tolerances allow it.
Secondly is the Primary side bearing, and the kicker side bearing. If either of those were going, You can generally hear a rumble. Get a stethoscope or use a screwdriver against the box and the handle pressed to your ear and it transmits the vibration/abrasion quite well and you can localise the noise.

The Layshafts on some boxs run on bushes but on this type they use needle bearings. That would not be evident by grabbing the CS sprocket.

What can happen if the mainshaft and layshaft get sloppy and crooked in respect to each other will result in grinding, debris in the lube, hard to shift and a tell tale is the kicker will start doing the chicken and flopping and twitching, which means a grenade is about to blow up. But this is more common on Nortons (Bad layshaft bearing, famous failure point) and BSA boxs with bushes.

pull off the kicker cover and fiddle with the lay and mainshafts... You will find the main will slide back and forth a little and its designed that way, Hard to explain in a posting. INSIDE there is thrust washers,, brass, again can tolerate slop but the looser they are the more the gear set walks around. Secondly,, many times the main shaft nuts on either end can come loose, THAT gets exciting as the mainshaft and clutch basket starts walking side to side, seen some primary covers where the Clutch basket ground big grooves in the outer cover,,
There is lock tabs, and I use loctite once I got the box set up right.

The most common problem I find with British gear boxs is worn out and sloppy fit, and if gentle on them they can still work, but rounded off dogs, worn shafts, sloppy shift forks is a problem renewing the bushes and bearings will not fix.

Secondly is mixed and matched parts. Domi Racer used to sell a huge wall chart with all the gears, alternative gearing, part numbers and IDs. You CAN run a late 70s 5 speed in a preunit box with mods,, although final drive is still 1:1, its not an overdrive it just gives you more gears to keep in the powerband. (Good for road racing, not great for the street or dirt).
I have one of these I built years ago..
But they changed tooth forms and engagements over the years so its a bad idea to mix gears and parts, Shaved vs non shaved and stepped vs non stepped. Incompatible. I was rebuilding a unit 650 once and couldnt figure out why the new CS sprocket wouldnt fit. Its because someone used a preunit gear set in a unit as the tooth patterns are different. It had me scratching my head for a while.

One other point few people today realize. On early triumphs, timing covers, gear box inners and outers,, Originally Triumph did not use a gasket. Most had a light smear of sealant or nothing at all. It was assumed the machined faces would seal. We all know how well that works, factored in Bodging mouth breathers with crude tools and most leak like a sieve.

So most places offer gaskets. However your end plays are now changed, so a little math and fettling (Adjustments) is needed to restore tolerances.

[Wickedwill]

A few pics of the complete gearbox may help to identify it. Read that numbers are difficult to determine year, may need to check with the VMCC.

Found this:

Re: Pre unit gearbox numbers?
"Another way to determine the year is by dismantling the gearbox. Starting with the inner cover, there will be (or should be) a two digit number inside a circle cast onto the aluminum. That number in there represents the year of manufacture. It could be in the same model year as the original bike it came with, or it could have been made from around September on up for the next model year.

So, if you took this apart, and found those two numbers and they were 57 for example, that's when it was cast and was destined for a 1958 model. We know this, since it is a 1958 on up gearbox. In most cases the circle has small lines around the perimeter of the circle pointing inward which indicate month of manufacture ( if familiar with a military map, it looks like a symbol for a depression in the ground). The inner gearbox cover and the gearbox shell will both have these 2 digit cast numbers on the inside.Hope this helps a little bit!"
http://www.britbike.com/forums/ubbth...&Number=104829

Thanks
Pic 2 : don't get confused by the 2 threads hanging out the bottom . Case was cut and a block welded on to suit the harley frame mounts

Up and down or a wobble is not good* but front to back across the tranny (Primary side to kicker side) is normal within a degree.
Its hard to tell from the video, all you can see is there is play. Now shot from above, it might be better.
There is limited places for wear and slop. 3 actually. There is a bushing on the mainshaft gear and those wear, You can kinda see it in the video. They lead a hard life, dont get a lot of lube so normal for some slop and I have seen some run for years with wear there, Not saying its good to do,, but the tolerances allow it.
Secondly is the Primary side bearing, and the kicker side bearing. If either of those were going, You can generally hear a rumble. Get a stethoscope or use a screwdriver against the box and the handle pressed to your ear and it transmits the vibration/abrasion quite well and you can localise the noise.

The Layshafts on some boxs run on bushes but on this type they use needle bearings. That would not be evident by grabbing the CS sprocket.

What can happen if the mainshaft and layshaft get sloppy and crooked in respect to each other will result in grinding, debris in the lube, hard to shift and a tell tale is the kicker will start doing the chicken and flopping and twitching, which means a grenade is about to blow up. But this is more common on Nortons (Bad layshaft bearing, famous failure point) and BSA boxs with bushes.

pull off the kicker cover and fiddle with the lay and mainshafts... You will find the main will slide back and forth a little and its designed that way, Hard to explain in a posting. INSIDE there is thrust washers,, brass, again can tolerate slop but the looser they are the more the gear set walks around. Secondly,, many times the main shaft nuts on either end can come loose, THAT gets exciting as the mainshaft and clutch basket starts walking side to side, seen some primary covers where the Clutch basket ground big grooves in the outer cover,,
There is lock tabs, and I use loctite once I got the box set up right.

The most common problem I find with British gear boxs is worn out and sloppy fit, and if gentle on them they can still work, but rounded off dogs, worn shafts, sloppy shift forks is a problem renewing the bushes and bearings will not fix.

Secondly is mixed and matched parts. Domi Racer used to sell a huge wall chart with all the gears, alternative gearing, part numbers and IDs. You CAN run a late 70s 5 speed in a preunit box with mods,, although final drive is still 1:1, its not an overdrive it just gives you more gears to keep in the powerband. (Good for road racing, not great for the street or dirt).
I have one of these I built years ago..
But they changed tooth forms and engagements over the years so its a bad idea to mix gears and parts, Shaved vs non shaved and stepped vs non stepped. Incompatible. I was rebuilding a unit 650 once and couldnt figure out why the new CS sprocket wouldnt fit. Its because someone used a preunit gear set in a unit as the tooth patterns are different. It had me scratching my head for a while.

One other point few people today realize. On early triumphs, timing covers, gear box inners and outers,, Originally Triumph did not use a gasket. Most had a light smear of sealant or nothing at all. It was assumed the machined faces would seal. We all know how well that works, factored in Bodging mouth breathers with crude tools and most leak like a sieve.

So most places offer gaskets. However your end plays are now changed, so a little math and fettling (Adjustments) is needed to restore tolerances.

The play is in every direction , looks like the mainshaft has a bit of movement and the bearing has a fair bit of play .
The 4 speed was nice behind the 45 sidevalve , big improvement over what they used to run .
Looks like I will pulling the box down , it was a supposedly rebuilt box when I got it 30 years ago, been parked up around 20 years . Hasnt done a whole lot of work and shifted nicely just used to leak a little oil . Any manuals for just the gearbox ?

https://youtu.be/icOG9ojjlrA

Cheers Will

[Dougtheinternetannoyance123]

Im out the door in a few minutes, But I just posted a ton of links to free downloads for manuals on another topic in the main forum, I also have them in digital for virtually every vintage Triumph so if you have issues PM me, But I never trust others works.
As Ronald Reagan said.........."Trust but verify" So best case you are out time, gaskets and seals but you have peace of mind, Worst case you avert disaster.
Im happy to coach the inspection and rebuild but some is just hard to describe. For the record,, thats a rigid frame gearbox. 1954 and earlier (Some models went swingarm in 54,but not all) Just for grins you might want to verify the year of the box. Many had a number on top, but I dont have a definitive year chart for gearbox #s but i am sure its do-able,
Also,, many parts will have casting numbers so write them all down and cross reference to see if the internals are later or period for the box. (It could be 65 internals for all we know.)

Someone did some trick stuff to modify that boxs mounts. But thats a common mod to go 4 speed.

Heres a trivia parts things. Used to be popular to use a BSA 54 and up Swing arm GB, Use a BSA 51-53 Semi unit main shaft, And a Norton Commando clutch basket (Diaphragm clutch, 68 and up) and then line up the triplex chain to the HD crank sprocket. As a result its VERY hard to find mainshafts for the BSA Semi unit boxs

[datadavid]

Looks like a slickshift box, only used for a few years in the 50's

[Wickedwill]

Im out the door in a few minutes, But I just posted a ton of links to free downloads for manuals on another topic in the main forum, I also have them in digital for virtually every vintage Triumph so if you have issues PM me, But I never trust others works.
As Ronald Reagan said.........."Trust but verify" So best case you are out time, gaskets and seals but you have peace of mind, Worst case you avert disaster.
Im happy to coach the inspection and rebuild but some is just hard to describe. For the record,, thats a rigid frame gearbox. 1954 and earlier (Some models went swingarm in 54,but not all) Just for grins you might want to verify the year of the box. Many had a number on top, but I dont have a definitive year chart for gearbox #s but i am sure its do-able,
Also,, many parts will have casting numbers so write them all down and cross reference to see if the internals are later or period for the box. (It could be 65 internals for all we know.)

Someone did some trick stuff to modify that boxs mounts. But thats a common mod to go 4 speed.

Heres a trivia parts things. Used to be popular to use a BSA 54 and up Swing arm GB, Use a BSA 51-53 Semi unit main shaft, And a Norton Commando clutch basket (Diaphragm clutch, 68 and up) and then line up the triplex chain to the HD crank sprocket. As a result its VERY hard to find mainshafts for the BSA Semi unit boxs

I will msg you about manual.
What I did for the bottom mount was get a block of alloy that fitted inn the harley mountvthenntap 2 threads in . Next it went to a local guy who back in the day built frames and did alloy welding . He cut the bottom off the box and welded that block on . Also the shift plunger had to have some mods to take the dome out the nut to clear the the frame .
I also have a bsa box in bits in my inventory . To get the bad box to fit was going to be easier but it was missing bits and I hung out with classic racers who said the triumph box was better ,i was just a kid back then . Made up offset motor mounts to line the triumph clutch with a custom front sprocket. Part of this rebuild is also converting to belt drive .
I do like the diaphragm clutches

[TriNortchopz]

This is interesting:

"Lytedrive fabricated a motor pulley for the Harley 45" engine to match the clutch basket(Norton diaphragm)... but unfortunately, it didn't match the crank pin! After months of trying to get it right, we gave up and bought a regular 45 motor sprocket and bolted it to the motor pulley and were set to go...The primary drive uses a Gates 8 960 8MGT 50mm wide belt...We replaced the stock 3-speed transmission, its foot clutch and hand shift with a British 4-speed and a regular shifter on the left side. The transmission we selected was a pre-unit A-10 from a 60-62 BSA Goldstar...The transmission mainshaft had to be modified a bit to fit the clutch basket and bring it in a little closer to the gearbox sprocket...We used a reproduction WLA rear wheel, hub, and brakes on the rear and matched it up with the gearbox sprocket on the BSA transmission. Rear sprocket has 41 teeth..."

http://www.velocedge.com/42harley/Drivetrain/Default.asp

and

THE NORTON COMMANDO DIAPHRAGM SPRING CLUTCH
"This is being written to give anyone interested FACTS about the clutch such as how it ‘works’. Why Norton employed several different diaphragm springs in the clutch while Commandos were in production; with each new spring ‘stronger’ than the previous one which resulted in not only increasing the amount of torque the clutch would transmit before slip occurred but also in clutch lever action increasing from the ‘light’ easy two finger operation of the original 750 clutch to ridiculously heavy on the later 750 and 820 models..."

http://a20b767e.magix.net/