Triumph Rat Motorcycle Forums banner

1 - 19 of 19 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter #1
Hi, I have a problem with my recently acquired Daytona. No tacho drive. I have disassembled the tacho gear box and all looks complete and engaging correctly with the exception that the tang on the end of the ‘driving gear’ (item 20 in attached from parts catalogue) appears too short (just) to engage with the slot in the ’tacho drive plug’ (item 33 in second attachment) on the end of exhaust camshaft. The tang appears complete but too short to engage. I have inserted a screwdriver into the drive plug slot and kicked bike over - all rotates and appears well. I have confirmed by measurement that tang will not engage adequately with the slot in the drive plug. Has anyone any ideas or experienced a similar problem. Are drive gears available it’s tangs of differing lengths etc. Hoping that someone can shed some light on this.
 

Attachments

·
Premium Member
Joined
·
9,682 Posts
Is it possible that the spade on the shaft broke off?
One way would be to photograph the shaft and measure it, compare it to a new one or ask a dealer to measure a new one. I do know that there was a triumph repair part to replace the spade on one model but no more than that? Is there a damaged spade inside the cam?
 

·
Registered
Joined
·
311 Posts
I have a 72 Daytona so my tacho drive is the same as yours. I did a total rebuild last year. AFAIK the drive gears are all the same. However, I wonder if yours is too short as a result of a bit breaking off the end. If the gearbox seized up at some point the tang will break - I had this problem on a 72 Tiger 750 I've just rebuilt.

Have a good look at the end of the drive gear and see if it looks broken. The photo in Dave M's post looks bang on for length.

If you get desperate I could take mine out and measure it, but mine on the 750 was definitely broken by a seized box.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #5
Is it possible that the spade on the shaft broke off?
One way would be to photograph the shaft and measure it, compare it to a new one or ask a dealer to measure a new one. I do know that there was a triumph repair part to replace the spade on one model but no more than that? Is there a damaged spade inside the cam?
That was my first thought, but the spade doesn’t look broken, it’s clean and square across the end. I’ll try and strip it down this week and post a picture. Thanks
 

·
Registered
Joined
·
11 Posts
Discussion Starter #6
I have a 72 Daytona so my tacho drive is the same as yours. I did a total rebuild last year. AFAIK the drive gears are all the same. However, I wonder if yours is too short as a result of a bit breaking off the end. If the gearbox seized up at some point the tang will break - I had this problem on a 72 Tiger 750 I've just rebuilt.

Have a good look at the end of the drive gear and see if it looks broken. The photo in Dave M's post looks bang on for length.

If you get desperate I could take mine out and measure it, but mine on the 750 was definitely broken by a seized box.
The spade looked in good condition. If it had been broken it’s a very clean break. I’ll try and take it apart again this week and post a picture. I guess one sure way is to measure it but I’ve nothing to compare it to. Wouldn’t want to put you through the trouble of disassembling yours. I’ll try and find a friendly stockist that carries the part and see if they can measure it. A bit difficult at the moment here with this damn Coronavirus. Many thanks.
 

·
Registered
Joined
·
311 Posts
I've just checked my parts books for my 72 Tiger 750 and the 72 Daytona, and the part number is the same for both - I did wonder if you'd got the wrong drive gear. Maybe you do have the wrong gear if it's off another model. StuartMac will no doubt have the answer to this shortly.

A thought - is the gearbox casing screwing right up to the side of the crankcase? Have you got the correct washer (mine's a Dowty about 3mm thick) between the gearbox casing and the crankcase? If the washer was too thick that would set the gearbox off too far and that could stop the tang engaging.

IIRC, when I found the broken tang off my 750 (in the bottom of the crankcase), it was a brittle failure as the tang broke in a very obvious and sharp way. No mistaking that it was broken.

Does the bike run OK? I.e., is the exhaust camshaft OK?
 

·
Moderator
Joined
·
6,841 Posts
Hi,

Firstly, welcome to the Forum. :)

problem
No tacho drive.
Absent broken bits, the problem is likely your bike has a pre-'70 exhaust cam. Although the ends of those were slotted, they took another part (the "Tachometer drive thimble") to actually engage the "spade" on the tacho. drive gear shaft.

The "thimble" is a pita - originals were a cheap piece of pressed steel sheet, which were/are easy to bugger-up; Meriden devised a couple of successive "repair parts" (with different part numbers); given what passes for 'product knowledge' amongst many of the eBay 'dealers', returns from a www search are predictably confused. :rolleyes:

Have a read of TR6R Tacho, including the linked Service Bulletins and earlier thread - I appreciate the bike there is a TR6R not a T100 but I suspect the problem's the same. If it still isn't clear, come back and we'll try?

Btw, changing cams is relatively easy on a 500, doesn't need the crankcases splitting. :)

Hth.

Regards,
 

·
Moderator
Joined
·
6,841 Posts
Hi Andy,

gearbox casing screwing right up to the side of the crankcase
correct washer (mine's a Dowty about 3mm thick) between the gearbox casing and the crankcase?
Should be the same 70-7351 Stat-O-Seal as fits on a fuel tap.

For clarity, Stat-O-Seal (with the 83-0001 steel washers that fit between the tap nuts and Stat-O-Seals):-



... Dowty:-



A Stat-O-Seal's outer is thinner than a Dowty's (if tacho. drive spade engagement in the cam is an issue). On fuel taps, the Stat-O-Seal's thicker central seal - when compressed by the steel washer and tap nut - deforms into the tap thread to seal on it, while the Stat-O-Seal's outer never touches the tank paint to scratch it (well,not unless the tap nut was tightened by Guy The Gorilla's bigger brother ... :rolleyes:).

Otoh, the Dowty's seal is barely thicker than its outer and, given any seal protrusion is just the thin edges, they're too thin to prevent the outer reaching/scratching tank paint. :( Aside, the basic Dowty seal was invented between the wars by the eponymous maker of aircraft landing gear suspension, to seal on a shaft moving through it.

Hth. :)

Regards,
 

·
Registered
Joined
·
11 Posts
Discussion Starter #12
I've just checked my parts books for my 72 Tiger 750 and the 72 Daytona, and the part number is the same for both - I did wonder if you'd got the wrong drive gear. Maybe you do have the wrong gear if it's off another model. StuartMac will no doubt have the answer to this shortly.

A thought - is the gearbox casing screwing right up to the side of the crankcase? Have you got the correct washer (mine's a Dowty about 3mm thick) between the gearbox casing and the crankcase? If the washer was too thick that would set the gearbox off too far and that could stop the tang engaging.

IIRC, when I found the broken tang off my 750 (in the bottom of the crankcase), it was a brittle failure as the tang broke in a very obvious and sharp way. No mistaking that it was broken.

Does the bike run OK? I.e., is the exhaust camshaft OK?
Engine runs fine. I’ll check the washer thickness. Thanks.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #13
Hi,

Firstly, welcome to the Forum. :)


Absent broken bits, the problem is likely your bike has a pre-'70 exhaust cam. Although the ends of those were slotted, they took another part (the "Tachometer drive thimble") to actually engage the "spade" on the tacho. drive gear shaft.

The "thimble" is a pita - originals were a cheap piece of pressed steel sheet, which were/are easy to bugger-up; Meriden devised a couple of successive "repair parts" (with different part numbers); given what passes for 'product knowledge' amongst many of the eBay 'dealers', returns from a www search are predictably confused. :rolleyes:

Have a read of TR6R Tacho, including the linked Service Bulletins and earlier thread - I appreciate the bike there is a TR6R not a T100 but I suspect the problem's the same. If it still isn't clear, come back and we'll try?

Btw, changing cams is relatively easy on a 500, doesn't need the crankcases splitting. :)

Hth.

Regards,
I think what you refer to as the thimble my parts catalogue calls a tacho drive plug - see item 33 in attachment. From what I can see of it, the solid plug is fitted to mine (as per the catalogue) and looks to be intact. I’ll disassemble and photograph this week.
Awattsy
 

·
Moderator
Joined
·
6,841 Posts
Hi,

I think what you refer to as the thimble my parts catalogue calls a tacho drive plug
Nope, two entirely different bits. The thread I linked has an image of an original Thimble in the end of a pre-'70 cam. Or you can go to an online parts 'library' like Vintage Bike Magazine » Parts Books or British Only Tech Library, click on a pre-'70 parts book and look at the same basic illustrations, you'll see the Thimble is quite different from what you pictured from a '71 parts book. You can then confirm this with the part number in an internet search engine.

From what I can see of it, the solid plug is fitted to mine (as per the catalogue) and looks to be intact.
If you read the Service Bulletin linked in the TR6R thread and similarly use the listed Meriden Thimble 'repair part' numbers in an internet search engine, you'll see they're also slotted, but aren't the '70-on 70-9988 "Tachometer drive plug".

Hth.

Regards,
 

·
Registered
Joined
·
11 Posts
Discussion Starter #15
I may be confused but my Daytona is a 1971 and I’m using a post 1970 parts catalogue from which the attachment was taken. The part in the end of my camshaft looks exactly like the catalogue - see attached picture from internet, and screws into the end of the camshaft. This is not the pressed part pictured in the link that you sent, but I believe should be similar to the part used on the service bulletins to replace it. I have also removed the drive gear (see pictures). As you will see the spade (tang) is in tact and I’ve measured as being .385ins long. The washer fitted between the gearbox and the crankcase is thin, so no scope for reducing thickness to gain more engagement. So in summary, as far as I can see all parts are good but still no location of drive gear into the plug on the end of the camshaft. I hope that this clarifies things and I appreciate all suggestions. Shorter housing on the tacho gearbox would do it - don’t know how to confirm if mine is the correct one - it looks ok.
I’ve also put a screw diver in the n the slot on the end of the camshaft and turned the engine - screw driver rotates, so I assume that all is ok on the camshaft.
Awattsy
 

Attachments

·
Registered
Joined
·
11 Posts
Discussion Starter #16
I may be confused but my Daytona is a 1971 and I’m using a post 1970 parts catalogue from which the attachment was taken. The part in the end of my camshaft looks exactly like the catalogue - see attached picture from internet, and screws into the end of the camshaft. This is not the pressed part pictured in the link that you sent, but I believe should be similar to the part used on the service bulletins to replace it. I have also removed the drive gear (see pictures). As you will see the spade (tang) is in tact and I’ve measured as being .385ins long. The washer fitted between the gearbox and the crankcase is thin, so no scope for reducing thickness to gain more engagement. So in summary, as far as I can see all parts are good but still no location of drive gear into the plug on the end of the camshaft. I hope that this clarifies things and I appreciate all suggestions. Shorter housing on the tacho gearbox would do it - don’t know how to confirm if mine is the correct one - it looks ok.
I’ve also put a screw diver in the n the slot on the end of the camshaft and turned the engine - screw driver rotates, so I assume that all is ok on the camshaft.
Awattsy
Hi, I’ve done some more investigation and measured everything and it would appear that the spade on the end of the drive gear is about 2mm short of engaging with the plug (slot) on the camshaft. The gearbox internals protrude about 22mm beyond the gearbox housing (See picture). I’ve measured the distance from the crankshaft seat to the top of the drive plug (slot) and its about 24mm - hence 2mm short. I’m at a loss as to why this should be, so any ideas much appreciated. I guess the housing could be incorrect, too long. Matching 4-5mm off the length at the crankshaft end could work, or maybe it’s the wrong housing.
Alternatively, the drive gear shaft could be too short - mine measures 43.84mm (see picture). Does anyone out there have a good part that they could measure.
All suggestions welcome.
Awattsy
 

Attachments

·
Registered
Joined
·
311 Posts
Hi,

I measured the length overall (with a caliper) at 54.82mm, and the length of the tang at 9.8mm.

Apologies, I'd forgotten you measured the length of the shaft up to the gear. I'm guessing, but I bet yours is the same length as mine, given your dimension up to the inside face of the gear.

You have to fiddle a bit to get the gear to locate in the end of the shaft when replacing it and meshing with the tacho drive spur gear - I had to nudge mine over on the k/s to get the tang to locate. There's a big space between the outer face of the gear and the outside edge of the gearbox housing - that space is filled by a bulbous protrusion on the inner face of the cover screw. When the tang locates in the end of the camshaft, the outer face of the drive shaft gear is about flush with the outside diameter of the tacho spur gear. Apologies, but are you getting the shaft fully home?

Should have taken a pic of that but I can easily get one if you need it.

20200408_180203.jpg
 

·
Registered
Joined
·
11 Posts
Discussion Starter #18
Hi, I think that after measuring the parts I may have got to the bottom of it. It would appear that whoever had the bike before me may have fitted a 650 gearbox rather than a 500. The internals protrude about an extra 10mm on the 500. I was going to try modifying the housing on mine but decided to buy a new one - mother £50 gone. I’ll end the post when I’ve fitted the new part. I bet I’m not the only one in this position. M any thanks to all who have replied with help.
Awattsy
 
1 - 19 of 19 Posts
Top