[Dr. Zo]

1971 T100C Refresh.

I came upon this 1971 T100C in a serendipitous way. With a little coaxing, and the permission of the owner, I got it started and took it for a brief spin. It had been sitting for awhile in his outbuilding. It followed me home (on a trailer) so it is now mine, at least for a bit.

There is an interesting back story to this bike that I am still discovering, but includes at least an association with the Pagans MC in the early 70’s.

It seems to be original, except for a Boyer ignition (still have the original parts), the exhaust system (I thought these had high pipes), it is missing turn signals and side reflectors (if it had them?), and I’m not sure there is anything else different from original. With a bit of tinkering it started right up, shifted properly and idled mildly. Compared to my 750, I can see why these were/are desirable bikes, enough power and easy to ride.

Engine and frame numbers match: XE 06741 T100C

I’d appreciate any information as you take a look at the photos about what seems to be original versus other on the bike. I’ll get some better photos up once I give it a wash and decide what to do with it. I think the tires are original too. Extremely low mileage. Thanks for any interest.

 

[StuartMac]

Hi,

seems to be original

You're correct about the missing high-mounted exhaust system, and they did originally have turn signals and reflectors - the front ones are a pita to fit with the tank front mounting, so might've been discarded at some point, followed by the rear ones ...?

View attachment 791410

That the top and bottom of the forkstop don't align might indicate a front-ender in the bike's past; could be what also caused the ding in the front fender?

The rear grab-rail and tail-lamp mount might not be original. The rear grab-rail appears to be '70 rather than '71 (particularly if the holes in the gusset plates between the horizontal tube around the fender and the pillion grab handle tube are 7/16" ID) and the tail lamp mounting should be black. However, the bike was built in December 1970, just after Meriden had managed to build the first batch of OIF 650's after The Cock-up, so could've used any parts just to get bikes out the door and across The Pond for the US selling season.

Hth.

Regards,

 

[Dr. Zo]

Hi,

You're correct about the missing high-mounted exhaust system, and they did originally have turn signals and reflectors - the front ones are a pita to fit with the tank front mounting, so might've been discarded at some point, followed by the rear ones ...?

View attachment 791410

That the top and bottom of the forkstop don't align might indicate a front-ender in the bike's past; could be what also caused the ding in the front fender?

The rear grab-rail and tail-lamp mount might not be original. The rear grab-rail appears to be '70 rather than '71 (particularly if the holes in the gusset plates between the horizontal tube around the fender and the pillion grab handle tube are 7/16" ID) and the tail lamp mounting should be black. However, the bike was built in December 1970, just after Meriden had managed to build the first batch of OIF 650's after The Cock-up, so could've used any parts just to get bikes out the door and across The Pond for the US selling season.

Hth.

Regards,

OK, thanks. I thought the X referred to December and the E referred to the year 1971? I think you must know better. I'll have to take a closer look at the forkstop alignment in good light. I didn't notice a front fender ding, perhaps it was how the light reflected - I'll attach another photo. On the exhaust - I've seen photos with both high pipes exiting on the primary side with a grill-like heat guard, and I've seen some with one high pipe on either side. I'm wondering if these were options or year/model differences?

 

[Dr. Zo]

Also, here are a couple of close up shots of the forkstop area. I don't see any damage or mis-alignment - but perhaps I am missing something?

 

[StuartMac]

Hi,

the bike was built in December 1970

thought the X referred to December and the E referred to the year 1971?

While the month is always the calendar month, the "year" is always the Model Year, never the calendar year.

Historically, Triumph (and parent BSA) changed Model Years anywhere between calendar June and October, although it was most usually in July, August or September, then the works would start producing the bikes of the next Model Year (equivalent to the following calendar year). E.g. the first bike of the '71 Model Year was KE00001, produced in calendar September 1970, the 1971 Model Year ran through to July 1971, the first bike of the '72 Model Year was HG30870 - Meriden only sometimes restarted the number sequence at 1 (or 100, or 101 ... ).

didn't notice a front fender ding, perhaps it was how the light reflected

Excellent.

exhaust - I've seen photos with both high pipes exiting on the primary side with a grill-like heat guard, and I've seen some with one high pipe on either side. I'm wondering if these were options or year/model differences?

Year/model differences. Afaict, C-range (unit 350 and 500) C-models (TR5AC, T100SC, T100C) never had one high pipe on either side as standard, it was always a 2-into-1; '67-on (coincident with the new frame?), standard was two separate high pipes and mufflers on the primary side, '67 without the grill heat guard.

Hth.

Regards,

 

[Dr. Zo]

Hi,

While the month is always the calendar month, the "year" is always the Model Year, never the calendar year.

Historically, Triumph (and parent BSA) changed Model Years anywhere between calendar June and October, although it was most usually in July, August or September, then the works would start producing the bikes of the next Model Year (equivalent to the following calendar year). E.g. the first bike of the '71 Model Year was KE00001, produced in calendar September 1970, the 1971 Model Year ran through to July 1971, the first bike of the '72 Model Year was HG30870 - Meriden only sometimes restarted the number sequence at 1 (or 100, or 101 ... ).


Excellent.


Year/model differences. Afaict, C-range (unit 350 and 500) C-models (TR5AC, T100SC, T100C) never had one high pipe on either side as standard, it was always a 2-into-1; '67-on (coincident with the new frame?), standard was two separate high pipes and mufflers on the primary side, '67 without the grill heat guard.

Hth.

Regards,

Well OK, model year versus the year of the bike - I'll have to look back at my engine and frame years from my recently rebuilt Bonneville as several times I seemed to have ordered the wrong part and perhaps that was due to my confusion on the dating of the bike - Thanks. Also thanks for the pipes info - I think I'll likely change the pipes to high ones, but am not particularly fond of the look of the grill heatguard - I've seen some photos of the 2 into 1 pipe with a more minimal heatguard. Great information - thanks.

 

[StuartMac]

Hi,

appreciate any information as you take a look at the photos about what seems to be original versus other on the bike.

Having stared longer at your photos, a few more non-standard parts:-

Carb. - It's a Monobloc, not the original Concentric. If the bike was used off-road, I've read that Monoblocs were better at low-speed mixture control than Concentrics?

Rider footrests - Can't tell if they're folding (standard on T100C and TR6C) or road-bike fixed ones?

Fender stays-to-fork sliders brackets - Not sure if it's just the angle in View attachment 791409 but they might not be the H1685 (97-1685) listed in the parts book; if not, for a good reason, Closer-up photo.?

Headlamp shell - Again could do with a closer-up photo. of the top of the shell but I think:-

. I'm seeing the black knob of a Lucas 31276 rotary on/off switch, fitted to '71 and '72 triples and 650's to turn the headlamp on/off;

. otoh, I'm not seeing the lever of a Lucas 35710 3-position lighting switch that should be there.

Photo. of the top of the headlamp shell, if I'm correct, while the '71 parts book does list the 31276 for the T100C, it isn't correct; the 500 doesn't have the same electrics as the triples and 650's, I'll post the differences for you.

Hth.

Regards,

 

[Dr. Zo]

Hi,

Having stared longer at your photos, a few more non-standard parts:-

Carb. - It's a Monobloc, not the original Concentric. If the bike was used off-road, I've read that Monoblocs were better at low-speed mixture control than Concentrics?

Rider footrests - Can't tell if they're folding (standard on T100C and TR6C) or road-bike fixed ones?

Fender stays-to-fork sliders brackets - Not sure if it's just the angle in View attachment 791409 but they might not be the H1685 (97-1685) listed in the parts book; if not, for a good reason, Closer-up photo.?

Headlamp shell - Again could do with a closer-up photo. of the top of the shell but I think:-

. I'm seeing the black knob of a Lucas 31276 rotary on/off switch, fitted to '71 and '72 triples and 650's to turn the headlamp on/off;

. otoh, I'm not seeing the lever of a Lucas 35710 3-position lighting switch that should be there.

Photo. of the top of the headlamp shell, if I'm correct, while the '71 parts book does list the 31276 for the T100C, it isn't correct; the 500 doesn't have the same electrics as the triples and 650's, I'll post the differences for you.

Hth.

Regards,

Stuart, thank you for taking a closer look. The foot pegs are the folding type. Here are a few more photos that might help you to see what I have more distinctly. Also, from the original owner’s handbook, which I have, it indicates the kill switch is on the left, however on my bike it is on the right. But this might be for the T100R model since the book covers both. Cheers.

 

[StuartMac]

Hi,

foot pegs are the folding type

Headlamp shell

From View attachment 791566 , I can see the bike has the correct '71 shell and 3-position lever lighting switch. What had me going in View attachment 791409 was the lighting switch lever is pointing almost directly at the camera and the shade over the right-hand idiot lamp caught the flash oddly.

Fender stays-to-fork sliders brackets

Those on your bike don't appear be the listed H1685 (97-1685); they appear to be H1688 (97-1688).

The black-painted steel-slider forks (correctly) on to your T100 were fitted to all Triumphs pre-'71; then, H1685 were fitted to road bikes but H1688 were fitted to off-road versions (T100C and TR6C).

Search online using the 97- part numbers; returned images should show you two similar-looking but different parts, different relationships between the oblong hole (that fits on the slider) and the round hole for the front fender stays' bolt. Same slider with the same oblong mounting for the bracket, H1688 stays' bolt hole will be higher than H1685's.

Then same fender stays bolted to H1688 mean an off-road version's fender is higher up, further away from the tyre - mud less-likely to clog between fender and tyre; plus, for a few years, T100C and TR6C had 3.50 front tyres as standard rather than road bikes' 3.25.

original owner’s handbook
indicates the kill switch is on the left, however on my bike it is on the right. But this might be for the T100R model since the book covers both.

Uh-uh, the book is wrong; not only were exactly the same handlebar switch clusters fitted to both T100C and T100R, exactly the same handlebar switch clusters were fitted to every '71 Triumph and BSA, from 250 single to top-of-the-range triple. If you look in the 350/500 workshop manual, both '71 models' wiring diagrams (pages 248 and 249) show the kill button White/Yellow wire to the ignition coils out of the right-hand (throttle side) switch cluster. Similarly, if you look in the '71 650 Owner's Handbook, .pdf page 11/manual page 10, the kill button is shown in the throttle-side switch cluster.

'71-'74 in the US, the kill button is always in the same switch cluster as the 'paddle' lever that works the turns signals; the other switch cluster, the 'paddle' lever switches the headlamp bulb between main and dip filaments.

Aside, turn signals/kill button on the right, dipswitch on the left was '71-only, '72-74, the clusters swapped sides (then the kill button was on the left 'bar, but still with the turn signals 'paddle' lever)

Hth.

Regards,

 

[Dr. Zo]

Hi,




From View attachment 791566 , I can see the bike has the correct '71 shell and 3-position lever lighting switch. What had me going in View attachment 791409 was the lighting switch lever is pointing almost directly at the camera and the shade over the right-hand idiot lamp caught the flash oddly.


Those on your bike don't appear be the listed H1685 (97-1685); they appear to be H1688 (97-1688).

The black-painted steel-slider forks (correctly) on to your T100 were fitted to all Triumphs pre-'71; then, H1685 were fitted to road bikes but H1688 were fitted to off-road versions (T100C and TR6C).

Search online using the 97- part numbers; returned images should show you two similar-looking but different parts, different relationships between the oblong hole (that fits on the slider) and the round hole for the front fender stays' bolt. Same slider with the same oblong mounting for the bracket, H1688 stays' bolt hole will be higher than H1685's.

Then same fender stays bolted to H1688 mean an off-road version's fender is higher up, further away from the tyre - mud less-likely to clog between fender and tyre; plus, for a few years, T100C and TR6C had 3.50 front tyres as standard rather than road bikes' 3.25.


Uh-uh, the book is wrong; not only were exactly the same handlebar switch clusters fitted to both T100C and T100R, exactly the same handlebar switch clusters were fitted to every '71 Triumph and BSA, from 250 single to top-of-the-range triple. If you look in the 350/500 workshop manual, both '71 models' wiring diagrams (pages 248 and 249) show the kill button White/Yellow wire to the ignition coils out of the right-hand (throttle side) switch cluster. Similarly, if you look in the '71 650 Owner's Handbook, .pdf page 11/manual page 10, the kill button is shown in the throttle-side switch cluster.

'71-'74 in the US, the kill button is always in the same switch cluster as the 'paddle' lever that works the turns signals; the other switch cluster, the 'paddle' lever switches the headlamp bulb between main and dip filaments.

Aside, turn signals/kill button on the right, dipswitch on the left was '71-only, '72-74, the clusters swapped sides (then the kill button was on the left 'bar, but still with the turn signals 'paddle' lever)

Hth.

Regards,

Stuart, OK, great info. I took a look at the 2 different types of brackets to attach the fenders (97-1685 and 97-1688) and see how they change the height of the fender. So, being as this bike is a T100C, I am assuming the 97-1688 is the original/correct bracket for this bike? This bike also currently has a 3.50 tire on front, though it is a road-going tire versus what I think would have originally come on the bike - something like a trials type tire. By the way, would you know of a tyre brand/type that might closely resemble the originals? Thanks.

 

[StuartMac]

Hi,

took a look at the 2 different types of brackets to attach the fenders (97-1685 and 97-1688) and see how they change the height of the fender. So, being as this bike is a T100C, I am assuming the 97-1688 is the original/correct bracket for this bike?

Mmmm ... 1688 weren't listed in '71 so difficult to say with certainty whether they were original on your bike, and missing from the parts books was a mistake, or if they were fitted by a PO (the one who also changed the original carb.?).

bike also currently has a 3.50 tire on front, though it is a road-going tire versus what I think would have originally come on the bike

I'm sure I've read that off-road versions were fitted with Dunlop Trials Universal tyres; however, 'course damned if I can find the reference now ...

tyre brand/type that might closely resemble the originals?

If I'm right above about the Dunlop tyres, Google says tyres called "Dunlop Trials Universal" are available (albeit not in either 3.50 or 3.25x19 or 4.00x18 in GB); you can see the images, hunt around for tyres in the correct sizes with the same or a similar tread pattern?

Nevertheless, not something I'd ever do. Generally, I only use original if it's also the best; tyres, my view is those two little contact patches are my sole connection to the rest of reality, ime the rest of reality and I do dumb stuff occasionally, one of the reasons I'm still around is I've always used pretty-much the best connections to reality available at any given time.

Hth.

Regards,

 

[Dr. Zo]

Hi,

Mmmm ... 1688 weren't listed in '71 so difficult to say with certainty whether they were original on your bike, and missing from the parts books was a mistake, or if they were fitted by a PO (the one who also changed the original carb.?).


I'm sure I've read that off-road versions were fitted with Dunlop Trials Universal tyres; however, 'course damned if I can find the reference now ...


If I'm right above about the Dunlop tyres, Google says tyres called "Dunlop Trials Universal" are available (albeit not in either 3.50 or 3.25x19 or 4.00x18 in GB); you can see the images, hunt around for tyres in the correct sizes with the same or a similar tread pattern?

Nevertheless, not something I'd ever do. Generally, I only use original if it's also the best; tyres, my view is those two little contact patches are my sole connection to the rest of reality, ime the rest of reality and I do dumb stuff occasionally, one of the reasons I'm still around is I've always used pretty-much the best connections to reality available at any given time.

Hth.

Regards,

Stuart, you are right on the contact patches. Best to use whatever is the best technology today than relying upon something older and likely less safe. That said, I'll look to replace with something that will be as good as modernly possible. Thanks.

 

[Dr. Zo]

Fibre Washers - Rather than getting fibre washers piecemeal (say from a vintage bike retailer) for my bikes when changing oil, etc, I am wondering if any member has had luck with finding a place to get an assortment of good quality fibre washers of various sizes useful on Triumphs? Thanks for any advice on this.

 

[StuartMac]

Hi,

No first-hand experience but McMaster-Carr usually featured in the answers to this sort of question in the past?

Hth.

Regards

 

[Dr. Zo]

Hi,

No first-hand experience but McMaster-Carr usually featured in the answers to this sort of question in the past?

Hth.

Regards

OK, thanks. I've been looking at their site in this regard.

 

[Dr. Zo]

I was finally taking my T100C out for a longer run, about 45 miles. I was returning on a parkway, driving at about 55 mph for 15 miles before turning off. When I turned off I slowed down then attempted to speed up and ship into 4th gear. The bike lost power and stopped running, so I shifted to 3rd and it started again, but would not keep running unless I had high revs. This happened several times on the few miles back home. It seemed like it might not be getting fuel, but then when I kept the revs up it was ok. I eventually turned it off and it restarted with no problem. Any comments are appreciated!

 

[newsh]

I was finally taking my T100C out for a longer run, about 45 miles. I was returning on a parkway, driving at about 55 mph for 15 miles before turning off. When I turned off I slowed down then attempted to speed up and ship into 4th gear. The bike lost power and stopped running, so I shifted to 3rd and it started again, but would not keep running unless I had high revs. This happened several times on the few miles back home. It seemed like it might not be getting fuel, but then when I kept the revs up it was ok. I eventually turned it off and it restarted with no problem. Any comments are appreciated!

Petrol tank vent blocked?

 

[Dr. Zo]

Petrol tank vent blocked?

OK, thanks. I'll haver to take a look. Didn't have a thought about that!

 

[Dr. Zo]

So, I made sure the vent on my petrol tank was clear and went for a ride. After about 15 minutes of riding I thought the problem, of cutting out at lower rpms, was solved so continued to ride. Then after another 5 minutes of riding it started to cut out again when the rpms got low, like when I stopped for a light it started to cut out and I had to give is some throttle to keep running. This also happened if I went to a higher gear and was sort of lugging the engine - it would start to cut out altogether so I had to downshift to keep the gas on and revs up. Any other ideas are appreciated on how to diagnose this.

One more thing. I went to replace the headlight bulb as it was burned out. I put the new bulb in and it would only light up when I had the switch fully on and pressed the high beam. So the parking light works as it should, the horn works as it should, but the headlamp only comes on when the lamp switch is fully on (to the right) and I press the high beam button. Any advice on how to trouble-shoot this before I start taking things apart?

Lastly, I was going to replace the fork oil. However I found that the fork drain plugs were fixed with a phillips screw head bolt. On my other bike I have a regular hex head bolt. These don't seem to want to come out easily and I wanted to see if anyone had any experience with this before I try to remove them? I may have to use an impact driver.

Thanks.

 

[newsh]

So, I made sure the vent on my petrol tank was clear and went for a ride. After about 15 minutes of riding I thought the problem, of cutting out at lower rpms, was solved so continued to ride. Then after another 5 minutes of riding it started to cut out again when the rpms got low, like when I stopped for a light it started to cut out and I had to give is some throttle to keep running. This also happened if I went to a higher gear and was sort of lugging the engine - it would start to cut out altogether so I had to downshift to keep the gas on and revs up. Any other ideas are appreciated on how to diagnose this.

One more thing. I went to replace the headlight bulb as it was burned out. I put the new bulb in and it would only light up when I had the switch fully on and pressed the high beam. So the parking light works as it should, the horn works as it should, but the headlamp only comes on when the lamp switch is fully on (to the right) and I press the high beam button. Any advice on how to trouble-shoot this before I start taking things apart?

Lastly, I was going to replace the fork oil. However I found that the fork drain plugs were fixed with a phillips screw head bolt. On my other bike I have a regular hex head bolt. These don't seem to want to come out easily and I wanted to see if anyone had any experience with this before I try to remove them? I may have to use an impact driver.

Thanks.

Headlight.
You don’t mention whether the headlight Hi/Lo switch is working or not.

Fork drain screws.
These are not Phillips heads they are Posidrive, a Phillips bit will “cam out” and ruin the screw.
Use the correct PZ bit, give it a sharp tap with a hammer, straight on, before attempting to loosen and they will come undone. I use a little 1/4” drive socket set with a hex bit adapter for jobs like this, works great.