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1971 T100C Refresh

6K views 48 replies 3 participants last post by  newsh 
#1 ·
1971 T100C Refresh.
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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.
 
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#2 ·
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,
 
#3 ·
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?
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#7 ·
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; :rolleyes: the 500 doesn't have the same electrics as the triples and 650's, I'll post the differences for you.

Hth.

Regards,
 
#8 ·
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; :rolleyes: 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.


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#13 ·
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.
 
#16 ·
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!
 
#19 ·
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.
 
#20 ·
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.
 
#22 · (Edited)
Hi
Excellent news on the fork drain screws! [emoji106][emoji106]

Below is a comparison picture showing the difference between Phillips and Pozi. At work I used to send pictures like this out to customers along with Pozi bits and bags of 100 replacement screws!

Yes it certainly seems like it’s the contacts in the Hi/Lo dipper switch, which is what I suspected.
It should respond to some careful dismantling and cleaning. You might find a loose connection that needs soldering.
Advice I’ve read on here is to disassemble the switch inside a large clear plastic bag to capture any small springs and ball bearings that have a tendency to launch themselves into the furthest corner of the workshop/kitchen. [emoji106]

 
#25 ·
I am rebuilding the carburetor on this bike as I believe that was the problem I was having with intermittent fueling. It turns out the float was worn through so was likely sticking. I've got the carb apart and waiting for parts.

I decided to redo the fuel lines also and when examining found that the petcocks were leaking, that is when fully closed there was still some fuel coming through.

I was hoping I could rebuild the petcocks also, as there seems to be a rubber washer inside the petcock that could be replaced. I haven't found anything on-line about rebuilding these so I am wondering if any of you have rebuilt your petcocks previously, and if so where did you find the new internal pieces?

Thanks for your help!
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#26 ·
So I never found a rebuild kit for my peacocks. I went to ace hardware and found some o rings the same size as in these old petcocks - as the old ones were hard as a rock. It was relatively easy to disassemble the petcocks, clean them with 000 steel wool, replace the o ring and put back together. Now to test them for leaks.

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#28 ·
Hi,

Consider electrical - the described symptoms are also of a poor electrical contact that heats up when conducting 'til it fails, cools after it stops working, works again once it's cooled. :(

Your original post says the bike has a Boyer-Bransden EI, please post which one. Nevertheless, an obvious test would be to connect a Voltmeter across the battery and see what the reading is:-

. before anything's turned on,

. after just the ignition is turned on.

If both of these meter readings are at least 12.5~12.6 Volts, with the ignition turned on, use the meter to measure between the battery +ve terminal and where the B-B Transistor Box White wire is connected to a bike White/Yellow wire (don't disconnect the wires, just expose the metal terminals for the measurement then cover them up again), post the difference between this latter meter reading and the "after just the ignition is turned on" meter reading.

Meter connected across the battery again, start the bike and watch the meter reading, note what the meter displays if/when the engine starts to run rough.

Hth.

Regards,
 
#34 ·
So Stuart, I started to trouble shoot this and determined I may need a longer time than a couple of hours to diagnose this.

I used a voltmeter to check the battery before anything was turned on: 12.21

After the ignition is turned on: 12.08

Obviously I haven't ridden the bike much lately and it is not on a trickle charger.

I was trying to find where the B-B Transistor box White Wire is connected to a bike White/Yellow wire, but they are pretty well covered and it looks like I will have to remove the gas tank to find this connection. So when I get a block of time where I can do this I will.

A couple of other things, however. I can get the bike to start, and now it never runs nicely, always rough and variable. A bit of smoke too. While it was running I disconnected the left spark plug wire and it kept running at about the same pace. So I reconnected the wire and again, while it was still running, I disconnected the right spark plug wire and it kept running, roughly of course, but similar to when I disconnected the left plug. Might this be diagnostic of anything specific? Thanks!
 
#35 ·
Hi,
started to trouble shoot this and determined I may need a longer time than a couple of hours to diagnose this.

I used a voltmeter to check the battery before anything was turned on: 12.21

After the ignition is turned on: 12.08

Obviously I haven't ridden the bike much lately and it is not on a trickle charger.

I was trying to find where the B-B Transistor box White Wire is connected to a bike White/Yellow wire, but they are pretty well covered and it looks like I will have to remove the gas tank to find this connection. So when I get a block of time where I can do this I will.
'Til you get time to work longer on this, whip out the battery and connect it to a low-Ah (1/10th battery Ah) trickle-charger at least overnight? This'll determine whether the battery can be charged or has turned up its toes.

can get the bike to start, and now it never runs nicely, always rough and variable. A bit of smoke too. While it was running I disconnected the left spark plug wire and it kept running at about the same pace. So I reconnected the wire and again, while it was still running, I disconnected the right spark plug wire and it kept running, roughly of course, but similar to when I disconnected the left plug. Might this be diagnostic of anything specific?
I'd suggest generally - both plugs are likely misfiring intermittently(?), might be an electrical problem affecting the EI, which'd affect both plugs, might be a fuelling problem, single carb. will affect both cylinders ...

Ain't old bikes fun ... :cool:

Hth.

Regards,
 
#37 ·
Electrical troubleshooting! I'm still having trouble troubleshooting my 1971, Triumph, T100C electrical issue. I checked the wiring of the Boyer-Brandsen MK IV and it looks to be properly appointed. As far as I can see it is getting juice. I made a YouTube video in case any members can take a look and help me a bit more with the diagnosis. Thanks if you'll take a look here:
 
#39 ·
I'm still trying to figure this out. So the bike starts easily, but still runs rough, like it is missing intermittently. When running I removed one the right spark plug wire and it kept running, but less firing. After connecting the right plug, I then removed the left, and it kept running, but just barely. So it would seem the left side is not running as smoothly as the right side. So could this be a left side coil or wiring issue that for some reason is not letting the left side spark as strongly as the right side? Thanks for advice!
 
#40 ·
OK, so I tried switching coils. I ran the bike with the spark plugs wires switched to the other plugs - ran the same rough. Then I started and ran the bike on the right cylinder only, once with the left coil and once with the right coil. I did the same with the left cylinder. All four times it seemed to run the same, no missing just running on once cylinder. So I am wondering what this tells me . . . it seems that both coils are working OK? Also both spark plug wires seem to work ok, even on just one cylinder. So when I hook the plugs up normally, it is still running rough, so more than one cylinder is firing, just not evenly. Any advice?
 
#43 ·
OK, just now getting back to diagnose and fix this T100. So I went ahead and got new coils and plug and leads and installed them. Now, when trying to start, my ignition switch seems to be on the fritz! I'm not getting that red light coming on when turning the key on. Any thoughts on how to troubleshoot this? Thanks.
 
#45 ·
Hi,
got new coils and plug and leads and installed them. Now, when trying to start, my ignition switch seems to be on the fritz! I'm not getting that red light coming on when turning the key on. Any thoughts on how to troubleshoot this?
:confused: Why buy new coils and plug and leads if you don't know they're the problem? Ime, while people who just throw money in the general direction of a problem do sometimes randomly solve it:-

. Best case, they've spent a lot of money replacing perfectly-good components before they eventually found the dud one.

. Worst case, because many new components are poor-quality, new components can introduce a problem that wasn't there before ... E.g. your "new coils", are they "Lucas"? If yes, they introduce a problem your bike didn't have before - they're unsuitable for use with any electronic ignition. :oops:

There is plenty of power at the battery and the coils
How did you establish that?

Given the ignition switch is between the battery and the electronic ignition (that supplies the coils), if "There is plenty of power at the battery and the coils", how can the ignition switch be "on the fritz"?

I'm not getting that red light coming on when turning the key on.
Have you checked the red light bulb hasn't simply blown?

On your bike (any '69-on Triumph or BSA), the red light is low oil pressure warning, it's turned on/off by oil pressure closing/opening the switch screwed into the front edge of the timing cover. Even if the switch is original, it opens at 5~7 psi (later switch less, pattern switch unknown). If you follow the standard method to ensure the clutch plates aren't stuck together - before turning on the ignition switch, pull handlebar clutch lever, kick over engine 'til plates free - have you considered the oil pressure increase from kicking over the engine has simply opened the switch?

Any thoughts on how to troubleshoot this?
I haven't been on the forum much and missed [your post #41]
Read my post #41? :cool:

Hth.

Regards,
 
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