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Hi Eric, Andy,

Did the change take some time, or were they able to begin producing the next model immediately?
Depends how you look at it. There was little or no break in production because the workers still had to be paid. One of the killer blows to BSA's (Triumph's parent company) finances in the early 1970's was that fiasco of the 650 engine not fitting in the new OIF - Meriden hadn't planned to produce 500's 'til later so production-line workers sat around, paid but not producing, while 500 components were readied, and changes to the 650 were designed and then made. :(

Some year-to-year changes were major; e.g. '69 saw the change from British Standard to Unified threads on the twins' engines. So obviously, components with the new threads had to be ready at the same time as fasteners with the new threads. Manufacture of the new components would've started well before the changeover day - I know assembly of the first triples began in June 1968 but, say, original cylinder heads on those early bikes usually have a March 1968 casting date.

Although not as often as claimed by some authors, the change from one model year to the next was sometimes arranged over the 'summer shutdown' - few production-line workers could take individual holidays without affecting the smooth running of the line, so it was usual to close lines for two weeks during the English schools' six-week summer holiday and send all the workers on holiday at the same time. That was usually the first two weeks in August in the Coventry area and the subject of much organisation and liaison between unions and rail and bus companies because component suppliers also closed their factories at the same time.

How many were they building in a model year around then?
About 30,000 twins; plus, before the September 1973 sit-in, Meriden also assembled triple engines built at BSA's Small Heath works into cycle parts and dispatched the complete bikes.

pretty sure the tank badge has been repainted. I've never found another example of white logo on black.
Likewise.

mud guards match the tank exactly to my eyes.
Daft thing about original Meriden-sprayed Cherry is they often didn't ... :) It was sprayed over a red-lead undercoat and, because sprayers were paid 'piece work' - their wages depended on the number of items they completed - the undercoat wasn't always fully-dry when the top coat was sprayed. If the undercoat wasn't fully-dry, it 'bled through' the top coat, changing the latter slightly (I suspect really bad parts weren't passed by the quality-control inspectors and were stripped and resprayed).

Other things in your images that make me suspect the parts have been resprayed:-

. Ime, the White flashes are too far towards the edge of the tank. As a general rule-of-thumb, the inner straight edges should run from the front point of each badge towards where the rear mounting tab's attached. However, I say "towards" because they shouldn't reach the mounting tab - the outer edge of each flash should start from the rear top corner of the corresponding badge and run in a smooth compound-radius curve to meet the inner straight edge in a point just above the top of the front of the seat. That said, note "general rule-of-thumb" - thanks to production differences, particularly rear points weren't always above the tops of seats and flashes don't always align exactly with badges if the latter aren't original; however, equally, original flash outer edges didn't parallel knee cutaway top edges for most of their length and then curve in a few inches to meet the inner straight edge ...

. The pinstripes appear to have tiny cracks across them? They also appear too regular :) ... Meriden hand-painted pinstripes so there were often tiny but visible variations in their width.

. Couple of places I can see Red between the pinstripe Black and the 'flash' White? Meriden painted the pinstripe over the joint between the two colours, and the joint is usually visible through the pinstripe ...

. Meriden didn't 'terminate' the front fender stripe at the back, the stripe and pinstripes just 'ran off' the lower edge.

One thing I can't tell from your pictures is what paint the Cherry is? Unusually for Meriden at this time, Cherry was a metallic, not the more-usual candy; also the original Cherrys I've seen are a relatively-coarse metallic - almost tending towards a fine Metalflake - than common modern automotive metallics.

they were built maybe only a week or 2 apart.
Likely less. ~30K bikes over ~48 weeks is ~600 bikes per week; plus, in December and the run-up to Christmas, despite 1970's generally-poor labour relations, workers might've been more inclined to work a full week for a full week's pay ...? :sneaky:

US handlebars
Afaict, the 'bars on Eric's bike aren't standard '72 US-market, the ends seem to be higher above the clocks and turned back more.

everything else I can see in the photos is identical
Might mean the mudguards on yours aren't original - GB-market were longer and the front would've had holes for the front numberplate.

Just a thought but ... December is unusual for Meriden to supply - and therefore build - a British-market bike; apart from a Christmas present, who'd buy a new bike to put on salt-covered British roads; British-market bikes were normally built and supplied to dealers closer to the spring/summer? Otoh, as your bike is so close in numbers to Eric's, if you checked original dispatch records with either the VMCC or TOMCC, you might find it was originally dispatched to the US but was returned unsold, later dispatched to a British dealer? Then it'd be the 'guards that are 'original' and the tank, 'bars and exhaust system were replacements? :)

Britain was just going decimal in its coinage!
:) 'Had gone' by the time these bikes were built, 15th February 1971 was the changeover day.

Hth.

Regards,
 

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Discussion Starter #22
Daft thing about original Meriden-sprayed Cherry is they often didn't ... :) It was sprayed over a red-lead undercoat and, because sprayers were paid 'piece work' - their wages depended on the number of items they completed - the undercoat wasn't always fully-dry when the top coat was sprayed. If the undercoat wasn't fully-dry, it 'bled through' the top coat, changing the latter slightly (I suspect really bad parts weren't passed by the quality-control inspectors and were stripped and resprayed).

Other things in your images that make me suspect the parts have been resprayed:-

. Ime, the White flashes are too far towards the edge of the tank. As a general rule-of-thumb, the inner straight edges should run from the front point of each badge towards where the rear mounting tab's attached. However, I say "towards" because they shouldn't reach the mounting tab - the outer edge of each flash should start from the rear top corner of the corresponding badge and run in a smooth compound-radius curve to meet the inner straight edge in a point just above the top of the front of the seat. That said, note "general rule-of-thumb" - thanks to production differences, particularly rear points weren't always above the tops of seats and flashes don't always align exactly with badges if the latter aren't original; however, equally, original flash outer edges didn't parallel knee cutaway top edges for most of their length and then curve in a few inches to meet the inner straight edge ...

. The pinstripes appear to have tiny cracks across them? They also appear too regular :) ... Meriden hand-painted pinstripes so there were often tiny but visible variations in their width.

. Couple of places I can see Red between the pinstripe Black and the 'flash' White? Meriden painted the pinstripe over the joint between the two colours, and the joint is usually visible through the pinstripe ...

. Meriden didn't 'terminate' the front fender stripe at the back, the stripe and pinstripes just 'ran off' the lower edge.

One thing I can't tell from your pictures is what paint the Cherry is? Unusually for Meriden at this time, Cherry was a metallic, not the more-usual candy; also the original Cherrys I've seen are a relatively-coarse metallic - almost tending towards a fine Metalflake - than common modern automotive metallics.

Afaict, the 'bars on Eric's bike aren't standard '72 US-market, the ends seem to be higher above the clocks and turned back more.
Very helpful, Stuart. I'm going to inspect the paint more closely. My phone's camera is on the fritz so I can't get good shots now. (The one I posted with the engine on the floor was taken with the selfie side.) Between pattern pipes, possibly 'bars, and paint I'm more curious than ever about my baby's history. Was it restored at some point? Why? The clock says around 13,500, is that accurate? How could I tell? What else may not be original? Doesn't really matter to me, my love is unconditional. :love: I've considered replacing the 'bars, I always liked the look of UK 'bars and low mirrors.
 

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You might get a clue at to whether or not the mileage is genuine when you take the head off. If the pistons are std, then the 13,500 might be true. Mind you, they could say +40 and that mileage might still be true if it had a hard life or a mechanical mishap - but maybe less likely. Who knows? Maybe it's been re-built - hence the non std pipes, and the clock was re-set to zero, so it's done 13.5k since the rebuild. When I re-build mine I leave the odometer alone.

Whatever, you have a detective job to do to see what you can find out.
 

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Discussion Starter #24
First look inside. Some hot spots on the right side head (left side of photos below) that concern me. The plug on that side was gray, the other black. The amount of carbon buildup is about what I was expecting. Next I'll put the bore gauge to the cylinders and see what I've got.

717817



717816
 

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Discussion Starter #26
Are the tops of the pistons marked? Std? +20 etc? The one on the drive side (no 2 AIUI) looks a bit oily?
I'm surpassing my knowledge here, so I haven't looked for those markings yet. Will do next time I'm there. I'm doing this work in the motorcycle lab at the school. That isn't oil, it's water from washing the outside of the motor off before disassembling, and that side's valve was open.
 

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No problem - we all learn most days. The pistons will (should) have a number stamped in the top - if you clean off the top of the piston there should be an oversize marked. Standard (as it left the factory) should be marked STD. If it's been rebored, then the marking should be +20, +40 or maybe +60, as in the number of thousandths of an inch that the barrels have already been bored out to to eliminate wear. Not sure what the maximum oversize is for a T100R but, say, if it's 60 thou and the pistons are already at that size, and bores are badly worn then they cannot be bored out again. Usually it's new barrels time - that's why this is a critical piece of information. If they are STD or marked say +20 and the bores are worn, then it's a simple matter of a rebore and new pistons and rings. The number on the top of the piston tells you the size of the bill! You are now at a fairly big moment in a rebuild!

I don't bother checking the physical bore size, I just take them along to a machine shop I trust and who know motorcycle engines, with the pistons, and get them to tell me what needs to be done. If you are lucky, all they will need is a hone to get rid of the glaze (shine) on the bore, and a set of new rings. The hone restores a slightly rough surface on the bore to help the new rings bed in quickly, so that you get good compression and minimal oil passing the rings. If the bores are too worn, then it's rebore time. Unless you are already at the maximum oversize of course.

The same applies to the big end bearings when you get to that point. If the engine has previously been overhauled, the big end journals may have been reground to eliminate wear and scoring through muck in the oil. When you take the big end shell bearings out they will be marked on the back, say STD, or -10 or -20. Since the crank journals have been ground they are now undersize (by say 10 or 20 thou), compared to how they left the factory, which is why it's a negative number. Again, there's a minimum undesize they can go to. Fingers crossed!
 

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Discussion Starter #28
Andy, I've been taking motorcycle tech classes and we learned how to measure cylinders, so I'm going to do that myself, with my instructor double-checking. He was a pro tech for a couple of decades before he started teaching. I had forgotten about the numbers on the crowns. The manual says suitable rebore sizes are +.010, .020. and .040. I look forward to seeing what I have, and how bad the cylinders are worn. I suspect a rebore is necessary and hope I have enough metal left.

I have been debating about rebuilding the bottom end or just the top, just because I haven't done it before and don't know how necessary it is. Probably can't tell without disassembly and measurement, eh?

Fun and scary!
 

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If it's a bike you don't know, now you've got it mostly in bits, I think it's worth going the extra mile and having a look at the bottom end. At least you then know what condition its in. If you rebuild the top end and then find that the bottom is suspect, you'll have to re-do a lot of what you did. IMHO, it's worth going that extra mile when you don't know the bike.
 

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You NEED to go into the crankshaft and clean out the sludge trap, especially considering the appearance of the top end. That'll give you a chance to check the crank journals, and all will be well.

UNLESS the cams have excessive play in their bushings, and/or worn/scarred lobes, LEAVE THEM IN PLACE and leave the cam pinions on.
 

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Discussion Starter #31
You NEED to go into the crankshaft and clean out the sludge trap, especially considering the appearance of the top end. That'll give you a chance to check the crank journals, and all will be well.

UNLESS the cams have excessive play in their bushings, and/or worn/scarred lobes, LEAVE THEM IN PLACE and leave the cam pinions on.
Seems like sound advice. Plus I think you know better than me. Thanks.
 

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Discussion Starter #32
Heavy scoring on the drive side. Time to measure bores and see what I need to do next – hone vs. rebore. Any recommendations on new pistons?

718466


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The DS piston marking suggests muck in the oil, and yet the TS piston doesn't. But the barrel marks that we can see look like marking around the wrist pin. Look to me like pistons/rings as a minimum, and the micrometer will decide about a rebore - but it looks likely to me. Have you found the piston oversize yet? That's a very clean looking barrel too - unless you've had it in the parts washer that is!
 

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Discussion Starter #35
I will be putting a bore gauge to it soon. Andy, I was able to see markings on one piston but couldn't read them. The other is so crusted with carbon I haven't tried getting down to the metal. And those cylinders have been wiped down. :)
 

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One cylinder looking worse than another can be signs of:

One cylinder mixture leaner
One cylinder's valve(s) left open while bike was stored for a long time, then run without cleanup
Primary side rod starves before timing side rod (typically) when oil flow stops
I'm sure there are other reasons...
 

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Discussion Starter #37
One cylinder looking worse than another can be signs of:

One cylinder mixture leaner
One cylinder's valve(s) left open while bike was stored for a long time, then run without cleanup
Primary side rod starves before timing side rod (typically) when oil flow stops
I'm sure there are other reasons...
Thanks! It sat for around 5 years before my dad gave it to me, so that's a possibility. But he said it burned oil on that side before it sat. He thought that might be because it leaned on the side stand for periods of time and oil drained into that side. It wasn't run that much in the years he had it. I put more miles on it this last season than he did in 15 years or so. I didn't know about cleanup, but I suspect because of the oil burn on that side the damage had already begun. I'll be checking out the pump soon. And I'll be checking the mixture when I get it running again. Much to learn!
 
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