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Rear sprocket 50 or 53 tooth
#814053 06/26/20 10:54 am
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BigBars Offline OP
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Hi Folks,

My rear sprocket seems original and it's 50 tooth type. manual says 53 /alternative 50. What are the pros and cons of the 50 versus the more standard 53? Better highway cruising? Vibration? Slightly lazier acceleration?

Thanks

BMF


3D TV: A format that lost a format war without even having an opponent.
Bikes: '69 T120 on average (1967 rolling frame and 1971 Bonnie engine) + '56 1/2 T110 on average (58 rolling frame - with 55 iron head engine) + 74 T150 Home model.
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Re: Rear sprocket 50 or 53 tooth
BigBars #814067 06/26/20 1:04 pm
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It depends on your gearbox sprocket, isn't it?
Triumph used different rear ratio for Europe then States / Canada, our typical is 18 to 53 t, GB and the rest of Europe started on 19 to 50 t.
Early triples with HDA cylinder head, original funky exhaust and 19 / 50 t ratio had all these "press speed records" ( 125 - 130 mph ), less vibes and slow acceleration below 3500 rpm. Later triples ( 73 on ) with choked AM head, choked exhaust and 18 / 53 ratio had decent acceleration from the start ( with a help of 5 speed gearbox ) but max speed around 100 mph and lots of vibes above 3500 rpm.
So speed and acceleration depends on what bike do you have.

Re: Rear sprocket 50 or 53 tooth
BigBars #814080 06/26/20 4:23 pm
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Hi thanks for that. I'm fairly sure mines original but can't really count the gearbox sprocket (is there an easy way to do it?).

It's a 74 european model.


3D TV: A format that lost a format war without even having an opponent.
Bikes: '69 T120 on average (1967 rolling frame and 1971 Bonnie engine) + '56 1/2 T110 on average (58 rolling frame - with 55 iron head engine) + 74 T150 Home model.
Re: Rear sprocket 50 or 53 tooth
BigBars #814116 06/26/20 7:40 pm
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So if everything is original you have AM head, those long and fat mufflers and 19 t sprocket, however I don't recall any method to make sure it's really 19 t. ( other than taking primary apart which sound little excessive ). What kind of gas tank do you have?

Re: Rear sprocket 50 or 53 tooth
BigBars #814119 06/26/20 8:35 pm
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Originally Posted by Adam M.
So if everything is original you have AM head,

Not necessarily as HDA heads continued to be fitted.

For instance, my T160 has an HDA head.

Re: Rear sprocket 50 or 53 tooth
BigBars #814141 06/26/20 11:19 pm
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Perhaps they came back to HDA for T160 model, after getting some complaints about AM heads?
I have some Triumph bulletin to dealers about machining those heads necessary to open up exhaust ports. Which I did with my head.

Last edited by Adam M.; 06/26/20 11:19 pm.
Re: Rear sprocket 50 or 53 tooth
BigBars #814147 06/27/20 1:38 am
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Not sure about the T160 but certainly for earlier triples there were two approved sources for cylinder heads—- AM and HDA.
The purchasing guys would then place orders from which of the two gave them the best price/delivery at the time.
BTW AM stands for Aeroplsne and Motor Aluminium Castings of Smethwick,north of Birmingham and HDA was High Duty Alloys some miles south west of Birmingham.
At the time AM was part of the AssociatedEngineering Group ( Hepolite, Glacier, Wellworthy etc) and HDA was part of the Hawker Siddeley Group.
HTH

Re: Rear sprocket 50 or 53 tooth
BigBars #814171 06/27/20 6:02 am
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Yes, the US models came with lower gearing via the sprockets. We Americans have this odd passion for getting to the next red light as quickly as possible.
My '74 came with 18/53 sprockets. I changed to 19t and got 65mph @ 4000rpm.
When I bought my '72 I changed to the 50t rear sprocket, mostly so I could use a 106 link chain without the half link. Unfortunately the only front sprocket available for the early 5-speed is 18t, and that is difficult to find. If my speedometer is accurate I get about the same MPH to RPM as my '74.
I'll be interested to see what difference the new 100/90 Road Rider makes replacing a 110/90 fake K81.


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72 T150V "Wotan"
Re: Rear sprocket 50 or 53 tooth
Adam M. #814173 06/27/20 7:58 am
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Originally Posted by Adam M.
Perhaps they came back to HDA for T160 model, after getting some complaints about AM heads?
I have some Triumph bulletin to dealers about machining those heads necessary to open up exhaust ports. Which I did with my head.


The copy of Norton Triumph Service Release I have (NTE 12/T3/4, November 1974) states...

"Lack of top-end performance on a small proportion of Triumph T150 machines..."

"...The cylinder head casting of one supplier only is affected, which is identified by a casting mark (A&M)..."

...which seems to indicate there was more than one supplier at that time.

Re: Rear sprocket 50 or 53 tooth
BigBars #814268 06/28/20 10:45 am
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Gearing: with a standard secondary ratio of 18:53 my 72 turns at just about the same speed in top as my 95 Daytona. This is considered a very low gearing in our Brit Bike world, were we habitually compare with Norton Commandos, Bonnevilles and such like. In my view the Triple should be regarded as a very different design approach, much more modern if you will. The Triple enjoys being revved, and those who find that difficult to adjust to, should perhaps consider trading the bike for something else.

AM vs HDM heads: The HDM usually appears better cast. My Trident wears an AM head, and apart from some rough and porous spots in the casting, the chambers and ports are fine. The center exhaust port was a bit smaller than the outer two, so I enlarged it some, but keep in mind that the outer ports are overly large, so there's no reason to overdo it. A friend has a 74 with an AM head, on which the center port is even smaller than mine was, but his bike doesn't lack any performance at all, in fact it goes very well. In real life I don't think there's much in it, but since they saw fit to issue a service note on it, there must have been some heads worse than others I suppose.

A comment on exhaust ports: Old school ports were big, followed by a large diameter pipe, to aid rapid scavenging.
Modern thinking is a small diameter, short port, exposing far less surface area to absorb heat. The exhaust pipe is stuck as close to the valve as physically possible for the same reason. Our triples have large and long ports, further compromised by the screw in adaptors. Machining the exhaust ports to take push-in pipes ala BSA and the T140 would possibly help reduce cylinder head temperatures on our bikes. Better still if we could leave a gap between the casting and the pipe, as on many modern designs. I've been thinking along those lines for a while, and have a spare head to experiment with. Maybe one day...

SR


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