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70 T120R flywheel confusion #331416
09/03/10 3:56 am
09/03/10 3:56 am
Joined: Sep 2010
Posts: 8
Columbus, OH. USA
shrugger Offline OP
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shrugger  Offline OP
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Joined: Sep 2010
Posts: 8
Columbus, OH. USA
To make a long story short. I'm pretty sure The machinist ruined
my crankshaft flywheel with a lot of large holes and a 50%
balance. mad

So I've been looking for another. The problem is the severely
confusing part numbers for them. My parts book has the early
numbers and it's E9687 However, the number stamped into it is 70-9745
Poor Trevor over at Britishonly has found several that look
identical. But every one of them has a different part number.
Hopefully, someone can help clarify this unruly number mess.
Thanks


"Thanks to denial, I'm immortal" -Phillip J. Fry
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Re: 70 T120R flywheel confusion [Re: shrugger] #331446
09/03/10 12:48 pm
09/03/10 12:48 pm
Joined: Nov 2005
Posts: 7,271
Back on the mainland!
JubeePrince Online content

Life member
JubeePrince  Online Content

Life member
Joined: Nov 2005
Posts: 7,271
Back on the mainland!
WTF!?

Hopefully you can get your "machinist" to pay for the new flywheel...

Part number should transpose to 70-9687. These flywheels were used late '69 - '70.

I know that there are lighter flywheels available out there.....your "machinist's" work not withstanding, perhaps you have the lighter version (70-9745).

AFAIK, the consensus seems to be the heavier the flywheel the better.

HTH,

Steve


'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
Re: 70 T120R flywheel confusion [Re: JubeePrince] #331453
09/03/10 1:58 pm
09/03/10 1:58 pm
Joined: Sep 2010
Posts: 8
Columbus, OH. USA
shrugger Offline OP
BritBike Forum member
shrugger  Offline OP
BritBike Forum member
Joined: Sep 2010
Posts: 8
Columbus, OH. USA
I kinda had a feeling the numbers might be different weight ranges.
So likely any number that falls between the parts book and my flywheel
will probly work fine.
Anyone got a 69 book to look up that part number?
I could have a leftover as the bike was built first production month. August 69

Last edited by shrugger; 09/03/10 2:02 pm.

"Thanks to denial, I'm immortal" -Phillip J. Fry
Re: 70 T120R flywheel confusion [Re: shrugger] #331458
09/03/10 2:17 pm
09/03/10 2:17 pm
Joined: Sep 2005
Posts: 5,963
NL
G
Ger B Offline
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Ger B  Offline
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G
Joined: Sep 2005
Posts: 5,963
NL
A fellow here in Holland posted pictures allmost similar to yours, Shrugger. The job was done in the UK and he was very content with the result.


Ger B

Re: 70 T120R flywheel confusion [Re: Ger B] #331461
09/03/10 2:32 pm
09/03/10 2:32 pm
Joined: Sep 2010
Posts: 8
Columbus, OH. USA
shrugger Offline OP
BritBike Forum member
shrugger  Offline OP
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Joined: Sep 2010
Posts: 8
Columbus, OH. USA
I'll never be comfortable riding the bike with this flywheel.
The thought of a hand grenade that could go off at any time
would always be on my mind. shocked


"Thanks to denial, I'm immortal" -Phillip J. Fry
Re: 70 T120R flywheel confusion [Re: shrugger] #331462
09/03/10 2:32 pm
09/03/10 2:32 pm
Joined: Jul 2009
Posts: 3,549
Vic. Australia
P
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
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Joined: Jul 2009
Posts: 3,549
Vic. Australia
'66-'68 had light flywheels ,they'll shake you teeth out at high speed.The flywheel is visibly different,about 2-1/2 lbs lighter.
'69-'70 was more comfortable with a heavier flywheel.

I've got a feeling they got heavier after that,but at some time the inner diameter changed and got bigger.'71-'72 has a different part number and I'm not sure if that will fit,maybe too big.

Re: 70 T120R flywheel confusion [Re: shrugger] #331465
09/03/10 2:44 pm
09/03/10 2:44 pm
Joined: Jan 2006
Posts: 6,810
Laredo (South) Texas, USA
GrandPaul Online content
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GrandPaul  Online Content
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Joined: Jan 2006
Posts: 6,810
Laredo (South) Texas, USA
Shrugger-

I don't believe the casting numbers have anything to do with the actual Triumph part numbers. At least, that's typically the case with almost any other part on the bike. Why? Heck if I know; "because THAT'S why"!

I've seen cranks drilled a lot worse than that, and made negative comments along the lines of your post, then got excoriated for being such a numbskull and not knowing what I was talking about (okay, sure).

Heavy -vs- light flywheels both have thier plusses and minuses. A heavy flywheel makes for a more stable idle and smoother torque delivery (an object in motion tends to stay in motion, and all that). A light flywheel builds revs quicker (some racing disciplines want that).

OEM flywheels are easy to differentiate:

Heavy - same width all the way around the edges

Light - wide at the "bottom", narrower at the "top".

Last edited by GrandPaul; 09/03/10 2:45 pm.

GrandPaul (does not use emoticons)
Author of the book "Old Bikes"
Too many bikes to list, mostly Triumph & Norton, some BSA & European
"The Iron in your blood should be Vintage"
Re: 70 T120R flywheel confusion [Re: GrandPaul] #331469
09/03/10 2:53 pm
09/03/10 2:53 pm
Joined: Sep 2010
Posts: 8
Columbus, OH. USA
shrugger Offline OP
BritBike Forum member
shrugger  Offline OP
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Joined: Sep 2010
Posts: 8
Columbus, OH. USA
LOL.
Guess I'll have Trevor pick one at random. Then I'll send it to
you so your guy can go over it properly.


"Thanks to denial, I'm immortal" -Phillip J. Fry
Re: 70 T120R flywheel confusion [Re: shrugger] #354717
01/25/11 3:39 am
01/25/11 3:39 am
Joined: Dec 2007
Posts: 81
florida
big head Offline
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big head  Offline
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Joined: Dec 2007
Posts: 81
florida
Gents,

Resurrecting this old post: while at the machinist its determined my crank ('66 t120) is no longer good. So they go and replace it with the later (heavier) '69 crank.

Questions:

- should i be concerned or will this crank run fine in my '66?
- am i going to have any power loss? I did have the head completely redone, .40 jugs, new pistons, etc.
- It seems I will benefit from less vibrations?

Thanks for any info.


1968 T-120 (In progress)
Re: 70 T120R flywheel confusion [Re: big head] #354733
01/25/11 5:19 am
01/25/11 5:19 am
Joined: Jul 2009
Posts: 3,549
Vic. Australia
P
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
In Remembrance
P
Joined: Jul 2009
Posts: 3,549
Vic. Australia
Don't be concerned;be thankful! You'll still make the same power at the crankshaft.
In the low gears you'll notice a little less acelleration and engine braking,like as if you added 30 lbs weight to the bike.In top gear,I doubt that you'd notice it (like about 1 % difference).
The cush-drive,clutch,and other transmission parts will have an easier life;not much,but a little.
The engine will idle smoother.
You will notice less vibration.Your crankshaft will be happy.

If you're still using '66 rods ('69 rods are better and heavier),check the balance factor.If its not more than 85%,don't change it.

Last edited by Pete R; 01/25/11 5:39 am. Reason: "If you're - - - don't change it."
Re: 70 T120R flywheel confusion [Re: shrugger] #354758
01/25/11 12:18 pm
01/25/11 12:18 pm
Joined: Dec 2007
Posts: 81
florida
big head Offline
BritBike Forum member
big head  Offline
BritBike Forum member
Joined: Dec 2007
Posts: 81
florida


Yes, forgot to add, new Rods as well and the Crank was Balanced to specs. Considering I'm doing a complete rebuild, the vast difference in performance will be very noticeable regardless. (i hope).

Thanks for the info...


1968 T-120 (In progress)
Re: 70 T120R flywheel confusion [Re: shrugger] #354760
01/25/11 12:32 pm
01/25/11 12:32 pm
Joined: Jan 2005
Posts: 1,658
East Bethany New York
Dick Harris Online content
BritBike Forum member
Dick Harris  Online Content
BritBike Forum member
Joined: Jan 2005
Posts: 1,658
East Bethany New York
I'm with Pete,I wouldn't worry a bit about the flywneel exploding.I also have seen worse. The only thing I would be a BIT concerned with, is the 50% balance factor,however,if the crank was dynamically balanced,which I doubt,because it appears the neither web has any sign of balance work,I doubt that you could notice a problem. Dick

Re: 70 T120R flywheel confusion [Re: shrugger] #354768
01/25/11 1:25 pm
01/25/11 1:25 pm
Joined: Dec 2007
Posts: 81
florida
big head Offline
BritBike Forum member
big head  Offline
BritBike Forum member
Joined: Dec 2007
Posts: 81
florida
by the way that crank pictured is not mine...I just brought up the question of the different cranks from '66 to '69. My '66 crank was no good and was replaced with the heavier '69.

thanks


1968 T-120 (In progress)
Re: 70 T120R flywheel confusion [Re: shrugger] #354782
01/25/11 2:49 pm
01/25/11 2:49 pm
Joined: Dec 2004
Posts: 9,129
Scotland
kommando Online content
BritBike Forum member
kommando  Online Content
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Joined: Dec 2004
Posts: 9,129
Scotland
I have just done same as an upgrade (well its a 65 so I just put it back to being heavy), next task is to get it static and then dynamically balanced.

Re: 70 T120R flywheel confusion [Re: shrugger] #354809
01/25/11 5:33 pm
01/25/11 5:33 pm
Joined: Oct 2006
Posts: 165
albion New York
C
charlie akey Offline
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charlie akey  Offline
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C
Joined: Oct 2006
Posts: 165
albion New York
Parts book 1969 e9686 (70-9686) crankshaft assembly .British cycle ref . you to 71-2600 crankshaft assembly . Charlie


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