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.
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
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
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; 09/03/102:45 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"
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.
- 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?
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; 01/25/115:39 am. Reason: "If you're - - - don't change it."
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