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Hello,
I am considering doing the T140ES mod to my D. Can anyone show details of the idler bush mod to accommodate this change?

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No details needed. Simply bore out the hole and crimp in a suitable bushing. You'll need the intermediate wheel/sprag to broach it to the correct size, that's all. Warning: do NOT use the timing case face as a datum for machining, on mine it wasn't parallel to the centerline.
Btw I never finished the project, so that's as far as I got.

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Originally Posted by Stein Roger
No details needed. Simply bore out the hole and crimp in a suitable bushing. You'll need the intermediate wheel/sprag to broach it to the correct size, that's all. Warning: do NOT use the timing case face as a datum for machining, on mine it wasn't parallel to the centerline.
Btw I never finished the project, so that's as far as I got.

SR
Bore out which hole? I am not familiar with this modification.

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Steven, it would appear that you aren't too familiar with the layout of the Triumph twin engine, or the lingo used to describe it? If so I would suggest you read the workshop manuals, which you can find here: www.classicbike.biz
Anyway, I have attached a drawing which shows the timing case. The two cam wheels and the intermediate, or "idler" wheel is shown, plus the crankshaft pinion. The intermediate or idler has a pin or shaft on which it spins. It's the "hole" for that shaft I'm talking about. With the electric foot set-up it's the shaft that spins, which is why the factory installed a bronze bearing in the exact same location as the shaft.
Hope this helps.

SR

twin timing case.jpeg
Last edited by Stein Roger; 09/01/21 5:14 pm.
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Roger, I have rebuilt two of these engines.

Is this what you are stating? 70-0375 locates in the right hand crankcase half. The fit of 70-0375 in the crankcase and the clearance to 70-6159 ensure that 70-6159 spins on the stationary 70-0375.

In the case of the electric start bikes the 70-0375 and 70-5159 are combined in to one part that spins in the right hand crankcase. Hence the hole in the right hand crankcase is bored out to accept a bronze bush.

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Sorry I didn't mean to doubt your abilities. I don't really have a head for part numbers myself, but the wheel is bushed and spins on the spindle, while the wheel with the sprag unit spins on bronze bearings, one in the timing case, the other in the Electric Start timing cover.
I'm told the set-up can be quite reliable if the engine is kept in tune and the battery is good, but to be honest I believe it's terrible solution.

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Is this starter a bit of a lash-up. It always struck me as a terrible idea to have an engine turned over via its timing gears. Steve Mcfarlanes electric start kit for pre unit BSA's looks a better solution, driving through the drive side of the crankshaft.

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Its problem is there is little protection against ignition backfires, it was updated several times, each update upgrading the part that failed until it was the crankcase that cracked. If you can guarantee no back firing then the issues go away.

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Simplest way to ensure no backfires is to use an ignition that limits the starting advance to TDC.

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Originally Posted by DMadigan
Simplest way to ensure no backfires is to use an ignition that limits the starting advance to TDC.
Good idea. Which ones are those?

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Why are you attempting to "re-invent the wheel?"
Just sell the bike, then find and buy one that already has what you want.

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Originally Posted by Irish Swede
Why are you attempting to "re-invent the wheel?"
Just sell the bike, then find and buy one that already has what you want.

maybe the shipping to OZ ?


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I’ll sell ya mine!!

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What do you need for it, DPO?
If you are serious, lets take this to PM

Last edited by Mike Baker; 09/12/21 12:12 pm.

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