Author Topic: Cleaning up the crank threads on the A7  (Read 202 times)

Offline barry2

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Cleaning up the crank threads on the A7
« on: 25.02. 2021 05:58 »
I mates
I need to clean up the threads on a A7 Crank, 1950-on , Drive side 3/4" x 20 tpi  ? ,,,,also the timing side look's like  1/2" 26 tpi BSC ,  is it l/h ? --Thanks Barry
WA

Offline barry2

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Re: Cleaning up the crank threads on the A7
« Reply #1 on: 25.02. 2021 06:10 »
Hi Mates l
Drives side looks like it's 3/4" x 20 tpi  BSC? ... any L\H threads--Barry
WA

Offline barry2

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Re: Cleaning up the crank threads on the A7
« Reply #2 on: 25.02. 2021 06:21 »
Hi Mates --
just seen 3/4" x20 UNEF, would they do?--
Barry
WA

Online Rex

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Re: Cleaning up the crank threads on the A7
« Reply #3 on: 25.02. 2021 08:45 »
I couldn't find a suitable tap when I needed to clean up my '51 crank threads so reclaimed them with a thread chaser, then carefully lapped in two new plugs using fine grinding paste and and a lot of to-ing and fro-ing.
{And before anyone says it, yes of course it was all washed and cleaned out thoroughly before building the engine ;)}

Offline JulianS

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Re: Cleaning up the crank threads on the A7
« Reply #4 on: 25.02. 2021 09:47 »
Timing side is 9/16 x 20tpi left.

Online orabanda

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Re: Cleaning up the crank threads on the A7
« Reply #5 on: 25.02. 2021 10:18 »
The 9/16" LH die (and tap) available from Tracy Tools.
Drive side IS 3/4" x 20 TPI BSC. Also available from Tracy Tools.

Richard

Online Rex

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Re: Cleaning up the crank threads on the A7
« Reply #6 on: 25.02. 2021 13:14 »
On my '51 both plugs are the same thread and dimensions.

Offline Swarfcut

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Re: Cleaning up the crank threads on the A7
« Reply #7 on: 25.02. 2021 14:37 »
 Correct Rex. The threads for the sludge trap are identical both sides. Actual thread size depends on big or small journal crank type. Cush nut thread is normal righty tighty, the oilpump drive and lock nut are left hand thread, loose off clockwise. These threads are standard across all cranks.

 From experience, treat this left hand thread with great care, the crank here is relatively soft, big hammers and frustration are the sure fire way to an expensive disaster. With care the threads can usually be cleaned up piecemeal with a fine file and a good known nut. Pattern replacement nuts are of varying standards, tight impossible threads are well documented on the Forum by those caught out.

 Swarfy.