The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: scotty on 31.08. 2009 04:20
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Can anyone tell me the die size that I would require to clean up the threads on the timing side of a small journal crank ?
Can't seem to get the worm gear started and the first few threads look dodgy.
I've ordered a recon pump c/w new worm gear
Bottom end is now re built with new ts bush, end play set and recon cam & followers , re bored barrels and +40 piston and rings installed, re con head with new valves and guides installed
The old relic just may run again
cheers
scotty
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Hi Scotty,
I seem to recall that it is a LH thread!
I had to buy a LH tap to suit; think it was 9/16" either 20 or 26 tpi; will be able to confirm later.
If you need a tap, Tracy Tools have them. However, make sure you are turning the drive gear counterclockwise in order to have it go on.
Richard
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Spot on, it is a L/H thread and its 9/16" at 20tpi. Before you start doing too much to the crank check that the problem is not the gear. I bought a new drive gear a couple of years ago and it was too tight a fit on the thread to use. Try your old gear first and if it goes on ok then a tap as Richard suggests and run that through the new gear.
If the problem is definitely the crank then maybe you could clean it up with a thread file or else put it in a lathe and re screw cut the thread. A die would be difficult to use because of the groove in the thread.
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Brian,
I have had the same problem with a couple of oil drive pinions, and had to purchase a tap and pass it through them.
I also got a button die off them, which I always use on the crankshaft thread.
Richard
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Richard, Brian
Thanks for the wisdom from down under.
I tried to fit the old pinion to the crank to see if it would turn out the obvious damaged threads on the end of the crank.
The female thread on the old pinion appears to be in good shape and yes it is lh thread.
The new oil pump & drive pinion should be winging thier way here any day now so I'll give them a go round then.
In the mean time I'll try a thread file and maybe source a tap and die
Cheers
scotty
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HI all - sorry off at a tangent here
Scotty I notice a SRM cushdrive nut on the end of your crank, I'm about to fit one of these and wonder how it is locked on, is it just torqued up and thats it or is there a lock washer ( if so I don't think I have one ), what are the two holes on the flange for ( wire ? ), or do some of you use a bit of locktie on it.
All the best - Bill
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Buy a new nut.
Cut it in 1/2 lengthways.
Pop each side on an oil stone and make the cut faces nice and flat.
Put the 2 1/2 nuts on the shaft, wrap a bit of tape around them to keep them together then slip a socket ove them and run it up and down the threads a few times, works to clean up a bad thread in no time flat.
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Trevor
I like your thinking and I'm going to give it a try it as I do have a spare nut
Bill, re: cush drive nut
I spoke with Gary at SRM when I purchased the cush drive nut and he informed me that you do not use the split pin on the cush drive nut, the torque of 65ft lbs will hold the nut,also use loctite thread lock.
cheers
scotty
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Thanksfor that Scotty
I bought a die for the other side of my crank (RH thread though) and run it on without putting it in a holder then clamped it with mole rips and screwed it off, did this a few times clamping it a bit tighter each time until it screwed on by hand (just leaving it a bit tight)
All the best - Bill
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A 1.25 mm thread file will work a treat to clean the threads up and be a whole lot cheaper than a weird-o LH BS die that nobody stocks.
Cheers.
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Hi All,
Any good cycle shop will have these taps and dies for restoring cycle pedal cranks
perhaps they will loan one to you or bring the engine with you *idea*
HTH
John O R
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John OR
your tip re: using a bicycle shop as a resource was a gem !
In exchange for a case of beer a thread file and a tap were loaned to me.
Threads on the crank cleaned up a treat !
Thanks for the tip
Cheers
Scotty
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Hi Scotty,
Thanks for the kind words, I have a friend with a cycle shop, and thats where I got the tap for mine.
Cycle shops are also a good source of inner and outer cable for throttle,AR, choke (making your own)
Cheers
John
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Re thread files, Sykes make one with 26 T.P.I. It also has 20 T.P.I. which makes it very handy for our Pommy bikes.
Trev.