Author Topic: Dragonfly of despair, Camshaft trouble  (Read 221 times)

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Offline AndyMorgan

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Dragonfly of despair, Camshaft trouble
« on: 22 Jan 2019 at 13:04 »
In the pile of bits that I bought there were three of the Left side camshafts, all were in rough condition but I chose the best of these and had it reground. However, now that I come to re-assemble the engine the bolt (20653) is a tight fit I can get no more than 1/4" in and comes out with worn threads, the bolt seats well in all my other camshafts. I expect that when the shaft was reground the thread became damaged by the tail stock  I thought to drill out the first few turns of the thread but it must be hardened steel. I thought to run a tap down it but a) I can't decide what thread it is my closest gauge says 19tpi but it's not quite right and b) it's hardened steel. I am going to try grinding out the first few turns with a die grinder and see what happens.

Any helpful suggestions would be most welcome

Offline eddie

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Re: Dragonfly of despair, Camshaft trouble
« Reply #1 on: 22 Jan 2019 at 13:28 »
Andy,
         As you can screw the bolt in by 1/4", the thread damage is not on the end where the tailstock centre fitted. It is more likely that the original bolt was fitted dry and the thread picked up. Whilst the camshaft has been hardened, the hardening inside the threaded hole should be minimal - I would suggest that you get a new plug tap (or use a die grinder to put a keen edge on a used tap) and clean the thread out. The thread is 3/8"BSF (3/8" x 20tpi). I have suggested a plug tap as that will take a relatively heavy cut as it clears the damage - a taper tap will probably just rub and quickly loose it's edge.  Also, bear in mind that if the camshaft was re-hardened when it was reground, the heat treatment may have caused some distortion or shrinkage - thus requiring the threads to be cleaned up before fitting the bolt.

   Regards,
                 Eddie.

Offline AndyMorgan

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Re: Dragonfly of despair, Camshaft trouble
« Reply #2 on: 22 Jan 2019 at 15:38 »
Thanks Eddie, got it sorted. I cleaned off the first turn of the thread with the die grinder and a small tapered stone then cleaned up the threads and gently advanced the nut in with plenty of copper grease backing off after every 1/4-1/8 turn and removing the nut after every turn to clean off the thread, there was some very fine swarf, and running it into one of the other camshafts to make sure. After a while it got easier and could be tightened by hand.

Next problem seems to be the crankshaft pinion. Having recently moved house all my parts were squirrelled away I probably put it somewhere safe and now can't find it. Most of my stuff is in a derelict farm cottage, soon to be my new workshop but currently without heat or light. The two gears I have found are probably from a mark series and only fit onto the outer alternator section of the crank.
 

Offline eddie

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Re: Dragonfly of despair, Camshaft trouble
« Reply #3 on: 22 Jan 2019 at 16:10 »
Andy,
         Crankshaft gears for the earlier Mark series engines have teeth 3/8" wide and are plain gears. The Dragonfly crankshaft gear has teeth 1/2" wide plus a boss on either side.

  Regards,
                 Eddie.

Offline AndyMorgan

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Re: Dragonfly of despair, Camshaft trouble
« Reply #4 on: 25 Jan 2019 at 11:11 »
Found them!