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This thread is privately moderated by Geoff Potter, who may elect to delete unwanted replies.
Jun 20, 2018, 10:54 PM
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O&R 60 Sideport Crankshafts


My friend Browny , had a bad day at our SAM Champs in Texaco this year , then at our Nats two weeks later due to wind when not needed . He crashed his Flamingo just after takeoff both times in the fly off of both events and bent the crankshaft in the original and then the replacement one that he had in a brand new engine which he fitted to the original engine .
He asked me if I could straighten them but after a couple of attempts it was a waste of time so I decided to make three new ones .
Was a bit difficult getting them out of the bronze bushed front housing and lost one bush because it was so badly bent but saved the housings and the new front end bush .
I decided to make them out of EN36A as it is reasonably tough in its normal state and turns well and wouldn't need hardening , so cut three pieces out of 11/4" bar . Faced and centred it and turned the thread/ prop area as it's hard to work up against the centre in the tail stock . Extended it out of the chuck and turned the rest of the straight shaft to 15 thou oversize , and did the grooves for the timer advance lock and the prop driver splines , also cut the prop nut thread as well and finished the prop area to size with a long tool but only needed a small clean up . Turned the outer diameter of the of the back end and then parted it off to suit the length of the crank pin . Then did the other two the same .
Transferred over to my smaller lathe as it has a collet head and I faced the back face and centre drilled it to put between dead centres in my cylindrical grinder to grind the shaft to size . Set up in the grinder with a drive dog on the back end and they came out right on size .
I then had to make a holder to hold the shaft so I could turn the pin to size and get the right throw for it as well . I made this out of a piece of 1045 steel with the hole drilled and reamed to the right size to suit the shaft diameter and offset the correct amount , then split it and drilled and tapped the lock screw holes so the shaft wouldn't slip in the jig . It did the three of them easily . I set it up in the three jaw chuck in the big lathe and turned the pin and the bob weight in the one setting and polished the pin rather than ground it as it's a pain to grind when the bob weight is in the way .
Had to then put the spline on the shaft for the prop driver ,which I thought would be a pain but with my small index head and a jig to locate the pin and centre , on the mill it worked out quite well .
We ran it last weekend and Browny was very happy but we haven't flown it yet so will hope he still gets his excellent engine run on petrol or maybe a bit better .
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