Author Topic: 1911 pistons and conrods  (Read 2850 times)

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Offline magoo39

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1911 pistons and conrods
« on: 28 Oct 2009 at 07:35 »
Looking for info on what i can use as the pistons and conrods that i have are in poor condition

Offline Chris

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Re: 1911 pistons and conrods
« Reply #1 on: 28 Oct 2009 at 10:35 »
Hi Magoo39
     I am fairly certain that you should be able to use conrods from the later 2.3/4hp models. These have the same distance between centres of the big and little ends and both have 3/8" diameter little ends The later conrods have this diameter as a result of bushing whereas the 1911 rods have the gudgeon pins running steel in steel. The little end has a much greater offset on the later rods and some modification to its width will probably be needed to ensure that this will fit between the bosses of the piston while permitting the barrels to enter the crankcase when the piston is assembled on the rods. The later rods have a larger bigend diameter so would need thicker bronze bushes and the width of the bigend is also greater by about 60 thou. or so and thus would need about 30 thou. shaved off each side to enter the narrower bigend journals on the crankshaft.
     There would appear to be sufficient space in the crankcase for the larger rotating assembly but it may be necessary to provide a slight relief on the inside of the mouths where the ends of the bigend bolts might interfere. In fact on my 1911 conrods the bigend bolts are appreciably shorter and do not even have locknuts on.  The original bolts for these early engines had the square heads of the bolts drilled so that they could be wired to prevent undoing.
     I know that the barrels can be bored to take the alloy +20 thou. JP pistons available for the 2.3/4hp. as I have done this on one of my engines. The other has also been re-bored many years ago and has slightly modified +20 thou. alloy pistons from a 1930s 350cc Douglas. Good luck.   Chris.