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Another die cast SureStar drawback?

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Another die cast SureStar drawback?

Old 02-07-2008, 11:32 PM
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lildiesel
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Default Another die cast SureStar drawback?

This evening I finally opened up the die cast zinc alloy crankcase Sure Start I intend to be the beater on which my son learns to start a Cox reedie and can fly into the ground repeatedly without me rolling my eyes. The engine was nice an clean inside, but the first thing I really noticed is that the ID of the crankcase is 5/8th of an inch. Since the OD of the reed valve holder is 1/2 inch there is a lot of extra volume in the crankcase compared to the machined aluminum crank cases, which have a 1/2 inch ID to fit the reed holder properly and the extra diameter for the lower end of the connecting rod only machined in at the bearing face for the crank. I wonder how much effect this added volume actually has on the compression of the fuel/air mix in the crankcase and the pumping of it up into the combustion chamber?

Anyway, something for the engine gurus to chew on. I can envision a way to stuff that extra volume with a piece of tubing, but that's probably too much work and bother for a beater that will go on a Brodak 1/2A trainer for only one summer's use.

addendum: does anyone out there have an RC Bee with the look-a-like die cast crankcase? It would interest me to know if they are the same as these Sure Starts or if Cox preserved the original crankcase volume and machined the extra 1/16th for the lower end into the zinc alloy casting.
Old 02-09-2008, 03:03 PM
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Default RE: Another die cast SureStar drawback?

I just disassembled a second Sure Start with a die cast crankcase. This one comes with an oversized red plastic reed valve retainer that effectively stuffs the 5/8th inch ID crankcase for about 300ΒΊ of its diameter and restores the crankcase to something near the volume of a machined aluminum. The retaining ring extends 4/16th into the crankcase almost butts up to the crank pin. Somebody at Cox must have seen the need to fill the extra volume on these engines.


Clearly this is some sort of parts mistake during assembly and I got shipped a real dud the first time I acquired one of these Sure Starts. I wonder how many other people got a Sure Start assembled the way my first one arrived?
Old 02-09-2008, 03:12 PM
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misfitsailor
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Default RE: Another die cast SureStar drawback?

Keep me in mind for any surplus cast crankcases! LOL
Old 02-09-2008, 03:23 PM
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Default RE: Another die cast SureStar drawback?

I thought the die cast ones were sold as not Sure it'll Starts.
Old 02-09-2008, 03:57 PM
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Default RE: Another die cast SureStar drawback?

Bah! Someday you will see pieces like these fetching enormous prices as Cox rarities at some fleabay auction site and rue the day you mocked my offer! Bah! A pox upon your Cox! Humbug!

ORIGINAL: misfitsailor
Keep me in mind for any surplus cast crankcases! LOL

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