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Speed,Combat,Scale,Racing => Speed Talk => Topic started by: Skip Chernoff on April 10, 2018, 07:25:14 PM
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As most of you know I'm dialing in my OSMaxIII for Brodaks this year. This engine has two long head bolts that fasten the head to the case and 4 smaller ones that hold the head to the jug. I'd like to change them out for cap type fasteners instead of the phillips type. Does anyone know what size metric fastener they are? They don't match up to anything I have in my fastener stash. Thanks,Skip
BTW I changed to a chicken hopper type tank and reduced the venturi size 15% , the plane is flying well now and the inverted speed is pretty close to upright speed. The engine didn't like the .308 original venturi.
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I take my engine and or muffler to my local ACE Hardware and start through the metric bolt section of allen head screws. They don't even ask if I need help anymore. The cashier just smiles at me when I walk in the door carrying my engine or muffler. I guess I should order in bulk from RTL Fasteners but I don't use that many metric bolts. D>K
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Good idea, I'll try my local Ace hardware.
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We used to use 5-40 (.1015" dia) as OS Max III bolts.
The metric size is M3 x 0.35 (.1024" dia).
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Paul thanks for jumping in. What I did was I went to my machinist buddy who orders stuff from Mc Master everyday. He measured my original fasteners and ordered me some new metric "cap screw head" type for my engine. I'll have them tomorrow afternoon. We indexed the crankshaft rotation on this engine and found out that it's .005 out of of not being perfectly true. The engine must have been crashed at one time. Should I find that even with new head bolts stuff keeps coming loose,I may have to look for a replacement crank for this engine......Skip
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We indexed the crankshaft rotation on this engine and found out that it's .005 out of of not being perfectly true. The engine must have been crashed at one time. Should I find that even with new head bolts stuff keeps coming loose,I may have to look for a replacement crank for this engine......Skip
Hi Skip
When dad started working on engines he discovered early on that virtually every engine had some run-out, straight cranks were extremely rare. Suspect it has something to do with rolling the threads into the crank. No matter how the run-out got there, straightening it out is a good idea for an engine meant to go fast!
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How do you suggest straightening it? I'll share your info with my machinist pal.Thanks,Skip
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Paul,McMaster didn't have the fasteners I needed so we're going with the 5/40 you mentioned. Thanks.Skip
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Thanks MM ,what is your procedure?
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Skip, I take it you don't have a local ACE Hardware Store or local supplier of metric stuff? D>K
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My local Ace Hardware didn't have it .It's some really weird in-between size. So we have decided to do what Paul suggested and make them 5-40. Thanks all for jumping in.
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I'm guessing that you place the crankshaft in a fixture to hold it and strike with some type of mallet in the direction you need to get the indicator back to zero. Am I wrong?
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MM ,is crankshaft straightening a "black art" that can't be discussed openly here ,or do I need to know the secret handshake and password? C'mon man, spill the beans.....Skip
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Thanks Much. Now armed with this info I'll share it with my pal (who has all of this equipment) and get the crank straightened.....Skip