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Author Topic: OS Max III Head Bolts?  (Read 794 times)

Online Skip Chernoff

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OS Max III Head Bolts?
« on: April 10, 2018, 07:25:14 PM »
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.


Offline john e. holliday

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Re: OS Max III Head Bolts?
« Reply #1 on: April 11, 2018, 03:10:05 PM »
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
John E. "DOC" Holliday
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Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #2 on: April 12, 2018, 08:25:59 AM »
Good idea, I'll try my local Ace hardware.

Offline Paul Smith

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Re: OS Max III Head Bolts?
« Reply #3 on: April 12, 2018, 09:57:29 AM »
We used to use 5-40 (.1015" dia) as OS Max III bolts. 
The metric size is M3 x 0.35 (.1024" dia).

Paul Smith

Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #4 on: April 12, 2018, 04:21:50 PM »
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

Offline Dennis Adamisin

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Re: OS Max III Head Bolts?
« Reply #5 on: April 14, 2018, 08:28:00 PM »
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!

Denny Adamisin
Fort Wayne, IN

"The good old days weren't always so good, tomorrow ain't as bad as it seems..."
- Billy Joel

Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #6 on: April 15, 2018, 02:14:09 PM »
How do you suggest straightening it? I'll share your info with my machinist pal.Thanks,Skip

Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #7 on: April 15, 2018, 02:16:34 PM »
Paul,McMaster didn't have the fasteners I needed so we're going with the 5/40 you mentioned. Thanks.Skip

Offline Motorman

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Re: OS Max III Head Bolts?
« Reply #8 on: April 15, 2018, 08:37:02 PM »
Skip, I have straightened many crankshafts for other people. 
There will be a sunny day and we will fly our airplanes.

Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #9 on: April 16, 2018, 06:18:46 AM »
Thanks MM ,what is your procedure?

Offline Motorman

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Re: OS Max III Head Bolts?
« Reply #10 on: April 16, 2018, 08:46:46 AM »
 I could have it done before I could tell you how.
There will be a sunny day and we will fly our airplanes.

Offline john e. holliday

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Re: OS Max III Head Bolts?
« Reply #11 on: April 16, 2018, 11:11:47 AM »
Skip, I take it you don't have a local ACE Hardware Store or local supplier of metric stuff? D>K
John E. "DOC" Holliday
10421 West 56th Terrace
Shawnee, KANSAS  66203
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Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #12 on: April 16, 2018, 12:45:07 PM »
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.

Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #13 on: April 16, 2018, 12:52:13 PM »
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?

Offline Motorman

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Re: OS Max III Head Bolts?
« Reply #14 on: April 16, 2018, 09:27:09 PM »
That could make it bent in two places.
There will be a sunny day and we will fly our airplanes.

Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #15 on: April 17, 2018, 09:59:58 AM »
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

Offline Motorman

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Re: OS Max III Head Bolts?
« Reply #16 on: April 18, 2018, 03:26:32 PM »
First you need a surface plate a V block and a last word indicator with a stand. Then you can turn the shaft to see where it's bent. Next you take two V blocks and clamp the shaft in a vise. Then you make the bender from a piece of 1/2" cold rolled steel and drill a 1/4" hole in the end. Slide this over the shaft to where it's bent and use it as a pry bar to bend the shaft straight. re-check on the surface plate until less than .0005" run out.

That works if the shaft is bent close to where it meets the main barrel. If it's bent where the threads end then you have to devise a way to hold the unthreaded prop shaft then double nut the threaded portion and use vise grips to bend it.
There will be a sunny day and we will fly our airplanes.

Online Skip Chernoff

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Re: OS Max III Head Bolts?
« Reply #17 on: April 19, 2018, 06:06:47 AM »
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


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