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Engine basics => Engine set up tips => Topic started by: frank mccune on May 27, 2015, 05:32:05 AM

Title: What is the thread size for O.S.engines?
Post by: frank mccune on May 27, 2015, 05:32:05 AM

     Hello:

     I would like to replace the head screws in my older O,S. 35S and .40S engines with SHCS.  Does anybody know the tread sizes and lengths of these screws?

                                                                                                                                               Tia,

                                                                                                                                                Frank

Title: Re: What is the thread size for O.S.engines?
Post by: Steve Helmick on May 27, 2015, 08:38:03 PM

Well...the closest size that you can buy or order is 5-40 thread. No idea about the lengths. Most or all of the engine tuners put 5-40s in the OS .35S, as well as ST G.21 .46's and .60bb's. The OEM thread was 3m x .6 pitch, which seems to have been changed to .5 pitch. This subject is occasionally brought up, and a search should turn it up.   D>K  Steve

Title: Re: What is the thread size for O.S.engines?
Post by: RandySmith on May 27, 2015, 09:11:24 PM

The only place I know you can get bolt assortment for the OS 30 - 35 S   is Micro Fastners , the have the  6 pitch  3mm  screws  that OS used

Randy

Title: Re: What is the thread size for O.S.engines?
Post by: frank mccune on May 28, 2015, 05:01:28 AM

   Hi:

    A big thanks to all of you who replied!
                                                                                                           Stay well my friends,

                                                                                                           Frank

Title: Re: What is the thread size for O.S.engines?
Post by: Andrew Hathaway on May 28, 2015, 07:55:17 AM

The 5-40s will generally thread right into the older SuperTigres, but the Max-S thread seems finer to me.  I didn't push it, but the 5-40s wouldn't thread in any of my OS engines.

Title: Re: What is the thread size for O.S.engines?
Post by: RandySmith on May 29, 2015, 06:59:00 AM

Quote from: Andrew Hathaway on May 28, 2015, 07:55:17 AM

The 5-40s will generally thread right into the older SuperTigres, but the Max-S thread seems finer to me.  I didn't push it, but the 5-40s wouldn't thread in any of my OS engines.

The 4-40 will  fit the 35S  fairly well, the 5-40 is too large, many people just use the 4-40 bolts

Randy

Title: Re: What is the thread size for O.S.engines?
Post by: RknRusty on June 10, 2015, 09:31:19 PM

You can screw 4-40 screws into m3x6 holes?
I guess you wouldn't want to unscrew and rescrew it if you didn't have to.