Does any old timer know the size of the bolts in a OS Max 35 S ? Thank you NEAL;) 
OS MAx 35 S Head bolts?
Stuka Stunt Main Forum · 15 of 15 known posts recovered
Steve Helmick · Jul 13, 2004 08:02 PM
#1 sourceAlmost. They're a metric size (3m x .6, as I recall) that either was special to OS & ST, or is are no longer a standard size. A 5-40NC is just slightly bigger. Buy a good tap (machine shop supply, not hardware store) and change to socket head cap screws. It's the best solution, honest. Steve
Steve Or, skip the tap altogether. The 5-40s will fit even better.
Currell
>Or, skip the tap altogether. The 5-40s will fit even better.
>
>Currell
>
>Currell
Ron B.
F4Fguy
The 5-40s wont fit at all! they may hold things together for a while after they cut their own(crossed) threads,but don't count on it.I just pulled two of my Max 35s's and measured the screws.They are,strangely, #4-48s! Apparently someone at O.S. thought they were "Americanizing".The 35FPs have 3mm x .5 socket heads,which are readily available.
Ron B.
I switched to 5-40s on more than one OS 29 Twinstack, and they worked fine.
I calculate the threads per inch for the originals (.6 is mm) as 42.66. (25.4/.6)
All I can tell you is that the motors ran fine afterwards, and the bolts held. Currell
>I switched to 5-40s on more than one OS 29 Twinstack, and
>they worked fine.
>
>I calculate the threads per inch for the originals (.6 is
>mm) as 42.66. (25.4/.6)
>
>All I can tell you is that the motors ran fine afterwards,
>and the bolts held. Currell
>they worked fine.
>
>I calculate the threads per inch for the originals (.6 is
>mm) as 42.66. (25.4/.6)
>
>All I can tell you is that the motors ran fine afterwards,
>and the bolts held. Currell
Ron B.
F4Fguy
The 29 Twin Stack is metric.The 35 S's I just measured are (apparently) not.The bolts don't measure "approximately" #4-48,they are #4-48.
Incidentally, 2.667 threads/in. is a whopping lead change!
Ron B.
Hi Folks
Try Microfastners.com for all model size screws. They are a US company that has great service. An order to Australia takes about 7 days if the stuff is in stock.
Regards John Quigley
John Quigley
LAST EDITED ON Jul-17-04 AT 08:45 PM (CDT)
The head bolts in my OS Max-S .35 engine are definitely 3mm x .6mm METRIC bolts. These head bolts actually measures to .1175 inch diameter, which is too big to make even the maximum size of a #4 bolt hole which is only .112 inch according to my charts (a 4-40 bolt from my shop actually measures only .107 inch). A 5-40 bolt from one of my Cox engine's prop bolts measures out to an actual measurement of .1195 inch with the maximum chart size being .125 inch for a #5 bolt.
The head bolts in my OS Max-S .35 engine are definitely 3mm x .6mm METRIC bolts. These head bolts actually measures to .1175 inch diameter, which is too big to make even the maximum size of a #4 bolt hole which is only .112 inch according to my charts (a 4-40 bolt from my shop actually measures only .107 inch). A 5-40 bolt from one of my Cox engine's prop bolts measures out to an actual measurement of .1195 inch with the maximum chart size being .125 inch for a #5 bolt.
As for the pitch at exactly .6mm "thread to thread" this equates to exactly 42.33 threads per inch, just as described by Currell above. According to my measurments I have to agree with Currell on this matter ..... being only an actual .002 oversize in diameter and with only 2.33 (25.4/.6 = 42.33) less threads per inch a 5-40 bolt would screw into this c'case very snuggly, though not perfectly ..... but once screwed in I doubt it would ever work it's way back out! On the other hand, if you tried to use a #4-48 bolt with too small a diameter and much too fine a thread (by almost 6 threads per inch) it would probably strip out right away.
The 5-40s twist in and out fine.
Use a little oil. Cutting oil, maybe.
Currell
Steve Helmick · Jul 17, 2004 10:45 PM
#9 sourceLAST EDITED ON Jul-17-04 AT 10:48 PM (CDT)
A couple years ago, this same subject came up. Phil Granderson sent me one of his OS .35S engines or crankcases to investigate. I looked at screwing a 5-40 Roll Tap into that case, and it seemed quite tight, so I didn't push my luck. A Roll Tap forms the thread, it doesn't cut or remove any material, and is excellent on soft diecast aluminum. It still could be a good way to go, but I'd prefer to try it on a junk crankcase before risking a good case. I recall that some of the screws in Phil's engine were something other than correct, maybe 4-40 or 4-48. It was pretty obvious, the way they fit.
A couple years ago, this same subject came up. Phil Granderson sent me one of his OS .35S engines or crankcases to investigate. I looked at screwing a 5-40 Roll Tap into that case, and it seemed quite tight, so I didn't push my luck. A Roll Tap forms the thread, it doesn't cut or remove any material, and is excellent on soft diecast aluminum. It still could be a good way to go, but I'd prefer to try it on a junk crankcase before risking a good case. I recall that some of the screws in Phil's engine were something other than correct, maybe 4-40 or 4-48. It was pretty obvious, the way they fit.
Anyway, per my first post to this thread, the 5-40 is the best solution. If you can get them in without threading, they'll reform the thread just like a roll tap. Use some good oily stuff, like STP.
Nobody has ever found a source for 3m x .6 screws, other than OS/ST factory replacement packs. I'm somewhat curious to find out if the size was special, or if they were standard at one time. They certainly are NOT a standard size now. Steve
>A couple years ago, this same subject came up. Phil
>Granderson sent me one of his OS .35S engines or crankcases
>to investigate. I looked at screwing a 5-40 Roll Tap into
>that case, and it seemed quite tight, so I didn't push my
>luck. A Roll Tap forms the thread, it doesn't cut or remove
>any material, and is excellent on soft diecast aluminum. It
>still could be a good way to go, but I'd prefer to try it on
>a junk crankcase before risking a good case. I recall that
>some of the screws in Phil's engine were something other
>than correct, maybe 4-40 or 4-48. It was pretty obvious, the
>way they fit.
>
>Anyway, per my first post to this thread, the 5-40 is the
>best solution. If you can get them in without threading,
>they'll reform the thread just like a roll tap. Use some
>good oily stuff, like STP.
>
>Nobody has ever found a source for 3m x .6 screws, other
>than OS/ST factory replacement packs. I'm somewhat curious
>to find out if the size was special, or if they were
>standard at one time. They certainly are NOT a standard size
>now. Steve
>
>http://www.nwskyraiders.com/index.html
>Granderson sent me one of his OS .35S engines or crankcases
>to investigate. I looked at screwing a 5-40 Roll Tap into
>that case, and it seemed quite tight, so I didn't push my
>luck. A Roll Tap forms the thread, it doesn't cut or remove
>any material, and is excellent on soft diecast aluminum. It
>still could be a good way to go, but I'd prefer to try it on
>a junk crankcase before risking a good case. I recall that
>some of the screws in Phil's engine were something other
>than correct, maybe 4-40 or 4-48. It was pretty obvious, the
>way they fit.
>
>Anyway, per my first post to this thread, the 5-40 is the
>best solution. If you can get them in without threading,
>they'll reform the thread just like a roll tap. Use some
>good oily stuff, like STP.
>
>Nobody has ever found a source for 3m x .6 screws, other
>than OS/ST factory replacement packs. I'm somewhat curious
>to find out if the size was special, or if they were
>standard at one time. They certainly are NOT a standard size
>now. Steve
>
>http://www.nwskyraiders.com/index.html
Ron B.
F4Fguy
I stand corrected,I just went back and remeasuredmy O.S. 35S. The bolts are,indeed 3mm x .6p.I must ,still disagree though on the suitability of #5-40s as replacements.In American(Unified) thread systems, the closest (standard) pitch is 48TPI*, which has a lead difference of a little over -.002".The 40TPI thread has over +.004" per turn.
*Actually a 44TPI is almost exact,but try finding one of those!
The diameter of a #4 is .1120" ,3mm is .1180",a difference of .003" per side,well within the abilities of the thread to carry the shear load.Truth be told ,however,now that I know,the situation,I wouldn't use either of them.It's just too easy to Helicoil or Timesert to a standard size metric or Unified thread to even think about (insert Ethnic slur of your choice) engineering a perfectly good engine.
Ron B.
>35S. The bolts are,indeed 3mm x .6p.I must ,still disagree
>though on the suitability of #5-40s as replacements.
And, once again, for the reasons stated above, I think they are quite suitable.
Proof of the pudding is in the running. Have you tried it yet? I have.
Currell
I'm somewhat curious to find out if the size was special, or if they were standard at one time. They certainly are NOT a standard size now. Steve
_____________________________________________________________________
These odd size metric screws (3mm x.6mm) were also used on the early
Enya engines .... Enya later went to the more common 3.5mm x .6mm screws. The 5-40 screw is NO DOUBT the best and easiest replacement if you cannot find the proper 3mm x .6mm screws ..... any #4 screw would strip out too easily, the 5-40 will never strip out!
I've used 1/8 BSW (Whitworth) with success!
Tony