stunthanger.com
Engine basics => Engine set up tips => Topic started by: Gary Dowler on September 30, 2018, 05:40:00 PM
-
Preping and old Ringmaster that I was given. Mounted a Fox 25 that I had, as my other OS 20FP is spoken for on my Flight Streak.
I have the muffler, a stock Fox muffler with mount homes both top/bottom and side/side. This needs the top/bottom holes. It's not for a 4-40 bolt, that seems certain. A 2-56 seems the right dia (a 5/64 drill bit shank (.077") will just slide into the hole) A 2-56 bolt is .085" dia and seems like it wants to start, but only goes in freely about 1/8".
What size is this supposed to be? I can redrill and tap for 4-40 easily enough, but I prefer not to.
Gary
-
I'm 99% certain the mounting screws are 3-48, that size between 2-72 and 4-40. I've dealt with Fox mufflers on my engines, too.
Bob in NEPA
-
This needs the top/bottom holes. It's not for a 4-40 bolt, that seems certain. A 2-56 seems the right dia (a 5/64 drill bit shank (.077") will just slide into the hole) A 2-56 bolt is .085" dia and seems like it wants to start, but only goes in freely about 1/8".
What size is this supposed to be? I can redrill and tap for 4-40 easily enough, but I prefer not to.
Probably 3-48. But, try to find a way to strap-mount the muffler. The over/under muffler connection was notorious for racking the crankcase out of "true", and also, for pulling a chunk out of the crankcase in a crash.
The short "ears" were slightly better, at least when they broke, it just broke the ear off. The only way that really worked was with the 50th anniversary "full length" lugs that looked like a crude version of the ST46 mounting lugs. You can sort of create the same thing on an "ear" crankcase by JB-welding some tubes to form the ST46-style mount, but that is not 100%. Straps for the "non-ear" version and the "no provision at all" versions (which are most of them...).
Brett
-
Yes, they are 3-48 for these muffler bolts. Locally there were no 3-48'st to be had that weren't for a flat screwdriver, which would be impossible to utilize because of the angle involved.
They were then drilled out and retapped for 4-40 thread, and hex headed 3/8" long bolts attached it just fine. A more secure strap might be a better solution down the road, but for now this will work.
Gary
-
Be very sure that those muffler bolts are not too long - if they contact the sleeve, they will push it out of round -- I speak from experience.
-
Socket head 3-48 bolts can be bought from either RTL or Micro Fasteners. i redid a bunch of Fox 25 4 bolt Backplate models from the 70s and put new gaskets on them and them sold them on this forum
-
Be very sure that those muffler bolts are not too long - if they contact the sleeve, they will push it out of round -- I speak from experience.
I measured pretty carefully and would drill/thread in stages until I got the muffler to seat, then stopped. I can detect no difference in how the motor turns by hand. I think it's ok, but running it will be the test.
Gary
-
I went to both sites as I too need some 3-48 bolts. None listed either site. HB~>
I decided to do a search on the internet for 3-48 screws/bolts. Nothing I found would serve our purpose. HB~>
-
McMaster-Carr at https://www.mcmaster.com/standard-socket-head-screws, 3-48 in carbon steel, and two different types of stain steel, lengths from 1/4 inch to 1 1/4 inch.
Randy Cuberly
-
I went to both sites as I too need some 3-48 bolts. None listed either site. HB~>
I decided to do a search on the internet for 3-48 screws/bolts. Nothing I found would serve our purpose. HB~>
John,
I went to the micro fastener site and found 3-48 socket screws from 3/16 to 3/4 inch. RTL would also have them. Fox engines are not so special that they need some unobtanium size bolt
Dennis
-
Locally my good hardware store, Ace hardware has #3 hardware in the specialty bolt section. Need to look around they are there.
Also try your local gunsmith.
ACE also had the hard to find 5-40 screws for cox prop screws.
-
Thanks for all the info guys! I would have preferred to have just used the correct hardware, but time was too short to order stuff. But now I have more info that I had yesterday!!
Gary