O.S. MAX 20 - which muffler?
05-13-2006 | 08:21 PM
#1
Thread Starter
Joined: Jul 2003
Posts: 1,043
Likes: 0
Received 0 Likes
on
0 Posts
From: Dunnunda, AUSTRALIA
O.S. MAX 20 - which muffler?
I have recently inherited a loop scavenged O.S. MAX 20 C/L sans muffler. Can anyone advise or confirm the original O.S. MAX muffler model # recommended and intended for fitment to this engine?
It only accepts the old spring metal band fitment type pre-dating the current bolt FPS/LA-S through types.
When the O.S. MAX 20 was originally introduced (1971), as best I recall they came supplied (as did all engines in those days) without mufflers, which were an optional spare. The same era muffler for the O.S. MAX 15 III and later MAX 15 fits the MAX 20's exhaust aperture perfectly, but the volume (#OS-702) seems on the small side for a 20.
It only accepts the old spring metal band fitment type pre-dating the current bolt FPS/LA-S through types.
When the O.S. MAX 20 was originally introduced (1971), as best I recall they came supplied (as did all engines in those days) without mufflers, which were an optional spare. The same era muffler for the O.S. MAX 15 III and later MAX 15 fits the MAX 20's exhaust aperture perfectly, but the volume (#OS-702) seems on the small side for a 20.
05-14-2006 | 06:11 PM
#2
Thread Starter
Joined: Jul 2003
Posts: 1,043
Likes: 0
Received 0 Likes
on
0 Posts
From: Dunnunda, AUSTRALIA
RE: O.S. MAX 20 - which muffler?
Update
Result posted for the record and info of any others who might search in future with a similar query.
Since found several different sites with online images of same model O.S. MAX 20, but of later era manufacture when it came supplied with muffler in box which illustrates the small volume OS-702 was its factory supplied and recommended muffler.
That the spring metal band fits, albeit requiring a longer bolt of the same diameter and thread than the one supplied with the same muffler accompanying the MAX 15, and that it fits the 20's exhaust aperture perfectly reaffirm this. I scavenged a bolt-through muffler screw from an OS 15 FPS as a substitute and its diameter, pitch and length allowed fitment of the muffler to the 20 like it was meant for it. The OS-703 (which I have) from an O.S. 35 is much larger in volume and doesn't fit also affirms the 702 as the muffler for this unit.
Bench running the engine with this muffler fitted confirms both work OK. And although dB weren't measured other than by Mk I Ear, standard issue, 2 thereof, with a noise level typical of that which would have been considered acceptable for a silenced engine in that era and as expected from the 702's minuscule volume on this capacity engine.
Result posted for the record and info of any others who might search in future with a similar query.
Since found several different sites with online images of same model O.S. MAX 20, but of later era manufacture when it came supplied with muffler in box which illustrates the small volume OS-702 was its factory supplied and recommended muffler.
That the spring metal band fits, albeit requiring a longer bolt of the same diameter and thread than the one supplied with the same muffler accompanying the MAX 15, and that it fits the 20's exhaust aperture perfectly reaffirm this. I scavenged a bolt-through muffler screw from an OS 15 FPS as a substitute and its diameter, pitch and length allowed fitment of the muffler to the 20 like it was meant for it. The OS-703 (which I have) from an O.S. 35 is much larger in volume and doesn't fit also affirms the 702 as the muffler for this unit.
Bench running the engine with this muffler fitted confirms both work OK. And although dB weren't measured other than by Mk I Ear, standard issue, 2 thereof, with a noise level typical of that which would have been considered acceptable for a silenced engine in that era and as expected from the 702's minuscule volume on this capacity engine.
05-19-2006 | 09:03 PM
#3
Banned
RE: O.S. MAX 20 - which muffler?
The 15 20 and 25 use the 702, The 35 and 40 use the 703 and the 60 used the 704. I own several of each. OS also made an adapter so you could use the strap on 704 on the 61FSR and the 60FSR. Saved the crankcase if you knocked the muffler off in a crash
