ROJETT .61 & .67 comparson

[John Leidle]

    I'd like some input about these engines unpiped if possible , is one stronger or how do their running characteristics differ.
          I posted here because more people will see this.
                          John

[frank williams]

John
The 67 is truely a unique stunt engine ....well, unique as a model engine too.  If you look through all engine data back through the years, its hard to find many (or any) glow engines that are under-square (longer stroke than bore).  The 67 has a 61 bore and a 76 stroke (.9385 bore .9626 stroke).  Its a pretty good runnin' motor either piped or muffler/header.
Frank

[John Leidle]

   Thank you Frank,  I was talking to RO before he got this engine & we briefly discussed the long stroke in an IC engine.   I'm leaning to the .67 ... but waiting for more input.
   John

[Randy Cuberly]

The 67 is essentially just what Frank said above.  It's the 76 crank configured into a case with the 61 piston and sleeve.  I have one (actually two of the 61's) of the 67's but have only run it on the bench to date.  It's slated to go in a Kaz Minato, Blue Max Eternal using a header muffler.  That's the only configuration I'v run it in on the bench.

Richard Oliver told me it was developed essentially to run on a header muffler and develop strong torque for a good conventional stunt run.

I'm sure it would run fine on a pipe but mine will be used without.  On the bench it appears to be exactly what Richard said...a very powerful, torquey, beast of an engine that is very controllable!  It is eager to turn very big props!

The 61 of course is very well documented as a National Championship engine by Brett Buck!  

Randy Cuberly

[Brett Buck]

I haven't run the 67 at all, so I can only compare what I see from the outside. I think the 67 would probably do better as an ST60 or Saito 56/72/82 upgrade than a replacement for a PA61. I

     know I will get flamed again, but I really don't see any good competitive reason to run in 4-2 with a muffler and giant 6" pitch prop like it was still 1985, even a really good one like the 67. But people still seem to want that, and do well in some cases, so, heck, I am probably just stupid like the hate mail said.

    I couldn't be happier with my RO-Jett 61s (140 and 144 exhaust duration, AKA "Brett version"). They seem to solve all the issues and nits I had to pick with others. It's not quite as easy to keep running perfectly as a OS40VF (which is far and away the most reliable/repeatable stunt engine of any kind I have ever seen) and it doesn't have quite the "power" as the PA61/65, but overall it works like a gigantic super-powerful OS46VF.

The setup has been repeated over and over, and I have varied it as an experiment over the years, but I always come back to the settings I discovered right before the 2003 NATs. Literally never think about it for *11 years* no matter what the conditions might be, adjust the nitro to get the same operating point, it runs the same. I have been running the exact same engine since right before the 2007 Team Trials, and while I don't think I fly very much compared to others, lots of cases of fuel have come and gone in that time.

   For what it is worth, I haven't seen the same sort of repeatability with the RO-Jett 65 that I have with the 61. That may be because all the 65's I saw and the one I ran was the 136-degree version. I never got the 136 "standard" version or either the 61 or 65  to run properly in the manner I like, it just didn't seem to be as stable at normal flight revs of 10800-11000.

     Brett

p.s. throwing caution to the wind, I would also note that the OS20FP and "new" 25LA are just about as repeatable and have the same outstanding run quality as the 40/46VF - if you leave them alone. "Fix" or "improve" them, and you are on your own.

[goozgog]

   I bought a .67 SE last summer NIB but "used".  
I broke it in according to Randy Smith's method,
then since I couldn't wait to fly it, I  changed it
out for the ST. 60 in the plane in the picture.
   The .67 is heavier than the ST V.60  but it was a
straight drop in. It runs great! Steady and
repeatable, but with a lot more power.
I ran it in a  "wet 2" on Power Master "Ro-Jett",
turning a Bolly 3 blade.

   The plane went from being a sweet flier to being
a "handful". The ST V.60 is back in.
 
  So what I've learned is that the .67 is a very
strong engine and that there is such a thing as
"Too much power".
  I'm very happy with the engine though.

BTW, I also run a Ro-Jett RE piped .65. which
is also great.

Cheers!

[john e. holliday]

No such thing as too much power,  has been stated on here many times.   I have even proved that to my self.  It is finding the right prop and venturi set up for the engine plane combination.   

[Brett Buck]

No such thing as too much power,  has been stated on here many times.   I have even proved that to my self.  It is finding the right prop and venturi set up for the engine plane combination.   

   Try putting a ~3 hp Zalp 2.5cc FAI speed motor on your stunt plane and see how it works. There is no prop in the world or that you can imagine, that makes that work. But it has way more power than a PA75, at least the way we run PA75.

      Brett

[Randy Cuberly]

I haven't run the 67 at all, so I can only compare what I see from the outside. I think the 67 would probably do better as an ST60 or Saito 56/72/82 upgrade than a replacement for a PA61. I

     know I will get flamed again, but I really don't see any good competitive reason to run in 4-2 with a muffler and giant 6" pitch prop like it was still 1985, even a really good one like the 67. But people still seem to want that, and do well in some cases, so, heck, I am probably just stupid like the hate mail said.

    I couldn't be happier with my RO-Jett 61s (140 and 144 exhaust duration, AKA "Brett version"). They seem to solve all the issues and nits I had to pick with others. It's not quite as easy to keep running perfectly as a OS40VF (which is far and away the most reliable/repeatable stunt engine of any kind I have ever seen) and it doesn't have quite the "power" as the PA61/65, but overall it works like a gigantic super-powerful OS46VF.

The setup has been repeated over and over, and I have varied it as an experiment over the years, but I always come back to the settings I discovered right before the 2003 NATs. Literally never think about it for *11 years* no matter what the conditions might be, adjust the nitro to get the same operating point, it runs the same. I have been running the exact same engine since right before the 2007 Team Trials, and while I don't think I fly very much compared to others, lots of cases of fuel have come and gone in that time.

   For what it is worth, I haven't seen the same sort of repeatability with the RO-Jett 65 that I have with the 61. That may be because all the 65's I saw and the one I ran was the 136-degree version. I never got the 136 "standard" version or either the 61 or 65  to run properly in the manner I like, it just didn't seem to be as stable at normal flight revs of 10800-11000.

     Brett

p.s. throwing caution to the wind, I would also note that the OS20FP and "new" 25LA are just about as repeatable and have the same outstanding run quality as the 40/46VF - if you leave them alone. "Fix" or "improve" them, and you are on your own.

I have found the same to be true with the 65...Good runs but not quite as consistent.

The 65 has a much thinner sleeve than the 61 and that may be a contributer to the inconsistence.  I was told that the 65 has actually been discontinued due to difficulties in keeping the cylinder round during manufacturing and a high scrap rate.

I'm not demeaning the 65 they run very well and have been used to win many competitions also.  In fact I believe Ted Fancher used one to win the NATs! (not sure about that>>>).  I know, He in fact did have a 65 in at least one of his TP's.

I'm inclined to agree with you about the lack of reasons to revert back to a Fox 35 type of run...even a very powerful one.
I don't however think the 67 is quite that drastic a difference.

Randy Cuberly