Matt
How is the fit of the sleeve into the case.  Raise the sleeve out of the case about a quarter of an inch and rock it back and forth.  If it rocks at all, the sleeve to case fit is suspect.  The engine won't draw well if this looseness is present.  There will be crankcase leakage from transfer ports to exhaust.  The sleeve should be almost all the way out of the case before you can rock it at all.  Also check the blowdown timing.  Is there a measurable distance from when the exhaust opens and the intakes open.
Frank 

If it jamming at TDC then perhaps the rod is in backwards?

(Grasping at straws here I know but I have had this happen before as it pushes the rod further back on the crankpin and that can rub internally against backplate or strike the internal arch of the casting.)

Like I wrote before, two front mounting lugs have been damaged in the Great White crash but I am using the clamp style mount and all four mounting screws are engaged properly.








I am of the opinion that the CC is bent since you had a crash unless it was running this way before the crash, then I don't know. 

I had a VECO 61 on an RC ship several years ago that crashed due to not enough rubber bands on the wing and it (the wing) departed when my student pilot was doing loops with it. Yes, I was quite embarrassed that I hadn't prepared the ship properly........
Anyway, my favorite engine got a bent CC (ever so slightly) and it had to replace.  Haven't flown the engine since, but have thought about converting it to CL. 

Jerry

Gerald,
Bending the crankcase that is aluminum cast will, in my opinion, cause the crankcase crack somewhere.
I do not see the indication of this as there is no weird leak anywhere.
I would see this leak as I was watching the engine from all angles while running it recently.

Everybody,
I got the ground RPM of 8,300 - 8,700 on 12x7 APC and my RToucan weights now 66 oz.
Is this ok? I mean these RPM on this prop for the plane weighting 66 oz. on 66' long lines?

Perhaps for THIS engine as it is now, on THIS prop and THESE lines I need 59 oz., 580 in^2 plane?

Maybe the plane weighting 66 oz. is simply too heavy for the engine as is?

What I am trying to avoid is three months of trying, erring, writing e-mails and swearing instead of one radical move, namely, using the lighter plane.

Well...

Maybe the plane weighting 66 oz. is simply too heavy for the engine as is?

What I am trying to avoid is three months of trying, erring, writing e-mails and swearing instead of one radical move, namely, using the lighter plane.

When Paul Walker strongly suggested that I put a 46LA on a 64 ounce airplane I privately thought he was crazy, and publicly said "yessir!"  (Because he's Paul).  I figured I'd try it and then put in something else if it didn't work.

It works splendidly.

No way is a Jett 60 too small for that sized plane.  I think the one radical move needs to be to send the engine to someone who can fix it, or declare it dead and keep it for parts.

Remember this is a 25 year old cast case George-Jett and will not run the same or have comparable power to a PA, RO-Jett BSE w/BB timing or run as fast as a 40 VF. Max RPM is not a good test for a stunt engine anyway and 12x7 is a terrible stunt prop as has been stated.

George engines are know for lower RPM and 4 or 4-2-4 cycle type runs.I wouldn't run it in a 2 cycle if it were my engine. 

   I think the idea is that most of the GMA stuff is removed. That is why Randy and I were attempting to check the head clearance, to see if it was still a GMA system, or the replacement parts (supposedly current RO-Jett parts). It appears that at least the head clearance is in the modern range like a conventional RO-Jett, compared to the GMA version (.030 vs anywhere up to .080-090 in the GMA). And the venturi also seems like a stock RO-Jett item as well - the ones with the GMA were usually massive, like .228 (#1) and even larger.

  I do know that having to run a 12-7 prop is like adding 2 pounds to the airplane in terms of performance.

   And, I might add, most of the performance problem with the original GMA-Jett is a function of the outlandish low compression. In many cases, we tightened up the compression to normal values (like this engine is, apparently), and the engine really came alive, to the point that the venturi (gigantic to go with the very low compression) was then FAR too big and it was difficult to get it to do anything but run dead lean at 13000 rpm.

   I wouldn't discourage anyone from continuing, but I have to pretty much punt at this point. Maybe if someone with experience had it in their hand it the problem would become obvious (and for goodness sake, DO NOT SEND IT TO ME), but with multiple rebuilds, a crash to the point the lungs broke off (which is one mighty whack indeed) and very bad baseline performance, it could be any one or more of a dozen issues and I think internet troubleshooting is unlikely to be a effective method to resolve it.

    Brett

A 0,003" change in a healthy .60's compression is so small that you propably won't notice much change. Also, amount of shims tells nothing as also in "better" engines the carter height tolerance can be quite wide. Especially engines from small production runs can have variations.
As I wrote earlier, you'd better measure the head volume with piston @ tdc and compare it with volume of another healthy engine, unless the difference is a clear, measurable one.
I don't know values for engines meant for nitro fuel, but when I do my experiments, I usually go in 0,1 cubic cm volumetric steps, with a typical 24mm bore of .60 engine that equals about 0,2mm (1/127") shim change, and then proceed to fine tuning.
But, most of many possible faults in engines cause low power. Without more accurate information all this speculation is quite useless. L

That is part of my point; to measure head volume you just need to revove the glow plug, then use a 2ml syringe with needle, and some fuel. No special tools needed.