HI All,

I have a ST 40 that was set up by Big Jim, Hemi head and all.  The piston uncovers at TDC, and I am wondering how this "sub piston induction" effects a stunt run if a muffler is used?  It is a twin ring engine, and the muffler lugs were present, but have been removed.

Plus:
1. what type of prop?
2. approximately how much fuel needed for 6:30 run time (it has a .271 venturi)?

Thanks!
Mongo

Thanks, Ed.  I meant to ask you about this one when I was at Huntersville.    With everything going on, I forgot.  This one seems to be in real good shape right now.  I have another one which is a single piston, stock.

Big Bear

Bill    Most of those early double ring 40's came from the factory with a hemi head.The double ring models also had a smaller crankcase port. There is also a difference in sleeve intake timing. I have a ledger I kept on all the different versions I worked on so I could keep the right combinations together as there were many variations of the .40&.46. Also your motor is more than likely the thin sleeve version.
Ed

Hi Ed,

I am hoping that I can get what little use I need out of it.  Good compression and seal right now, and it is a Big Jim engine.  Nothing has been done to it since Jim reworked it.  The "other one", much newer I think, is the single ring but it needs bearings and a new ring.  Just a substitute in a plane where I was initially was going to use a ST .46.  The plane is smallish, and the .40 will be plenty for it (won a NATS with a Fox .35)...

Fuel amount?  I am trying to decide how big a tank to install.  Pretty sure I can fit a 4 1/2 oz, "maybe" a 5 oz., before I have to go to a weird size/shape one.

Big Bear

Bill the thin sleeve version runs fine. For RC use with big props thay gave problems. If you remove the bearings on the other one and use the crock pot cleaning method there is a good chance there is nothing wrong with them. They will not clean up as well if you leave them in the motor when using the pot method.
Ed

Thanks, Ed.  The bearings are out, I haven't tried cleaning them, just thought I would replace them.  Going to contact Frank for rings.  THEN i will give you a call! LOL!!

Will a 4 1/2 oz tank be enough for 6:30 on 5% fuel?  Gotta see if a tank will fit into the plane, not sure a 5 oz will fit.

Thanks, again!
Bill

Hi Ed,

I am hoping that I can get what little use I need out of it.  Good compression and seal right now, and it is a Big Jim engine.  Nothing has been done to it since Jim reworked it.  The "other one", much newer I think, is the single ring but it needs bearings and a new ring.  Just a substitute in a plane where I was initially was going to use a ST .46.  The plane is smallish, and the .40 will be plenty for it (won a NATS with a Fox .35)...

Fuel amount?  I am trying to decide how big a tank to install.  Pretty sure I can fit a 4 1/2 oz, "maybe" a 5 oz., before I have to go to a weird size/shape one.

Big Bear

Well, you got the engine from me, so I'll tell you how I used it.

It was mounted in a slightly modified/enlarged Tutor that had a 25% foam wing and flew beautifully.

I always ran Taff's 10% PA Blend fuel with Caster oil, a 4.5 oz tank (IIRC) , a Big Art strap-on tube muffler with the tail pipe opened up a little, ST-40 NVA and the same venturi thats in it now, plus two or three head shims, with a 10/6 wooden prop. Top Flite or BY+O.

It was always a stone-reliable, no-nonsense, no-fiddling engine that made good power. In fact, once it was set-up, I never even touched the needle valve but with a larger venturi I have little doubt that theres more power available.

I still have the mate to it if you decide that you want/need it.

Good luck with it.