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Nov 02, 2017, 08:59 PM
Dinosaur
Twodor's Avatar
Discussion

Another Unknown Engine


This one came from the collection of an old flyer who can't remember what it is. It was in sad shape when it came to me, dirty, seized up with gummy stuff and had no compression. I cleaned it up, inside and out and if it runs as good as it looks I'll see how it flies on a 60 size Ugly Stick. It now has a surprising and impressive amount of compression and is ready to run. I'll probably mount it to a test bench this coming weekend.

On the right side it says, 91. On the left is a logo that looks like an elongated letter 'O' with an aircraft in the center. On the left side mount tab it says, Made in Taiwan. There is no brand name but the engine has a distinctive one piece aluminum valve cover and the carburetor is not like anything I've ever seen. I'm thinking a clone of an OS, maybe? I like the cooling fins cast into the intake manifold. It really is a good looking engine.

Can anyone identify this engine for me. Thanks in advance.

Tom
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Nov 02, 2017, 09:10 PM
Registered User
It looks like a thunder tiger 91 4 stroke, I had one once. made to run on around 5% nitro can throw the prop nuts .
Nov 02, 2017, 10:21 PM
Registered User
Yup, TT 91 4 stroke, Double nut that hub prop nut, they sell flat nuts that match for that purpose. Good engine though.
Nov 02, 2017, 10:39 PM
AMA 46133
I have to go with Thunder Tiger also. You can see the Thunder Tiger logo on the left side of the crank case. Thunder Tiger was made in Taiwan.
Nov 02, 2017, 10:56 PM
Registered User
marmalade1's Avatar
Great engines by all accounts. As I recall reading here, it was the most powerful (naturally aspirated) 4 stroke in its size, albeit the heaviest.

PD
Nov 02, 2017, 11:59 PM
Registered User
Yep, later versions had lower compression and ran great on 25% nitro. It would turn a 14-7 at almost 11,000. I think it was actually 10,700 or 10,800. Stronger than an OS or Saito but heavy.
Nov 03, 2017, 01:28 AM
Registered User
Thunder Tiger .91 for sure...
I have two, good power for a .91 but a bit heavy as suggested.
Not as much power as a Saito100, still heavier...
Nov 03, 2017, 01:34 AM
Registered User
Quote:
Originally Posted by Twodor
the carburetor is not like anything I've ever seen
What you see at the bottom of the carb is the removable choke used for priming the engine, mostly useless, I have two somewhere...
Nov 03, 2017, 09:09 PM
Dinosaur
Twodor's Avatar
Thank you, gents.
The Thunder Tiger I.D was also confirmed today by a club member who reported he had several and all performed great. I guess I'm lucky to have acquired it for free.

I put it on my test bench today and it started with about 1/2 revolution of the starter. It runs and idles nicely swinging a 14-6 prop at 10,500 with no problem. It runs and looks so good I'm glad its going on a stick where it is exposed and not hidden by a cowling.

Thank you again for your help identifying this engine.

Tom
Nov 04, 2017, 08:38 AM
Registered User
I TOBOR's Avatar
https://www.towerhobbies.com/cgi-bin...&I=LXL761&P=ML

A better prop lock nut by Harry Higley, I have a few of these and they are a quality item.
Nov 04, 2017, 09:01 AM
Engine Frankensteinerô
1QwkSport2.5r's Avatar
Quote:
Originally Posted by I TOBOR
https://www.towerhobbies.com/cgi-bin...&I=LXL761&P=ML

A better prop lock nut by Harry Higley, I have a few of these and they are a quality item.
+1. I use these as well. The brass is a little more stout than the aluminum ones - as far as stripping goes. It doesn't take much effort to strip the aluminum jam nuts.
Nov 09, 2017, 06:25 AM
Registered User
Why causes this engine to throw props?

carl
Nov 09, 2017, 06:34 AM
Engine Frankensteinerô
1QwkSport2.5r's Avatar
Quote:
Originally Posted by carlgrover
Why causes this engine to throw props?

carl
Backfiring from a lean fuel mixture.
Nov 09, 2017, 07:46 AM
Registered User
I TOBOR's Avatar
Very early ignition caused by the fact that a lean mixture ignites easier and burns faster. Although a too rich mixture can cause it too, I'm sure we've all had the chicken stick removed from our hands by kick back's caused by too rich a mixture.


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