I have a tiger 2 that I just finished rebuilding. I put a used OS .40 FX on it that was given to me and it flew great but was finicky at idle and very sensitive to needle adjustments. I decided to take it apart and clean it all out and found that the cylinder liner was toasted and flaking off. Being that I raced nitro cars I figured i would toss a new cyinder and piston in it like we usually do every few gallons
on the buggy engines.

Is it worth the $58 dollars for a new cylinder and piston. bearings and the rest of the engine are fine? or should I buy a new engine.
the problem is with the car engines a new sleeve and piston is about 1/3 the cost of a new engine, but I see these GMS and similar
engines for about $10-$20 more than a rebuild.

What should I do?

I actually created a poll and asked for opinions about .40-sized glow engines in the sub-$60 price range:

http://www.rcuniverse.com/forum/m_5207614/tm.htm

There are some excellent engines available for about the cost of the parts you need to rebuild your O.S. .40 FX. With the Super Tigre GS-40 being available for $49.99 and also being the most popular choice as the answer to my poll question, it seems to be an obvious winner.

The $64.99 Super Tigre GS-45 ABC engine would also be a terrific choice, and would provide plenty of power.

The OS is not worth the trouble, keep it for the carb which will work on some other engines like Magnum.
I personally would not use the plain bearing TT as it does not have the power of your OS.
There are a lot of really good choices to be had in that size range, one choice would be a Super Tiger 51, same size as many 40-46 engines but strong. It does require a fair ammount of break-in.

TT46pro, ST 45, both are equal in performance to the OS 46fx. I have all three.

I agree with the TT46 pro. A great engine, easy to break in, easy to tune, and has plenty of power for your application.

Any flaking is likely getting into the bearings...I would replace the engine instead of rebuilding it...Rog

The Thunder Tiger Pro .46 is a wonderful engine, but the prices on Thunder Tiger 2-strokes seem to have been creeping upward over the last year or so. The TT Pro .46 is only $20 less than the O.S. Max .46 AX at Tower Hobbies. A $58 rebuild would still save $32 versus buying the TT Pro .46.

Thunder Tiger engines have slowly risen to premium product pricing status, and all of the TT Pro series and 4-stroke engines are now significantly more expensive than competing products from Super Tigre and Magnum.

If you shop around, you can still find good pricing on Thunder Tiger engines. It takes a lot more work than it used to, however. Fortunately for Thunder Tiger, their engines are top quality and are still a very good value at the prices now being offered.

How old is the engine? O.S. had problems with liners peeling on .46SF engines a couple of years ago. They replaced the line and piston for me ( I installed them). Might be worth a call to Hobby Services and check out whether there was a problem with .40's also. Who knows, maybe they'll help.

Dave

Dave the fx is about a year and a half old. It has not seen that much fuel or time.

Like most other things in life......You get what you pay for. Spend the money now or in the future, one way or another you will spend the same amount in the long run. Go with a better engine and you will be happier because less tuning and repair time.