[bugsmasher]

I wonder if some of the dieing breed of nitro flyers could give me some of their thoughts on my Thunder Tiger 46 pro. It doesn't seem to be making good power but....it seems to have good compression, it idles really nice, and the transition to full power is excellent. Although it has good compression, it turns very freely/loosely before the compression part of the stroke. The bearings seem smooth but how freely it turns and the lack of power make me think something is worn out. Bearings? Ring? I think it's a ringed engine. Thanks.

[Mike Sebastien]

it's a great engine. first define good power and low power. answer these questions.

FuEL?
prop?
How long have u had it?
Airplane?

[Cougar429]

Will need some more info, but can make a few guesses.

First need to know if it is a ringed engine, (easiest method is to remove the muffler and look in the exhaust port at the side of the piston just below the top). If so the sleeve is straight bore and will normally feel loose until the piston ring passes the transfer ports and closes them off. Only then will you start to build compression.

If non-ringed the sleeve is usually taper ground and you may start to feel drag when cold as the piston climbs to the top. This is made this way since when running the temp increase actually makes it grow till straight. I never like to turn them dry as you can cause excessive wear.

Any engine with bearings can suffer wear, a lot depending on your care and feeding. If lubed and kept clean they will normally be pretty durable, but if any residue fuel is sitting in the case at the end of the flying session it will mix with atmospheric moisture that attacks any ferrous bits in the engine. The liner, crank and in particular the bearings are vulnerable.

If the bearings have enough wear or damage to allow the crank to float it will start to wear the inside bore in the case. This requires a tight fit to have oil seal between the two and only feed air/fuel through the cut in the crank. That sets the intake timing and if you have excessive wear air can enter through the front bearing and reach into the case. Mixture and performance will suffer.

I always replace shielded front bearings with sealed to help prevent this and in the case of some engines this is the only fix for poor QC where that gap is excessive, (there are two I have lots of experience with that suffer this problem).

Some of the other questions that may help determine if you have a problem:

What history of this engine? Lots of hours, etc.?

What prop are you running? What fuel? How old is the fuel and has it been exposed to the atmosphere? Does it have a milky or dark appearance? any signs of solid contaminants?

Have you adjusted the High Speed needle to peak then back a click or two?

How is the engine mounted, straight up, side or inverted? Signs of overheating?

Have you tried a new glow plug? Do you find difficulty keeping it running after external heat removed? Does the RPM drop regardless of mixture when heat removed?

[frenzy]

What prop are you using?

[bugsmasher]

Thanks for the replies. The engine is on a old Ultra Sport 40 ARF mounted sideways. I bought it as a package on here so I have no idea how much time is on the engine. I'm guessing it's fairly high time but like I said the compression seems good. I thought it was ringed based on this.

http://stock.thundertiger.com/product/9141.html

but looking in the exhaust port it doesn't appear to have a ring. The glow plug is new as is the Byron 10% going into it. I was running about a quarter turn rich of peak. There is no drop when the external heat is taken off it and it idles great. The metal piece that goes on the needle and provides the clicks disintegrated so no clicks. Based on the questions I did discover it has an inch too much prop. It has the prop that the previous owner installed which I assumed was correct but it's not. It's a 11x7 and Thunder Tiger says 10 x7. Does an inch too much prop make a huge difference? I used to have a tachometer that would have came in handy in this instance but I somehow lost it. Do you think an inch too much damaged it? I'm going to put the proper prop on it next time but the plane needs a bunch of things fixed so I don't think I'll be flying it again for a while. Thanks

[BillGreen]

Originally Posted by bugsmasher

Thanks for the replies. The engine is on a old Ultra Sport 40 ARF mounted sideways. I bought it as a package on here so I have no idea how much time is on the engine. I'm guessing it's fairly high time but like I said the compression seems good. I thought it was ringed based on this.

http://stock.thundertiger.com/product/9141.html

but looking in the exhaust port it doesn't appear to have a ring. The glow plug is new as is the Byron 10% going into it. I was running about a quarter turn rich of peak. There is no drop when the external heat is taken off it and it idles great. The metal piece that goes on the needle and provides the clicks disintegrated so no clicks. Based on the questions I did discover it has an inch too much prop. It has the prop that the previous owner installed which I assumed was correct but it's not. It's a 11x7 and Thunder Tiger says 10 x7. Does an inch too much prop make a huge difference? I used to have a tachometer that would have came in handy in this instance but I somehow lost it. Do you think an inch too much damaged it? I'm going to put the proper prop on it next time but the plane needs a bunch of things fixed so I don't think I'll be flying it again for a while. Thanks

A quarter turn rich from peek is too rich, one click is better. 10X7 APC on an ultra sport will give plenty of performance.

[bugsmasher]

I ran and flew the 46 again today finally with a 10x6 prop. I was getting a bit over 12 000 rpm but that was well rich of peak as the needle is definitely vibrating rich without the clip. I could hold it at peak buts as soon as I let go it moves quarter turn rich and as I fly it gets richer and richer till it dies. Cougar429 if you have a clip it definitely would be appreciated. 12 000 rpm seems low but it definitely can be leaned higher than that.

[Cougar429]

Can you post a pic of the engine, specifically the HS needle? I have some spare clips and could send you one if compatible.

Regarding the prop, yes that could make a difference in performance. Either too much pitch or too large a diameter can cause enough drag to prevent the engine from reaching peak RPM. 2-strokes have a rather narrow peak band so you can see a large drop in performance if it cannot get up there.

This is the reason in 3 decades of testing I have never been able to get any 2-strokes to work properly with a 3-blade prop. Regardless of the conversion listings there simply is too much drag unless you drop the diameter so much the loss of performance makes the use of them moot unless you just like the looks.

With higher nitro you may be able to gain some performance, but I live by the rule that if you require more than 15% nitro to get what you need then there is a mismatch between airframe, engine and/or prop. Helis are a different story.

4-strokes have a much wider torque band so this is not a problem. I frequently run 3-blades for both scale looks and clearance.

Looking at their specs it appears this engine is ABN construction. The last letter states the brass sleeve is nickel plated. Not as hard as chrome, (ABC) and does not tolerate overheating as well or last as long. Having said that, with good care you should still see relatively normal life if treated properly.

It may be worthwhile to pull the head and look down at the liner. If no scoring, obvious wear or loss of plating, (sometimes starts around the sharp port cuts) then you should be fine. Just be sure you don't lose or move the thin alloy or brass spacers that fit between the sleeve and heat cutout. They are there to set compression and seal between the two.

NOTE: From the spares listing the piston pin is retained at one or both ends by formed wire circlips. These have been known to fatigue or rust and break. The result will be grooving in the liner from the remains of the circlip or end of the pin and cannot be seen looking through the exhaust port. If severe enough you will not build compression till the top of the piston raises up above that grooving, which will be below the top of the piston at TDC. If that is the case the only repair is a new liner, piston and retainer clips. Very likely the piston may appear fine, but the grooves cut in the pin bore will be damaged and not work well with new clips. Besides it is always best to match the piston and sleeve with this type engine. A ringed type is a different story and you could sometimes get away with just a ring replacement. Some Fox engines had fully hardened liners and I could wear through the third ring before it needed a new liner.

[aspeed]

Maybe the previous owner assembled the liner backwards. Normally there is a locating pin and it is pretty much impossible. The exhaust port should be a bit higher than the bypass. I would guess an extra inch of pitch and diameter is what is the problem. Just to compare, Mine measures 14,400 rpm with a 10-6" Master Airscrew prop. That is comparable to most other .40 size stuff, and a bit less than a typical .46. Around a good 1,000 rpm better than most plain bearing LAs and GP, FP types.

[stegl]

An 10x7 or a 11x6 should work well. Lots of good points to check out in above postings. A lot of engine manufacturers over past years switched from chrome plating the cylinder lining to nickel plating. Don't think the wear tolerance was as good . My first preference was a piston with a Dykes ring and then a conventional ring. If the TT was run under dirty conditions ; compression can be lost thru micro groves worn at the top end
Of the piston/liner. Top end can be felt tight when cold but when up to running temp is were compression is lost.
Don't recall brand of prop being used but my choice is a APC as it outperformes most others.