kfla

Guys Iv'e got a problem with my Thunder tiger GP 61. The end play on the crank seems exsessive (about a .100 of an inch). I bought it off of a friend of mine. ( what can I say the price was right). Should I tear it down? or just run it? Does anyone know what the problem might be? Thanks Kevin

JustErik

Unless I'm mistaken, the GP series is bushed; no bearing, which means (I think) it can't really be repaired. I'd just run it 'til it dies.

YUKONFLYR

Bushing engines have some end play in the crank, which is normal, may seem like a lot however things do line up when the prop puts pressure on the crank.

You could look down the exhaust port and or remove the back plate of the engine and have a look inside, should be shiny, if you see black like when you polish aluminum then things are not good. Carbon in the exhaust port and on the piston and cyl head is normal for a used engine. I think you will find that the engine is good.

If you run the engine, check the exhaust, oil discharge should be clear to amber with no black, If you hear it squeeking or making a squeeking noise, usually the crank bushing, check that your fuel has at least 20 - 22% oil in it....

Hope this helps

Richard

XJet

I think this is normal with a GP61. Mine was the same -- and it made an awful knocking noise at idle/low-throttle settings as the crank moved back and forth.

Make sure you're using a *good* fuel with plenty of castor oil and it won't be an issue. I used Omega (70% synth, 30% castor) in mine and it lasted almost two years before blowing up (split the crankcase due to ovalling of the main bushing -- there are pictures on RCU somewhere). If I get another, I'll use 20% castor oil and I'm sure it'll last a lot longer.

N1EDM

My Feedback: (2)

I dunno... if the end play is really .100 inch, something is wrong... that's more than 3/32". I had a TT GP40 and it had only a bit of end play.

Can you look up a TT GP engine manual on line and see if you are missing a washer or a shim somewhere? Or perhaps something is not totally seated.

If you measured correctly and the end play is really .100, that's waaaaay too much, IMHO.

Bob

XJet

I thought exactly the same thing with my own TT61GP so I checked and it did have the prescribed single thrust washer.

My TT42GP has nowhere near this amount of slop in the crankshaft either.

downunder

YUKONFLYR hit on something. If you're checking that end play with no prop then what you're seeing is the clearance between the end of the crankpin and the backplate. With a prop fitted (even finger tight) then the crankshaft can only move back until the prop driver contacts the steel shim thrust washer. Usually this will only allow maybe .020" or thereabouts, just enough so if the crankcase gets hot the expansion won't bind the crankshaft. The thrust washer is only there to prevent damage between the prop driver and crankcase when you use an electric starter.

buzzingb

My Feedback: (2)

Good or Bad, run it till it quits and replace it. It will be too expensive to fix. Bushed engines do have endplay.

kfla

Thanks for everyones input, My friend Nick brought the engine in (it's his engine) and upon further inspection the endplay is only about .020 of an inch, not as excessive as first thought. He has decided to run it till it dies. Thanks again Kevin and Nick

YUKONFLYR

Just for kicks I measured up an OS 40FP that was gifted to me, basically only been run twice, so almost new.

The endplay gap was 0.037", which is quite a lot if your just looking at the gap [X(],

Richard

rcdude7

My Feedback: (264)

My .40fp is the same way, despite the noise at idle from the crank sliding back and forth, it's a great running, dead reliable little engine.

Mike

DarZeelon

The raison d'etre for this gap in a bronze-bushed engine, is to allow for differential expansion of the dissimilar metals.

The crankshaft is made of steel that has a heat expansion coefficient, which is low compared to the aluminium of the crankcase.

When both heat to the normal engine operation temperature, the size of this gap grows smaller as a result.


With the prop tightened on, the crankcase is flanked by the crank-web at the rear and by the thrust-washer at the front.
The amount of friction between the bronze bushing and both steel items is pretty low and there's nearly no wear, with all that castor oil lube (I suppose none of that green, synthetic 'engine killing fluid' is being used in that bushed engine...).

Most of the force is applied between the bushing and the crank-web (due to thrust produced by the spinning prop).
A minority of the force is applied between the thrust-washer and the front of the bushing, if an electric starter is used (or in crashes...).

YUKONFLYR

LOL......

I remember back about 8 years ago on the online fourms calling cool power.......cruel power[:'(], I remember getting flacked by the SYN only crowd something awful.......Now it seems like it is common practice, as I read the forums.

I do however like your description above, Dar................., Green[:'(], SYN, LOL, engine killing fluid..............lol

Ever hear a TT GP42 being killed by the green fluid of death, squeels awful.......... When I was learning a guy at our field got his green fluid juiced by castor, and Im not admitting nothing.......Did make his engine happy for the balance of that gallon however, hey even my omega got juiced by somebody else saying it did not have enough castor

DarZeelon

Richard,


The © on that statement (i.e. engine killing fluid, in some sort...) belongs to Dave Hobbs, who used in a recent thread...

I thought I was the first to use 'CruelPower' here, but I'm probably wrong... I did because I saw the results of its use...

blw

My Feedback: (3)

I add a couple of ounces of castor to my Omega.

YUKONFLYR

Ok, did not see that thread............Thanks for clearing that up.....

I got my first taste of what CruelPower does to an engine, back in 2000 when my instructor / friend let me fly one of the speed planes that he made. It was a 20 size Mustang with a Rossi 40, with full pipe. Did not run at idle or mid, only at full tilt. Got about 4 laps in when it locked up solid. Now we were using a 50/50 castor / klotz oil in homemade fuel. The engine was gifted to my friend by someone who used the green fluid / green snot[:'(] only in this poor engine. A piece off the small end of the rod let go and it came up thru the transfer ports, stuck in the head and top of piston. That event ruined my fun for the day[:@]
I can tell you that what it was called that day could not be printed in these forums. But back then it was very non-politicaly correct to blame the Cruel power for killing an engine, and if you did...................like I did..........you took major flak for it. Now it seems that everyone knows what it does to an engine and I have seen some very colorfull remarks from members, in reference to the green stuff, I like this symbol as well to describe it---------->[:'(]

Richard

YUKONFLYR

I add castor also.

After my first jug got juiced my TT GP42 ran much better and I have been adding ever since

Richard

DarZeelon

Richard,


...But it keeps your plane cleaner... not gooey like castor oil...[:'(]

So, who cares if it kills your engine[:@]... as long as the plane stays relatively clean.

NM2K

My Feedback: (14)

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Boy! Talk about anal retentive!!!


Ed Cregger

downunder

See also post #7 but I managed it in about 2 lines .