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My Thunder Tiger F-91 ate the cam....

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My Thunder Tiger F-91 ate the cam....

Old 04-18-2010, 09:27 PM
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scooterinvegas
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Default My Thunder Tiger F-91 ate the cam....

Broke it in with three tanks @ 4600-4900 RPM. Flew it yesterday for 8min till I lost the prop. Put 8 tanks through it today with a 13x8 prop and it ate the cam. What gives? Till it stopped running, it pulled strong, had a faint smoke trail and ran 9600 RPM on the ground. I pulled the rocker cover, and everything was nice and oily, but the intake push rod had like .060-.070 gap! When I turn the motor over, I hear and feel a scratching / grinding noise in the front of the motor.

What do you think I did wrong? I ran it yesterday with a 13x6 prop, but didn't run it wot for more than 10-15 sec. I ran magnum 4 stroke fuel (18% oil syn/castor).

I was super happy with the way it pulled my Hobbistar 60 around the dry lake, till the motor got hungry.... Scoot


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Old 04-19-2010, 12:58 AM
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Default RE: My Thunder Tiger F-91 ate the cam....

More answers. I pulled the cam cover off, and the cam was bone dry. Sense the front crank bearing is sealed, does the cam get oiled from the top? Im guessing the blow-by from the valve guides run down the push rod tubes to oil the cam. Any way, Im going to make the nornal round of phone calls tomorrow to see what TT says. The sad part is, after the first few flights, I was sold on Thunder Tiger and was planing to buy two more F-.91 motors in the next couple of weeks. Scooter
Old 04-19-2010, 10:48 PM
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Default RE: My Thunder Tiger F-91 ate the cam....

I sorta feel like Im talking to myself here, but thats ok

I talked to Jonathan at Thunder Tiger (Ace Hobby) today, he said not to worry about it. I just have to send it to them and they will repair/replace it. He said they start asking questions when you warranty the same motor more than once. Cool! I also talked to the motor tech guy, and he said there is a tinny hole between the cank case and cam to oil the cam. Ether the hole is plugged, or not there. If there is no hole, they are going to send me a new motor. I asked if I could put a drop of oil down the push rod tubes once in a while as a preventive measure once in a while, they said yes. I'm very happy with the way they are handling this motor failure so far. I will keep you guys posted. Scoot
Old 04-20-2010, 10:38 AM
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Default RE: My Thunder Tiger F-91 ate the cam....

Hi!
Simply put...running it too lean!
Second ...ingested some of that dry lake...!

13x6 is way way too small prop for a .91 four stroke.
14x6 APC or RAM is what I would use ...I would also try the new Graupner "Cam-prop" and "Sonics"props.
15x4, 15x6 APC in slow flying planes like a CUB.
Old 04-20-2010, 11:35 AM
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Default RE: My Thunder Tiger F-91 ate the cam....

If the cam was dry you answered your own question. As a new engine there could have been shavings from the machining that plugged things up, it happens. 9600 is not over reving the engine. At one point Thunder Tiger made a pretty good four stroke engine but they sort of disappeared from sight for a lot of years, They may be having some quality control problems at the moment? When you get your repair done they usually will tell you what they found wrong. It does sound like you are out of tune a bit if you tossed a prop but to destroy a cam is an oil problem, it's very rare for a cam to have any problems at all. I tend to run bigger props on my engines with lower pitch and I use the 13s on .70s. I doubt the prop is a cam problem though, you were still in the rpm range. Let us know what your report says. I fly off of the El Dorado LB.
Old 04-20-2010, 03:25 PM
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Default RE: My Thunder Tiger F-91 ate the cam....

With the 13x8, I was getting 10000 max, but tuned down to 9600. I ran fine with a nice smoke trail. Right after landing, I would feel the motor to see how hot it was, and it wasn't overly "hot" at all. It ran great, crank had plenty of oil inside, but the cam was dry and the int lobe was flattened.
Old 04-20-2010, 03:28 PM
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Default RE: My Thunder Tiger F-91 ate the cam....

Hi!
Don't rely on seeing a smoke trail!
Engines are set by ear! Not by what comes out from the exhaust!
Old 04-20-2010, 10:51 PM
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Default RE: My Thunder Tiger F-91 ate the cam....


ORIGINAL: jaka

Hi!
Don't rely on seeing a smoke trail!
Engines are set by ear! Not by what comes out from the exhaust!
Cool! I will keep that in mind! Thanks for your advice!

Im tone deaf and a newbie, so Im using a tack to try and learn the "sound" a properly tuned motor. Scooter


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