"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

Close look at GP .07 Thunder Tiger

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Old 12-06-2007, 01:19 AM
  #1  
grassroots
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Default Close look at GP .07 Thunder Tiger

Just bought one of these to use on my Sig Hummer I am building.
So far I really like this engine, it may be a little heavy but it has a lot of big engine features.
Upon the first run it was very tight and hard to turn over, I thought the piston cylinder was going to scuff or seize.
I ended up pre-heating the cylinder with my covering heat gun to get it to free enough to start.
It runs smooth and the throttle respones is great.
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Old 12-06-2007, 01:56 AM
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Remby
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Default RE: Close look at GP .07 Thunder Tiger

Nice picts!

Never seen the "inards" of this one, looks to be well made. I've always been a Cox user, will do so as long as I can find parts and use them, but it is nice to see other, well made engines for the A class flyers.

I do like the look of this engine, and may try and pick up one when I can.
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Old 12-06-2007, 09:43 AM
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Default RE: Close look at GP .07 Thunder Tiger

4000686798,

Have you tried running it yet without that "Heavy" looking muffler? Just curious what the prefromance would be without it. One of the places I fly dosen't require a muffler.

chuck
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Old 12-06-2007, 10:42 AM
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Default RE: Close look at GP .07 Thunder Tiger

I don't think it's quality or swell throttling have ever been in question. If you tach it and weigh it the problem with this engine begins to surface. You'll need a light and lightly loaded airframe. If that's your style of flying, it's a decent engine. Kinda heavy compared to other engines with similar performance. Take OK Cub's for instance... no, really, take them. Take them away!


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Old 12-06-2007, 12:53 PM
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Default RE: Close look at GP .07 Thunder Tiger

let me start by saying that I don't have one of these yet but I have been considering.

From what I have read about others experiences and a couple of published reviews I think this engine has more potential that many give it credit for.

Randy Randoplh did a review and quite like it (not that you would expect anything else of a published report in MAN). However, his report of RPM versus propeller indicates (to me at least) that most users tend to over prop the engine with 7" dia props. Randy's report indicated that it seemed happier on a 6" prop - perhaps something inbetween might be better still.

Also, a button to take a Turbo or Nelson plug would probably see and increase as well.

And, like many of these sport engines (AP 09 and 15) they also seemed somewhat constricted in their breathing. If you opened them up a bit to let them breath a bit better you might just see more than a small incrimental improvement for just a little change.

I am open to donations if anyone has one lying around they are not happy with. I would certainly like to have a go to see if my thoughts have merit or whether I am just blowing in the wind as it were.

cheers, Graham
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Old 12-06-2007, 01:01 PM
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Default RE: Close look at GP .07 Thunder Tiger

We had one of these on a small plane recently.
Ran well but heavy & weak output.
Bob G
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Old 12-06-2007, 02:43 PM
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Default RE: Close look at GP .07 Thunder Tiger

Hey 4000-
Do you see any mis-match between the transfer ports in the case and the openings
in the sleeve? An earlier post suggested that a little tweaking to make the ports
line up better resulted in much better RPM's
Dave
See post #15 by Cat 1:
http://www.rcuniverse.com/forum/m_96...anchor/tm.htm#
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Old 12-06-2007, 08:05 PM
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Default RE: Close look at GP .07 Thunder Tiger

Right now I am getting 16,200-16,500 with a 6x3 prop with 15% nitro.

Is this a good RPM?

I don't have much to compare it to for an engine this size?

I did try it without the muffler, it ran with the needle backed way out, but would probably need the case tapped to pressurize the tank. I didn't tach it with the muffler off because the sun was getting low and my tach would not work in the low light.

When I had the engine apart I didn't check the transfer ports to see if there was any miss-match. I wanted to try the stock out of the box set up first anyways.
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Old 12-06-2007, 09:41 PM
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Default RE: Close look at GP .07 Thunder Tiger

Yeah, those are pretty good RPM numbers... for an .049. Unfortunately, despite the fact that it is probably the best running engine under .10 that I have seen, it just doesn't have much power. I had one of these for a while but sold it. The engine ran beautifully but it was only suitable for .049 applications where you will have to add nose weight otherwise.

Brian
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Old 12-06-2007, 09:45 PM
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Default RE: Close look at GP .07 Thunder Tiger

I wonder if DDD could be induced to produce a diesel head for the TT .07? That would be a combination I'd like to try.
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Old 12-06-2007, 09:49 PM
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Default RE: Close look at GP .07 Thunder Tiger

Would this engine respond to high nitro content to produce more revs? Also as has been pointed out in another thread, revs aren't much good without torque. Will this plane swing a seven incher with any authority? I have my doubts for sure but I just hade to ask.
???

Robert
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Old 12-06-2007, 10:37 PM
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Default RE: Close look at GP .07 Thunder Tiger

I can see where this little guy could be made to turn well with some tender cutting here and there, the only thing that really turns me off about it is that carb being intrigal with the case.
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Old 12-06-2007, 11:18 PM
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grassroots
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Default RE: Close look at GP .07 Thunder Tiger

I have some wildcat 35% 1/2A.

I had planed on trying it on this engine after some break in.

Do I need to do anything to the engine before trying this higher nitro fuel?

When using high nitro do you want to raise or lower compression?
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Old 12-07-2007, 01:09 AM
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Default RE: Close look at GP .07 Thunder Tiger


ORIGINAL: 4000686798


When using high nitro do you want to raise or lower compression?
Lower the compression a tad...

When trying out new fuel, I will put 3 extra head gaskets in and then remove one at a time, until the RPMs don’t increase, monitoring with a tachometer.
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Old 12-07-2007, 08:39 AM
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Default RE: Close look at GP .07 Thunder Tiger

I can see where this little guy could be made to turn well with some tender cutting here and there, the only thing that really turns me off about it is that carb being intrigal with the case.
I was thinking the exact same thing. I have often thought about getting one of these and seeing what could be done.

Anyone know if it is true hardchrome plated cylinder? it looks a little yellow and nickel like in the photos- not that thats so bad.

J.M
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Old 12-07-2007, 04:14 PM
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Default RE: Close look at GP .07 Thunder Tiger

Okay today was a frustrating day!

I was excited about this engine but............

Today it would not hold the 16,500 I got yesterday.

It would get about 15,000-15,500 with a good throttle transition etc.

When I could get 16,000-16,500 it would hold it only for a few seconds then drop off like it was going to sag out from being to lean.

So I brought the 35% nitro to try out, and no change in performance, it just ran hotter so I discontinued using it. I don't have any extra head shims to add maybe that make a difference? I don't know?

Maybe I have done something wrong but I have had lots of engines with good results, just nothing this small.

The quality looks good both in materials and machine work, but something just doesn't seam right and I can't put my finger on it yet.
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Old 12-07-2007, 06:19 PM
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Default RE: Close look at GP .07 Thunder Tiger


ORIGINAL: lildiesel

I wonder if DDD could be induced to produce a diesel head for the TT .07? That would be a combination I'd like to try.
Bob Davis did make a head for this motor a few years ago. Best to check with him as to availability, he just might have some.
Dennis
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Old 12-07-2007, 08:09 PM
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Default RE: Close look at GP .07 Thunder Tiger


ORIGINAL: 4000686798

So I brought the 35% nitro to try out, and no change in performance, it just ran hotter so I discontinued using it. I don't have any extra head shims to add maybe that make a difference? I don't know?
What did you use to measure the tempreture? Did you use the same needle setting as the low nitro fuel?
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Old 12-07-2007, 10:52 PM
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Default RE: Close look at GP .07 Thunder Tiger

Luna,

It just felt hotter to the touch, I was not accurate enough to tell the difference between needle settings. I did back the needle out a turn before starting the engine using the 35% then advanced it in from there to get back to the top end.

By the way I have noticed from the begining that the clearence betwen the case bushing and crank seams more than other bushed engines I have had. You can actually displace the crank from side to side. Also the clearance between the prop hub and case is more than I would like about 0.10-.015 when you pull on the crank. When running you can see the crank pull out at high speed then cycle back at low speed. Another steel washer would cure that though.

I called Ace Hobbies to talk about the crank side to side clearance, almost right off the bat the tech said maybe your propeller or spinner is off balance and that wore the bushing out. I reminded him that at that time it has less than 4 tanks of fuel through it. Plus it comes with it's own spinner.

I just felt I was already getting set up to eat the cost of a possible factory defect.

I think this little engine has potential, just not out of the box potential, which is a shame, because from what I have read it has already fallen short by most accounts, and will probably be discontinued due to decreased sales.

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Old 12-08-2007, 12:49 AM
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Default RE: Close look at GP .07 Thunder Tiger

If you can wobble the crank and come up with any axial play, the engine will lose crankcase pressure out the front end and run weakly. I've got a coffee can full of engines like that waiting to be rebushed. A 10 digit inmate number! What are you in for?
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Old 12-09-2007, 01:34 PM
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Default RE: Close look at GP .07 Thunder Tiger

OK Y'all, I ran across some good info for the TT .07 here:
http://community-2.webtv.net/RICHARD...EFEATEDFORMER/

Quote:
"So far the "magic formula" for the .07 seems to be between an APC 5.7x3 at 21k plus rpm and a Tornado Magnum 5x3 (or equivalent load) at 25k rpm."

Good info available here and I am sure this fellow will be glad to communicate with others.

Robert
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Old 12-09-2007, 07:54 PM
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Default RE: Close look at GP .07 Thunder Tiger

Making the clearance between case and crank excessive, is a way to get a few extra hundred RPM out of an engine. A SLOPPY way because you get a lot of raw fuel out the front end. The Wasp .06 is done this way. Too much slop though, can put you in reverse and lose you some power. In my opinion, this is not a factory defect but has been done deliberately to get a bit more power.

A real shame because both engines are brass or bronze bushed. Fit correctly, they'd last a long time and not end up like CP's collection. The Wasp somehow manages to avoid any problems this sloppy clearance might give you. However, your erratic performance with the GP might be on account of this.

But I must say, I'm impressed with the connecting rod. If it's a drop in replacement for the Norvel .074 rod, that would revive a few of that engine that I own. I can make rods alright, but after the first three or four, the novelty wears off and then it's a chore.

Would anyone know what the dimensions of this rod might be??



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Old 12-09-2007, 08:15 PM
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Default RE: Close look at GP .07 Thunder Tiger


ORIGINAL: fireman7875

Yeah, those are pretty good RPM numbers... for an .049. Unfortunately, despite the fact that it is probably the best running engine under .10 that I have seen, it just doesn't have much power. I had one of these for a while but sold it. The engine ran beautifully but it was only suitable for .049 applications where you will have to add nose weight otherwise.

Brian

Norvel .074,,, lighter by far and far more powerful. There's one on #Bay right now, last I saw. Plug's a problem but even a drilled and tapped insert will give you more than the stock GP.
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Old 12-09-2007, 08:22 PM
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Default RE: Close look at GP .07 Thunder Tiger

Back in the 70's, Wally Booth proved that you could make anything run if you throw enough time, energy and moolah at it. He won NHRA Pro Stock with a Rambler.
If you take a strong running TD with a 5x3 and JB Weld about 4 or 5 lug nuts to it, then you'll come away with about the same thing as a TT .07.
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Old 12-09-2007, 09:25 PM
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Default RE: Close look at GP .07 Thunder Tiger

I could see a tight bushing causing drag on the crank, but after some runing in it should loosen up and give a good seal.

I think the erratic operation is air leaking around the shaft because of the excesive side to side play, and since the shaft also moves forward on HI-revs, back on LOW-revs that would also contribute to the amount of air getting in between these two settings.

When I ran it rich at first and the transition was rough from HI-LOW there was alot of vibration involved and the spiner would become a blur that's when I started really looking into the play in the crankshaft.

At first I was hoping nothing was wrong because it's a brand new toy going bad, but my gut feeling is that there is something wrong.

Either all the GP 07 are this way or this one slipped through and I just happend to be the lucky winner of the Friday 5:00pm lemon engine.

No matter what it's still going to be heavy when considering it's only able to do 16,500 with a 6x3 prop!

Correct me if I am wrong but the little AP WASP can do that, and it's much smaller and lighter.

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