TT GP 07 "Shudder"  
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TT GP 07 "Shudder" - 5/12/2008 11:27:18 AM   
tipstall 131



Posts: 23
Joined: 1/27/2008
From: Limpopo, SOUTH AFRICA
Status: offline 		I have a couple of questions regarding the Thunder Tiger GP 07. I have recently aquired a used GP 07 from a friend. Now I know that this is not the best glow engine ever made and I know that most of the 1/2A guys out there are using Cox and the like but I got the thing for a very reasonable price (100 Rand= 13US$). There is also another thread on the performance of the 07 but this did not help very much.

I ran the engine as stock standard and it had needle valve trouble becuase of the cast-in carburator setup. I then proceeded to make e remote needle valve for it using the original needle valve as a base. I did this because when the engine ran a while the heat from the crank case would male the NV expand a lot, leaning out the mixture. When this happend the engine would gain and lose rpm in an oscillating fashion. The remote NV stopped this from happening as the fuel line acted as a thermal insulator. Now the actula problem is this:

Question 1: The 07 runs very well after the upgrade and I don't know what the rpm's are becuase I don't own a tach( student budget ) however it sounds pretty good and throttle transition and idle is very good. However, when the ingine is running at full tilt, there is a strange shuddering noise from the crankcase. It is quite loud and I am afraid it might ruin the engine. I dont know whether the prop might be out of balance although i did check it on a balancer and I could not see any balance problems. Could it be that the crank to case tolerance is too big? It is running on a Master Airscrew 6x3 at the moment.

Question 2: If the crank to crankcase tolerance is too big how does one go about replacing the bushes? I only own other IC engines that run on ball bearings.

Any help would greatly be appreciated.

Cheers Marius

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RE: TT GP 07 "Shudder" - 5/12/2008 12:21:16 PM   
Mr Cox



Posts: 280
Joined: 7/20/2007
From: Gothenburg, SWEDEN
Status: offline 		It is probably just the crankshaft moving forward and backwards in the case. Check the play, there should be a washer between the propdriver and crank case. All bushed engines will have this ,more or less, at certain rpms. On my TT07 it happend more at intermediate revs and it went away with a larger prop (i.e. 7x3) which then seems to pull enough to keep the crank in a forward position.

There is along thread on this engine where I have described a few fairly simple tuning tricks that will improve the performance.

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RE: TT GP 07 "Shudder" - 5/12/2008 12:41:39 PM   
digital_trucker



Posts: 1145
Joined: 2/4/2006
From: Dorr, MI, USA
Status: offline 		A 6x3 seems like an awful small prop for this engine (bear in mind I don't own one). I would think a 7x3 or 7x4 would make the engine much happier. Judging by the reviews, it's not a revver to begin with.

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RE: TT GP 07 "Shudder" - 5/12/2008 1:49:20 PM   
tipstall 131



Posts: 23
Joined: 1/27/2008
From: Limpopo, SOUTH AFRICA
Status: offline 		Mr Cox, the engine as you said has some forward and backward play but the drive washer is there and is still fine. The thing is, when the engine is running at half throttle, everything is okay. I do have a APC 6x3 lying around and will give that a try. At present I don't have any 7x3's on hand and they are kinda hard to aquire as I am about 200km away from the nearest decent hobby shop. There is however a small bit of play from side to side on the crankshaft. I reckon it's aboout a 10th of a mm. Would using an electric starter agravate this? Could you also please include a link to your thread on this engine?

Thanks a lot,
Marius

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RE: TT GP 07 "Shudder" - 5/12/2008 2:17:22 PM   
Sport_Pilot



Posts: 7450
Joined: 1/21/2002
From: Acworth, GA, USA
Status: online 		What fuel are you using? The sound could be light detonation from too much nitro, or too hot of a plug. What RPM's are you hitting? Sometimes when an engine overrevs it makes a noise from various parts flexing.

< Message edited by Sport_Pilot -- 5/13/2008 12:47:27 PM >

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RE: TT GP 07 "Shudder" - 5/12/2008 2:26:57 PM   
Mr Cox



Posts: 280
Joined: 7/20/2007
From: Gothenburg, SWEDEN
Status: offline 		Ok, the thread is here: http://www.rcuniverse.com/forum/m_6720213/mpage_11/key_/tm.htm

Some data and modifications (from that thread):

Ok, we finally had some sun here today and I have some tachreadings. Used a graupner 6x3 and a less than 15% nitro (lowered bacause I added a bit of extra castor to a 15% blend).

Original head and OS#8 plug: 17400 rpm at max with a very nice idle at 3000 (min around 2800), very smooth running.

Home-made turbo head and OS P7 plug: 18700 rpm at max with good idle at around 3200 (min appr. 3000), a destinctive change in note compared to the standard head and a nice "scream" to it.

For the turbo head I just tried to copy the original head dimension but with a turbo fitting using the guidlines by Japanman and Andy. I used a center drill for the most part and only finish the vary last bit using a sharpened PH#3 bit. To mee it seems like the center drill doesn't quite have the angle to it, while my PH#3 bit wasn't good enough to really cut away material it only seemed to scrub material away...

I have made a few other alterations but nothing major really:

- sealed the back cover with teflon tape
- made a growe for the o-ring in the muffler
- deburred the exaust to 4 mm
- dremeled out the throttle barrel to an more even diameter of about 3.5 mm. The original tapers from about 3.5 to3.2, and I think this restricts the intake as well as rendering the air bleed screw useless.


One odd thing remains to be fixed. The pin that aligns the liner is the hollow type (!) and this of course leaks... I will try to fit a solid pin there instead.
I haven't touched the transfer channels (yet) but there is probably a bit more to gain there, I'm not sure that I will nead that in a sports engine though.


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RE: TT GP 07 "Shudder" - 5/12/2008 2:53:42 PM   
tipstall 131



Posts: 23
Joined: 1/27/2008
From: Limpopo, SOUTH AFRICA
Status: offline 		At the moment I am using coolpower 10% nitro fuel. I am using this becuase I had for my bigger engines. TT recomends anything up from 5% nitro so I figured I would be safe with 10% nitro. I don't own a tacho so there is no telling what the revs are but i think it's for from over revving as I am using the stock muffler. Could you please inform me on what a turbo plug is better yet a pic or diagram. This is my first 1/2A project and I am not familiar with these items.

Would using a bigger prop be better? What is the stroke on a Norvel 074? If the stroke on the GP 07 is longer, I am thinking bigger props-less revs. Longer stroke equals more torque, not so? I think my next "investment" will be a tacho to get a better idea of whats going on on the engine.

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RE: TT GP 07 "Shudder" - 5/12/2008 6:23:31 PM   
digital_trucker



Posts: 1145
Joined: 2/4/2006
From: Dorr, MI, USA
Status: offline 		Thou shalt use fuel containing at least a 50/50 mix of castor and synthetic lest thy engine eat itself and return to the dust from whence it came. Seriously, these little devils like to have some castor, the RPM and so forth ya know.

I personally use Sig 1/2A fuel, which is 25% nitro and 50/50 castor/klotz oil. Your engine will thank you for it.

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RE: TT GP 07 "Shudder" - 5/12/2008 6:46:53 PM   
Mr Cox



Posts: 280
Joined: 7/20/2007
From: Gothenburg, SWEDEN
Status: offline 		Turbo (and Nelson plugs, who might have been "first" ) plugs have a different design for the seal. The threads of the plug are never in contact with the combustion chamber and this give a large boost in the power for these tiny engines. You would have to make a new head to fit a turbo plug. Attached image shows the regular head on the left and a turbo head with plug on the right. This is only to improve the power once you have the engine running correctly.

If the crank is moving backwards and forwards you can see it while the engine is running. But if the problem is at top rev then it is probably something else. I would check the balance of the prop again, and make sure you use a balance that is sencitive enough for these small props, also it is very important that the prop is centered on the prop axis or alse the balancing is pointless. (sorry if I'm stating obvious things here but it is not that easy to know the level of experience of other members)

Attachments
Click to see fullsize image.
Click for fullsize


< Message edited by Mr Cox -- 5/12/2008 6:47:58 PM >

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RE: TT GP 07 "Shudder" - 5/12/2008 8:27:35 PM   
tipstall 131



Posts: 23
Joined: 1/27/2008
From: Limpopo, SOUTH AFRICA
Status: offline 		Thanks for the help so far guys. I have thought about it and this is what I came up with. The fuel I am using is pure synthetic which as digital trucker stated is wrong. I have an un-opened can of Beetle juice(local brand I think) which contains 50/50 castor/Klotz blend. Sadly this is only 10% Nitro but I think it is a start until I can get back to civilization to get the required 25 or 30%. Number 2 I came up with is the fact that the prop I am using is either out balance or out of alignment and I will refrain from using it again. This I think is a good start. I have not had time to tinker with it again but will keep you guys in the loop. Meanwhile Mr. Cox, what are the dimensions of this wonderful power giving device called a turbo head or is it patent pending? Seriously though I would like to get my hands on one to see what it does for this little machine.

Thanks again for your help you guys. It's good to know there are people us youngsters can turn to for help.
Cheers,
Marius

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RE: TT GP 07 "Shudder" - 5/12/2008 8:44:59 PM   
digital_trucker



Posts: 1145
Joined: 2/4/2006
From: Dorr, MI, USA
Status: offline 		That 10% should be OK, especially with a standard plug.

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RE: TT GP 07 "Shudder" - 5/12/2008 8:50:33 PM   
tipstall 131



Posts: 23
Joined: 1/27/2008
From: Limpopo, SOUTH AFRICA
Status: offline 		I sure hope so, the plug I am using is a OS A3 and I got it with this engine. Will this be okay? the only other plugs I have at the moment are OS#8's.

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RE: TT GP 07 "Shudder" - 5/13/2008 3:14:52 AM   
digital_trucker



Posts: 1145
Joined: 2/4/2006
From: Dorr, MI, USA
Status: offline 		I would think that the plug that came with the engine should be right for it.

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RE: TT GP 07 "Shudder" - 5/13/2008 3:46:39 AM   
combatpigg



Posts: 9255
Joined: 11/22/2003
From: arlington, WA, USA
Status: offline 		Any engine as heavy as this one needs to be spinning a 7x3 to justify its' existence.

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RE: TT GP 07 "Shudder" - 5/13/2008 6:45:02 AM   
tipstall 131



Posts: 23
Joined: 1/27/2008
From: Limpopo, SOUTH AFRICA
Status: offline 		Then that's the way it will be. I will try and procure said 7x3 and give it a try.

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