TT GP 07 "Shudder" (Full Version)

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

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[:D]) 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



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

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.



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

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.



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

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



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

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.



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

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.




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

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.



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

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.



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

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)



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

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?[:D] 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



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

That 10% should be OK, especially with a standard plug.



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

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.



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

I would think that the plug that came with the engine should be right for it.



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

Any engine as heavy as this one needs to be spinning a 7x3 to justify its' existence.



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

Then that's the way it will be. I will try and procure said 7x3 and give it a try.



Sport_Pilot -> RE: TT GP 07 "Shudder" (5/13/2008 12:59:26 PM)


quote:

ORIGINAL: tipstall 131

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.



The A3 should be good for the 10% nitro. That is a very hot plug, and it may be too hot for higher nitro such as 25% which is probably the most common percentage for small engines.



tipstall 131 -> RE: TT GP 07 "Shudder" (5/15/2008 9:28:24 AM)

Mr. Cox, the turbo head that you are using, is it still the same as the origanal as the same head insert in that it uses the screw on lock ring that keeps it down or is it a unit on its own thats srews onto the cylinder by itself? I would like to try and have one machined to see what the difference is to the stock head. Also, are you using the stock muffler or have you made a replacement? My idea is to make a new muffler that is not as heave as the stock one to see if I can shake some weight off. My plan is to use the 07 on an ACE simple series P51 Mustang. The recomended flying weight of the P51 is 18oz but I think the manufacturer determined this using a cox .049. The problem with the 07 in this plane will be the added weight from the engine and also that another servo has to be acounted for to run the throttle. Any opinions?



Mr Cox -> RE: TT GP 07 "Shudder" (5/15/2008 11:21:28 AM)

The head I made is just an aluminium "disk" holding the turbo plug (same principle as the original head), and the original clamp is holding it in place.
Japanman and Andy has shown how to make the fitting for the turbo plug using simple tools.

I've made two heads and the one that worked best is simply a copy of the original head with a turbo plug instead of the traditional plug.
Using that I didn't even have to play around with the compression, there was just an instant gain of about 1400 rpms.

I have also thought of making a lightweight muffler. The weight of the engine itself is actually very close to the weight of a Norvel .074, so with a turbo head and custom muffler it should be very competitive it terms of weight vs power.



tipstall 131 -> RE: TT GP 07 "Shudder" (5/15/2008 11:53:00 AM)

That is my theory as well. Is there a thread on how andy and japanman made those fittings? I have weighed the engine alone and that comes in at about 55 grams without the muffler. If one was to make the muffler from extruded aluminium tubing with small and light machined endcaps one could make a muffler for about half the weight of the original. There is a lot of weight stashed in that manifold part of the muffler that could potentially be shed. I will try to come up with a design and list of the materials needed to make one. Hopefully I could get this done by the weekend. I know this is a stupid wuestion but I am still a noob in 1/2A but what is the phisical difference between a standard plug and a turbo plug. It is the first time that I have heard about it and some people have explained it vaguely but I am still not sure. You stated that the seal of the plug never protrudes into the combustion chamber. If this is the onlu difference then surely a head machined so that the plug threads don't protrude would do the same? I say this because I don't know if one can even find turbo plugs in SA



digital_trucker -> RE: TT GP 07 "Shudder" (5/15/2008 12:07:56 PM)

A regular plug is threaded all the way from the bottom of the HEX to the end of the plug. It seals at the TOP of the plug with a washer. A turbo plug has a taper at the bottom below the threads, and seals at the bottom of the plug. They're also different thread sizes, they're not interchangeable.

Standard plug: http://www2.gpmd.com/image/o/osmg2693.jpg

Turbo plug: http://www2.gpmd.com/image/o/osmg2695.jpg


As an aside, according to Tower the TT07 calls for a 6x3 or a 6x4. I also note that you can get one for $50 at thundertiger4u.com (but I've never ordered from them to know their service), whereas Tower wants $62.



Mr Cox -> RE: TT GP 07 "Shudder" (5/15/2008 12:55:04 PM)

Here is Andy's thread on how to make the turbo plug: http://www.rcuniverse.com/forum/m_4533758/tm.htm

Finding the right tool for making the taper is the tricky part. I bought a few Philips bits and with careful sharpening it would give the desired shape.

Out of the box performance is probably best with 6x3 or 6x4 but after modifications it will swing a 7x3 happily too (while the 6x3 then felt too small doing near 19000 rpms [8D]). I will try to get some numbers from mine on a 7x3 this weekend.




Falco250 -> RE: TT GP 07 "Shudder" (5/15/2008 1:53:16 PM)

Here are a few more how to articles on Turbo and Nelson (turbo like) plugs:

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=272831&mesg_id=272831&listing_type=search

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=273582&mesg_id=273582&listing_type=search

Luciano ///



tipstall 131 -> RE: TT GP 07 "Shudder" (5/15/2008 3:01:28 PM)

Thanks guys for all the info, this is really a big help. Okay here's the deal. I have never own a cox or norvel engine thus i don't have an old glow button lying around. What I will do however is try to get turbo plugs and then have a button machined at the local engineering shop. Hopefully this won't be too costly and will turn out a success.



combatpigg -> RE: TT GP 07 "Shudder" (5/15/2008 4:39:34 PM)

The problem around here is getting past the shop mimimum charge. It helps to find a shop where someone there enjoys model engines.



digital_trucker -> RE: TT GP 07 "Shudder" (5/15/2008 5:06:48 PM)

Try to find someone that has their own machine shop that still does piece work, a mom-and-pop sort of thing.



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