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Old 06-18-2002, 11:30 AM   #1
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Red face Thunder tiger pro 15 motor HELP

Can anyone help I have a thunder tiger pro 15 motor, I've removed the pull start assembly i.e backplate, fly weight & drive shaft & replaced it with an alloy backplate I manufactured.
Ran the car at the club unfortunately the con rod/big end has snapped, my question is does the backplate/plug act as a retaining device as the con rod seems to have moved towards the back of the crank case, twisted and broken the big end. If I'm correct i'll manufacrture a new backplate with a deeper plug.
one other question the piston has a hole/port drilled in it's skirt when I first dissmantled the motor the hole was facing the boost port which doesn't seem to have been machined into the alloy case.
should this hole face the boost port or the exhaust port.

Last edited by Raw40; 06-18-2002 at 12:55 PM.
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Old 06-18-2002, 01:51 PM   #2
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Well I will take a stab at this. I do believe that the back plate is used to hold the con rod in place. Did you shave off the pull start pin on the con rod pilot shaft. If you didnt do that then more than likely that is the reason it broke. The hole/port on the piston skirt is for clearance over the crank. You want to put it back in the way it came out. Hope this helps alittle.
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Old 06-18-2002, 06:09 PM   #3
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Thanks for the info ballpy,I've already made a longer backplate pic attached. Still not quite sure about the hole/port in piston i've attached a photo for you to have a look at it.
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File Type: jpg piston6.jpg (56.5 KB, 680 views)
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Old 06-18-2002, 06:15 PM   #4
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here's the backplate, one on the left is the original that I think caused the problem.
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File Type: jpg piston7.jpg (47.6 KB, 528 views)

Last edited by Raw40; 06-18-2002 at 06:19 PM.
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Old 06-19-2002, 08:01 AM   #5
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I have never seen that before. To tell you the truth I would get rid of the Thunder Tiger, but since you do already have it you might as well use it. But I will talk to some guys at my LHS and see what they say. I do some work for them from time to time and they are pretty smart guys.
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Old 06-19-2002, 10:38 AM   #6
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thanks again Ballpy, have just ordered a new MTX-2 for my son so I'm (dad) has the hand me down ( thunder tiger).
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Old 06-19-2002, 12:01 PM   #7
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The TTR Pro .15 is basically a O.S. CV .15 copy, except it has a chrome sleeve (which is better). You should just get a backplate for any O.S. Cv for it ($4.95) . The reason it broke is that the rod DOES run against the backplate to keep it in place as the crank "walks" back and forth and with the first backplate it would run off the pin and break! You have to grind the pullstart pin off even then install a regular backplate. The backplate also serves to "stuff" the crankcase for better velocity of the air/fuel mixture.
The hole in the piston is a boost port that feeds the middle port in the sleeve since there is no case port feeding it, if you face it to the exhaust it will vent all pressure in the case and lean the engine or it won't run at all.
Tip: always mark the rod with a small permanent marker dot on the side facing you before removing from the engine so you know how to re-install it. Also never mess with an engine if you don't know what your doing unless you don't care if it is ruined. Always ask the help of a knowledgable person at the hobby store or at your local track.
Hope this helps!
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Old 06-19-2002, 01:07 PM   #8
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Thanks ronin, I'll definatley ask next time before carrying out any mods
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