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Old 06-22-2003, 10:45 PM   #1
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Default RB Engine "Sticking"

I've got an RB C12 engine that has had approx 2 gallons through it. Over the past half gallon or so, it seemed to be "sticking" when the piston would start reaching the top of the cycle. It has now gotten to the point where I can't start the engine. I was told this was due to the engine gumming up from something in the fuel (Blue Thunder).

So I took the engine apart and have polished the piston and sleeve with Mother's Aluminum Polish, and it removed all of the blue stains on them. But the engine is still "sticking".

When I have the p/s out of the engine and push the piston up the farthest I can push it is about 4.5mm from the top of the sleeve and it sticks.

Anybody have any ideas on what I can do?

Thanks
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Old 06-22-2003, 11:01 PM   #2
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time to replace your con rod.
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Old 06-23-2003, 05:07 PM   #3
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I don't really understand how the conrod could be causing this...or am I missing something?

Thanks
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Old 06-24-2003, 10:03 AM   #4
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Quote:
Originally posted by Impreza
I don't really understand how the conrod could be causing this...or am I missing something?

Thanks
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Old 06-24-2003, 11:08 AM   #5
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I have the exact same problem with my RB X12. It has about three gallons through it. After about two gallons, I noticed that the piston would get locked right before TDC and the engine would not top out anymore . It feels like an extremly tight brand new engine . I haven't tried polishing the P/S yet. I own four other Novarossi engines with about the same milage and none of them have experienced this problem.
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Old 06-24-2003, 01:45 PM   #6
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From what I can see, a streched out conrod would cause the piston to move further up in the sleeve causing it to get stuck at the top. Am I right?
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Old 06-24-2003, 02:13 PM   #7
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I dont think you have anything to worry about. My RB has been used for over 2yrs now and still locks at TDC. But there is nothing wrong with the engine. Just really good compression. If you want to ease the problem add shims to the head to make it 0.5mm clearance. (silver shim and 2 bronze shims).

I have so much compression I have to use a 1:8th scale on-road starterbox to turn the engine over. It has actually stopped the majority of the modern 1:10th scale starter boxes which were all running of 12V Gel cells.
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Old 06-24-2003, 10:43 PM   #8
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actually, it's so tight that it hinders high RPM operation. It still sticks a little even at 280 degrees.
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Old 06-24-2003, 10:46 PM   #9
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compression and friction are two very different things !!!
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Old 06-25-2003, 05:50 AM   #10
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Quote:
Originally posted by FREAKAH
actually, it's so tight that it hinders high RPM operation. It still sticks a little even at 280 degrees.
Ah, if it hinders high RPM then you will most likely need a new conrod. It sounds like your conrod has stretched. I dont have any hinderance when the engine is running.

Manticore - You are correct, there is a huge difference between compression and friction.
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Old 06-25-2003, 08:11 AM   #11
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I'm no expert but having worked on gasoline engines for over 30 years I think it's extremely unlikely that the conrod has stretched enough to cause the piston stroke to grow long enough to bind up the P/S. Put a micrometer on the rod you think has stretched and then measure a "good" rod ... I would bet $$$ the difference is in the thousandths, if any, and not the cause of the sticking piston.

It sounds just like when I've had OSRocket squish a used sleeve, it's way tight at the top of the stroke until it breaks in again. I don't see the sleeve "shrinking" after 2 gallons of fuel, at least not equally around the diameter. My best guess is that either the sleeve, the piston, or both are somehow warped (oval, no longer round) either from excessive heat or a super hard crash. Have you run a couple of tanks of very high or very low % nitro thru it lately? If you have a small dial micrometer you could check the roundness of the piston and the ID of the sleeve to be sure they're not warped. OR, any chance the rod or piston got turned 180 degrees during reassembly? Check the piston pin for being bent. If you have spares to compare with, try your piston in another sleeve, or a new piston in your sleeve and see how they compare.

Damn odd problem ... I need a "grasping at straws" smilie icon!

-John
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Old 06-25-2003, 08:31 AM   #12
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Quote:
Originally posted by FREAKAH
actually, it's so tight that it hinders high RPM operation. It still sticks a little even at 280 degrees.
I have in my expirience cases like that. Some aluminum aloys for some reason by the time of usage has grown in size. We faced this kind of problem couple times and there was only one solution for it-take lapping tool and lap piston back to the size and geometry (if you know how to do it, if you don't better to ask somebody to do for you-very delicate procedure). After couple times we had faced this kind of problem, before we made piston (after material alloy was made) we put that alloy for 6 month to the cold water to make aging threatment. Aluminium alloys before use has to go through the aging process to stabilize structure. It might happened, when the material was made for this partcular engine they didn't do aging. But this apply only in case if the rest haven't been changed-engine assembled correctly, nothing has bent etc (it easy to check-if you can see shainy spots on the piston-you got some problem with assembly or straight parts), if you see shainy ring arround the top of the piston-alloy grown up .
From my expirience I have never seen conrod got streched, so most likely it has nothing to do with conrod (my opinion).
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Old 06-25-2003, 08:34 AM   #13
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Quote:
Originally posted by Manticore
compression and friction are two very different things !!!
It is exelent post-compression and friction it is absolutly two differnet things.
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Old 06-25-2003, 09:10 AM   #14
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Quote:
Originally posted by Top Gun 777
From my expirience I have never seen conrod got streched, so most likely it has nothing to do with conrod (my opinion).
I have stretched a few conrods over the years. It mainly happens when the engine is revving at really extreme rpms. Before it gets the chance to snap the conrod starts to stretch (normally at the big end) and the piston travels further creating too much compression which can stop the engine just before the snapping point.

But as you know they dont make the conrods the same as they used to. Just not as strong and the material is not as good as the V95 alloy.
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Old 06-25-2003, 05:43 PM   #15
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Let me also say that compression and friction are two very different things!!

Chances are that your piston or sleeve is wraped.
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