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Broke on break in - 5/22/2007 6:31 PM   
jdoug


 

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Status: offline 		Do they make thrust bearings for Nitro boats? I just started breaking in my WT .15 (aircooled OS) when I heard a clicking sound coming from engine after the first tank. It would not start after that. It looks like the crankshaft was being pushed back and the connecting rod started to bind. Now, I think the connecting rod's bushings are wore out as there is a spot at TDC where the con-rod moves but the piston doesn't.

How can I get the force from the prop to the strut instead of the crankshaft of the engine while using a flex collet?

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RE: Broke on break in - 5/22/2007 6:40 PM   
330T


 

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Status: offline 		on all of my boats the prop shaft has a drive dog on the boat end of it that rides on a thrust washer that transfers thrust to the strut.

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RE: Broke on break in - 5/22/2007 7:14 PM   
jdoug


 

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Status: offline 		I do have thrust washers. On my gas boat the flex cable is square on the collet end so it is not clamped. This allows for the flex cable to tighten and become shorter if need be when running. My nitro boat has a collet so I'm under the impression that for this setup I need a gap at the strut to allow the cable to tighten. This gap makes it so the prop is not pushing on the strut but rather on the crankshaft which I don't want.

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RE: Broke on break in - 5/22/2007 7:19 PM   
piper_chuck



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Status: offline 		None of my boats run with thrust bearings between the drive dog and the strut and I have not had any such problem. In fact, if the drive dog is right up against the strut, or a thrust bearing, the shortening of the shaft when it runs can pull on the engine shaft, leading to damage to the bearings and even engine crankcase.

Moving on the the problem described, many engines have a small bit of play when the piston is at TDC. This is entirely normal. Damage to the conrod bushing is more likely to come from over-revving than anything going on at the prop end.

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RE: Broke on break in - 5/22/2007 7:29 PM   
Square Nozzle


 

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Status: offline 		"Breaking In" is the key phrase in this problem. Whenever I read that someone was breaking in their boat engine and they hear funny sounds from inside the engine, I can almost be sure that the "breakin" caused the problem.

Ditto on the TDC click and the thrust washer. Always leave a gap between the drive dog and strut so when the shaft winds up and shortens it doesn't damage the engine bearings.

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RE: Broke on break in - 5/22/2007 7:44 PM   
jdoug


 

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Status: offline 		I guess it looks like I'm fine running the way I was. I was breaking in the engine, but it was a piston/sleeve rebuild on a cheap $90 OS. I suppose I should of replaced the conrod too. Oh well, now it gets a new OS .18.

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RE: Broke on break in - 5/22/2007 8:26 PM   
Square Nozzle


 

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Status: offline 		Sounds like something I learned about changing rings in a car engine without changing the rod bearings. The added drag from the new rings causes the already worn rod bearings to accelerate wear till they fail also.

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RE: Broke on break in - 5/22/2007 10:09 PM   
jdoug


 

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From: STARID, USA
Status: offline 		Yeah, the added drag of the new parts and way more compression took out the worn in connecting rod pretty quick.

So, pushing on the crankshaft with the prop will not hurt anything on the engine? Just want to double check before it gets a new engine.

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