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Post  jbanes1961 Mon Nov 18, 2019 1:27 pm

Hi all, how do you know if it is time to reset piston/rod assembly?


Last edited by jbanes1961 on Thu Nov 21, 2019 12:34 am; edited 1 time in total
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Post  balogh Mon Nov 18, 2019 1:47 pm

In my subjective judgement - having no tools for exact measurements - the good fit allows just a hardly sensible play when you pull on the rod. It means that the free play of the prop at the top dead center without the piston moving is maybe plus minus 5..10 degree. Loosen the glow head to allow the piston to move up without compression till the TDC. Torque the head. Try swinging the prop around the TDC with the piston staying at top. The free swing of the prop will tell you if the connection is too loose
Not exact measurement because the play of the crankpin in the lower rod end is also included.
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Post  getback Tue Nov 19, 2019 6:27 am

The way i do it is w/o prop on , put piston at tdc / comp. stroke look through exh. port for piston movement and turn C/S over slightly to feel for movement before the piston actually moves . Correct set is .002-.003 " It's easier with engine tore down though >> Beware there are 3 piece pistons out there on older engines that are NOT resettable << You can look inside the ball / piston cup and if you see a cap clip retainer that is a 3 piece . Old Bugger
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Post  jbanes1961 Wed Nov 20, 2019 12:42 pm

Ok guys, thanks for responses..is there a physical indicator that it's time for a reset. Does the engine run poorly?
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Post  balogh Wed Nov 20, 2019 12:58 pm

As the gap increases the engine may start running erratically because exhaust and charge timing may go off. But I would not wait till that symptom because the engine may end up with a damaged balljoint cap.
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Post  getback Wed Nov 20, 2019 3:16 pm

Do you have one running poorly ? And Yes as Andras said timing will bee affected:cox logo:
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Post  Mlemble Wed Nov 20, 2019 6:03 pm

May be a closely related quest: I just acquired a used golden bee 049. There is play in the drive shaft (in/out not side play) it does run, but should I be concerned?
The rest of the engines I've acquired, new and used, do not have this play.
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Post  balogh Wed Nov 20, 2019 6:54 pm

Some axial play like 0.01"..0.015" is there even in new engines to prevent constant friction between the prop drive plate and the crankcase. In long pusher mode or with aggressive use of electric starter the gap may grow until the crankpin touches the backplate. Then a thin steel or bronze washer of proper thickness put between the drive plate and the crankcase may still help keep the engine in service.


Last edited by balogh on Thu Nov 21, 2019 12:30 am; edited 1 time in total
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Post  jbanes1961 Thu Nov 21, 2019 12:11 am

Ok thanks again for the responses, no, I don't have a poorly running engine. But, I do intend on getting into this hobby more. So I'm just trying to gather as much information as possible. I know in the future, in going to be disassembling these engines (I've already purchased most of the tools). I'm also looking at possible symptoms of trouble with these engines, besides not starting. So when something goes wrong, I will know what to look for and how to fix it. Like the boy scouts say...be prepared, and that's how I roll....
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Post  getback Thu Nov 21, 2019 7:37 pm

Cool , i have several sets of reset tool but i hear your good to go , nothing wrong with beeing prepared Very Happy
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