Author Topic: Re-use rods  (Read 9238 times)

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Offline NH Mowster

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Re-use rods
« on: November 28, 2012, 07:39:02 PM »
I have a 42 series 18 hp oppy that I'm rebuilding and it has some wear on the cylinders so I'm going to bore it .020 over. Now I mic'd the crank and its still at factory specs and so is the rods. What would the disadvantage of re using the old rods? I've seen people post don't reuse but don't give a good reason. I will be turning this engine about 4500K and may hit 5k from time to time and I will be running a billet flywheel. Also I'm trying to find Don's video for the oppy but can only find engines 101 or is that one for the oppy? It says for 8hp on up.


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Offline carolinablue

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Re: Re-use rods
« Reply #1 on: November 28, 2012, 08:11:46 PM »
I dont know much about oppys but if your spending the money for boring and alum flywheel i would spend the extra for a good set of billet rods. Rooster the guy you need to talk too.
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Offline NH Mowster

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Re: Re-use rods
« Reply #2 on: November 28, 2012, 08:39:44 PM »
Yeah I know if I'm spending the money get them but if I don't have to spend $120 for new rods I would be a little more happier and so would the misses  :rofl:
The $350 flywheel and the $100 pistons already put a big dent in my wallet and I haven't got a rebuild kit yet or other parts. So if the rods will last me till next season that would help. The rods look in good shape. It was a grass cutter before I got it and the previous owner took good care of it and was spotless. I was really excited to get this motor
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Offline FlatheadPuller

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Re: Re-use rods
« Reply #3 on: November 28, 2012, 09:37:53 PM »
The stock rods are fine depending on wich ones you have. The dull colored 40 rods are the best. Put the 40 rods on the 42 crank and cut the top of piston off to get zero deck hieght. Lightens the rotating assembly. Just make  your oil clearance is correct and look thru heymow for rod mods to make them live.
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Offline cycloneracer

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Re: Re-use rods
« Reply #4 on: November 28, 2012, 11:38:35 PM »
If you have extra blocks and cams run the used rods.  That way when one blows you only have to buy pistons again.  


When a rod blows it tears up a bunch of stuff!  
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Offline Rooster

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Re: Re-use rods
« Reply #5 on: November 29, 2012, 12:45:14 AM »
Lots of oppy's out there running stock rods. keep an eye on them.
BTW…everyone will say "Ask Rooster"…
When Rooster learned, He asked Flathead Puller ;)
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Offline NH Mowster

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Re: Re-use rods
« Reply #6 on: November 29, 2012, 05:57:53 AM »
It has 42 rods in it now but I do have a 40 engine that I ran last year so I can reuse those rods. How much of a pop up will that leave me that I have to cut off the new pistons? What's the best way to cut them down? I'm a machinist so I have an array of machines to choose from. Hey Rooster, everybody has to learn from somebody lol thanks for the advice guys
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Offline garrywarber

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Re: Re-use rods
« Reply #7 on: November 29, 2012, 06:53:52 AM »
Also I'm trying to find Don's video for the oppy but can only find engines 101 or is that one for the oppy? It says for 8hp on up.

Go to the G-Team site if it isn't there in the eBay G-team store.  Same price in the end.  Mine states "Motor 101 opposed" on the dvd case...
Garry
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Offline NH Mowster

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Re: Re-use rods
« Reply #8 on: November 29, 2012, 07:26:31 AM »
OK thanks Gary. By the way if you use 40 rods and mill the piston would all that change the displacement of the engine? If so would it be after all that?
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Offline Jeff McKelroy

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Re: Re-use rods
« Reply #9 on: November 29, 2012, 10:01:48 AM »
Lots of oppy's out there running stock rods. keep an eye on them.

 ;)

Offline willenglish

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Re: Re-use rods
« Reply #10 on: November 29, 2012, 10:13:27 AM »
It would not change the displacement of the engine. Only bore or stroke changes would affect that. It could...and probably would change the compression ratio though.
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Offline Rooster

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Re: Re-use rods
« Reply #11 on: November 29, 2012, 10:18:09 AM »
It would not change the displacement of the engine. Only bore or stroke changes would affect that. It could...and probably would change the compression ratio though.
Not a noticeable change in Compression.
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Offline NH Mowster

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Re: Re-use rods
« Reply #12 on: November 29, 2012, 11:18:58 AM »
 Oh OK. I didn't know if using .020 over pistons and a longer rod would change anything. I guess milling the piston would keep it close to stock stroke.  :lol: should I recon the 40 rod to make it fit the 42 crank with .004 clearance? I just plan in lightly sanding the crank journals to make sure they are smooth then polishing it. They want $80 to do that in town. I've got some plastigauge somewhere in the shop I will use before I do anything first to see where I'm at on clearance. Going to get a price today to see how it will cost to bore this thing in my dads friends engine machine shop. I would do it but my cutter only goes down to 3.500 and I think that will be a little too much
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Offline Huffy044

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Re: Re-use rods
« Reply #13 on: November 29, 2012, 11:26:31 AM »
 . I guess milling the piston would keep it close to stock stroke.   

Little clarification: Piston or rod has no bearing on the stroke, to change stroke you must change the location of the rod journal, bring it closer to the centerline ofthe crank and decrease the stroke or move it away from centerline and increase.

Also, longer rods GENERALY are better because, it raises the angle of the wrist pin in relation to the stock agle of the rod allowing less side load on the piston, also makes a longer lever to turn the crank.

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Offline NH Mowster

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Re: Re-use rods
« Reply #14 on: November 29, 2012, 11:28:48 AM »
Thanks for the info. Learn something new everyday.
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