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Old 05-29-2011, 06:31 PM   #1
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Default When to replace connecting rod

Hey guys,

How do you know when its time besides knowing how much fuel has been used?
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Old 05-29-2011, 07:28 PM   #2
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Hey guys,

How do you know when its time besides knowing how much fuel has been used?
By visually checking the rod from time to time and seeing if there is any slop, and seeing if it is stretched or not.
Normally you would put the piston right to the top, and then gently rocking the crank to see if it moves around. Normally it does a little bit, you can't stop that, but it depends on how much the crank moves without the piston moving.
If you think it's too much, replace the rod and piston pin.
I've heard of people replacing rods after 5 gallons after the engine is completely run-in, but it's their words against the world, and it depends if you are racing hard or just having a bash.
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Old 05-30-2011, 12:01 AM   #3
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The 1st rod you have used to run in the engine must be replaced within 5 liters, some brands advise to replace the rod after running in. The Novarossi R7 rod has no problem reaching 5 liters.

Play is one thing to look at but the metal of the rod will get tired taking out the strength which you can not see, thats why it is best to change the rod once in a while even if the play is OK.

Racing or bashing has nothing to do with it. Bashers running a racing engine on long straghts do harm the engine more with higher revs for a longer time.
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Old 05-31-2011, 06:45 AM   #4
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That's how i checked it by rocking the crank with the piston at the top. It does have some rocking with the plug out, but with the plug on you dont feel any rocking. Does it matter how I check it?
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Old 05-31-2011, 08:17 AM   #5
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That's how i checked it by rocking the crank with the piston at the top. It does have some rocking with the plug out, but with the plug on you dont feel any rocking. Does it matter how I check it?
Not really, with the plug on the rod with have that constant force pushing down while the engine is running or not, so as long as the rocking movement is very little it should be fine. If you think it is too much, or you start getting some tuning/running issues, then replace the rod (this is if you think the rocking motion is too great.)
But if the rod feels snug and you get issues, check the play in the bearings - if they rock, replace them.
Every tiny movement that you feel shouldn't be there is greatly amplified (the way the engine sees this) at 40K RPM. Even so, you would be better off paying 40 or so for a rod, then 3-400 for an entire engine!!
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Old 05-31-2011, 08:21 AM   #6
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Every tiny movement that you feel shouldn't be there is greatly amplified (the way the engine sees this) at 40K RPM. Even so, you would be better off paying 40 or so for a rod, then 3-400 for an entire engine!!
Absolutely the reason why I asked
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Old 09-08-2011, 06:27 PM   #7
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I never replace my conrod until the the engine itself is worn out. Been running Novarossi for seven years and never had a problem....
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Old 09-09-2011, 12:30 AM   #8
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I never replace my conrod until the the engine itself is worn out. Been running Novarossi for seven years and never had a problem....
depends what kind of engine you have. Racing engines see a lot more abuse than engines such as the N12 for example. They have more power, see much more RPM and so just the tiniest flaw could destroy it in a matter of seconds.

It doesn't mean that every rod has a "used-by" date, some can last 10 litres without needing to be changed, some can only take up to 4 litres of use.
It depends on how the engine is maintained and how it's designed really.
Just replace it when you think it should be replaced or you have doubts about its integrity.
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Old 09-09-2011, 05:02 PM   #9
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When to change the connecting rod by R.Poage

The connecting rod is one of the most stressed parts in any engine, and therefore needs to be checked frequently to avoid expensive engine damage due to failure. Some factories suggests that connecting rods be subjected to a measured operating life, and replaced maximum after 5 liters of fuel under normal operating circumstances. Some factories suggest visual inspection to determine rod life.
We feel that a combination of the two methods is best to ensure catching a rod before it goes bad. It is also very important to check the condition of the connecting rod periodically during this operating life to ensure that premature wear has not developed.

We recommend that this check be performed before each race day, and the easiest way is to remove the rear cover from the engine (raise the piston up into a compressed position first! before removing the rear cover) then gently rotate the crankshaft in both directions to determine the amount of play in the connecting rod. If the amount of play seems excessive (you can detect movement / play with your eye), we suggest carefully disassembling the engine and measuring the crankshaft pin and connecting rod for excessively wear, a maximum differential of 0.04 and 0.05 mm in diameters is acceptable.

The fact that the crankshaft pin must be absolutely round (as must be the hole in the connecting rod) is one of the most overlooked aspects of engine wear, and can result in damage even with a brand new rod. The proper way to measure this is to measure with a micrometer on one axes (in line with the direction the rod would travel) and then again on the axes perpendicular to the first. The difference of these two measurements should be < 0.002 if any. The connecting rod should also be visually inspected for signs of wear in the bushing areas, and the oiling holes cleared of any debris.

Obtain the correct factory replacement conrod and "new wrist pin clips". Install the new rod exactly like the old one was before you removed it. Note the oil hole in the conrod should be towards the crank.

We also suggest that you inspect and consider replacing the rod if the engine has seen any trauma such as a failure of the two-speed one-way (over revving the engine) or a significant over heating of the engine.

As a general rule engines that are run hard should have a rod replacement at least every
1.5 gallons of fuel regardless of visual inspection. It is very hard to standardize how hard customers run their engines, or what kind of gearing or temperatures these engines see, but is impossible to rebuild and engine with a hole in it, so error on the conservative side is in order.

Nova .12 based engines’ crank pins are 4.27mm when new, and should be changed when pin is 4.23mm.
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Old 08-27-2015, 08:50 PM   #10
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Hi folks,
A quick question. How do you guys remove and replace the retaining pins on the con rod. I can't seem to do it without damaging the piston.

I've just replaced my p/s and con rod. Should I use my old con rod to break in then replace it to the new one?

Thanks guys
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Old 08-28-2015, 02:26 AM   #11
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Hi folks,
A quick question. How do you guys remove and replace the retaining pins on the con rod. I can't seem to do it without damaging the piston.

I've just replaced my p/s and con rod. Should I use my old con rod to break in then replace it to the new one?

Thanks guys
Put the piston/rod in a plastic sandwich bag (to protect your eyes from flying clips). Using needle nose tweezers to remove the clip. If the piston pin is tight I use a Cork that I've cut a recess in to hold the piston so I can lightly tap out the pin without damaging the piston. Use new clips when you fit the new rod again installing them while the piston/rod is inside the bag.

I wouldn't use an old rod to break in a new piston/sleeve. Run it in as all new the same way you did when the engine was new. Replace the rod at the first 5 litres. Changing a rod is all about fatigue and very little to do with wear. Fatigue becomes an issue before the wear does in my experience in racing engines.
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Old 08-28-2015, 02:57 AM   #12
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Put the piston/rod in a plastic sandwich bag (to protect your eyes from flying clips). Using needle nose tweezers to remove the clip. If the piston pin is tight I use a Cork that I've cut a recess in to hold the piston so I can lightly tap out the pin without damaging the piston. Use new clips when you fit the new rod again installing them while the piston/rod is inside the bag.

I wouldn't use an old rod to break in a new piston/sleeve. Run it in as all new the same way you did when the engine was new. Replace the rod at the first 5 litres. Changing a rod is all about fatigue and very little to do with wear. Fatigue becomes an issue before the wear does in my experience in racing engines.
Thanks for your reply.
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Old 02-06-2017, 04:19 PM   #13
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The plastic bag trick is a great idea. Besides protecting your eyes, it keeps them from getting lost when they fly out!!!
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