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Old 11-19-2006, 09:48 PM   #1
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Default Reasons for lower part of connecting rod failure!

Hey all I recently had the lower part of my connecting rod fail and I am curious what the reasons for that are.Before all this happened I had been having running problems(stalling ,flameouts,always running like it was rich).This connecting rod only had a little less than two gallons on it.Is the cause heat,lubrication or what? I am leaving this general ie brand or model as I want true opinions.My bearings are good and I use 20% Sidewinder race fuel.
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Old 11-20-2006, 07:15 AM   #2
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When you say fail do you mean broke or did it just ware out? Was this a replacement rod in an a used engine? The two most common reasons would be out of round crank pin and dirt. With dirt being #1.
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Old 11-20-2006, 09:58 AM   #3
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Ok this was the original connecting rod and the bushing in the lower part of the connecting rod failed(broke apart).
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Old 11-20-2006, 11:20 AM   #4
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Had the same thing happen to my 21BF. I chalked it up to general abuse since I did tend to run the motor around 290* but thats the only way it would run right. got 3.5 gallons through it before it went and it still has good compression so I could just replace the rod
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Old 11-20-2006, 12:21 PM   #5
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And that brings me to my next question.Now that this has happened my back plate is scraped up some,one small scratch on the piston and some metal throughout the motor.Is it safe to say I need to replace the bearings as well since I am not sure how much metal has been distributed in them.Also can I lightly sand the backplate to get the heavy scratches off.I did measure the point on the crankshaft where the connecting rod sits and it is not out of round in fact it is almost perfect.I would love to hear some more opinions on this subject.
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Old 11-20-2006, 12:45 PM   #6
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Could be lack of lubrication. Bad fuel maybe? Did you have the rod installed correctly? IE: The lubrication hole facing the front of the engine? If the hole is facing the rear, the bottom half of the rod will be starved of lubrication and will eventually fail.
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Old 11-20-2006, 01:12 PM   #7
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Hey there,
There is no lubrication hole on the connecting rod!The lubrication hole is on the crank hhhmmm do you know what you are talking about? Well thanks for the thought maybe other motors have them on the connecting rod
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Old 11-20-2006, 01:22 PM   #8
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Nope, I don't know what I'm talking about!

What engine do you have? I have an OS RG, RB S7 and a JP B5N and every one has a lubrication hole in the rod. I'm sure you are right, because there are engines out there with lube holes in the crank pin. You never specified what brand you have.

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Old 11-20-2006, 01:43 PM   #9
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Its cool I was not trying to be a jerk just trying to get some help for my issues.OK dammit I have a Vspec I didnt want to say it because I wanted honest opinions from cool people and didn`t want people bashing OS motors or saying ya buy an X brand and you won`t have any problems.I really do like this motor but it has been giving me many problems.At first it ran so good then I did a stupid thing and had to replace the piston and cylinder so I also decided to replace the bearings since I was already there.But since then it has not really run steady like my first go around.So yes the Vspec does not have a lube hole like the one you pictured.I think some of the metal might be from the lower bushing on the conecting rod and some of the metal is from the backplate as it does have some pretty good scratches on it.Thanks again for the help ridgeway
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Old 11-20-2006, 03:02 PM   #10
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V-Specs are nice. When you replaced the piston and sleeve, did you replace the rod as well? Not sure what happened prior, but if you needed to replace the piston and sleeve, it would have been wise to replace the rod as well. Was both failures on the same gallon of fuel?
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Old 11-20-2006, 03:19 PM   #11
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Yes I replaced the connecting rod,the only thing I didn`t replace was the piston pin.I also totally sealed it up with RTV orange.Now I just don`t know which way to go.As you know money wise it costs quite alot to change out these items again(Piston & cylinder,connecting rod,bearings,pin,clips & head seals I`d be near the 200$ mark)Just have been trying to figure out why it happenend before I go any further.
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Old 11-22-2006, 03:40 AM   #12
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Backplate,what to do can I use it as is or maybe some scotch brite to relive some of the scuffs and scrapes???????????/
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Old 11-22-2006, 11:49 AM   #13
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Quote:
Originally Posted by motomanpat
Yes I replaced the connecting rod,the only thing I didn`t replace was the piston pin.I also totally sealed it up with RTV orange.Now I just don`t know which way to go.As you know money wise it costs quite alot to change out these items again(Piston & cylinder,connecting rod,bearings,pin,clips & head seals I`d be near the 200$ mark)Just have been trying to figure out why it happenend before I go any further.

I'm from Singapore We have the same problems over the connecting rod fail on our V-specs engine and also the front end bearing.
The cause as you know, the new piston and sleeve is very tight when it reach the TDC ( top dead centre ), so when you try to breaking a new piston and sleeve, the crank pin that hold the lower part of the connecting rod is compress again the inner ring, whenever the piston is on the TDC position. As the inner ring of the OS conrod material is soft compare to others, so it will wear off while your engine is breaking.
To solve the problems Replace the connecting rod after the engine has breaking, before you race tune your engine. happy racing
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Old 11-22-2006, 12:02 PM   #14
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Quote:
Originally Posted by motomanpat
And that brings me to my next question.Now that this has happened my back plate is scraped up some,one small scratch on the piston and some metal throughout the motor.Is it safe to say I need to replace the bearings as well since I am not sure how much metal has been distributed in them.Also can I lightly sand the backplate to get the heavy scratches off.I did measure the point on the crankshaft where the connecting rod sits and it is not out of round in fact it is almost perfect.I would love to hear some more opinions on this subject.

The scratch mark on the back plate is cause by the rotating crank pin, due to the loose front end bearing. need to replace after about 2gal of fuel run.
A lightly sand on the back plate is fine.
Try to source for the high speed bearing from your local hobby shop Happy racing
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Old 11-23-2006, 01:32 AM   #15
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Hey Leng,

Thanks for the insight on my motor issue.My bearings are very new as I replaced them not long ago as a preventitve measure.Tonight when I got home I started looking at the motor and thinking what could have happend.Now yes it is possible that it was caused by the break in but then I put the crank back in and put the backplate on pulled the crank firm against the bearing and looked down from the top.It is funny there is a decent amount of clearance between the pin where the connecting rod goes on and the backplate,but lets say I installed my flywheel but when I did maybe it was not as far up the shaft as it could have been then there would surely be enough play for the side of the connecting rod to keep coming in contact with the backplate and making it heat up.Not saying that the flywheel was not tight but maybe not as far up the shaft as it could have been.The reason that I was thinking this is because the backplate has some pretty good scratches on it but when I was taking off or shall I say trying to take off the bottom of the connecting rod the bushing was not destroyed but it was cracked and broken but still intact(no loose pieces outside of the area).What do you all think about that.I would also say that the swirls are pretty deep on the backplate just to reaffirm my thoughts.
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