Connecting rod bolts coming loose

Mrdavid78

Member
Hopefully someone can give me reasons as to Why are my connecting rod bolts coming loose ? It has happen to me 3xs now, and after each time they were to have been replaced along with piston,rings wrist pin and crank. Is starting to get expensive and Extremely annoying, seems i havent been able to finish a feature in 4 wks. Help!!!
 
Yeah very odd, after it was "fixed" the 1st time nothing was said to me about anything being "wrong", i was just told it happens occasionally, but occasionally isnt 3xs. Im fixing to replace All the internals besides the cam, in hopes it doesnt happen again this season. Is there something i can use to prevent it ? I know loctite wont work cause of the heat but...
 
Yeah very odd, after it was "fixed" the 1st time nothing was said to me about anything being "wrong", i was just told it happens occasionally, but occasionally isnt 3xs. Im fixing to replace All the internals besides the cam, in hopes it doesnt happen again this season. Is there something i can use to prevent it ? I know loctite wont work cause of the heat but...
find someone else to work on your stuff. unfortunately after the second time its on you
 
find someone else to work on your stuff. unfortunately after the second time its on you
A engine place did it originally the first 3xs, and kept saying it was "odd" or "it was the parts"., im doing the work this time, thats why i asked if there was an reasoning for it or anything I can do this time to maybe prevent it.
 
That is odd! Only things I can think of is make sure the bolts are made for that rod, with proper washers, some have an towards cap line or groove in the washer, and torqued properly. When the bolts come loose,does it take out the whole bottom end?
 
A engine place did it originally the first 3xs, and kept saying it was "odd" or "it was the parts"., im doing the work this time, thats why i asked if there was an reasoning for it or anything I can do this time to maybe prevent it.
Is it a stock rod? If yes it should have been a new one every time. If it’s an arc rod it should have been returned. If it keeps happening it’s either the assembler or the crank. And the assembler should have caught it whatever it is/was
 
That is odd! Only things I can think of is make sure the bolts are made for that rod, with proper washers, some have an towards cap line or groove in the washer, and torqued properly. When the bolts come loose,does it take out the whole bottom end?
No when the bolts come loose it knocks like a Jehovahs witness and loses power.
 
Is it a stock rod? If yes it should have been a new one every time. If it’s an arc rod it should have been returned. If it keeps happening it’s either the assembler or the crank. And the assembler should have caught it whatever it is/was
It is a stock rod, and everytime ive bought new rod, piston, rings, wrist pin and they were to be replaced. Only have to take their word that they replaced the parts i bought. This time ive bought everything except the camshaft and gonna rebuild myself so fingers crossed.
 
It is a stock rod, and everytime ive bought new rod, piston, rings, wrist pin and they were to be replaced. Only have to take their word that they replaced the parts i bought. This time ive bought everything except the camshaft and gonna rebuild myself so fingers crossed.
Must be the crank. Are you going to hone the rod ? Lube the threads to get proper torque. I know raging bull had issues with over tight bolts using fancy moly lube.
 
There are two torque specs, one for dry bolts and a higher number for oiled bolts. Don't have that info right in front of me right now but I'm sure it's on these forums somewhere.
 
There are two torque specs, one for dry bolts and a higher number for oiled bolts. Don't have that info right in front of me right now but I'm sure it's on these forums somewhere.
Actually, based on a quarter of a million dollars worth of friction coefficient research that my employer at that time funded for me to get done by a contractor, there isn't a significant difference in the preload generated by bolts torqued up dry and bolts lubed up with motor oil, the reason being that motor oil doesn't contain the type of anti-friction additives that significantly reduce the friction between the threads and the nut and between the nut and the clamped surface. It feels like less friction when you spin the nut up by hand to first contact, but once you start generating the loads that arise from applying the required torque value, the extra smoothness of oiled threads vice dry threads isn't a factor. Molybdenum disulfide is a totally different matter; anti-seize compounds that contain that require about a 50% reduction from a dry torque table value. The more common anti-seize compounds with graphite and some metallic additive (usually aluminum or copper, sometimes lead) in a petroleum carrier also require a significant reduction over a dry torque table value - on the order of 30-35%.

Nothing wrong with using the torque specified for the rod bolts by the engine manufacturer with engine oil as a thread lube. The tightening procedure you use can make a big difference, though, due to a factor called short term preload loss - this may be the reason that the nuts are coming loose. Tighten the bolts up to the final torque using either 3 or 4 equal steps (more, smaller steps don't gain anything). After applying each step, do not apply the next step until at least 2 minutes have elapsed - longer if you desire (the bulk of short term preload loss occurs in the first 2 to 5 minutes after each step is applied). When you have applied the final step, reaching the specified torque, leave it for 5 minutes or so, then come back and conduct a check pass, re-applying the final torque. If neither nut moves, your done. If either one moves during the check pass, leave it for another 5 minutes or so, then again apply a check pass with the final torque. The second time you apply the check pass, neither nut should move, but if either one moves, just keep re-applying the check pass until neither one moves.

And you don't want to know how much the device that measured the preload at a specific torque cost, lol....
 
Actually, based on a quarter of a million dollars worth of friction coefficient research that my employer at that time funded for me to get done by a contractor, there isn't a significant difference in the preload generated by bolts torqued up dry and bolts lubed up with motor oil, the reason being that motor oil doesn't contain the type of anti-friction additives that significantly reduce the friction between the threads and the nut and between the nut and the clamped surface. It feels like less friction when you spin the nut up by hand to first contact, but once you start generating the loads that arise from applying the required torque value, the extra smoothness of oiled threads vice dry threads isn't a factor. Molybdenum disulfide is a totally different matter; anti-seize compounds that contain that require about a 50% reduction from a dry torque table value. The more common anti-seize compounds with graphite and some metallic additive (usually aluminum or copper, sometimes lead) in a petroleum carrier also require a significant reduction over a dry torque table value - on the order of 30-35%.

Nothing wrong with using the torque specified for the rod bolts by the engine manufacturer with engine oil as a thread lube. The tightening procedure you use can make a big difference, though, due to a factor called short term preload loss - this may be the reason that the nuts are coming loose. Tighten the bolts up to the final torque using either 3 or 4 equal steps (more, smaller steps don't gain anything). After applying each step, do not apply the next step until at least 2 minutes have elapsed - longer if you desire (the bulk of short term preload loss occurs in the first 2 to 5 minutes after each step is applied). When you have applied the final step, reaching the specified torque, leave it for 5 minutes or so, then come back and conduct a check pass, re-applying the final torque. If neither nut moves, your done. If either one moves during the check pass, leave it for another 5 minutes or so, then again apply a check pass with the final torque. The second time you apply the check pass, neither nut should move, but if either one moves, just keep re-applying the check pass until neither one moves.

And you don't want to know how much the device that measured the preload at a specific torque cost, lol....
interesting however there are torque specs for lubricated bolts and torque specs for dry bolts. for example the torque specs for wheel lugs are DRY. engine bolts are subjected to being stretched by the expansion of of the metal parts through heat cycles. the correct way torque rod bolts is the ARP method (speciality lube and checked for stretch using a micrometer). unfortunately the low grade material used in these import engines does not allow for this.
READ THIS THREAD BEFORE YOU PROCEED!!!!
https://4cycle.com/karting/threads/mystery-rod-failures.118235/
 
you may want to PM Raging Bull Racing with questions on this matter. he is very knowledgeable with these motors.
that is unless he built it;)
 
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