conrod broke

[Deleted]

gday, anybody ever seen a conrod break here before, ? heres some details, engine rebuilt, 2mm oversize, about 250-300km's on engine , still being run in and not thrashed, getting plenty of oil, i dont know myself, and an engine builder with 40 years experience hasnt seen a rod go there. any thought welcome , ken

[Shytalk]

Never seen that before, seen plenty of bent rods, maybe a faulty batch

[m1ke]

To me it looks like someone could have torqued up the crankshaft end nuts using a bar through that little end....

Or a faulty rod.....

[Deleted]

i never thought of that,i did indeed put a bar thru there,and on that side aswell, im sure i read in 1 of the manuels it said you could do that, i wont do it again , thanks

[midlifecrisisrd]

Hi,

Were the rods new?

Did he remove the tang off the back of the piston, is there any chance the piston has jammed in the inlet on the down stroke and pulled the end off?

Steve

[m1ke]

Alot of manuals do recommend it, and I imagine it is fine most of the time, but it is a lot of force to be putting into that rod's small end. More than it will see in running.......

Were they new rods or did you resuse the crank as is?

If new rods, then you probably want to be getting them sent back to the manufacturer to see if they can spot any defects in there....

If used rods, then undoing the crank nuts and then doing them back up again may have been enough to damage that rod enough so that it let go with the high number of cycles it see's during running....

[Deleted]

hi, they were new rods and the crank was inspected and new bearings on both ends were replaced, as far as pistons are concerned no tang was removed,and the inlet port is good, 1 theory is the small end bearing failed and the needles rolled over each other and broke the conrod like that, anyway,ive tracked down another barrell and hopefully early next year it will be up and running,and can try again, thanks for your replies, ken

[m1ke]

With new rods id be less concerned about just tightening the rod that way then.....

can you get some close ups of the broken ends of the rod?

[Deleted]

sorry i cant find the other end of the conrod and the picture ive got with the busted end is as good as i will be able to do, i tried the piston from the good side in the bad barrell and it feels a bit looser, you can make it rattle but not in the left, heres a photo of damage to the exhaust port

[Norbo]

I have seen stuff like this before its not common but im not shoked. Thats some damage to the barrels though

[db8888]

Hi just looking at the last picture of the top of the barrel and its been bored off centre if you look at the amount of liner showing on the left side compared to the right side there is a big difference
in sizes if the bore is not true to the base this will cause stress on rod and cause all sort of problems basically your barrel was leaning to the right bore wise if its not true to the base this might not be the case and its just off centre but is still true ...

[Deleted]

now that yourve bought that to my attention, im going to have a close look at that and make sure its not the photo, very interesting thanks,