piston pins keep failing

[ben4221]

i have an issue where the little end bearing keeps eating the piston pin. im running 32 tooth rear sprocket and a 26" tyre with a 40mm fm80 con rod and high hole piston with fairly low 120psi compression, this issue is the only thing holding back the engine. the fm80 crank has the most torque has very little vibration compared to the 10 or so other cranks ive had the worst was a ZL crank, but every one has done this exact problem where the little end bearing eats the piston pin when going over 70kmh for more than 20 seconds. ill upload some photos of the damaged pins, the little end bearings them selves wernt too damaged just full of tiny metal shavings. id like to know if anyone has used titanium pins from what ive heard there softer than steel and wear out quicker but i could be wrong and has anyone ran a brass bush intead of a little end bearing

 

[ben4221]

 

[ben4221]

 

[Will'smotobikes19]

This is a strange problem first time I’ve seen it actually. I wonder if there’s too much space between the needle bearing and the pin. That could cause a hammering affect. Probably machined wrong on the rod. What gas to oil ratio are you using? There are motors that have run for thousands of miles that don’t look that worn on the piston pin, something is definitely wrong.

 

[ben4221]

i really hope its not a case of bad rod machining, ive ran oil mixtures from 15:1 to 30:1 but its normaly run 25:1. i dont think its a case of too big space between needle bearing and pin because with a band new pin and bearing it feels nice and tight and runs smooth with no little end noise and i have had it last months when i ride it below 70kmh, i do around 250 kms a week on it, but every time i get in a cop chase and go over 70 i have to rebiuld it straight away or the rings and bore will be destroyed haha and its happend on 3 different cranks 2 brand new but only since i have ported it to go over 70

 

[HumanPerson]

every time i get in a cop chase and go over 70 i have to rebiuld it straight away or the rings and bore will be destroyed haha and its happend on 3 different cranks 2 brand new but only since i have ported it to go over 70

WOW

Don't fall olff of the porch or the catdog will git yoew!!

 

[Street Ryderz]

i really hope its not a case of bad rod machining, ive ran oil mixtures from 15:1 to 30:1 but its normaly run 25:1. i dont think its a case of too big space between needle bearing and pin because with a band new pin and bearing it feels nice and tight and runs smooth with no little end noise and i have had it last months when i ride it below 70kmh, i do around 250 kms a week on it, but every time i get in a cop chase and go over 70 i have to rebiuld it straight away or the rings and bore will be destroyed haha and its happend on 3 different cranks 2 brand new but only since i have ported it to go over 70

Every one of those wrist pins was hard to remove from the piston right? I mean tight you may have had to punch it through or use some force to get them out?When you instal the pin through the bearing in rod there is end play that allows the bearing to walk and when it does the rod is then not evenly putting pressure on the roller witch causes extra heat from the friction.Then the piston having extra heat in it's bosses/shoulders cooks out the thin layer of oil and freezes the pin and now the wearing really get pronounced.Also when the big end is getting lose the little end will walk more and more.You can space the bearing with bronze bushings to stop the bearing end play/walk but the rod can still move,this can again be cured with the spacers but the bearing then has to be wider than the rod.

 

[ben4221]

cheers for that ill make some spacers out of old bearings and give that a go, i know theres a fair bit of end play in the little end

 

[Street Ryderz]

cheers for that ill make some spacers out of old bearings and give that a go, i know theres a fair bit of end play in the little end

You may also wanna go just a bit richer from the looks of it,the oil is burnt on the pin!

 

[Will'smotobikes19]

70 km >43 mph you must have done some porting and a pipe right? People say to use 20:1 but everyone seems to run a different ratio. Try using non ethanol petrol (gas). I’ve heard the ethanol affects lubrication in a 2 stroke.