200hp hpdi problem

[fred klauk]

I have recently rebuilt my 2nd of twin hpdi engines on my 26 regulator. Under extended warranty on this first but at my expense on the second. Both had wrist pins wear loose in the pistons on cylinders 1&2 only. All other rod bearings and main bearings in perfect condition. Pistons in cylinders 3,4,5,6, were in perfect condition. Looking for a reason why? Called customer service and didn't get any where.

[Tucker]

Need to keep this at the top. Many techs say this is the best motor Yamaha made. Lets see what the big-guns have to say about this. I always thought wrist pin failure was because of running at sustained high RPM's. And...some of you guys on the Regulators love keepin' 'em pinned. What year are the motors?

[rodbolt17]

is it worn at the piston or the pin to bearing area?
the pins are not press fit but they are monted on caged needle bearings.
if they wear either the bearing stuck due to rust or debris or a lack of oil.
did the oil line check valves get tested ?

[fred klauk]

2003 with 1100 hours. I never run them wide open usually 4500rpm

[fred klauk]

worn in piston. My mechanic checked lubrication as was fine.

[Tucker]

So the needle brg wore into the piston right. What were the symptoms of the failure, knock at idle?

[fred klauk]

yes. my mechanic caught it before engine totally failed

[fred klauk]

Wrist pin was fine but the pin enlarged the hole in the aluminum piston by at least .040. Needle bearing on the rod was perfect, as were all other bearings, no lubrication problems. Engine did knock at idle. This was only on cylinders 1&2, all other were perfect. Your thoughts.

[rodbolt17]

the ONLY way the pin wore into the piston is because the pin was rotating in the piston and not the bearing rotating around the pin.
pin isnt supposed to rotate.
I would carefully measure the rod little end for being round.
needle cant wear into the piston as the piston has no bearing surfaces.
now if the bearing gets debris,the rod end isnt round or anything else that stops the rollers the pin will start rotating and can wear into the piston.

[Tucker]

Fred said both brgs were perfect assuming he meant small end too. Any chance the wrist pin was installed wrong?

[seahorse5]

What oil are you using?

Back in the '80's many Yamahas showed signes of elongated wrist pin holes. It was determined that it was from light detonation over a long period of time, mostly due to overpropping of the motor. Yamaha changed the formulation of their 2M oil in the later '80's to include more anti-wear additives and insisted that motors always be propped in the upper half of the rpm range.

Worn wrist pin holes have not been a common occurance for a lot of years.

What kind of boat, prop size, and top rpm do you have?

[fred klauk]

I have a 26ft regulator With the standard 21 pitch props the boat came with. The max rpm is 5200 but I never run mine over 4700rpm. The wrist pins only were worn in the pistons in cylinders 1&2, all others were in perfect condition.

[99yam40]

sounds like it is over proped to me , but what do I know