Do I need to replace the crank pin when I replace the connecting rod bearing?

[thefox]

Do I need to replace the crank pin when I replace the connecting rod bearing? I have already replaced the crank bearings and have a new wiesco piston in a fresh bore.

[hondakid200x]

Its good to do, but if you're talking of the piston pin(connects to the rod), then no it is not neccesary. Its just good insurance, but you should be fine. Usually wiseco pistons come with it...

-Max.

[Mr. Richard]

you didn't like the response you got at 3ww????

why would you even think about not changing a critical part like that in a brand new engine???? EVEN if your a starving student:D :D can you afford to fix it if it grenades at 5000rpm's???

[hondakid200x]

Guys, am I an idiot, or are we talking about the the piston pin that goes through the small end bearing? If so, their should be virtually no wear on the pin at all, and usually there isnt.

-Max.

[Mr. Richard]

ever hear of FATIGUE????? :D :D :D :D

[thefox]

Originally posted by kasey
you didn't like the response you got at 3ww????

why would you even think about not changing a critical part like that in a brand new engine???? EVEN if your a starving student:D :D can you afford to fix it if it grenades at 5000rpm's???

If you look at the post date kasey I posted here before I got any responces at 3ww.
I have never had to replace any of the bearings on the crank before, they have never needed it. I kind of figured that I should replace it but I wanted another opinion. I guess that means you want me to replace the rod now too:D .

hondakid - I am talking about the pin that attaches the two halves of the crank together, a new piston pin can with the new piston. Sorry, I guess I should have stated that it is for a 4 stroke in my first post.

[Mr. Richard]

see you never posted it was the lower rod bearing,,,, there are measurable tolerances which will tell you if you need to replace it,,,,

[thefox]

Yeah I forget how many terms everybody uses. I call the top the piston or wrist pin and the bottom one the crank pin. I should have also mentioned that it is for the Yamaha in my sig., a 4 stroke (no bearing on the top part of the rod).

[hondakid200x]

Ahhh righteous.

And just to push for further arguement (just kidding, haha) I do agree that ALL parts should be replaced during a rebuild. BUT I was told by my engine teacher last year that the piston pin is pretty much a indestructible part. Then again, I proved him wrong on a test question, sooooooooo I dont know how reliable of a source he is, haha. Also that is in little tecumseh and briggs engines.

One question though. How does the wristpin/piston pin have no bearing in it? I am not exactly familiar with these trike engines, but engine technology hasnt changed in years..I am not questioning you're knowledge, just out of curiosity.

-Max.

[my90rulz]

the pins in the 4 strokes do wear when they heat up too much :p i could feel the groves on the one from my atc 90, they dont have bearings in there becuse it gets lubricated from the oil off the crank when it gets to BDC becuse its submeged in it cuze its a 4 poke opps i mean stroke,.... :D

[Mr. Richard]

the wrist pin only articulates a few degrees ,,, so in lower rpm engines a bearing is not neccessary,,,,, but think of the fatigue factor :D :D :D

[Mr. Richard]

when it gets to BDC becuse its submeged in it cuze its a 4 poke opps i mean stroke,....

AT NO TIME IS THE ROD EVER SUBMERGED,,,,, oops maybe if your upside down :lmao: :lmao: :lmao:

[hondakid200x]

Ahh, good to know. Ya learn something new every day! Haha, thanks.:headbang:

[Tecate performance]

if you get a rod kit it will come with everything you need to rebuild; rod, crankpin, thrust washers and bearing. i don't know about yamaha, but some of the honda motors had different sized bearings and pins to get the correct clearance instead of buying a whole rod kit.

[my90rulz]

Originally posted by kasey


AT NO TIME IS THE ROD EVER SUBMERGED,,,,, oops maybe if your upside down :lmao: :lmao: :lmao:
thats not what i ment...lol i ment theres oil at the bottem of the crank from the trans.....so it gets oil in there....right?;)

[turbo]

i will just add alittle bit to this, any time you have to press apart a crankshaft, replace the crankpins, not just because of fatigue, or wear, but also because it is a pressed in part. every time that part is pressed apart, or together from the manufactorer, there is a small amount of metal that is taken off, that amount may only be a ten thousanths thick, but that small amount of metal is what keeps the two halves together, and keeps it from grenading when a high amount of stress is put on it.

[BIG BAD RED]

just a quick question mate...how did you balance your crank after you put a new big end in it? seems a little scary to me if its a redneck mechanic job...


someone else said you get it all in one con-rod big end, crank pin, thrust's...not true...try ordering oem you need all diff part numbers

[Tecate performance]

right, honda usually sells the parts separately to allow you to use over the parts that are good, thats why they have bearings and pins in different size increments. that way you can choose the right size to use with the original part to arrive at the correct clearance. or you can go aftermarket, like vesrah and get a kit for like $70 that comes with everything. the parts are matched to the correct clearance, no measuring, just install and go.

when you rebuild the crank,you usually don't balance the crank, unless you wanted to have it done, but you have to true it. its pretty simple with the right tools.

[BIG BAD RED]

not in a regular garage it isnt that simple to balance it...which is trueing it...:booty: and nothign you buy from the factory is in groups...unless its a new bike..they have diff part numbers for every part so that they can use a part in varius aplications...for exaple...they want to run a 590mm rod in ____ bike but a 580 in ____ but they also want to run a 40mm pin in both...

[Tecate performance]

truing is not the same as balancing. truing is aligning the crank halves, balancing is done on a machine that measures imbalance at a certain rpm, with weight added or removed accordingly.

balancing definitely isn't a regualr garage thing, but truing is if you have a dial indicator and v blocks. in my opinion, pressing the crank apart/together is harder than truing it afterwards.

[BIG BAD RED]

a minimum your going to need is a lathe to true it with a soft brass hammer....but back to if he should replace the pin...this is one of those Q's....do you even need to ask, you just replace it from the risk of fatigue from pressing it out and in and the original wear..ontop of it all now it will wear even more un-even becuase unless he put the pin in exact same then when the compression stroke and power stroke happen it will the top more than the bottom....JUST REPLACE IT...thats like puting new crank bearings but not seals...like doing fork seals and using the old oil....