When is a crank not usable anymore?

[Rustbucket]

I mic’d the rotation of my crank on my 61x and it’s 4 thousands of an inch off of true. Is this still ok? Will it grenade the first time I run it? Will it be fine to run? Has anyone run into this before and what did you end up doing? All help is appreciated. Thanks

 

[restosud]

assuming you measured it at the flywheel snout?
it won't grenade on you but 4 thou is a fair bit of runout and will only get worse over time.0 to1 thou is acceptable,3 to 4 is pushing it.
either get it rebuilt or put new one in.

 

[Tyler Zane]

Bearings should be smooth and quiet. It should be free of cosmetic damage and rust. Rod end play should definitely be in spec for me to run.

 

[McDog]

When it won't.

....sorry. I couldn't help myself.

 

[DAG]

Greater than one and two tenths = out of spec

 

[Rustbucket]

 

[Rustbucket]

What do you guys think about this?

 

[DAG]

I mic’d the rotation

Indicated?

 

[Rustbucket]

Indicated?

0.04 off

 

[DAG]

That's only a multiple of 33x what Yamaha recomends. But if you used mics vs a indicator then who knows what was measured?

 

[Harbor]

I think he ment .004.....lol

 

[jo5hi3]

Not worth the risk. Cranks are cheap.

 

[Rustbucket]

I think he ment .004.....lol

Crap I did mean 0.004. Thanks for clearing that up

 

[DAG]

.004 is 3 times over spec.

The question isn't will it run, the question is for how long. As long as you are prepared for the worse case scenario (blows up on you while you're riding and leaves you stranded). Hopefully you don't take that into the surf

 

[Blue]

Probably great for a 61x beater ski for the kids where cases are cheap but may be not so good in a ported set of cases where you have more money at stake.

Sent from my SM-N950U using Tapatalk

 

[Christian_83]

This is "out of the box" (or 5 hours from brand new) PHP light weight pork chop crank. In a high spec engine.

so thats 4 times OEM max limit (i have 0.05mm in my manual).
So i think you will be ok with your crank.

 

[restosud]

@christian_83,Your way of checking runout on this light crank is wrong.support the end bearings or better yet support the crank tail and snout directly on v blocks

 

[Christian_83]

@christian_83,Your way of checking runout on this light crank is wrong.support the end bearings or better yet support the crank tail and snout directly on v blocks

Well they guy who helped me check the runout, and later trued the crank, has 15 years+ building jetski engines (not just bolting parts together) But rebuilding cranks, porting engines, custom machining ect.
So not to sound ignorant, but im confident Bo has his stuff together

 

[restosud]

happy for you!
can't argue with 15 years of experience i guess.

 

[Jonsson]

I just change rod. I made tools for Autodesk and local plasma burn me pcs. Then use mill to fix.