Crank - how straight is mine?


Crank - how straight is mine?

Postby Kool_Biker » Fri May 18, 2012 11:53 am

Honda's service limit for the 79 crank measured as shown below, is stated in the manual as .050 mm.

P1110219 (1).jpg

I've measured mine at .075 mm (.15 mm total run out, divided by 2).
This is clearly beyond the above Honda service limit, and wonder if this could account for my engine being quite vibey at anything over about 4K RPM, and becoming more so all the way to its 9K RPM limit.
Any thoughts?
Thanks, Aris
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Re: Crank - how straight is mine?

Postby NobleHops » Fri May 18, 2012 11:59 am

Whoa, isn't this the new-to-you part?

N.
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Re: Crank - how straight is mine?

Postby Kool_Biker » Sat May 19, 2012 6:42 am

Bot really Nils,

It is my original, supposedly rebuilt and tested crank ...
Looks like I will be needing a replacement part soon.

But would love to hear an expert's opinion as to how bad would such a run out be in the smoothness of the engine.

Aris
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Re: Crank - how straight is mine?

Postby EMS » Sat May 19, 2012 7:17 pm

Aris: This is again one of these questions for which it is difficult to give a definite answer. Normally, I would say the runout measured as shown will not create a vibration. Then again....
My concern with the runout would be the load in the main bearings. It could very well be that you have an imbalance of some sort also and that would be a more likely culprit for a vibration. Now, a runout can cause an imbalance also, of course. As you see, one turns in circles trying to give an answer.
Do you have a possibility to have the crank checked for dynamic balance?
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Re: Crank - how straight is mine?

Postby FalldownPhil » Sat May 19, 2012 11:26 pm

Aris,
I am going to suggest that you contact Jay at APE in Roseamond, CA.
Here is a link.
http://www.aperaceparts.com

Jay has done consideable head work and crank work for me on CBX's and is very respected in this field.
Ask him and I am sure that you will get a good answer to your question.
Very Best,
Phil :mrgreen:
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Re: Crank - how straight is mine?

Postby cbx6ss » Sun May 20, 2012 10:45 am

just give it a few light taps with a hammer on the high side :^)
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Re: Crank - how straight is mine?

Postby Kool_Biker » Sun May 20, 2012 2:55 pm

Thanks for the suggestions chaps, I will pursue and share back what I have learned.
Cheers, Aris
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