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xwhatsit
14th June 2008, 02:30
I've got spare three crankshafts sitting around. One has massive big-end play, one is still inside an engine; however the third one I have out of the engine and it seems maybe OK.

My Haynes manual says to grab the conrod and firmly push/pull it. There is a small amount of radial play (supposedly normal), but I'm 99% sure I can't detect any longitudinal play in it, with my `naked hands'. Is that good enough? Any other tips on making sure of big-end condition?

The small-end is another story. Haynes says the gudgeon pin should be a light sliding fit -- but definitely no radial play. It also says radial play should be very unlikely. With an old gudgeon pin (from a rather mangled piston), it slides, until it gets halfway, then there's a sort of seam on the pin that makes it difficult to go further. There does seem a small amount of radial play, difficult to notice. There's no bush. What's the normal approach in this case?

Patch
14th June 2008, 07:32
What's the normal approach in this case?
Give it to an experienced engine builder who knows what the fuck they are doing :done:

tri boy
14th June 2008, 10:03
No good checking for sm end play with a worn pin.:nono:
A dial gauge may help in identifying big end brg wear, but on a built up crank, I would be happy with smooth rotation of the rod and not feeling any wear, side clearance to the crank web/big end is about .15mm I think, by memory.
Also getting the rod checked to see if it's not bent, and a set of V blocks and dial gauges to check for crank run out helps.

Signing onto a polytech night class on engineering practice, opens a world of tools n skills to those who like to tinker. Imagine having access to a million dollars worth of tooling, and grumpy old blokes to show you how to operate lathes, mills etc....
Many project bikes have been built using polytechs.;)

xwhatsit
14th June 2008, 11:28
Give it to an experienced engine builder who knows what the fuck they are doing :done:
Now where would the fun be in that? :laugh:

No good checking for sm end play with a worn pin.:nono:
A dial gauge may help in identifying big end brg wear, but on a built up crank, I would be happy with smooth rotation of the rod and not feeling any wear, side clearance to the crank web/big end is about .15mm I think, by memory.
Also getting the rod checked to see if it's not bent, and a set of V blocks and dial gauges to check for crank run out helps.

Signing onto a polytech night class on engineering practice, opens a world of tools n skills to those who like to tinker. Imagine having access to a million dollars worth of tooling, and grumpy old blokes to show you how to operate lathes, mills etc....
Many project bikes have been built using polytechs.;)
Cheers man -- I suspected using an old pin might not be much help, but that's what the Haynes book of lies said :crazy:

Polytech sounds like fun, but I have enough grumpy lecturers on my plate right now as it is.

Thanks!

EDIT: One more thing, Honda never sold separate bits. If the rod or bearings were fecked, you had to buy a whole new crank assembly. However I've seen conrods on Japanese sites; it's therefore possible to pull it apart? Maybe put new bearings in? Might be cheaper than a new crank if it needs doing.

Ixion
14th June 2008, 13:50
With a built up crank, condition checking is really a matter of feel and experience.

Wash the big end out with petrol. Hold the crank in a vice (so it doesn't move at all, in your hands it will). Now hold the rod vertically and move it up and down . Repeat at 90 180 and 270 degrees. Do this in a very quiet environment and listen hard. You'll hear and feel even a very slight movement. Turn the rod listening for any 'bad' noises.

Put the crank pin at bottom dead centre , so the rod is coming up between the flywheel faces. There will be a small amount of sideways rock at the small end. We are looking for "rock" here, NOT sideways movement. There will always be some. I use a rough rule of thumb that less than half the distance between the rod and the flywheel web is OK. The manual may specify a figure.

Some cranks have thrust washers on the big end . Check for sideways movement (not rock). There should always be a bit, a few thou. The manual may have figures.

Look for scoring on the shafts, ovality of the little end (put a good condition gudgeon pin in and try to rock it, there should be none).

If all that looks OK, I'd use it, unless it was a racer or something.