How to measure your crankshaft while it is still in the engine

Making it easier to wade through the data :-)
Brakes, Suspension, Carburetor, Bottom end, Top end, Chassis, Discontinued parts, Wheels, Plastic, Tools
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Sandblaster
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How to measure your crankshaft while it is still in the engine

Post by Sandblaster » Tue Jul 14, 2015 8:30 pm

So you decided it's time to check your top end out.
Good for you!
Too many guys ride around with worn out top ends :o

But while you have the top end off, why not take a moment to check out your crankshaft?
This isn't 100% insurance against a catastrophic failure but it is by far better then doing nothing.

First off roll the crank around in neutral.
Do you hear any rough sounding bearings?
Are there any rough spots?
If so something is not right... The crankshaft should roll smooth with a very light resistance.
measuring your crank while it is still in the engine 101.JPG
measuring your crank while it is still in the engine 101.JPG (97.99 KiB) Viewed 932 times
You have rolled it, wiggled it, slapped it back and forth and as far as your concerned it's good right?

Maybe :shock:

Do you have a feeler gauge set?
If not you can get them at your nearest Auto parts store for about 3 dollars on up to whatever you want to spend...
Take your feeler gauge and put it between the crank half and the connecting rod as shown below:
measuring your crank while it is still in the engine 102.JPG
measuring your crank while it is still in the engine 102.JPG (48.32 KiB) Viewed 932 times
Keep putting the gauge in there and changing the thickness until you can just barely slip the gauge in there.
Any bigger won't go in and any smaller is too loose.
Ours measured .024"

Now, get out that bright shiny new Service Manual and look up the specs for the crankshaft..
It's ok to get some greasy finger prints in your book.. :lol:
measuring your crank while it is still in the engine 103.JPG
measuring your crank while it is still in the engine 103.JPG (42.13 KiB) Viewed 932 times
Ah,,, found the section on Connecting rod side clearance.
Your manual may call it something more technical like connecting rod lateral play or big end connecting rod to crankshaft clearance but it all means the same thing.

Here's what our Manual shows..
measuring your crank while it is still in the engine 104.JPG
measuring your crank while it is still in the engine 104.JPG (40.27 KiB) Viewed 932 times
So .016-.020" is factory new specs.
And we can run the crankshaft all the way to .028" before it's reached it's service limit.
Our crankshaft is in usable spec but not new spec.
Depending on how worn your crankshaft is you have a choice to make...
If you want the utmost in reliability, rebuild it...
If your going to ride it for a summer and then rebuild it, cool, put it back together and go for it.

Any questions?
Feel free to ask..
If bikes are for kids I'll never grow up.

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