Crank play after rebuild

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chrisfer

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Apr 30, 2008
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I rebuilt my Johnson 70 due to low compression and replaced the all the lower bearings as well. Now it has some small amount of play in the crank from front to back. This is causing the engine to make knocking noises when coming off higher RPMs when out of gear and just be louder than it should be generally. I have another Johnson 70 and it has no play. I don't believe there was any play before the rebuild. I was extremely careful during the rebuild, used a torque wrench on everything, and did everything per the manual. Does anyone have any idea what could be wrong?
 
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petryshyn

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Oct 3, 2001
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2,851
Re: Crank play after rebuild

Are you feeling the play on the flywheel? If you greased the needle/roller bearing with regular grease upon assembly, it is possible that the rollers aren't turning and are sliding instead. This would cause flat spots, bearing and crank failure. I hope I'm wrong.
 
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chrisfer

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Re: Crank play after rebuild

I used bearing grease and 2 stroke oil on the bearings. Is there a different type of grease for roller bearings?
 
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petryshyn

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Re: Crank play after rebuild

conventional grease will not wash away quickly and may prevent needles from turning. vaseline is often used, cause it melts and dissolves quickly.

Where are you checking the play?
 
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chrisfer

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Apr 30, 2008
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Re: Crank play after rebuild

I am checking the play at the flywheel. I am hoping it is somehow loose, but i doubt that. I am going to pull the flywheel and see if I can move the crank end. I used MIL-G-25013 grease which is what I used for the wheel roller bearings in my airplane.
 
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F_R

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Re: Crank play after rebuild

chrisfer said:
I am checking the play at the flywheel. I am hoping it is somehow loose, but i doubt that. I am going to pull the flywheel and see if I can move the crank end. I used MIL-G-25013 grease which is what I used for the wheel roller bearings in my airplane.
Click to expand...

I think you are on the correct path, remove the flywheel and chect the play at the crank, preferably with a dial indicator. A roller bearing cannot be run "tight", they need a small amount of clearance. So the question becomes just how much play do you have. I'm assuming you are saying you replaced the bearing. Did you mike the shaft?

If you can hear it knocking above all the normal rattle sounds, either you have a great ear, or there is something very wrong in there. Heck, it might have even broke the crank. Rare stuff happens.
 
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chrisfer

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Apr 30, 2008
Messages
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Re: Crank play after rebuild

I didn't measure the shaft when I had it out. I will check this tonight when I get off work. The knocking isn't noticeable under load and the motor seems to run fine, but when coming down from higher RPMs under load, it is loud. I've only put about 1 hour on it since rebuild.
 
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chrisfer

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Apr 30, 2008
Messages
16
Re: Crank play after rebuild

I found that the crank play is very small, but is probably causing the knocking. The noise is significantly amplified when the flywheel is installed. I don't have a dial gauge to measure it exactly. The case bolts in the area of the main bearings are torqued to 25 ft-lbs.

I installed my spare powerhead tonight and I suppose I will need to tear this one down again to find out what the problem is.
 
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