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Question for the outboard gurubs 70hp johnson b81 model

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wvidal

New member
I've stumped two pretty ex

I've stumped two pretty experienced outboard mechanics with this one and I am looking for some advice. I am cruising down the lake and the motor bogged down I shut it off and pulled the cover to find the bolts from the exhaust housing sheared off and the power head was no longer attached only the drive shaft and transmission linkage holding it together. I took it to the guy who has worked on this motor before and he put it back together for me and it was running fine in the driveway. I take it out make about a 20 minute ride and it does the same thing again. Any suggestions to what is causing this or where to start looking would be greatly appreciated.
 
sure I'll take one tomorro

sure I'll take one tomorrow and post. The bolts come up through the exhaust housing into the power head.
 
the first time they had gotten

the first time they had gotten loose and broke off but the second time they just broke off
 
"I think the 'key' lie

"I think the 'key' lies in the first incident.
Had the powerhead been off withing the last 20 or something hours?
Was it original screws that came loose/broke?
Was it used 'anti seize' or similar lubrication on the threads?
To prevent it from happening again I would suggest to install Heli-coil in all threads as the threads have possibly been damaged and expanded.
Use original screws and washers ('rolled' threads and not 'cut').
Cower the whole screw with Sealing Compound or similar, no grease/anti seize.
Check the sealing surface between block and exhaust housing for warping/damage.
torque to correct specs."
 
thanks I'll give it a try

thanks I'll give it a try I have never had the powerhead off but it was rebuilt before I got it.
I did find that two of the motor mount bolts were missing after the first incident.
 
Any chance the first incident

Any chance the first incident bent the driveshaft and is causing enough vibration to loosen the powerhead mounting bolts???
 
that was what I thought origin

that was what I thought originally but when they put it back together for me the first time they said the driveshaft looked ok just some wear on the splines.
 
"Wear on the splines is a dead

"Wear on the splines is a dead give-away. Either the driveshaft is bent, the midsection is out of whack, or the lower unit has issues with alignment.

Dcramer"
 
"If the drive shaft is bent to

"If the drive shaft is bent to an extent that it will cause vibrations big enough to break the bolts holding the power head, the splines would no longer be there, and most likely even the drive shaft bearing under the water pump will be gone!
The missing motor mount bolts is a more serious issue. Which bolts?"
 
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