Threading a new engine

Geonosian Accountant

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Mar 17, 2019
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I’m installing a new 18 hp Briggs engine on a riding mower. The new engine is not threaded to secure it to the frame. I’ve never tapped a screw hole before. Will it be just as secure with a longer bolt and nut to keep it in place, or is tapping absolutely necessary? Thanks for any help.
 

ILENGINE

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A bolt and nut was used for years on various engines so I don't see an issue. Also most mowers with tapped holes use self tapping bolts to mount them.
 

bertsmobile1

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You will be very lucky if you can actually get nuts onto the bolts , there is very little space.
Add to the the upper surface is not machined flat for the nut to press against.
So self tappers are the only way to go.
If the engine did not come with them get 5.
One to cut all the threads with and 4 to mount the engine.
Thread the holes before you fit the engine to the mower.

I use an air wrench , powered screwdriver or electric drill depending upon where I am doing the job.
I have a mounting bolt that has been turned down slightly smaller ( running it againts a grinding wheel ) that I use to pre thread the holes.
Thus the holes ar threaded a just a little smaller so a drill / driver will wizz them up no problems and the small bit of deeper thread they cut will keep them in there nice & tight.
You really can not use a standard Unified thread tap as the bolts are not unified pitch and the tap will cu the threads too deep so the bolts will tend to come loose in use.
 
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