Score!!! Well Maybe.... 3hp Water Pump BriggsI/C

#1
I Got a 3 Hp Briggs today in near mint shape.
But it has a 5/8's shaft end with no Keyway but with external thread's on the last 3/4" of the shaft.

Whats the chances on using this on a Mini with no keyway?

Im Sure I could Drill a set screwhole in the shaft. I wonder if that will hold up?

Anyone use one of these?
 
#3
I'd go the other way...a bushing threaded internally, larger bore clutch.

I've busted some 5/8" Briggs cranks before...the cast iron has such a crystaline molecular structure that is shears along any plane created by alterations to the shaft, like shallow detent holes.

The 3hp Briggs recommends for minibike use has a 3/4" shaft...the 5/8" has trouble standing up to the rapid onset of torque applied by the clutch, and just twist-snaps right off under heavy load. A shame, because the engine is so readily available at swaps and fleas...I buy edgers for $20-$50, depending on age and condition.

It's up to you, but you're a machinist, so I thought you could pretty easily make a bushing...
 
#5
Horizontal milling machine works better for cutting keyways...if you lock the crank into position so it can't rotate, you don't even need to remove it from the block before milling...just bolt the block to the table of the mill.
 

65ShelbyClone

Well-Known Member
#6
I have a 3hp Briggs IC also off of a water pump, but it has the regular 5/8" keyed shaft. I don't think it will be very practical trying to stick a new keyway in your funky crankshaft.

I took my 3hp engine and reduced the base circle on the (plastic)cam, put in modified Tecumseh lifters, back cut valves, portwork, and milled the head just for kicks. Now it has about .320 lift and a lope to the idle.
 

minidragbike

Supporting Speed Nut!
#7
I think I know what your talking about. What my friend has done with his motor something like that was to drill a good dimple into the shaft. Most stock clutches have a set screw that can be tighten with a allen wrench. Simple drill the dimple were the set screw tightens down.

You will want the dimple to at least be half as deep as the set screw. That way it would tighten and hold well.
 
#8
Im going to go check the Shaft again.
The guy I got it from said it was a 5/8's shaft....I never checked it.

I guess if its a 3/4 shaft I'll just hack the threads off the end and see if I can get a mill free'd up at work and run a keyway into it like YH talked about.
 
#9
Sorry, Dennis...I hate saying that I don't like someone's idea, and I would have kept my mouth shut if I had better experiences with these 5/8" crankshafts, but I've already had years of bad luck with them.

I did the drilled-dimple for the set screw on one, and it broke, right at the shallow dimple...nobody wants to drill very deeply into a cast iron crank...the tensile strength is so much lower than steel to begin with, and the hole disrupts the strength gained from the full diameter of the shaft...much like a cut keyway.

I have a shortened shaft I'm currently running on one bike...the length protruding from the case bearing is decreased from threaded end removal.

Some of these older shafts weren't tapped for a retaining screw, and that's important to keep the clutch from walking out...that will snap the crank quickly.

It's up to you...try whatever you think is best and let us know if it worked for your application. Sometimes it's flex in the mounting base that snaps them...it's just that the 5/8" shafts give us so little room for error.
 
#11
Yeah I Checked mine and its .750 as well.

I'll throw a key into it and cut off the threaded end.

Its a Good Running i/c engine and I hate to leave it sit.
 
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