Small Engine Swap Challenges... because of course it can't be easy

[carbureted iron]

Summoning my inner Toolman Tim, I was compelled to swap a 7.5hp B&S engine of one yard widget in place of a 5.5hp B&S engine bolted on to another. The two engines are visually and dimensionally identical, and all mount holes line up precisely. Easy-peasy, thought I.

Jinx.

Of course there had to be a difference: the output shaft on the 7.5hp is ~0.75-in" and the 5.5hp shaft is ~0.875-in tapered.

Full stop.

I really want that a 7.5hp engine to work where it is now bolted. And I need to "sleeve" the output shaft to make it happen... safely.

I'm open to constructive, do'able suggestions.

 

[Ohmthis]

What is the engine turning? Sheeve, clutch, cvt? I’d replace that with the right size. I’ve never tried to use a sleeve (I want to call it a reducer bushing).

 

[The Cobbler]

as above, depending on what it's driving, a new one would be ideal... but a sleeve should work for you . down the list would be to see if the cranks are swappable ( providing the 5.5 is good)

 

[The Cobbler]

as above, depending on what it's driving, a new one would be ideal... but a sleeve should work for you . down the list would be to see if the cranks are swappable ( providing the 5.5 is good)

 

[kaymccampbell]

What goes on that shaft?

 

[rsanter]

I have used sleeves and oversized and even stepped keystock a number of times to do what you are needed to,do.
It’s no big deal.
I have a lathe so I generally make what I need

 

[john.k]

All the import engine sellers quote the shaft size ...........Id be inclined to get a taperlock if possible ,but thats going to add $50 to the cost.

 

[PugetDude]

Lovejoy coupling.
One half .75"
One half .875"
Rubber spider will accommodate a bit of misalignment if you're not nuts- on parallel or centerline.

 

[four.cycle]

What is the engine turning?

Depending upon what you're using it for, you should be able to find a blade adapter that will accomplish what you need to do.
(Also called a "Hub" by some.) (The steel widget on the drive end of the crankshaft.)
B&S used a few different output shaft diameters - I run into it on big Snapper walk-behinds and Toro walk-behinds.

 

[Yankeefarmer]

Check an outfit like smallenginewarehouse.com or similar. IIRC, years ago, when I swapped a B&S snowblower engine onto an Ariens that originally had a Tecumseh Sno-king, the place I bought the engine from sold a swap kit that included a sleeve and stepped key to adapt. Maybe a web search on repower yard equipment.

 

[Waterlooboy2hp]

Summoning my inner Toolman Tim, I was compelled to swap a 7.5hp B&S engine of one yard widget in place of a 5.5hp B&S engine bolted on to another. The two engines are visually and dimensionally identical, and all mount holes line up precisely. Easy-peasy, thought I.

Jinx.

Of course there had to be a difference: the output shaft on the 7.5hp is ~0.75-in" and the 5.5hp shaft is ~0.875-in.

Full stop.

I really want that a 7.5hp engine to work where it is now bolted. And I need to "sleeve" the output shaft to make it happen... safely.

I'm open to constructive, do'able suggestions.

============================================
Everybody all the way out to their 11th cousin is selling them on E-bay.

Pardon Our Interruption...

 

[four.cycle]

^ that or go to a lawnmower shop and show them what you need to do.

 

[DGersic]

The Predator on my Frankenstein yard vac fits with a sleeve ordered from eBay. Works fine.

 

[American Locomotive]

Just an FYI, there was a point where Briggs (and others) were esentially making up the HP numbers on the engine's stickers. The engine manufacturers got in a lot of trouble, with some manufacturers advertising near double the actual power.

So assuming both engines run, and you're doing this in an attempt to gain more power, I think you should post both engine's model numbers so we can verify if you are going to gain more power.

Briggs stamps the model number on the fan shroud somewhere usually.

 

[four.cycle]

^ A class-action lawsuit in 2004 put a stop to that.
It's because of that lawsuit that lawnmower engines are no longer stickers with "horsepower" ratings, but rather "foot pounds of torque" (whatever that means when applied to a rotating blade.)

 

[dcg9381]

The Predator on my Frankenstein yard vac fits with a sleeve ordered from eBay. Works fine.

I made a franken-cart and made the mistake of "going up" one (Predator) motor size, which ended up being a massive pain in the *** all around.

Motor was great though. Too much power for zero suspension.

 

[carbureted iron]

The 7.5hp B&S engine, model 126312-0413-E1, drives a (Troy-Bilt) pressure washer. Output shaft is 0.75-in dia. x ~2.9-in.
The 5.5hp B&S engine, model 120312-0143-E1, drives a chipper (MTD). Tapered output shaft between 0.875-in to 1-in dia. x ~3.25-in.

The tapered output shaft can't be sleeved, so no swapping btwn these two B&S engines. The tapered output shaft (and matching tapered receiver on the chipper impeller) means I cannot swap in, say, a Predator engine... implying when this aged B&S goes, so goes the entire appliance.

I presumed small engines were standardized. But output shafts vary in myriad ways: straight/tapered shaft; shaft diameter; keyed/smooth; keyway dimensions; internally tapped bore/external threaded; thread pitch & length; etc etc... I had absolutely no idea. Oy.

 

[carbureted iron]

I have a lathe so I generally make what I need

For want of a lathe...
Had I that widget I wouldn't have begun this thread.

 

[rsanter]

The 7.5hp B&S engine, model 126312-0413-E1, drives a (Troy-Bilt) pressure washer. Output shaft is 0.75-in dia. x ~2.9-in.
The 5.5hp B&S engine, model 120312-0143-E1, drives a chipper (MTD). Tapered output shaft between 0.875-in to 1-in dia. x ~3.25-in.

The tapered output shaft can't be sleeved, so no swapping btwn these two B&S engines. The tapered output shaft (and matching tapered receiver on the chipper impeller) means I cannot swap in, say, a Predator engine... implying when this aged B&S goes, so goes the entire appliance.

I presumed small engines were standardized. But output shafts vary in myriad ways: straight/tapered shaft; shaft diameter; keyed/smooth; keyway dimensions; internally tapped bore/external threaded; thread pitch & length; etc etc... I had absolutely no idea. Oy.

You should be able to make an adapter with the ID tapered and the OD straight if you really need the equipment to be fixed.
There is always the option to pull the crank out and either turn down the shaft to a straight shaft or have an engine shop weld it up and turn it down. Kind of like they fix car engines with damaged journals.
You just have to figure out the value of the equipment verses the cost of the repair

 

[SteveH - CO]

I had a 7.8 horse Craftsman (Generac) generator engine with a tapered output shaft that engaged with the input shaft/sleeve on the generator. I sawed the stub of shaft off the generator with a slicing disk, and had it machined to a 1" OD, and installed it on the engine with sleeve retainer liquid, and a bolt (IIRC).

I then installed a Lovejoy coupler and used this Generac engine to power my log splitter.

 

[mike93lx]

You should be able to make an adapter with the ID tapered and the OD straight if you really need the equipment to be fixed.
There is always the option to pull the crank out and either turn down the shaft to a straight shaft or have an engine shop weld it up and turn it down. Kind of like they fix car engines with damaged journals.
You just have to figure out the value of the equipment verses the cost of the repair

Or just turn the engine on and grab an angle grinder...

 

[Milton Shaw]

60 years ago I worked in a small engine repair shop. Engines and machines were so expensive that we sold short blocks on B&S equipped machinery. The small block fit book listed all model and series numbers and listed all required parts to exactly replace motors. The book listed carbs, breathers, shields, housings and ignitions so that a factory exact motor could be assembled from stock. We would look engines up and sell the right short block, crankshaft, etc to give the exact engine. Most of the time the short block assembly was all that was replaced. These engines were used on a lot of construction equipment such as concrete trowels, vibrators etc. where the engine was a small part of the overall price of the equipment.

 

[Metallitubby]

Motor was great though.

Considering who did the R&D, it should be.

 

[Farmall450]

============================================
Everybody all the way out to their 11th cousin is selling them on E-bay.

Pardon Our Interruption...

What he said ^

 

[nadogail]

Lovejoy Couplings can be had with different size bores, an example would be 7/8" diameter on one half, 1" on the other.

Check with Motion Industries or an industrial supply house.

 

[theoldwizard1]

Lovejoy coupling.
One half .75"
One half .875"
Rubber spider will accommodate a bit of misalignment if you're not nuts- on parallel or centerline.

How much torque can one of those handle ?

 

[Firebrick43]

How much torque can one of those handle ?

Which size?

Lovejoy makes sizes that can carry only 3.5 inch lbs to ones that can carry 170,000 in/lb (14,000 ft/lb)

The sizes that are stock and support those shaft sizes can carry 8 hp at 3600 rpm to 266 hp at 3600 rpm, also dependant on which spider material you choose

 

[carbureted iron]

I grudgingly put the engines back on their respective cradles and reattached their respective widgets to their output shafts.

<plaintive sigh>

I am... defeated.

 

[PugetDude]

I grudgingly put the engines back on their respective cradles and reattached their respective widgets to their output shafts.

<plaintive sigh>

I am... defeated.

If the engine with the tapered shaft still runs you can remove the taper while it is running with an angle grinder; finish it with a file.... Just go slow, measure often and you'll have a straight shaft with no more runout than what you started with.
Then install couplings, sleeves, or whatever is commercially available to fit the respective shaft ends.

Edit: Looks like tapered adapter sleeves for small engines are readily available on eBay...might check there to see if you can find a combination that works.



No way I would give up on this yet.