# Advice Needed - Engine Replacement



## tufcat (Mar 9, 2020)

I have a 1999 Craftsman lawn tractor. The stock 21 HP Briggs (V-Twin) has a bent rod(s). I have considered replacing the heads, but can purchase a new 22 HP Briggs (V-Twin) for not a lot more money.

Is the current 22 HP Briggs a "drop in" replacement for the older 21 HP Briggs? Do the mounting holes match? Is the shaft size the same? Is it "plug and play" on the electrical connections?

Are there any other concerns/thoughts?


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## BigT (Sep 15, 2014)

Measure the diameter and length of the shaft on your old 21 HP engine, and compare to the specs for the new 22 HP engine.


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## Bob Driver (Nov 1, 2017)

Should be a pretty straight forward swap, but having the specific model #'s of both engines would really help with the discussion.

The engine mounting holes usually aren't a problem. As BigT said, you need to know the length and diameter of the shafts match, or you'll have to do a little more work and spend some $$$ to get the belts to work correctly.

The exhaust manifold/muffler shouldn't be a problem either. Where you may run into a problem is at the throttle/choke control plate. Does the existing engine run a Choke-o-Matic (one cable for both throttle and choke) and the replacement run the traditional 2-cable set-up, or vice versa?

If they do, you can either swap control plates, or buy a separate choke control linkage, Briggs # 691021 for less than $10. It mounts on two little plastic tabs on the bottom of the manifold, if you're running a 2-barrel Nikki carb. However, the separate choke cable has to be long enough come around the right side of the engine and I find the throttle cable works the smoothest routed around the left side of the engine to "raised" throttle cam connection. The picture below is upside down from the way this linkage sits on the engine, but shows how the 691021 plate mounts on the manifold tabs. Let me know if this problem pops up, I'm doing that exact set up on a customers machine right now and I can send you pictures (that's if the damn Post Office actually delivers the Briggs # 691021 I ordered 9 days ago)









The engine electrical set up may, or may not, be the same depends on which OEM machine the replacement engine was mounted. You'll have to check the function of each terminal at the female engine connection and make sure it matches the male OEM wiring connector leading up to the key switch. On an older Craftsman, it should just be a simple 5-prong switch, but there are a least 10 different configuration as to the way it can be wired going to the Key switch. I posted a thread back in June ("Ever Smoke Test an Ignition Switch?") that should help you figuring the wiring out


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## tufcat (Mar 9, 2020)

BigT said:


> Measure the diameter and length of the shaft on your old 21 HP engine, and compare to the specs for the new 22 HP engine.


Hi BigT,

Thanks.


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## tufcat (Mar 9, 2020)

Bob Driver said:


> Should be a pretty straight forward swap, but having the specific model #'s of both engines would really help with the discussion.
> 
> The engine mounting holes usually aren't a problem. As BigT said, you need to know the length and diameter of the shafts match, or you'll have to do a little more work and spend some $$$ to get the belts to work correctly.
> 
> ...


Hi Bob, 

Thanks for taking time to provide such a detailed response.


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## andyvh1959 (Jul 1, 2015)

Yup. Shaft extension and diameter. Hopefully the bottom of the crankcase and bolt hole patterns are the same also. 

Back in 05 I installed a B&S 15.5hp Intek single in place of a B&S 14hp v-twin (engine was gone) in a Ingersoll lawn tractor. Bottom of the crankcase, bolt pattern, output shaft diameter and extension were all the same. The Intel single bolted right in, but I had to make my own exhaust header/muffler mount from other parts I had.


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