2hp to 3hp conversion

[Bluecamaro]

Does anybody know what it would take to put a 3 horsepower crankshaft with an inch and 3/4 stroke into a two horsepower motor with a inch and 1/2 stroke, is it the connecting rod the Piston or is the whole block different

 

[cl350rr]

What brand of engine?

 

[Bluecamaro]

Old school Briggs & Stratton

 

[cl350rr]

Thanks, you will need the crankshaft and the connecting rod with oil slinger from the 3hp.

2hp rod bolts are inline with the length of the rod, 3hp are at an angle. When you install the longer crank, the angle allows clearance to install the rod bolts. The oil slinger is angled on the 3hp also for clearance:

 

[Havasu Dave]

@cl350rr Awesome detailed response!

 

[Bluecamaro]

Perfect awesomerrrr! response, Thank you verry much.. Does anyone make performance cams or any other parts for these engines?

 

[cl350rr]

If I could suggest, before you go searching for aftermarket power, put a ball bearing on the output end of the crankshaft. That will free up a considerable amount of the power you are losing to friction.

 

[Havasu Dave]

And a round slide carb and external fuel tank.

 

[Bluecamaro]

If I could suggest, before you go searching for aftermarket power, put a ball bearing on the output end of the crankshaft. That will free up a considerable amount of the power you are losing to friction.

If I could suggest, before you go searching for aftermarket power, put a ball bearing on the output end of the crankshaft. That will free up a considerable amount of the power you are losing to friction.

That make good sense.

 

[Bluecamaro]

That make good sense.

Have you ever seen anybody weld up the cylinder head to increase compression, I also think I've seen a cylinder head with a channel down the middle to increase or Aid in flame travel

 

[Bluecamaro]

And a round slide carb and external fuel tank.

Any suggestions on size

 

[Bluecamaro]

I think what I have here is a pretty pristine low hour motor, no Ridge at the top of the cylinder, good compression, just want to have some fun!

 

[Bluecamaro]

Thanks, you will need the crankshaft and the connecting rod with oil slinger from the 3hp.

2hp rod bolts are inline with the length of the rod, 3hp are at an angle. When you install the longer crank, the angle allows clearance to install the rod bolts. The oil slinger is angled on the 3hp also for clearance:

View attachment 329858

Do you know if balancing or a flywheel is of any concern

 

[Minimichael]

Any suggestions on size

I would guess about 17-20mm (as in mikuni VM20), or not much wider than the intake port at the block.

 

[cl350rr]

By installing a longer stroke crank, you have already increased compression.

Do you know if balancing or a flywheel is of any concern

The early Briggs 2, 2.5, 3, and 3.5hp all share the same block, head, piston, valves, etc. all you are doing is changing the parts to make it a 3hp out of a 2hp, if you are running reasonable rpm, balancing should not be needed. If you intend to run this thing wide open without a governor you need to look into a billet rod and flywheel at a minimum. At that point, why not just buy a 5hp?

 

[Minimichael]

If I could suggest, before you go searching for aftermarket power, put a ball bearing on the output end of the crankshaft. That will free up a considerable amount of the power you are losing to friction.

And with just two posts, @cl350rr educates us all on building a stroker from spare, out-of-business parts. Rock on, man!

 

[Havasu Dave]

Any suggestions on size

Running a Kiehin PZ 19 on a 3 hp . Also installed a roller sump cover. I did have to machine the crank shoulder a bit.

 

[Bluecamaro]

By installing a longer stroke crank, you have already increased compression.

The early Briggs 2, 2.5, 3, and 3.5hp all share the same block, head, piston, valves, etc. all you are doing is changing the parts to make it a 3hp out of a 2hp, if you are running reasonable rpm, balancing should not be needed. If you intend to run this thing wide open without a governor you need to look into a billet rod and flywheel at a minimum. At that point, why not just buy a 5hp?

I hear you on the five horse, no I wanted to keep it within reason so it wasn't just a time bomb waiting to happen, the five horsepower machines seem to have much more available parts at least from what I have seen, I have not seen a lot of Billet rods and or things like a camshaft for these smaller Motors are they still available

 

[Bluecamaro]

Running a Kiehin PZ 19 on a 3 hp . Also installed a roller sump cover. I did have to machine the crank shoulder a bit.

When you say some cover I'm assuming your meaning the side cover, can the factory one be machined for a roller bearing or ball bearing or is there not enough material there

 

[Bluecamaro]

By installing a longer stroke crank, you have already increased compression.

The early Briggs 2, 2.5, 3, and 3.5hp all share the same block, head, piston, valves, etc. all you are doing is changing the parts to make it a 3hp out of a 2hp, if you are running reasonable rpm, balancing should not be needed. If you intend to run this thing wide open without a governor you need to look into a billet rod and flywheel at a minimum. At that point, why not just buy a 5hp?

I've noticed that the 3.5 horsepower has a different chamber is this going to be advantageous on a two horsepower motor, possibly fly cutting it to get the clinch back down or maybe that is a mistake on a small motors