should I go with a cheap engine to start with?

[trevmust]

should I just buy a 7-8hp engine to start off with and get a bigger one later?

 

[r_chez_08]

Would be better just to save for the bigger one first IMO, saves you buying a second.clutch, redoing throttle setup etc

 

[trevmust]

I was getting a torque converter. cant find a clutch good enough.

 

[OzFab]

A torque converter is, technically, a clutch; chez was generalising.

That actually reinforces his point: a 7 - 8hp engine will have a 3/4" shaft, anything bigger will have a 1" shaft. Do you really want to spend an extra $300 if you don't have to?

 

[r_chez_08]

I was getting a torque converter. cant find a clutch good enough.

As fabroman said, a 7-8hp motor generally would have a 3/4" shaft, and would only require a torque converter such as a TAV2 rated for 8hp. However, when you upgrade your motor for, say a 16hp, the TAV2 driver would have a bore too small for the motor, and even if it did work, you would be tearing up belts. This means $300+ then needs to be spent on a beefier torque converter and sprockets and jackshaft, and the $200 spent on the tav2 would be wasted.

A larger motor also generally has a larger mounting footprint. Therefore a new or modified motor mount would be required.

You would also need to redo the throttle setup, and if you are building from scratch, a larger motor may not fit without extensive modification.

IMO either go with a larger motor or a smaller motor.
Another option is go with a smaller motor with a stronger torque converter (with shaft adapter from 3/4" to 1"). Then modify the motor as and when you get the funds to do so. This is what I ended up doing (without planning!)

 

[trevmust]

shaft adapter? that works.

 

[r_chez_08]

I had a pic somewhere, dunno where tho.
Basically I got a piece of bar 30mm diameter (1 1/8")x the length of the TC bore.
I turned the majority down to 1", left around 1/4" on the end as 30mm (this stops the torque converter mounting too close to the engine and catching on the side cover)
I then drilled a 10mm hole down the middle (enough for the retaining bolt) and bored a 3/4" hole from the stepped (30mm) end, far enough that the shaft could fit on.
Then I cut two keyslots either side, one 1/4" x 1/8" for the tc key, another 3/16" all the way through so I could put some keystock in to retain the adapter.
I then applied a little grease to all mating parts, and assembled. Held the TC on by an 8mm bolt and a penny washer. Works great!

Dunno if that makes sense. You can make a real simple one with a grinder and some tube 3/4" id and 1" od. I will look for the pic.

Edit: \/

 

[Doc Sprocket]

Shaft size adaptation or not, I don't see the point. If you are bent on getting a larger engine later on, then it makes a lot more sense to just hold off on buying an engine until you can get what you want. Why do things twice?

 

[r_chez_08]

My point with the shaft adapter was- buy a cheap easy to mod engine under 8hp with 3/4" shaft (like a 6.5hp clone.)
Put a 40 series on it.
As and when funds are available modify the engines. Soon you would be over 10hp. You don't need to worry though, cos the 40 series would handle anything.

Say you get the 40 series and a 6.5hp clone. That is $400. However, say you invest another $300 into the clone. You now have the hp (not torque, gear down) of a larger 'big block' engine, but in a small block.

JMO, if you do not have the funds for a bigger engine straight away this may be an option, as it saves you buying 2 engines and clutch assemblies, and in the process you learn more about engines by modifying.