K301 engine issues

uk301 · Feb 23, 2018

Hello to all from the UK.

I have a K301 which I'd like to increase the output but am told that if I increase the bore to 3.5 inches I will have to re-balance the engine. Is this correct and if so, how would I go about doing that?

I also have a couple of wheelhouse raiders, one of which runs lie a watch and the other is for parts.

Many thanks in advance

Martin

Bob_Bainbridge · Feb 23, 2018

I'm not familiar with the K301 but as a hot-rodder , drag racer in my youth (many many years ago) I've rebuilt many engines and once got lucky with a good engine block that I successfully bored 3/16 inch oversize. I've never had to rebalance an engine strictly because of increasing the bore size. OTOH I don't think the expense and work of overboring will give you enough increase in power to justify the expense, unless the engine is in need of this due to wear and tear. In my case the Cadillac V8 I had bored was increased from 331 to 365 cu inches which was a substantial increase but was risky if the block was not perfect. Most overbores for engine rebuilds are limited to .030"

Bob B.

oldnslo · Feb 23, 2018

What is the bore size today?

What is available for oversized pistons?

From memory the K301 is 12 HP

mddorange · Feb 23, 2018

:welcome:
To the TBN forum Martin. You came to the right place to get answers.

RandyT · Feb 24, 2018

oldnslo said:
What is the bore size today?

What is available for oversized pistons?

From memory the K301 is 12 HP

The K301 is 3.375 and the K321 is 3.5ish so he is wanting to turn the K301 into a K321 I would worry possibly about making the cylinder walls too thin but then again maybe both blocks are milled from the same chunk of iron and it wouldn't make a difference. I know that the same crankshaft, counter balance gears and camshaft are used on both engines. Also on the hydrostat versions where the engine is mounted on rubber bushing instead of solid bolted to the frame they didn't use counter balance gears.

uk301 · Feb 25, 2018

The current bore size is 3.375 inches and I am proposing taking out to 3.5 giving me a very useful 20% power jump. I have since been told that if I buy a stock crank and re-build kit (including piston and con rod) for a K321 (14hp) I can skip the re-balance.

They also advised to leave out the balance wheels as they just get in the way. Seems a bit strange that a manufacturer would go to the expense of installing them if they were superfluous.

Thanks for all input.

Martin

oldnslo said:
What is the bore size today?

What is available for oversized pistons?

From memory the K301 is 12 HP

shaeff · Feb 25, 2018

The problem is that the balance wheels eventually fail and destroy the motor. Most guys leave them out during a rebuild, and many will remove them from an already in-use motor as a safeguard against failure and loss of the motor.

I've got a K301 on my Economy Power King tractor that I'd like to bore out, struggles a bit with the 48" snowblower. More power is always nice.

Bob_Bainbridge · Feb 25, 2018

The recommended overbore for a K301 is .030". Going to a 3.5" cylinder would require a .125" overbore which would remove over .060 of metal, possibly resulting in a thin cylinder all. If the horsepower was increased from 12 to 14 that would be a 16.7% increase. The later K321 engines also had an exhaust valve size increase from 1-1/8 to 1-3/8 inches so you wouldn't gain whatever increase that gives. One owner successfully bored his K301 to 3.5 inches and it's been running a long time although he says it runs hotter now.

Bob B.