MWSC FAQs: V-Twin Kohler Command 18-30 HP Engines
Posted by Devin Daniels on
Are the Commands V-twin metric or SAE measurements?
The Command V-Twin is an all metric engine, with exception to the valve lifters. The lifters are 0.842” in diameter, which is the same diameter as the Small Block Chevy (SBC). The Command lifter spacer is wider than the SBC.
What is the stroke on the Command crank?
All commands have the same stroke 2.640” (67 mm), with exception to the 30 HP (Model CH750) which has a stroke of 2.716” (69 mm).
What is done to these engine blocks?
The 18-22 HP engines have a 3.032” (77 mm) bore, the 23 HP a 3.150” (80 mm) bore, and the 25-30 HP has a 3.268” (83 mm) bore.
Back around 2002, we coated some 25 HP blocks with Nikasil, which turned out to be hard to work with. Since then we’ve been able to bore them out to the bigger bores and coat them with NiCom. (NiCom is the new and improved version of Nikasil, consisting of Nickel and Carbide.) This is the same stuff used on NASCAR engines, outboards, and snowmobiles.
How big can we go with these bores?
With the 18-22 HP engines the largest over-bore you can go is 3.110”, the 23 HP 3.228”, and the 25-30 HP up to 3.327”.
You can bore out the existing sleeve in the engine or re-sleeve it to the larger bore.
If you want to go to a 3.385”, a 3.425”, or a 3.445” bore, it is best to use an 18 HP (or one of the older 25 HP Nikasil coated) engine and have it NiCom coated. (These bigger bores will also require stud-ing the block.)
How much can these blocks take?
Based upon our experience, if your engine is making over 90 ft-lbs of torque - you are running on borrowed time. Anything in the 90’s will have a chance to tear the block apart. (It’ll start just below the oil filter mount, across and through the (rear) main bearing area, then up through the lifter bores.)
What size (connecting) rods are used?
The Command has a stock rod length of 4.495” that goes with our 1.040” pin height custom Diamond piston.
If you use a 0.750” pin height custom Diamond piston and a stock crank, it would take the 0.290” longer rod (4.785”).
If you run our stroker crank it will take the 0.750” pin height custom Diamond piston, along with the corresponding rods (see page 28 in our 2019 catalog).
If you’re using the 3.220” stroke crank, you would use the 0.750” pin height custom Diamond piston and a stock length rod (4.495”).
Are you guys making cranks?
We have an economical stroker crank setup that works very well for surface-drive mud boats and stock governed pulling engines. The kit includes a Ductile Iron 3” Stroker Crank, corresponding rods for use with stock pistons, and rod bearing inserts for the rods. Our dyno tests show over 20% increase in torque over a stock engine.
Will there be clearance issues with the stroker crank?
One caveat of running the stroker crank with a larger lift cam can be the connecting rod clearance past the cam lobes. You can get around this clearance issue by running a reverse ground cam, and flipping the heads around on the engine to get the carb out in front.
(Typically you’d want to run a smaller base circle cam for this, but stock cams will actually clear the rods with our 3” Stroker Crank.)
What’s the stock Command cylinder head like?
The stock Command cylinder head is somewhat limited (short of breaking out the spool gun and welding up around the outside of the ports), but we build 100 HP V-Twins all the time without welding.
One of the things with stock valves and springs is, the spring is rather short. A short spring won’t allow you to put too big of a lift on your cam without running into coil blind issues.
We use our Roller Rocker Kit # 52386, 0.300” valves, and double valve springs to jump up the lift.
What is the stock rocker ratio?
The stock rocker ratio is 1.5:1. This set is good up to about 7500 RPM.
With a stock valve train and our single valve springs, you can run a 0.275” lift cam (which would produce a 0.412” lift at the valve.
Our $2,000 engine special on your 25 HP engine will bring you to nearly 60 HP and equal torque.
Interested in the Roller Cam, what should I know?
When choosing to upgrade to our Roller Cam, we would suggest using the upgraded PAC Double Valve Springs # 51840 (see page 27 in our 2019 catalog), Titanium Retainers, and ARP Studs. With this setup, you can run up to 10,000 RPM without floating the valves.
Our regular roller rockers are limited to 350# of spring open pressure, and the standard DVS will be good up to 8500 RPM.
Interested in the Roller Lifters, which Tie Bar should I get?
Our Roller Lifter Kit (see page 27 in our 2019 catalog) comes with your choice of a Vertical or Horizontal Tie Bar. The Horizontal Tie Bars don’t require any machine work to the block, but the Vertical Tie Bars are stronger.
How are the stock carbs on the 25 and 27 HP engines?
Well built. They come with an accelerator pump in them, and have a larger butterfly and venturi than the stock carbs on the 18-20 HP engines.
Which intake is recommended?
When using a stock downdraft carb, it is best to use the plastic intake.
If you port the inside of your manifold out, the vertical intake paired with an adapter is the best choice.
But for most all governor engines, use the plastic intake.
The 2 Barrel Intake isn’t that helpful when paired with just a stock engine; a downdraft with a plastic intake will outperform it on the dyno over and over again. To get the most out of our 2 Barrel Intake you must use our 1.2 Carb and 1.2 Carb Adapter, then you’ll see a performance gain.
Our Ported Intake will outperform the 2 Barrel Intake by sometimes as much as 15 HP more.
(See page 29 in our 2019 catalog)
What should my flywheel be at to start?
A stock engine is best to start with around 32 degrees timing.
Our adjustable steel flywheels weigh around 25 lbs.
Recommend upgrading the coils?
Stock coils have a pretty weak spark so they don’t work sell with high RPM applications. We recommend our E.I. setup with Voodoo coils. (Most of the newer stock coils have built in rev limiters too.)
Where do I get a service manual for these Kohler Commands?
With high RPM Commands, make sure you set the end play toward the upper end of the Kohler Specs; otherwise you could stick a main bearing to the crank.
For other important specs DOWNLOAD A FREE service manual from Kohler at: www.power.kohler.com/en/engines/manuals
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