Installing an RC Boat Clutch



OK – So here’s my story…   About two years ago, I traded a guy an airplane for this RC boat. When I got it, I didn’t know much about RC boats, but I had a friend that was into racing – In fact, he had a boat very similar to the one I received in the trade! As it turned out, I got a good deal on the boat, despite having to make some substantial repairs. For those repairs, you can check out my article Here.

The one part of the whole experience that I really didn’t like was the racing aspect. The boat had no clutch, making it difficult to really enjoy running it just to have fun. Because of this, the whole project was sidelined for a couple of years. It actually got to the point where I had the boat for sale in the local hobby shop, but nobody was very interested for the very same reasons as I wasn’t very interested in it. So, rather than let it go for next to nothing to a guy that didn’t know anything about it, I decided to take it home and install a clutch! I got to searching for a clutch, and found one on ebay for $20.00 with free shipping from China, but that turned out to be a bust. After waiting for 6 weeks, I got my money back and started looking again. I couldn’t find anything else nearly that inexpensive, so I settled on a $52.00 clutch that I found on Amazon. About 6 days after placing the order, a plain brown box arrived with the clutch inside, but there were no instructions of any kind! At this point, I decided to write a ‘How to’ article on installing an RC boat clutch.

Getting Started

The first thing you’ll need to know is what brand and size your engine is – this will determine the clutch you need. Some of them are fairly generic, like the one I purchased. It will fit ZENOAH, CRRC, RCMK, and CY marine engines.

As you can see here, my boat has an RCMK engine – the 25.4cc engine to be exact. Whoever set this boat up originally, did a pretty decent job as afar as I can tell!

The tuned pipe length was marked, and then the pipe was removed. With the pipe out of the way, the header and cooling flange were removed. At this point, I cut and removed the throttle pushrod, because it will require a longer rod when the clutch is installed. The Tygon fuel line was removed from the carburetor, and the engine was removed from the rubber mounts.

With the engine now on the bench, I could get to work! The old collet and retaining bolt were removed. In order to remove the collet from the RCMK tapered crankshaft, I installed a longer bolt, clamped the collet in a Vice Grip pliars, and tapped on the bolt with a hammer. A few taps is all it took to break the collet free from the tapered crankshaft.

Here, you can see the old collet after it was removed, and the tapered crankshaft on the RCMK engine.

Here is what the new clutch looks like prior to installation. In the second photo, you can see the inner part of the clutch, and the flyweights. It’s a simple setup, but it’s proven to work for many, many years!

The first part of the new clutch to be installed is the center shaft. The four machine screws that hold the rear engine mount to the engine had to be removed, The flyweight was then threaded onto the center shaft.

I placed the clutch drum over the flyweight, and the outer housing was attached to the engine mount and engine with four machine screws. To create the needed clearance between the housing and the drum, I had to add a 5x 1.5mm washer under each of the housing spacers. Not pictured, is the machine screw and washer that secures the center shaft to the crankshaft – it was installed and tightened before the collet was spun onto the drum. The collet has a spot to put a wrench on it to tighten it, but to do so, I had to removed the pull starter from the front side of the engine. The pull starter was held in place by four machine screws, so removal was easy.

The collet insert and nut were installed next to complete the clutch install, only to find out that the driveshaft was too large to slide in place this way. I had to put the nut and insert on the driveshaft first…

…And THEN thread it onto the collet. This was slightly more difficult this way, but was still manageable. But, now, I ran into another little issue – with the clutch installed, the engine mount holes needed to be re-drilled, and more clearance was needed around the carburetor.

I removed a small portion of the engine mounting rails with a razor saw, to provide carburetor clearance, and slid the engine back in place.

A permanent marker was used to locate the new engine mount holes, and the holes were drilled. The original stainless steel mounting hardware was reused to secure the engine/clutch assembly in place. Two things to keep in mind is that I needed to tighten the collet nut before marking and drilling the engine mount holes, so that there was no extra load put on the clutch. I also adjusted the engine to the point where I had the least amount of friction on the drive shaft while the clutch drum and driveshaft were spinning as an assembled unit.

the last things to reassemble were the steering/throttle box with a longer pushrod, and install the tuned pipe. The silicone water lines were reconnected to the head and exhaust flange, and the Blast Cat was ready to hit the water!

Running Report

Since the weather looked as though it would cooperate over Memorial Day weekend, I loaded the boat, transmitter, and a can of 30:1 mixed gas into my van as we prepared to spend the weekend at my in-law’s place on the Mississippi River in Brainerd, Minnesota. My Father-in-law has a really nice dock, and an old aluminum Crestliner – it’s always best to run an RC boat with a rescue boat on hand. The weather Saturday night was warm, but there was a slight breeze and a nice little chop on the water. There’s a ‘back-water’ area of the river on which my in-laws live, so the current is almost non-existent. This makes the area much more like a lake than a river, and it’s great for fishing too!

I got the boat gassed up and ready to go, and then carried it down to the water. Sitting in the custom PVC stand, I started the boat and put the cover in place. With that, the boat was raring to go! I set the boat in the water, tested the clutch engagement – it worked perfectly, so I climbed onto the dock, and walked to the end so I could have a good vantage point from which to pilot the boat. Once in position, I pulled the throttle trigger and the Blast Cat was MOVING!

Being my first time piloting the boat, I wasn’t sure exactly what to expect – my concerns quickly faded into a great big smile, and I was off to the races – well I was having a lot of fun!

This boat was a lot of fun, and really easy to use – thanks to the clutch! While installing the clutch took some top-end speed off the boat, it was well worth it to make the boat much more user-friendly.

Check out my video to see the boat, engine and freshly installed clutch in action!

A Few Photos on the Water…


I’m so glad I took the time to install the clutch, rather than sell this awesome boat! The install, despite not having instructions, was pretty straight forward, and would be an easy add-on project for anyone with some mechanical experience. The clutch cost me $52.00 on Amazon, but the fun it will now provide is priceless! -GB





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  1. Justaddwata

    A good article and decent install job. Something worth noting is that most people who install a clutch also install a water pump to ensure water flow through the motor at idle or slow speeds. Boat typically needs to be moving at around 10-15mph before any water will reach the cooling jacket otherwise.

    • You are correct – I think this will be the next add-on I do for this project. Not Sure, yet, if I’ll do a ‘shaker’ type pump or an electric pump. But, the engine ran cool throughout testing, and the boat performed fairly well! I do believe I will add a degree or two of ‘up’ trim to the drive to get the bow a little higher out of the water as well. -GB

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