What is a Driveshaft on a Jet Ski? [Explained]
The driveshaft on a jet ski is a heavy-duty metal shaft connecting the engine to the impeller. The main role of the driveshaft is to transfer engine power towards the jet pump. Yamaha WaveRunners have a two-piece driveshaft design attached to the engine with a coupler, while Sea-Doos feature a one-piece driveshaft sealed by a carbon ring.
If you want to find out more about jet ski driveshafts, you’ve come to the right place. We at JetDrift have compiled all you need to know under one roof!
What is a Driveshaft on a Jet Ski?
Just like on most jet-propulsion vessels, jet skis feature a direct-drive system. A jet propulsion system is very simple compared to sterndrives and inboard/outboard drives.
The system’s heart is the jet pump mounted on the bottom of the jet ski. This pump is virtually invisible since it’s placed in a nook and covered by the ride plate.
This pump houses the impeller, which is a close relative of propellers. The main idea behind this enclosed design is to generate a much greater thrust to make the jet ski extremely powerful and maneuverable.
However, engine power must be transferred from the crankshaft to the impeller.
This is where the driveshaft comes into play. The driveshaft on a jet ski is a stainless steel shaft intended to connect the crankshaft to the impeller. Regarding dimensions, this shaft is typically 1 inch in diameter and 17-36 inches long.
Vintage 2-stroke jet skis featured significantly shorter driveshafts, measuring 17-21 inches in length, while modern 4-stroke machines come with 22-36-inch shafts.
The driveshaft typically features splined or threaded connections on their ends depending on the model:
|Design||One-piece||Two-piece (with a mid-shaft)||One-piece|
On Sea-Doos, a one-piece driveshaft connects the impeller directly with the engine crankshaft. In contrast, on Yamaha WaveRunners, the driveshaft is connected to the crankshaft with a mid-shaft and a coupler.
The mid-shaft is pressed into the bearings enclosed in a shaft housing (also known as a bearing housing). This assembly is bolted on the inside of the hull, ensuring proper water sealing.
This two-piece driveshaft design with the coupler has many advantages over the one-piece driveshaft, including:
- Absorbs misalignment between the driveshaft and the crankshaft
- Doesn’t transfer engine heat towards the pump
- Absorbs engine vibration
In contrast, the one-piece driveshaft on modern Sea-Doos can cause many headaches. Just a little engine misalignment or running the engine too long/too high RPMs out of the water can cause damage to the carbon ring.
And a damaged carbon ring always results in leaking. In a worst-case scenario, it can even sink the entire machine! This is why Sea-Doo’s driveshaft, motor mounts, and carbon ring require special attention.
(It’s good to know that vintage 2-stroke Sea-Doos also featured a two-piece driveshaft design with a coupler.)
Regarding Kawasakis, these jet skis come with a one-piece driveshaft that features a coupler on its threaded front end. The rear splined end of the shaft is attached to the impeller just on Sea-Doos. The major drawback of this design is that you have to pull the engine out to remove the driveshaft.
For a better understanding, we compared the driveshaft of the competitor Sea-Doos and Yamaha WaveRunner models in these pictures:
As a takeaway, we’ve compiled the most common questions about a jet ski driveshaft!
What Is the Driveshaft on a Jet Ski?
The driveshaft on jet skis is a durable metal shaft designed to connect the engine to the impeller.
What are the Dimensions of a Jet Ski Driveshaft?
As a rule of thumb, a jet ski driveshaft is 17-36 inches in length and about 1 inch in diameter.
Vintage 2-stroke jet skis were manufactured with shorter, 17-21-inch driveshafts, while their 4-stroke brothers come with longer 24-36-inch long shafts.
How Much Does a Jet Ski Driveshaft Weigh?
The weight of a jet ski driveshaft varies from 2.5 pounds up to 8 pounds.
How Much Does a Jet Ski Driveshaft Cost?
The price of a jet ski driveshaft starts at $170 and goes up to a whopping $400.
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