2005 Sea Doo RXT (Oscar)

2005 Sea Doo RXT – Rotax 1503 Engine engine rebuild

This is Oscar. As his name reflects his true personality. He has been problematic from the on set. He has been my learning experience and clearly it shows by the number of times I’ve been through the engine. Lots of lessons learned here. It’s not really his fault, it’s my lack of patience and forgetfulness.

2005 Sea Doo RXT (Oscar)

This is one of the two Ski’s I got from Jimmy. They both powered by Rotax 1503 Engines. As result, to get these registered the understanding was I needed to show him these were in working order. Secondly, I had to purchase some specialty tools that I did not have at the time (Drive Shaft Removal Tool). Oscar was motor was locked up due to a supercharger failure. It’s very common problem on these Ski’s. It is important to realize that these ski’s will only take a very specific types of oil (Shell Rotella T6), Conventional or Semi Synthetic. There is a wet clutch and the Mobile One Synthetic won’t work.  Hence, the 3rd rebuild I will find this out at the end of his 2nd year.

What is the difference in Rotax 1503’s

So there are three possible Rotax 1503 motors that go in these Skis for 2003-2006 :

Rotax 1503 – 155 Block , high compression pistons
Rebuilt Block 185/215 block with Dished Pistons and ARP Studs
  • 155 Horsepower Normally Aspirated Engine (Rotax 1503)
    • Cast Flat Top Pistons (High Compression 10:1)
    • Forged Crankshaft
    • Four Valves Per cylinder
    • Single Stator Gear
  • 185 Horsepower Supercharged Engine (Rotax 1503)
    • Forged Dished Pistons (Lower Compression 8:1)
    • Forged Crankshaft
    • Four Valves Per cylinder
    • Specific Fly Wheel for Supercharged engine
    • 17 Tooth Double Stator Gear
  • 215 Horsepower Supercharged Engine(Rotax 1503)
    • Forged Dished Pistons (Lower Compression 8:1)
    • Forged Crankshaft
    • Four Valves Per cylinder
    • Specific Fly Wheel for Supercharged engine
    • 16 Tooth Double Stator Gear

The reason why I bring this up is that if you are looking for parts, know that the block, crankshaft, Connecting rods and heads are interchangeable.

These Blocks are Unique

It took me a while to find a shop that would machine these blocks for me. I also had to purchase a hone plate. So, my 1st block came from eBay and 155 Ski. They are a split case design, and require a bore plate to hone/bore these blocks out. You can not buy a bottom or upper case if something happens to the case. They are an aluminum block with cast iron inserts. These motors operate at close to nine thousand RPM. Its a dry sump oiling system with two gerotor oil pump’s.

Oiling System

The oiling system on these older skis is rather unique. But there are some things to be aware of about the overall design. It has is an front and rear oil pressure switches. But that is all that it is, a switch. It’s on or off depending on the RPM /PSI. The front switch triggers at 7PSI and the Rear at 30 (Closed to Open). With this design there is there is no oil pressure indicator or information to or from the ECU other than on of off.

In theory, the way the oil system works is if the rpm’s are below 2500 RPM the switch(s) are closed. If the RPM’s are above 2500 RPM the switches are open. At higher RPM’s the oil pressure regulator runs bypass mode. A result oil does not run through the oil filter. I believe that occurs as the engine RPM’s increase passes 4000 RPM . You could in theory have zero oil pressure and ruin an engine the way this system works. It’s a mystery as to the reasoning behind this design.

Oscar always seems to be grouchy. Oscar on the Third teardown, he gave me a low oil pressure warning going from wide open to closed throttle. What it took was using an external oil pressure gauge to figure out what was going on. As a result it was a bad oil pressure switch when it was all said an done. secondly, this took weeks to sort though this. I have extra ski’s so not a big deal.

Oscar’s Original Motor is Junk due to a Supercharger failure

216 supercharger failure

When I first acquired Oscar he had spun a main #2 and rod #2 bearing when the supercharger impeller disintegrated due to bearing failure. The main bearings were fused onto the crankshaft. There was was little left of the rod bearing. There is a front a rear oil pump that pushes the oil into the number two cylinder. When there is a failure all of the material front gets pushed there. The block parts that were left useable were :

  • Head and Vales (Will need to be Checked)
  • Rear Oil Pump Housing (Rebuild Housing & Pump)
  • Two Connecting Rods (Will need to be checked)
  • Double Stator Gear, Stator Cup and Magneto
  • Front PTO Housing & Oil Pump (Will need to be sent in to be reconditioned)
  • Intake & Injectors (Will need to clean the intake)

I found a 155 block on eBay and replaced the pistons. This is how I learned about the differences in the motors. I had at this time not found a engine builder. I buy most of my parts from Short Block Technologies (SBT) , eBay, Amazon and Partzilla. There are some cases where the used part is as much as the new part. I would line out what parts you need and order them. Be careful of where you order parts from. Do research on the vendor you are buying from. It will save you a headache, money and time.

How do work on this motor?

Now there is some significant points to make about how to work on a Sea Doo Ski. Major work, which is the case of Oscar. The motor should be removed from the Ski. Now this is going to require removing some parts and tools to accomplish the. To remove the motor you will need to remove or disconnect:

  • Drain the coolant and oil
  • Remove the Inferior Engine Cover (Two Seaters Only)
  • Disconnect Exhaust Water box
  • Supercharger (If Applicable) – Special Tool
  • Jet Pump
  • Impeller Shaft – Special Tool
  • Intake manifold
  • Coolant hoses to the ride plate
  • Motor Mount Bolts

Required Tools

Most of the bolts are Torx, get a good set of Torx Sockets. At this point, you will need a special tool to remove one of the supercharger bolts because of the clearance. In addition, you will need a Impeller Shaft removal tool. There is a bellow you need to push back to remove a clip. You can not remove the Shaft from the boat without this easily. In one of my boats someone tried to force this out and got it stuck under the carbon ring retainer. I had to cut this off to get the shaft out. The clip according to Jimmy is a SOB clip. It is a pain in the $ss to get on an off even with the tool.

Remove the Oil & Coolant

To start pump out the oil. As a result. I’m not going to start the engine because this is not a conventional oil change. I use a inexpensive oil extraction pump I bought on amazon. You insert it in down the oil dipstick tube.

Oil Fill Cap / TOPS

Remove the oil cap and remove the oil filter. Connect to the battery, and pump the oil out. Do not run this pump dry! Drain the oil. Now move on to draining the coolant. Remove cap on the coolant recovery tank. Remove the 5mm Allen head bolt on the bottom of the ride plate into a five gallon bucket. Disconnect and remove the battery!

Remove the Seat

To start by removing the seat and remove the mount. It’s these four 10mm bolts.

Remove the Water box

To remove the water box, remove or loosen the clamp from the exhaust to to the water box. Now to start there is a 8mm nut, and you will need a deep socket. to back the nut off so you can loosen the clamp. Next, disconnect the hoses that connect the water box to the exhaust manifold. Removing these are going to be tricky because there is one on the underside of the manifold. There is also one on the top of the exhaust manifold. These are like a 4.5 or 5mm band screw if they have ever been removed. Otherwise cut / remove the Otiker Clamps. Next remove the rubber clamp that hold the water box to the hull. It’s easier to get off than on, and its it a tight location. Once you do that you can either push it out of the way or remove it.

Remove the Supercharger

This is the tool to remove the top supercharger bolt

If this is the supercharged version of the ski, you need to remove the supercharger. At this point, you should have the water box out of the way or removed. You will need it moved or removed to access the top screw. Remove the Supercharger inlet and outlet hoses. Set these aside. Now remove the top Torx bolt. It’s the one that screws into the back of the supercharger. You will need a special tool to remove this bolt. It going to be a little difficult to remove. Remove this bolt and remove the bottom two bolts. they are tucked up under the supercharger.

All the bolts are in 1a. There are a total of three of these bolts. I’ve highlighted two of them. To get the supercharger off turn left and right while pulling it towards the back of the ski. I also have used a pry bar that I place between the PTO housing and supercharger.

Inspect the supercharger for signs of wear

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