Why Rebuild an Autoprop Propeller?

Autoprop Sailboat propellers are the market leader for self-pitching propellers. The design is simple robust and very effective. But like all well oiled machines there comes a time when you need to service them. If you have kept up with the yearly service routine of replacing the zinc anode and pumping grease over the bearings, the process of rebuilding the propeller should be straight forward. If the yearly service has not been kept up or you purchased a boat already with an Autoprop propeller that had not been serviced things can get a little tricky.

The Autoprop sailboat propeller has a unique balancing system for each blade allowing them to move independently, yet perfectly in balance. If the bearings are not maintained then the balance can be affected. Each blade is built up using thrust and taper bearings that depending upon the model can be partially or fully swapped out. The propellers have evolved over the years as the design improved and new materials and manufacturing processes were leveraged to keep Autoprop the premier sailboat propeller.

Before rebuilding one of the Autoprop propellers you must know what model you have. The easiest way to do this is to find the AP number. The serial number for each blade is located at the base of the blade. The serial number is in the following format – AP XXXX LH where the XXXX are the 4 digit serial number and the LH (or RH) denotes the hand of the propeller. Once you have this crucial piece of information you can contact King Propulsion and we can provide the correct bearing replacement kit. As a guide however the earlier models used a water lubricated ball bearing system, the later models used a cartridge style (caged) bearing system that needs to be encapsulated in grease. If that was not all the method of locking the blades in place has also evolved from tab washers to tab screws, both are methods of stopping the propeller nut from unwinding. But don’t fear, all the latest models use sealed bearings and tab screws, we also have a full database of our models from AP#1, currently in the Science Museum in London!

What you will need to rebuild an Autoprop Propeller

So, you order all the parts for the rebuild, you want to do this yourself (good!) what can you expect. Well the rest of this post and also the enclosed video shows you the contents for an Autoprop H6 Propeller using the new tabscrew style bearing kit. You will also need the instructions. They come with the kit but if they get too oily to use fresh sets are available here in the download section Autoprop service guide.

Autoprop H6 tools live

Finally there are a couple of tools that you will need.  The tools again vary with the propeller model so please do check with us if you are unsure. For this rebuild we needed the following tools (in the order we used them). All of the tools will be explained in detail in the series but it is important to understand at this point what you need and what… you can get away with.

First you need a peg spanner to remove the blade caps.  This is a simple spanner and something many of my customers make themselves.  It is really a pin spanner with a hole between the pins to account for the curvature of the blade cap.  Once the blade caps are removed the tabscrew (or lock screw) needs to be removed.  This is a left handed thread and again uses a smaller pin spanner or made in the workshop like the cap spanner above.  Finally the blade nut needs to be removed.  This uses a specific socket style fitting, which maters with 2 slots on the blade nut.  The latter is more complicated in design and whilst it is still possible to fabricate this item, most customers purchase this item. The only other items you truly need to check for is a grease nozzle that came with the Autoprop propeller to cover the M5 grease port threads to the 1/8 NPT standard used on US grease guns (the prop is British after all!) and lithium grease.

Finally a good bench, about 1 hour per blade, general tools and you are good to go.  The propellers can be rebuilt in the yard on the boat, they cannot however be rebuilt underwater – people do ask! There is also a special prop puller tool available to take Autoprop off the shaft, if rebuilding at the yard is too difficult.

What is in the rebuild kit

The rebuild kit is ‘soup to nuts’ everything you need to rebuild the propeller including the zinc anode.  All items (excluding the anode) are supplied based on the number of blades, 3 blade propeller – 3 sets of parts and so on.

The Autoprop H6 bearing kit contains the following:

  • M5 grease port screws complete with O-rings
  • Tabscrew locking screw (left hand thread)
  • Blade nut
  • SKF thrust bearing
  • SKF taper roller bearing
  • Lip seals to seal each blade
  • O ring to seal the blade cap
  • Loctite (red)
  • Zinc anode with fasteners

Autoprop H6 rebuild kit live

This rebuild of an H6 Autoprop sailboat propeller is also part of a video series giving a blow by blow account of how to service one of these propellers.  Below is the first part of the video series giving the unboxing of the parts (sounds terribly exciting!).  Each week for the next 8 weeks I will update the blog with the next steps in the process and show you how to do it on camera.

If you like the video please do leave comment on the Youtube website or in the comment box below.  I post regularly with tips and tricks so if you hit the subscribe button you will be notified when I post the next one!King Propulsion YouTube Channel