You must know the motor make, year, HP, long or short shaft, remote or tiller steering, number of cylinders and whether it’s through hub exhaust or not.
It depends on the boat and the weight. A good setup will get about 80% of propeller speeds when using mid range prop pitch. A light weight prop boat using a high pitch prop can run twice our outboardjet speed.
A heavily loaded prop boat using a low pitch prop can haul much more weight than we can.
No. Unlike a propeller drive, a jet can develop full HP at a standstill. We choose an impeller that gives rated factory RPM at full throttle. RPM hardly varies between a heavy load and running fast with a light load.
We manufacture over eighty models. Demand varies and motor designs change. We build for nine different motor makes, from six different motor manufacturers.
The clearance is approximately 1/32 of an inch (.03125). There is some off center between impeller and liner due to manufacturing tolerances so check at the closest point. Less than 1/32 of an inch is ok if the impeller does not rub. More clearance than 1/32 of an inch will drop pressure and performance.
The height is approximately six inches higher than with a propeller. It varies between different motors and boats. When the jet drive is on the motor, set the height so that the leading edge of the intake is flush with the boat bottom. Then test the boat and adjust the height, if necessary, as high as possible without air entering the pump and causing cavitation (slippage).
No. There are too many differences in motor mounting bolt patterns, water pumps, driveshaft diameters, length, spline and shifting mechanisms. The model letter designation will fit only those motors listed in our jet drive kit list
There is a plastic bushing which centers the impeller on the shaft. The impeller never sticks to the shaft, but the drive key will stick in the impeller. On current design, we use a key with a tee cross section which rests on a flat, milled to the end of the driveshaft, including the thread.The impeller with the key in it will slide off the end of the shaft. Under torque, the key cams itself against the flat on the shaft. It is usually necessary to bump the impeller counter clockwise on the shaft until the keyway is perpendicular to the flat, (centered over the flat). Two 3/4 x 1 1/2 x 12 inch pine levers against the housing flange will slide the impeller off. On earlier designs where the keyway in the shaft traps the key, and it is also stuck in the impeller, it is necessary to drill out the brass key to free the impeller. Use a 3/16 drill in the large series and a 1/8 drill on the medium and small series.
10. Can you use any other grease besides Lubriplate 630 AA and why do you recommend against using a lever type grease gun?
Any grease of the same consistency (NLGI 2) which is water resistant should do the job. The main thing is to keep grease in the bearing cavity and water out. We prefer a hand held jiffy lube since it does not create high pressure. If a cartridge type lever gun is used, it should be pumped gently! Excessive pressure will invert the rubber seal lips and seals will no longer keep water out.
No. Unlike propellers, an outboard jet drive at full throttle will turn up to rated RPM even tied to a dock. It is not possible to use a lower pitch for load carrying and a higher pitch for speed. The impeller pitch is chosen to provide rated RPM at full throttle regardless of the weight in the boat.
We lose about 30% of the HP when converting from propeller to jet drive. With less than 25 HP, it is difficult to plane a boat with two people. If it won’t plane, it will not operate successfully in shallow water.
The water intake grill slopes down to the rear to give a scooping effect. The leading edge is flush with the bottom of the boat. The trailing edge is about two inches lower.
Stainless steel impellers work well on motors above 100 HP. They give less slippage on start up and therefore can pickup a heavier load. Top speed of, maybe, one to two mph or better. Below 100 HP, the main advantage is longer wear life.
With lots of luck, Liquid Wrench, Kroll, WD-40, heat, chisels and drills. Salt water is murder. We use all stainless steel hardware and aluminum, but the best way is to remove the jet drive once a year, wire brush the hardware, lubricate with grease or “Never Seize,” and reassemble. You won’t have difficulty after that
Load has nothing to do with RPM on a jet drive (see question number 4, 11). Impeller pitch and diameter is based on sea level operation. At higher elevation, you will lose RPM and may have to drop down one impeller size. Long use in corrosive conditions may create pin holes in the exhaust tube which builds up back pressure and reduces RPM. Excessive RPM is usually caused by air entering the pump. It can be caused also, during start up, if the leading edges of the blades are blunted from gravel. A rough boat bottom, keels or damage ahead of the intake can introduce air, as well as setting the motor too high.
Grease coming out the lube hose is usually light gray. If droplets of water appear, then the seals are leaking and should be replaced. If you grease after the days use, so that the bearing is not stored with moisture in it, you can delay replacement until it is convenient.
This stands for Spot Facer and Drill kit. It is used to drill a hole and spot face a seat to receive a bolt from above at the rear of the engine midsection. This is not used on all motors. See the Jet Drive Kits list.
We have an instruction sheet entitled “Impeller Sharpening” which can be faxed to the customer, or open the Impeller Sharpening pdf.
Since it is necessary to raise the engine about six inches higher when attaching our jet drive, some people use a jack plate instead of fabricating a transom riser block. It is not necessary to use an hydraulic jack plate since once the correct height is established for the jet drive, it is not necessary to change it. Due to a four to five inch set back when using a jack plate, it is usually necessary to attach a twelve inch wide plate to extend the bottom of the boat back to the jet intake to control water height reaching the intake. We have a manual jack plate, part no. 1570, which includes this plate and provides eight inches of travel so that either the jet or propeller drive can be used without removing the motor.
Gouging from gravel is normal. There is considerable surface on the liner to provide pressure sealing. If it is worn such that all the shim washers are on top of the impeller, and blade clearance is still more that 1/32 inch, the liner and/or impeller need to be replaced. If you do replace the liner because of gouging, check performance before and after replacement to see how much, if any, loss the gouging caused.
Early jet drives used a single bearing with two rows of balls. Present design uses an angular contact bearing with a single row of balls, but with higher thrust capacity. The backfit kit allows use of the higher capacity single row bearing in place of the double row bearing.
23. Explain the difference between early type and new type intakes and flanged liners in the large jet drive series.
The early type intakes use liners for 6 5/8, 6 7/8 and 7 3/16 impellers. If the liner is removed, and the mounting holes plugged, a 7 3/8 impeller can be used, but there is no replacement liner for wear. The new type intake uses a liner for 7 3/8. The casting is larger on the outside to accommodate the 7 3/8 liner. It is identified by the bolt head relief in the castings for wrench clearance at the six holes.
The flanged liners eliminate the need for side bolts to hold in the liner. Six studs are held in the main housing with Loctite and fiber lock nuts are used in place of the six mounting bolts. New type 7 3/8 intakes can be modified for flanged liners by removing the centering ring on the intake flange face and chamfering the sharp edge.
On jet drives in which the cooling pump is attached to the top of the bearing housing, it is not possible to provide a flushing inlet. Immersing the jet drive in a barrel of water doesn’t work either, because the water is thrown out. Backing the boat into some fresh water is the only solution. Present production provides a flushing inlet where it is possible to do so, depending on the model. If the parts book shows a flushing bolt and sealing washer, and your early jet drive does not have this, it can be added. Where to locate this threaded hole is called out on our engineering drawings.
The outside diameter is the same, but the pitch is steeper going from 7 3/8 to 7 3/8 D to 7 3/8 V6 to handle higher HP.
About one hour; more the first time, less after you have done it. Raising the boat transom approximately six inches takes longer, depending on how you do it. If you plan to switch between prop and jet, depending on water conditions, winter, summer, etc., purchase a second cooling water pump so that each, the prop and jet drive, have one installed and you don’t have to transfer the pump back and forth.
No. The jet drive shaft length must match the motor shaft length, or you would have to change the entire mid section of the motor.
28. How do we determine what shifting mechanism (cable or rod) to provide with tiller handle steered motors?
If the shift handle is on the side of the motor, it usually requires a shift rod. The shift arm which attaches to the shift handle may be different for cam gates than for the earlier bell crank. If the shift handle is on the front of the motor or on the tiller handle itself, it usually requires a cable assembly. Refer first to the jet kit pictorial / parts list. This will refer you to the pages showing the shift rod and cable mechanisms.
Approximately a 30% HP loss – multiply your motor HP by .7 – example: 50 HP with jet is approximately equal to 35 HP prop drive ( 50 x .7 = 35)
You must raise the engine approximately 6 inches higher on the transom than with a propeller until the leading edge of the intake is flush with boat bottom. (See earlier question and answer)
The boat is important. The best is a flat or slight vee, 10° per side maximum. Aluminum is the best because it is light, easy to repair with minimum maintenance. Fiberglass is heavier and shatters on impact. Inflatables with flexible bottoms introduce air.
Weight is important. Use the chart in the brochure which is based on sea level. Three thousand feet up and higher requires more HP.