Water Pump Impeller Tips for a 35 Johnson Outboard

Written by will charpentier
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Water Pump Impeller Tips for a 35 Johnson Outboard
There are tips and tricks for any outboard, including the Johnson 35. (toy outboard motor image by pearlguy from Fotolia.com)

Outboard motor technicians always have a few shortcuts that save them time and you money. Like most outboards, a Johnson 35-horsepower outboard motor's water pump undergoes an invasive inspection every year. As with any outboard motor, there are a few tips and one rather large trick that make installing the impeller in water pump a little less of a hassle -- if you turn the inspection into a maintenance opportunity.

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Beyond the Scope of Inspection

Replacing the old impeller with a new one during the inspection is a good idea since the pump housing and the impeller are already off the outboard. Pulling the insert from the housing and the O-rings on the top of the pump housing can also be done at this time. Doing this kind of maintenance during an "inspection" helps ensure that your pump won't fail you on the open water.

The Impeller Plate

Inspection provides an opportunity to put new gaskets go on the impeller plate. Don't waste time trying to salvage the old one -- and be sure to scrape away any gasket material remaining on the plate itself. Use a wooden spatula -- the kind you'd find in your kitchen, to avoid scratching the plate. Of course, if the plate is damaged, replace it with the plate from the replacement kit.

The Trick

Pushing the impeller into the pump insert before you smear the gasket sealer on the outside of the insert will save you a world of trouble. While this method isn't found in the shop manual, it is found in the repair manual. Getting the impeller into the insert when it's in the stable pump body is difficult at best. Doing so while there's sticky glop, like the required coat of gasket sealant, on the outside of the insert is almost impossible.

If It Sticks, Oil It

You have to hold the impeller steady in the pump body while you insert the driveshaft through it. Otherwise, the driveshaft will push the impeller out of the insert. You can avoid a large part of the problem if you put a wee bit of household oil on a clean rag and wipe the driveshaft with oil. Then, put a few drops of oil in the hole in the centre of the pump, at least enough to oil the hole in the impeller. It's like drinking water to lubricate your throat, so you can swallow a pill.

The Driveshaft Turns Counterclockwise, But....

Both the driveshaft and the pump impeller turn counterclockwise. You have to turn the driveshaft to align the pin with the slot in the pump, the insert and the impeller, but since you're looking up at the bottom of the pump as you slide it down the driveshaft, you need to turn the shaft clockwise, at least from your point of view. If you forget this, you will damage the impeller beyond repair and require another replacement.

Ensure a Lasting Engagement

A driveshaft that spins without turning the impeller doesn't deliver the cooling water your needs motor needs. This means that your motor will -- not may, but will -- suffer catastrophic internal damage. If you look through the top of the water pump housing where the driveshaft penetrates the pump before you set the driveshaft seal in place, you can ensure that the impeller pin has fully engaged the impeller drive pin. If it hasn't, it's cheaper to take the pump apart again and start the project over than it is to buy a new motor.

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