Water Pump - How to Test

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StalkerFox
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Water Pump - How to Test

Post by StalkerFox » Wed Jan 24, 2018 8:03 am

I am suspecting my 1994 CB 400SF picked up heat-damage from running dry. And I am wondering if there is a way of testing the pump while on the bike for proper operation?

The Long Story:
We bought 1994 model CB 400 SF a year ago for a good price. I paid and drove the bike home in the rain over 200km. Only hassle was woody front brakes and the steering being loose (lock washer on the retaining nut was missing). Bike cruised at 110km but I dared not pressed it further due to the brake and steering issues.

During the next weeks we re-sealed and re-filled the fork (the thicker oil make a hell of a difference), rebuilt the front and rear brakes and fitted new pads. This made a world of difference. When I check the water on the over-flow tank I noticed it was dry ... and dusty. So I washed it out and checked the radiator. Adding a small amount water filled it up. No problem right?

As time goes on the bike has trouble idling when hot and one or twice cut out while driving. Figured the issue was carburetor related. The bike was running rich and the boots between the Carbs and the air-box had perished many years ago. Took the bike in for a oil change and to have the carbs cleaned and balanced. A few weeks later I get a call from the mechanic saying the bike wouldn't start and there is no compression. Fetched the bike and pulled the head off.

Massive amounts of carbon build up on the valves. Decided to re-ring the pistons since we had a set of stock tings and +0.25mm rings. Motor still had original sleeve hatching so installed and checked stock rings. Notice 'water-line' marks on the one decliner (#3 if I recall). Due to this we have the head skimmed and cylinders pressure tested. Barrels are fine but head had slight warp before machining.

Spend weeks finding shims and eventually had some machined to fit. So now the valves are lapped and gaped. Compression at started RPM comes in a bit low but uniform between all the cylinders. Figure this would be due to the new rings and low turning speed of the motor.

And then we installed the head cover ... and we snapped four of the cover bolts at 10 Nm ... I am taking them in today to have them extract the bolts/install helicoil'ed. But the bolts that broke appear to brittle/soft under the file compared to regular 8.8 grade bolts. Which makes me think that they annealed under overheating?

And thus we have stripped and check the cooling system finding noting wrong but lots of rust and a missing drainage bolt. This might have been taken out by the mechanic while working on the bike, but I picked up the bike dry from the work shop.

Stated filling the radiator last night and made sure the inlet to the pump had water. Ran the bike on the started and you can see the water in the outlet pipe drop and rise, but nothing to the effect of 'pumping'. I have checked the impeller and it appears to be fine and rotates along with the motor under the starter. I imagine I would need more RPM than the started can provide in order to get any flow due to the simple design of the impeller.

Thus the question: How do I test the water pump while attached to the bike?


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