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View Full Version : Harmonic Vibrations and Crank Drive water pumps



CDMA
06-19-2002, 10:01 AM
In my recent musings with my new “350” I have rigged it with a crank drive water pump. This is an OEM pump used on a 350 Volvo engine. I have the option of using either this pump or a belt drive mercruiser pump. I elected to use the crank drive pump for simplicty reasons. I really liked not having the additional belt and the Crank drive pump seemed like a nicer packeage. Well after running the boat this weekend I have a few concerns. First of all it was very expensive to have my 350 all internally mallory heavy metal balanced but I thought it was a good investment. Now I get the boat running and I see this raw water pump hanging off the crank. While I made sure I got her on straight there still is a slight “wobble” in it and I was wondering if this is going to basically defeat all the effort I put into having a properly balanced engine. I made up all custom spacers and I am confident the pump is on straight but I still see this slight wobble. It is minor enough that I could see it being considered normal but I wanted to hear if any of you have had any experiences with this. I would prefer to stay with the crank drive pump but I do not want to damage my new engine. Any thoughts from the peanut gallery?

Chris

Forrest
06-19-2002, 11:12 AM
One of my crank driven pumps (Johnson F6B-9) on my Magnum has an ever-so slight wobble to it. The other is dead-on straight. Also the crank mount pump on my X-18 is straight as well. Without taking it out and checking the roundout of the flange with respect to the impeller shaft, I would suspect that's where you would find the problem. Also, did you use a factory steel Volvo-type crank pulley that has the pump alignment bosses, or did you go with an aftermarket aluminum pulley, like I did?

CDMA
06-19-2002, 11:31 AM
Forrest I was hoping you would respond. Does this wobble bother you?

I am actually using a Merc pully. I hade to made sleves ( 3/8 id and 1/2 od) to go over the bolts to make sure it was in straight. Seemed to fit in straight. I think I might try to find another way to make it not wobble. Maybe some sort of centering thing. I don't know.

Forrest would you happen to have that picture of your x-18 383 floating around?

Chris

Forrest
06-19-2002, 11:44 AM
Chris, I would perfer to get rid of the wobble and if you bought your pump new and can show that it is not straight to whoever you sold it to you, you may have a valid warranty claim for a replacement. If that's the case, I would go that route.

I may have a picture of it floating around, or maybe on the trailer . . . let me check.

CDMA
06-19-2002, 12:00 PM
Not a new pump but this thing has a serious cast iron flange. And I trued it up on the surface mill. I am confident that is straight. Looks more like a not centered deal then a mis-aligned flange....to me.

Chris

GEOO
06-19-2002, 03:30 PM
Chris,
My old one had a slight wobble in it, not sure about my new one. (Johnson F6B-9) Next time I run I'll take a look. GEOO

Forrest
06-19-2002, 03:50 PM
Chris, I was referring to the flange face with respect to the centerline of the impeller shaft. If the shaft was not pressed on exactly straight or if the hole in the flange for the impeller shaft is mis-aligned in any way, it will wobble. The only way to know for sure is to remove the pump, mount in a vice and use a dial indicator to measure the run-out of the flange both axially and laterally.

CDMA
06-19-2002, 03:51 PM
Ok so other people also have had a slight wobble. Now the question is how bad do you think this is for the engine? Is this something that will have little to no effect or a big deal. I look at it from an engineering sense and I think that it would mess up the internal balancing then from another side I see it practiacally having little effect.

Thanks as always

Chris

CDMA
06-19-2002, 03:56 PM
Here we go. Forrest's engine.... Note the pump on the crank.

http://imagehost.auctionwatch.com/bin/imageserver.x/000e5ad0/bowtiekid/x18motor.jpg

Forrest
06-19-2002, 04:24 PM
I thought that picture looked familiar! That pump doesn't wobble at all. I think its a Johnson F5-something. Also note that there is no pump body anchor arm. That is not recommended, but this crank mount pump replaced the Mercruiser belt drive pump and the plumbing is on the starboard side of the engine. All of these Volvo-type crank mount pumps when mounted with the pump arm attached, make the in/out ports point to the port side of the engine, and that wasn't going to work with the closed cooling system. I've been running it that way for over 40 hours and have not had any problems, but then again, it the pump bearings ever seize, it will probably wrap the hoses around the pump body and tear 'em out by the roots! The pump you are lookin at is aligned by nylon bushings inserted tightly through the bolt holes in the flange using Allen-headed cap screws and washers to hold it on.

Ralph Savarese
06-19-2002, 07:25 PM
Chris,
My pump wobbles, New pump and pully and balancer. Also so did my old one .I don't feel there is a need for concern my pumps have been wobbling for at least 7 years never had a problem. I run constantly 5k rpm.
Ralph

MOP
06-19-2002, 11:21 PM
This works!! Find an O Ring kit, find one that fits the bore and the bolts fairly snug. Put them on the bolts down near the thread top even if they slide up a little they will center things up. I have run these Volvo pumps over 6k smooth as glass. There are some very good after markets with higher volume if you need them.