Knocking noise in gimbal when trimmed up

[Boze816]

I need to start at the beginning here. I have a 2005 Chaparral with a 4.3GL and a volvo penta sx outdrive.

This all started when I was getting water into the bellows. I pulled it all apart and found the salt water rusted the gimbal bearing. the gimbal bearing housing was a mess, so I cleaned it all up and didn't see any damage where the bearing sits. Once the housing looked good I replaced the gimbal bearing and seal. I did have some surface corrosion on the outdrive shaft. I cleaned the shaft, changed the oil in the outdrive and reinstalled the assembly. When I went to test, I noticed a knocking when trimmed up. I realized it went away when trimmed down and went ahead for a water test.

On the water I noticed a knock when turning the boat. So I brought it back home assumed it was the u-joints. I ordered a new outdrive shaft. Once it came in I took the outdrive off and replaced the shaft. When removing the outdrive I noticed the gimbal bearing on the shaft and the outer grease seal of the bearing bent over. So, I ordered another bearing and waited for its arrival.

In my mind it makes sense that the gimbal bearing was pulled out of its spot and slapping around when the u-joint is being bent. I installed the new bearing with the outdrive with the new shaft. Buttoned all up and started the engine up and as it was running I trimmed the outdrive up and I hear it knocking again. Well I assume its the gimbal bearing sliding out of its housing and slapping the sides again. I pull the outdrive off again and the gimbal bearing is sitting in its housing as it should. I also checked used an alignment tool to verify the alignment of the engine which seems to be good.

I've searched around for answers, but not finding anything. Does anyone have a possible idea. Thanks

 

[Scott Danforth]

your u-joints most likely need to be replaced.

 

[Boze816]

your u-joints most likely need to be replaced.

The outdrive shaft had new U-joints that came with it.

 

[Boze816]

 

[Bondo]

Ayuh,...... Welcome Aboard,..... Yer raising the drive well past trim, into the tilt range, which is waayyy to high for u-joints,.....
Does it knock when only in the trim range,..??

 

[Boze816]

Ayuh,...... Welcome Aboard,..... Yer raising the drive well past trim, into the tilt range, which is waayyy to high for u-joints,.....
Does it knock when only in the trim range,..??

So this is a normal sound?

 

[Bondo]

So this is a normal sound?

Ayuh,...... overstressing the u-joints leads to all sortsa odd noises,....

 

[ESGWheel]

It’s all about 2 things: terminology and the limits of U-joints, so was glad when you posted the video.

Terminology: Trim and Tilt.
Trim is the small angle that you can move the drive up and down from its “down” position. It effects how far the bow of the boat rides up (or down) while under power and again is very limited. Probably not needing to be said but you start out with the drive fully down and as you get up on plane, you “trim” up a little, like a few seconds. Trimming up more puts you into the “Tilt” range.

Tilt is when you have raised the drive up past about 6 degrees and now you are operating in the “need to be careful” range. See picture out of my VP Operator’s Manual. I suspect that regardless of the sterndrive these guidelines apply as there are physical limits to U-Joints. BTW I have a 2005 SX on my Larson.

As you can see the range of 6 to 29 degrees is considered the be careful range > limit RPMs to about idle. Higher (more raised) than that and, if running, you start to destroy U-Joints and as you are experiencing damage to the gimbal bearing, etc. While I do not recall ever seeing it defined “Zero Degrees” is when that double U-Jointed drive shaft is a straight line. So, when trimming all the way down, it is considered a slightly negative angle. Others will know about this better but in my mind, this is how I think about it.

Limits of U-Joints
One aspect dictating the angular limit of a U-joint is the rotational speed. For something like your steering mechanism on your car a double-jointed u-joint (like the sterndrives have) can accept something like 60 degrees because its not spinning fast. Bump up that speed to 1000 or more RPM and ouch.

And another limiting aspect is simply the design. Thinking in terms of extremes you can imagine a U-Joint not being successful trying to be at a 90-degree angle and rotating. But a 5-degree angle, no issue. So somewhere in between is where it can successfully operate. And they make it a double U-Joint in part due the need for power transmission at angles greater then 1 U-Joint can handle (with 2, the angle of each is ½ of what it would be with one) and to allow the sterndrive to tilt all the up as it does.

Suggestion: pull the drive again and see if you have popped that gimbal bearing and check the U-Joints.

 

[Horigan]

Bottom line, don't start or run your engine until the drive is down. You can trim up a bit while running within the operational range for raising and lowering the bow. If it's quite in that range, while turning, you're good to go with all the new parts you've installed.