I just changed my stuffing box this year to a dripless model. Since launching, I'm hearing a rhythmic "thump" when the engine is in gear (nothing in neutral). As the engine speed increases, the noise seems to dissipate. My best guess is that I either have a bad strut bearing or the shaft is out of alignment. I guess my big question is, How do I determine which it is, and can it wait until the fall haul to repair it? Has anyone done a shaft alignment themselves? How difficult is it? Thanks! Ernie
What does a bad strut bearing sound like?
- Thread starter capejt
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Shaft Alignment
Disconnect the shaft coupling from the transmission (4 bolts) Push the coupling up to the transmission and check the clearance all the way around using s feeler gauge. If it's tight on one spot and you can slip the blades of the feeler gauge in other spots it's time to adjust the motor mounts. Adjustment is required if a blade or more than .002 - .003" easily slips in. By the way it is common to replace some mounts after 10 -15 years of service or so. Since it's summer jump in the water and try and wiggle the shaft in the strut. If you get more tha 1/8" of free play change the bearing
Disconnect the shaft coupling from the transmission (4 bolts) Push the coupling up to the transmission and check the clearance all the way around using s feeler gauge. If it's tight on one spot and you can slip the blades of the feeler gauge in other spots it's time to adjust the motor mounts. Adjustment is required if a blade or more than .002 - .003" easily slips in. By the way it is common to replace some mounts after 10 -15 years of service or so. Since it's summer jump in the water and try and wiggle the shaft in the strut. If you get more tha 1/8" of free play change the bearing
Shaft Contacting Log Tube?
The packing in the original gland had the effect of centring the gland over the prop shaft. Dripless glands do not do this so, if your rubber extension on the log tube is a little askew, the vibration of the shaft can cause it to knock. Another source is if the shaft can contact the inside of the log tube. I fitted a dripless gland and immediately had this problem. The cure is to move the engine so the shaft is centred in the log and then do the alignment with the flanges and feeler gauge. Good luck.
The packing in the original gland had the effect of centring the gland over the prop shaft. Dripless glands do not do this so, if your rubber extension on the log tube is a little askew, the vibration of the shaft can cause it to knock. Another source is if the shaft can contact the inside of the log tube. I fitted a dripless gland and immediately had this problem. The cure is to move the engine so the shaft is centred in the log and then do the alignment with the flanges and feeler gauge. Good luck.
What Does a Bad Strut Bearing Sound Like
CapeJT: The thump you are describing sounds like a cavitation problem. This generally happens when the prop is too large for the boat and its blades are too close to the hull. I don't know why it would go away when you increase speed. Probably it doesn't and you just can't hear it. Your diver can easily check the clearance between the blade and the hull for you. You could then contact a prop shop for advise. Your diver can also check the strut. If the strut bearing is going bad, it creates a screeching sound sort of like running your fingers down a blackboard!! When you hear it for the first time you won't forget it. If it is cavitation, you can live with it until the end of season. If it is the cutlass bearing, it is not a good idea to put it off. It is not a big deal to replace and could be done as an "in and out" and in a couple of hours.
CapeJT: The thump you are describing sounds like a cavitation problem. This generally happens when the prop is too large for the boat and its blades are too close to the hull. I don't know why it would go away when you increase speed. Probably it doesn't and you just can't hear it. Your diver can easily check the clearance between the blade and the hull for you. You could then contact a prop shop for advise. Your diver can also check the strut. If the strut bearing is going bad, it creates a screeching sound sort of like running your fingers down a blackboard!! When you hear it for the first time you won't forget it. If it is cavitation, you can live with it until the end of season. If it is the cutlass bearing, it is not a good idea to put it off. It is not a big deal to replace and could be done as an "in and out" and in a couple of hours.
thanks for the ideas
Thanks for the responses. I don't think it's the cutlass bearing since there's no screeching noise. I doubt it's a cavitation problem, since the prop is the same as before the stuffing box replacement. Although it sounds like a lot of work, I tend to think it's more like Donalex was describing. I'm going to have to check out a few things when I go get to the boat next. Of course, I'm still open to any other suggestions. Thanks again!
Thanks for the responses. I don't think it's the cutlass bearing since there's no screeching noise. I doubt it's a cavitation problem, since the prop is the same as before the stuffing box replacement. Although it sounds like a lot of work, I tend to think it's more like Donalex was describing. I'm going to have to check out a few things when I go get to the boat next. Of course, I'm still open to any other suggestions. Thanks again!
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