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Driveline vibration, what’s normal?

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chris.nackers
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Driveline vibration, what’s normal?

Post by chris.nackers » Mon Oct 05, 2020 10:07 pm

Been doing a bunch of work to the sportsman. One thing I’ve noticed especially when running it on the dry, is some vibration shaking the boat. Believe it’s coming from the driveshaft or prop.

Not sure if it should vibrate at all or be smooth as butter. Definitely noticeable at 1500 rpm’s.

I do run a hose spraying on the strut in addition to water for the engine to mar sure those bearings/bushings are getting water.

I was doing some engine work so needed to run and test on land.
'47 Sportsman/Deluxe Utility U-18-123

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Bilge Rat
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Re: Driveline vibration, what’s normal?

Post by Bilge Rat » Tue Oct 06, 2020 6:37 am

I would suggest disconnecting the prop shaft from the transmission to isolate the engine, then run it in gear. If you have enough clearance between the drive flanges and prop log to uncouple, try that first. If the flanges aren't already marked, mark then so they can be reassembled the same as before. Have you tried to move the prop shaft sideways in the cutlass bearing to see if there's play? These bearings do wear and dry out from storage and running in the water might mask the vibrations. You also could have the prop shaft rubbing on the shaft log indicating a misalignment.
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chris.nackers
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Re: Driveline vibration, what’s normal?

Post by chris.nackers » Tue Oct 06, 2020 7:17 am

Ok I will try those things. I was thinking if I disconnected the shaft I would have to do a alignment again but based on what I was reading that shouldn’t be the case.

I would say there is a tiny bit of play in the strut.
'47 Sportsman/Deluxe Utility U-18-123

chris.nackers
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Re: Driveline vibration, what’s normal?

Post by chris.nackers » Tue Oct 06, 2020 7:21 am

I’m not sure where I could get replacement cutlass bearings from as well.

Still going through the boat, but I am concerned that the strut might be bedded in 5200. The bottom was redone years ago.
'47 Sportsman/Deluxe Utility U-18-123

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Re: Driveline vibration, what’s normal?

Post by jfrprops » Tue Oct 06, 2020 8:26 am

just kicking this around in my mind: I don't think vibration on the hard, water applied as you say, is necessarily relevant. In my experience running on the water is another thing entirely. Sadly we must often launch and relaunch and fiddle and test...but to condemn the components based on a land test would not be wise. I think you need to launch and test. Might be good to replace the cutlass bearing while on the hard...but alignment, even on a runabout and certainly on a big cruiser, can change when ON the water. IMHO.....John in Va.
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Re: Driveline vibration, what’s normal?

Post by chris.nackers » Tue Oct 06, 2020 8:08 pm

jfrprops wrote:
Tue Oct 06, 2020 8:26 am
just kicking this around in my mind: I don't think vibration on the hard, water applied as you say, is necessarily relevant. In my experience running on the water is another thing entirely. Sadly we must often launch and relaunch and fiddle and test...but to condemn the components based on a land test would not be wise. I think you need to launch and test. Might be good to replace the cutlass bearing while on the hard...but alignment, even on a runabout and certainly on a big cruiser, can change when ON the water. IMHO.....John in Va.

Appreciate it. I will replace the cutlass once I figure out where to get one. I have no issues replacing that as I have zero clue as to when it was done last.
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Re: Driveline vibration, what’s normal?

Post by maritimeclassics » Wed Oct 07, 2020 7:55 am

Vibrations are usually one or more of 4 things. 1. Miss alignment from engine which can be fairly easy to fix. It should be .003 face to face coupler to engine. 2. Prop is bent or out of balance. You can remove it and send it it for repair. 3. Shaft is bent. 4. Cutlass bearing is worn. To check it grab onto the prop and push up and down, there should be no play in the shaft to cutlass bearing. We can get any size you need. Just need to know the size of the shaft and the then the inside diameter of the strut shaft hole minus the cutlass bearing and then the length of the strut where the bearing goes. The outside diameter of the shaft hole minus the diameter of the shaft gives you the size of the cutlass bearing needed then you need the length. If it was in our shop I would check the bearing and replace if needed then align the engine to the shaft and run the boat in the water. Process of elimination and you just knocked out 2 of them.
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Re: Driveline vibration, what’s normal?

Post by chris.nackers » Wed Oct 07, 2020 8:00 am

Great will check those things.

Another question, I noticed the prop is a little loose. As in I can move the nut a little bit on the shaft, as much play as the cotter pin allows. I assume that should be tight and not have some play?

I was on the water for 6 hours yesterday, so got some good time in. I have some engine hesitation around 1500 rpms as well. Runs great above 2k and runs fine at 1k. So I’m assuming that is the carb and probably the mid jet. Need to dig into more but I believe I saw the Zenith had idle, mid jet and full throttle jet.
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maritimeclassics
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Re: Driveline vibration, what’s normal?

Post by maritimeclassics » Wed Oct 07, 2020 11:02 am

Yes it should be tight.
Family member of Chris Craft founder
Owner of Maritime Classics
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Ph# 231-486-6148

Restoration Projects:
1936 25' Gar Wood Custom
1947 Ventnor Hydroplane
1957 17' Deluxe Runabout
1948 25' Chris Craft Sportsman Twin
1959 19' Sliver Arrow Hull #75
1929 26' Chris Craft Custom Runabout
1937 25' Chris Craft Custom Runabout

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Re: Driveline vibration, what’s normal?

Post by chris.nackers » Wed Oct 07, 2020 1:30 pm

Ok next one since you are on a roll.

Boat had a 13x13 prop on it, but also came with a 12x14

What’s appropriate for a 18 foot sportsman with a Chrysler Crown M7?
'47 Sportsman/Deluxe Utility U-18-123

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maritimeclassics
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Re: Driveline vibration, what’s normal?

Post by maritimeclassics » Thu Oct 08, 2020 7:38 am

That all depends on the RPM rate on the engine. I don't have a manual for that engine so I can't tell you what that is but you should not exceed that RPM rate. The 12x14 is going to give you more RPM but not by much. The best thing to do is to find out the rating for the motor and then run the boat wide open and see what the RPM is on both props. Your hull card from Mariners Museum would also have the prop number the boat came with.
Family member of Chris Craft founder
Owner of Maritime Classics
http://www.maritimeclassics.com
Ph# 231-486-6148

Restoration Projects:
1936 25' Gar Wood Custom
1947 Ventnor Hydroplane
1957 17' Deluxe Runabout
1948 25' Chris Craft Sportsman Twin
1959 19' Sliver Arrow Hull #75
1929 26' Chris Craft Custom Runabout
1937 25' Chris Craft Custom Runabout

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Re: Driveline vibration, what’s normal?

Post by chris.nackers » Thu Oct 08, 2020 8:21 am

Well I have the hull card but that would have been for the M6, and I have the M7 which is 115 hp over the 95 hp M6. It’s 115 @ 3200 rpm’s. So I’m assuming that’s the speed I don’t want to exceed.

I could only run about 3000 rpm with the 13x13 prop at full throttle. I put the 12x14 on and will test that out today or tomorrow to see how it runs.

I did measure up the strut so I’ll give you a call to order that cutlass bearing.
'47 Sportsman/Deluxe Utility U-18-123

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