Cruising to Idle Speed Vibration

[tahoejag]

While coming off cruising speed (2800 -3000rpm) going to idle speed (no wake speed) Note: it happens when I gradually yet quickly change this throttle speed....I would get a great amount of vibration within the boat when slowing down. However, the vibration is not noticed if I slowly reduce speed.

Once at idle speed, no more vibration. Also while running at cruising speeds no vibration. (boat runs fine) and going from idle to cruise speed all is good.

Is this vibration normal and caused by slowing down too quickly?? If not, what to look for? Thanks in advance for the input.

 

[tpenfield]

Re: Cruising to Idle Speed Vibration

There are a lot of things that it could be. . .

U-joints, gimbal bearing, engine alignment, engine mounts, propeller., etc.

it would be best if you could isolate specifically where the vibration is coming from.

 

[tahoejag]

Re: Cruising to Idle Speed Vibration

There are a lot of things that it could be. . .

U-joints, gimbal bearing, engine alignment, engine mounts, propeller., etc.

it would be best if you could isolate specifically where the vibration is coming from.

I would (dont like doing this) but assume that this is not normal then....???

The vibration is coming from aft and also noticeable in the floor...it would be compared to having a bad prop maybe. However, the prop visually is in good cond, but could be out of balance??? Other mechanics of boat check ok.

 

[Fishermark]

Re: Cruising to Idle Speed Vibration

Try a spare prop and see if that helps. If you don't have a spare prop, now is a good time to get one.

 

[achris]

Re: Cruising to Idle Speed Vibration

Sounds like over-run on the dog clutch...

 

[tahoejag]

Re: Cruising to Idle Speed Vibration

Try a spare prop and see if that helps. If you don't have a spare prop, now is a good time to get one.

Yes...have one and will try it.

Sounds like over-run on the dog clutch...

Honestly...A bit familair with the operation of the dog clutch but haven't a clue what over-run means/is. Is over-run normal?

 

[achris]

Re: Cruising to Idle Speed Vibration

When the propeller is being spun by the water faster then the propeller shaft is being turned by the engine, the dog-clutch will ratchet over... That is over-run. Go outside and put the engine in forward gear (with it NOT running). Now spin the propeller in the forward direction... That clunk-clunk noise is the dog clutch 'over-running'. It will always happen when you pull the throttle back quickly while remaining in gear.

Try this next time you're out. Pull the throttle back quickly (as you normally do to get the vibration), but pull it all the way back to NEUTRAL... I'll bet the vibration disappears...

Chris.......

 

[tahoejag]

Re: Cruising to Idle Speed Vibration

When the propeller is being spun by the water faster then the propeller shaft is being turned by the engine, the dog-clutch will ratchet over... That is over-run. Go outside and put the engine in forward gear (with it NOT running). Now spin the propeller in the forward direction... That clunk-clunk noise is the dog clutch 'over-running'. It will always happen when you pull the throttle back quickly while remaining in gear.

Got it on the over-run. Its funny you mention about the dog clutch noise...previously I posted that I get a ratcheting noise in neutral on the trailer and it was recommended that I adjust shift cable and/or replace it. Could be related.?. I can do the cable adjusting and any other testing on the trailer but water testing will have to wait til spring.

 

[achris]

Re: Cruising to Idle Speed Vibration

Has the noise only started since you adjusted the cable? If so, it may have been just on the edge of engagement in FORWARD. You may have adjusted it too much towards REVERSE...

 

[tahoejag]

Re: Cruising to Idle Speed Vibration

Has the noise only started since you adjusted the cable? If so, it may have been just on the edge of engagement in FORWARD. You may have adjusted it too much towards REVERSE...

The ratcheting noise in neutral was there before it was recommended to adjust cable (which I have not done yet :facepalm but it was said, as you stated, could be just off a bit. Will most likely be spring maintenance.....

 

[achris]

Re: Cruising to Idle Speed Vibration

ok.. You have plenty to check in the spring. Might be nice to try and work out which way the cable is out of adjustment before you adjust it. If you can get wife/child to move the gear lever very slowly while you turn the prop you can see which way the adjustment needs to go. While you are turning the prop forward, have them move the lever forward. If you feel the clicking stop before the drive engages forward, you know the adjustment is too far to reverse. If it just gets worse, then the adjustment is too far towards forward... easy....

Chris.......

 

[tahoejag]

Re: Cruising to Idle Speed Vibration

ok.. You have plenty to check in the spring. Might be nice to try and work out which way the cable is out of adjustment before you adjust it. If you can get wife/child to move the gear lever very slowly while you turn the prop you can see which way the adjustment needs to go. While you are turning the prop forward, have them move the lever forward. If you feel the clicking stop before the drive engages forward, you know the adjustment is too far to reverse. If it just gets worse, then the adjustment is too far towards forward... easy....

Chris.......

Will do.... I'll adjust cable then run boat first and see result; which I do know for fact it does need to be adjusted. If need be, then switch to spare prop.

Thanks again for all the input!