Prop shaft - how can you check it is straight enough when removed from the boat

[seumask]

We have been wondering what the source of vibrations on our SO 37 have been at revs higher than 2000. So to this end now the boat is on the hard I have removed the Maxprop and sent it off for servicing. I'm going to replace the Shaft seal and cutless bearing so the propellor shaft is currently out of the boat. It seems to be straight but are there any do at home / in the garage diy checks that I can do to verify it is straight.

 

[scottie]

Yes find truly flat table and roll it
If you want you could get 4 roller bearing set up to support it and rotate check with fixed pointer
There are other variations that will do same job

 

[Tranona]

Take it to an engineering shop or where you are located suggest Hamble Propellers and get it checked out. Simple 5 minute job for them. You need 2 rollers and a dial gauge, so not really a DIY job. Equally getting it straight is simple if you have the gear.

 

[Bobc]

Roll it along a flat floor. You'll soon see if it's bent.

 

[penfold]

Take it to an engineering shop or where you are located suggest Hamble Propellers and get it checked out. Simple 5 minute job for them. You need 2 rollers and a dial gauge, so not really a DIY job. Equally getting it straight is simple if you have the gear.

+1 Quick and easy job for an engineering works.

 

[seumask]

It seems to roll very nicely on the dinning table, smoothly no wobbles. Placing my meter ruler on it looks good too, although its slightly longer than the rule.

 

[fisherman]

I checked all the bits of the drive train, no problems, complete puzzle, until I found the female register in the gearbox flange was ten thou out.

I found it by enhancement. loooong lever (broomstick) bottom end in the keel, with a nail through, which I ran against the register tick over in gear. I could even measure the run out at the top and identify the fault pretty accurately. Took it to a proper, ex Holmans, engineer.

 

[Bobc]

It seems to roll very nicely on the dinning table, smoothly no wobbles. Placing my meter ruler on it looks good too, although its slightly longer than the rule.

Sounds like it's fine

 

[Farmer Piles]

Assuming that your dining room table is truly flat in the engineering sense. Unlikely. The shaft only need be a few thou out, almost imperceptible, and it may cause vibration. I'm a plus one to take it to an engineering works given the little effort involved now that the shaft is out - the hard work done.

 

[Refueler]

With small stuff - rolling on plate glass is the DIY way ... or put into drill chuck and spin ... if its bent or out - you soon see !!

But something like a prop shaft as OP ? Needs serious rotation and Dial Gauge.

Vibration IMHO is usually down to prop ... any nick / inbalance can create vibration. Next is whether shaft is correctly centred in coupling or coupling square to gearbox shaft etc. Next is bearings .....

 

[Rum_Pirate]

We have been wondering what the source of vibrations on our SO 37 have been at revs higher than 2000. So to this end now the boat is on the hard I have removed the Maxprop and sent it off for servicing. I'm going to replace the Shaft seal and cutless bearing so the propellor shaft is currently out of the boat. It seems to be straight but are there any do at home / in the garage diy checks that I can do to verify it is straight.

Is your propellor properly balanced ?

 

[Refueler]

Another question is : Is the vibration at one specific rpm or narrow band ? Most boats will have a 'harmonic or resonant freq' that if engine is at a particular rpm - can lead to vibration. Some boats are worse than others ....

 

[wilkinsonsails]

We had a lot of Vibration at certain (1800) revs from a worn Max prop . Solved with New prop as Darglow recommended.
Also another boat with a new Auto prop , only in higher revs .That turned out to be loose engine mount

 

[IanCC]

Just had mine checked by auto prop shaft place. £10.

 

[ithet]

Take it to an engineering shop or where you are located suggest Hamble Propellers and get it checked out. Simple 5 minute job for them. You need 2 rollers and a dial gauge, so not really a DIY job. Equally getting it straight is simple if you have the gear.

Agreed, get it checked properly to be sure. Swanwick Engineering checked one for me some years ago at no charge.

 

[seumask]

Thanks all for your replies, I'm pretty sure the wear in the prop is the main culprit, but If I can find the time I will try to get it to a proper engineering shop for assessment.

 

[Neil_Y]

If you feel so inclined you can with bearings that are made as a clearance fit...chock shaft and slide bearing by hand along shaft into P bracket/stern tube, this shows up any bearing carriers that may not be inline. If you can slide it in and rotate it by hand then coat in epoxy and the bearing is then inline with shaft and carrier.

 

[fisherman]

Vibration IMHO is usually down to prop ... any nick / inbalance can create vibration.

Except with a big reduction, one of mine was 3:1 so the prop was mostly doing 650rpm and even when badly damaged, or when the cutless neoprene disappeared completely, only vibrated a little. However, the 188hp 1.1:1 used to tell us about every little issue it had. Both of these had the gearbox flange female register out of true, the gearbox maker told me ten thou was within paramaters. The engineer who fixed it scoffed more then a little. He bushed it and machined it true.

 

[Bobc]

Take the shaft AND the prop to someone like Hamble propellers or Sillette, and they will tell you where the problem lies and sort it for you.

 

[fisherman]

Take the shaft AND the prop to someone like Hamble propellers or Sillette, and they will tell you where the problem lies and sort it for you.

With all due respect that's what we did and it was all OK.