My poor prop

martx007 · 10 September 2006, 20:16

Folks,

just chipped one of the blades on my new honda engine whilst coming to.
Think it hit a still submerged metal post. (See attached pic)
Would you still continue to use it, as the engine was ok afterwards or do you think I should replace the prop right away?
Would it effect engine performance much?

cheers
Martin

BogMonster · 10 September 2006, 20:34

I would have thought you may get a lot of turbulence off that?

I changed my prop for a new one and one of the things I noticed (apart from a better top speed which was the main point of the change) is that it seems to run noticeably smoother than before at a fast cruise. The old prop has some damage to the blade tips and leading edges that had been "cleaned up" by the previous owners using a file or something; whether it was putting the prop out of balance, whether it was tip turbulence, or whether the new one is just a better prop I don't know, but the damage was nowhere near as bad as that and I noticed a difference as soon as I opened it up above about half throttle for the first time.

Paul · 10 September 2006, 20:44

I would send it off for a repair. I have recently damaged a prop and it was repaired within a week by steel developments for £50 including p and p. A new prop was £200. My engine manual says that if the prop is out of balance it could damage your engine/gearbox if used for extended periods.

martx007 · 10 September 2006, 22:03

I didin't run it long enough after the accident to notice any turbulence so quit possible.
Cheers Paul, looks like steel developments for me. Having paid out for a new engine, I don't think i'll take a chance doing any more damage!

jyasaki · 11 September 2006, 08:11

That's going to put the prop pretty seriously out of balance. Lots of stress on the bearings and seals in the lower unit. Have it repaired.

jky

Paul · 11 September 2006, 19:46

By the way the other thing that steel developments offered was a change of pitch by 1 inch for no extra cost so if you are unhappy with your maximum rpm maybe you should consider this.

martx007 · 12 September 2006, 08:29

Thanks paul, i've already sent it to them! But it revved up to honda's 6000rpm so I assume it's ok

martx007 · 12 September 2006, 09:35

Just a quick question about prop removal. After removing the cotter pin I was able to unscrew the nut holding the prop on by hand. Is this normal or should it have a torque rating?

Nos4r2 · 12 September 2006, 10:26

It would have a torque value- it's a bad idea for a castle nut to be able to move against a split pin-the pin is there as a lock not a substitute for the right torque.

As to what the torque value IS, I don't know.

BogMonster · 12 September 2006, 10:37

Quote:

Originally Posted by martx007

Just a quick question about prop removal. After removing the cotter pin I was able to unscrew the nut holding the prop on by hand. Is this normal or should it have a torque rating?

Don't know exactly what the mounting arrangement is on yours but on mine there is a metal thrust washer, then the prop, then a nylon washer, then the nut and split pin. The nut on the new prop was only supposed to go to 14nm on a Johnson which is not very tight, I would guess that if the nylon washer compressed over time (the old one on mine had started to split) you might find the nut would be loose enough to undo with fingers. Mine wasn't, but I think it was stuck on the shaft, it needed a few good smacks on the spanner to shift it as it was turning the engine over in gear.

Nos4r2 · 12 September 2006, 19:49

Torque setting for the prop nut for my 50hp Mariner is 55ft/lb-I'd asssume it's going to be around the same on most outboards. In other words, do it up bloody tight!

BogMonster · 12 September 2006, 21:00

Quote:

Originally Posted by Nos4r2

Torque setting for the prop nut for my 50hp Mariner is 55ft/lb-I'd asssume it's going to be around the same on most outboards. In other words, do it up bloody tight!

Not on Johnsons anyway - the figure I quoted for mine was from the "ofishul workshop manual" and if you did the prop nut up very tight the nylon washer under the nut would just split.

I was surprised it was so low, but I suppose the torque from the shaft is taken by the splines, and the thrust force by the metal thrust washer in front of the prop, so maybe it doesn't need to be tight. Other engines may of course be different again, no idea about Hondas.

jyasaki · 20 September 2006, 18:01

My Yam's prop nut torque spec is more like the Honda's: 40 ft-lbs (55Nm.)

Stephen; you can avoid manually turning your motor over by sticking a piece of 2x4 between the prop and the anti-ventilation plate and using that to block the prop as you crank on the prop nut.

jky

BogMonster · 21 September 2006, 03:32

A few good thumps on the spanner while in gear shifted mine, it hadn't been off for six years and seemed as if it wasn't greased. The new prop fitting kit went back on with liberal helpings of the Johnson blue waterproof grease so hopefully will be OK next time