Have a prop problem...

[JC]

Went in last friday with scuba tanks to change props with brand new ones... First thing that was obvious to me is the sbd nuts were loose and the prop too... came out by hand and not with an extractor!!! I tried to figure out what is wrong and decided I was going to put in a new key I have because I felt the one that was there was too big and prop was riding on the key....

So i did that ... I slid the prop back in and immediately noticed the prop could go further up... So I thought everything was good... When I started tigheteing the nut i Got to a point I coulnt go forward... I carefully observed the nut and I made a discovery... the screw at the shaft ended and the nut did not touch the prop!!!!! Can you believe that... What do I do know???

I thought maybe get some big washers to use in between the nut and the prop??? HELP PLEASE...

JC

[Brewster Minton]

prop is not for that shaft or vise versa ? I dont think there should be any washers in there when its done right.

[Capt Dick Dean]

I would not do the washers. Some half ass mind did another half ass job. Take the prop off again, bring it down to the shop and get the measurements. On a 31, it (the prop) should be for a 1 3/8 shaft.

[JC]

I have 1 1/2 shafts..... The props I got are Hy-Torq for 1 1/2 shafts also... The shafts are both 1 1/2 ...on the port side the prop sits in well...the nuts gets a good grip and tightens well (took me about 30 minutes with extractor to take out) on the starboard the problem is it fits well but the screw on the shaft finishes before the nut hits the shaft.... Arent all props standard???

JC

[Carl]

Try prop on a spare shaft and see if it is the prop. causeing the problem.

Prop Bore can be too large, or some yahoo hit the face of the prop hub making too short.

If prop is correct then the culprit may be the shaft, a few thousands too small on the taper and you will have the problem.

Yes they are supposed to be standard making everything interchangeable, but poop happens.

Can a washer be placed between nut and prop? Yes, but you will need to make sure you have adaquete clearance between prop and cutless. 1 to 1-1/2 times the shaft diameter should be your clearance.

If you got a great deal on the props maybe its worth it to use a washer/shim, otherwise I'd bring them back for a new matched set.

[In Memory Walter K]

I know it's a pain in the ass but if the port one fits right, pull it and slip it on your starboard shaft. If you have the problem again, it's the starboard shaft. If it fits, it's in your new starboard prop's hub. Walter

[scot]

The only way to solve your mistery is to measure/Mic BOTH prop bores OFF the boat. If the props ARE the same then the problem is that the shaft machine tappers are not correct.

If the props are NOT the same...send them back, or over-bore the bad one to 1 5/8" or 1 3/4" and add a spacer to achieve the correct 1 1/2" bore.

Washers are cheaper "IF" the prop bore tapper angle is correct and the prop doesn't whobble on the shaft....but not recommended practice. Make sure you have enough space between the prop hub and the strut..target distance here is around 1".

Scot

[Rawleigh]

Scot makes a good point about whether the taper is correct or not. If it is just a little off the prop will move under power and destroy itself over time.

[JC]

I am trying to decide what to do. As allways living far away from where we purchased the props is not very helpfull...

Taking the props out ...inside the water can be a pain in the but but If I have to do it I will.... my guess its the shaft thats the problem.. I dont think the taper is wriong I think the screw wasnt advance enough.... the key I had in there was bigger than it should by a couple mm so when the prop was tightened it helped tighten the prop... When I put in the original key the nut did not touch the prop so something is not right... the prop looks like it fits snug to the shaft so maybee just some washers can help...

I took the boat out after puting the bigger key in and the prop and could not fee any vibration and boat ran great....

Some additional information I find curious is that on that same shaft the zincs are deteriorating faster and the nuts where being corroded... could it have something to do with the prop not binding to the shaft???

Thanks,

JC

[Rawleigh]

JC: You shouldn't have to rely on the key for anything but rotational torque. The propeller should fully engage the taper and be pressed on by the nut even without the key in place! A properly fitted taper can produce enough friction, even with lubrication, that it actually absorbs some of the rotational torque and helps save the key and keyway. That is why they are so hard to take off sometimes. Most people in the know recommend that you lap the wheel to the taper with valve lapping compound to remove any high spots so that you have uniform interference fit along the whole taper. The wheels and shafts should then be cleaned of all compound and the wheels put on with a light coating of grease, tef-gel, etc. so that you can get them off again. Hard to do in the water though!!!

[In Memory of Vicroy]

JC - I see nothing wrong with putting some washers between the rear of the prop hub and the nut if you can maintain the "one shaft diameter" distance between the rear of the strut and the forward end of the prop hub. That rule of thumb is the maximun, so if its a little closer, that's OK.

Yes, a loose prop will cause the zinc to corrode faster since the props may no be firmly (electrical-wise) in the bonding system.

What you are seeing may be as simple as whoever cut the threads on the shaft left them a little short. I'm assuming that using some washers (you know this I'm sure, but use stainless, pref. 316) should be fine as long as you get a full nut on the threads and can get a good cotter pin thru the hole or crown slots in the nut.

Simple fixes are better than hard ones. Remember, none of these boats are "stock", especially the ones that have been repowered.

UV

[Carl]

Your prop is riding the Key, not a good scenario.

Your prop has to go up the taper the same distance with or without the key installed fit for a proper install.

If the prop rides the key (Binds on the Key) yes it will tighten up as it is wedgeing itself in place. This will throw your wheel out causing your shaft to fatigue.

If you go washer route, naval bronze will work well also.

Uncle Vic, yes our boats may not be stock, however we can try to keep our components stock. If you whack a log cruising out of a distant Port, it would be helpfull if you can call the local shop and ask for Wheel, Shaft, Nut Set, Cutless Bearing etc for a 1.5" shaft and know if it is machined correctly it will fit, as the 1.5" assemble is stock.

Old Chris Crafts had there own stlye of Shafts and it caused havoc.

[IRGuy]

There was a discussion about prop mounting on shafts in the Boatdiesel forum a short while ago. The bottom line was that props should mount tight on their taper, with the key only serving as an alignmant tool.. in fact it was implied that the key is only necessary if the props are not mounted correctly. It was also suggested that the props and shafts should be lapped for a tight fit, reference was made to the common Morse taper used on tools such as drill presses and lathes, where the taper is all that holds the chucks in place, and there is no key.