New member looking for prop repair help

[thenline]

Good morning, everyone, and thanks in advance for your help. I googled prop repair last night and found this forum; I'm amazed at the wealth of information and knowledge found here, and the willingness of members to help out fellow boaters. Very impressive!

I recently purchased a project boat - a 16' Starcraft deep-V w/1987 Mercury Classic Fifty outboard. The boat was rough and the outboard in need of service. It was thrown together by a dealer looking to dump it at a consignment auction, and the tech that did the work has since been fired (I spoke to the owner after finding numerous issues - but that's a whole nother story). After rebuilding the carbs, pump, lines, etc., and having my local dealer adjust all the linkages and timing, it runs well and moves the boat around on the Mississippi pretty well. However, the prop - which looks like it's almost new - has a couple dents on it that I'd like to address. I also noticed that the aluminum trim tab above the prop is broken off.

I've had the boat out on the water a couple times since getting everything back together/the outboard serviced and I've noticed a couple things. One, it's a pooch out of the hole. Two, while running at lower speeds (i.e. no-wake zones on the river, the outboard seems to shake/vibrate more than I would expect an inline 4 to do). I'm wondering if the prop is to possibly blame for both items.

The outboard was tilted up higher than it should have been (w/the limiter bolt/rod in the third hole from the bottom on the power tilt/trim unit), so I just dropped it down one hole (I probably butchered terminology there - sorry - but hopefully you follow what I'm referring to). The outboard now sits more parallel w/the boat in the fully trimmed down position. I'm hoping that this will help with getting the boat out of the water more quickly/planed out, and keep the engine from what I believe was ventilation, when turning sharp and/or going over other boats' wakes. The dents in the prop maybe were contributing as well to possible ventilation?

There are no chunks missing or burrs on the prop so I'm not sure if the prop can be out of balance by simply being bent in spots, but I'm hoping that might explain some of the low speed vibration seen. There's no water in the lube, so I don't think the shaft is bent.

Attached are a couple pics of the prop (along with one of how the outboard now sits being fully trimmed down). I'd like to bend the prop back myself, if possible. My questions pertaining to doing so are these:

1) Does the damage look ok, and within reason, to hammer back to shape?
2) I assume the prop must be removed to do so, but wanted to confirm.
3) I've seen references to using a ball peen hammer and also a rubber mallet (along with a block of wood); which is the better tool to use?
4) Should heat be used?
5) Lastly, what is the main function of the trim tab, and would it being broken cause any of the issues I'm seeing?

Thanks so much for your time and help; I really appreciate it!

 

[thenline]

Re: New member looking for prop repair recommendations

Re: New member looking for prop repair recommendations

I forgot to mention; the prop has the following markings on it, in case it matters for anyones' responses:

48 816704A40 13P

 

[steelespike]

Re: New member looking for prop repair recommendations

Re: New member looking for prop repair recommendations

No heat.
While you could straighten the prop that one ding may need a professional massage.
It could have pushed the blade out of shape.If you don't get it right it could wear the bearings and seals in the gearcase.The trimtab is an anode to control corrosion.
It also can be adjusted to control prop torque.
If the motor shakes rythmically it could be the prop but I'm inclinded to think its idle speed(600-700 and or idle mixture adjust.Both should be done warm in forward.
When you get to it check the vertical height. There is no set height.The higher the better without having venting(cavitation) problems.Usually the anti vent plate(just above the prop ends up about an inch higher than the bottom.

 

[thenline]

Re: New member looking for prop repair recommendations

Re: New member looking for prop repair recommendations

No heat.
While you could straighten the prop that one ding may need a professional massage.
It could have pushed the blade out of shape.If you don't get it right it could wear the bearings and seals in the gearcase.The trimtab is an anode to control corrosion.
It also can be adjusted to control prop torque.
If the motor shakes rythmically it could be the prop but I'm inclinded to think its idle speed(600-700 and or idle mixture adjust.Both should be done warm in forward.
When you get to it check the vertical height. There is no set height.The higher the better without having venting(cavitation) problems.Usually the anti vent plate(just above the prop ends up about an inch higher than the bottom.

Thanks so much for taking the time to respond, I really appreciate it! I'll try to respond to each of your comments.

So it sounds like I might be able to try hammering it out, then, if I understand correctly. The bad dent may need to be done professionally, but is it probably likely to wear the bearings/seals more-so if it's run the way it is, than if I try hammering it out? I'm assuming so, but want to make sure. If I try it, should I use a ball-peen hammer or a rubber or plastic mallet?

Thank you for the explanation on the tab; I contacted the closest Merc dealer and they have one on hand, so I'll pick it up and get it installed.

In regards to the carb adjustment, I should give you a little bit of my history, just in case it helps with diagnosing. For the past 11 years I worked for a high-performance V-twin engine manufacturer, doing engine controls work (carburetion, FI, ignition). I did all the emissions calibration work and am pretty good around carburetors, etc. When I bought the boat, it wouldn't run over 2500rpm under load. Figuring ethanol claimed another undeserving soul, I started pulling the carbs off when I found that the Mercury tech who had "gone through the engine" before the consignment sale created a disaster - a pinched fuel line under the bottom carb, carbs wouldn't go to WOT (only about 1/2 way), stripped screws, etc, etc. So, I rebuilt the carbs, repaired/replaced what needed it, and took it to the closest Mercury dealer to help me time it and adjust all the linkages per Mercury spec, as at the time, I didn't have a factory service manual.

As for the motor shaking, it is rather rythmic, not typical of a misfire, rich blurble, etc. The engine only shakes at low speeds (above idle) in gear. There isn't a tach on board, but if I had to venture a guess, I'd say it's the worst around 2000 rpm. Again, that's a guess. It clears up at higher speed, which makes it confusing if it were a prop issue. I know everything has a natural frequency, a point where vibration is most evident, it just seems extreme for an inline 4.

Regarding verticle height: As the boat sits on the trailer now (it doesn't sit parallel to the ground; the front slopes upward quite a bit), the very back and bottom of the hull is about 18 1/8" off the ground. The leading edge of what I believe is the plate you're referring to (the bottom-most plate, immediately above the prop where the trim tab mounts into) is about 18". The tail end of the plate is about 17 1/2" w/the motor trimmed all the way down.

Thanks again,
Tom

 

[thenline]

Re: New member looking for prop repair recommendations

Re: New member looking for prop repair recommendations

I'm heading to the river tomorrow, and wanted to get the prop taken care of, so I did it myself and it turned out great. I thought I'd share how I did it as to maybe help others who were in the same boat (pun intended) as I was.

After pulling the prop off and cleaning it, I made reference lines on each blade using tape (see pic). The edges, for the most part, of each blade were still smooth and in great shape, so it was easy to take measurements from each edge, as well as from different casting lines, etc. on the prop. The first picture shows just one of the sets of references I used.

The other picture shows the contour gauge I used. This was the key in the process. It allowed me to verify the contours on each blade. Because I had one blade that showed no signs of any damage (and another that was identical to it w/exception to the very edge), it allowed me to reshape the third; the one that was badly dented. I realize that not everyone will have a contour gauge laying around in their shop, but they're readily available at hardware stores and very inexpensive.

I tried several different types of hammers. The one I had best luck with was my large ball pein hammer, however, the flat end was used moreso than the ball end. I used a 4x4 piece of treated pine for the "anvil", stood up on end.

The whole process took about 45 minutes, but it was time well spent. I'll report back with any effects it had when I get back from the river this weekend.

 

[thenline]

Re: New member looking for prop repair help

The good news (after being out on the river today): no more vibrating engine and no more venting/cavitation! Bending the prop back fixed the vibrating and lowering the motor down one set of holes fixed the latter of the two issues.

The bad news: my electric choke plunger broke so I have to take the cowling off to manually choke it (I've got to locate one of those plungers if anyone has one laying around). Oh well, a pretty small issue! I'm just thrilled to have the other two problems solved!