Prop mercury 500 thunderbolt

[dutchman89]

Hello,

i recently busted my prop on some rocks down the river:facepalm:.

Now I`m looking for a replacement. I`ve found one on the internet from a nice guy. The prop is from a 50 hp mercury from bj 2000 also a 2 stroke. My motor is a thunderbolt 500 from '78.

The prop numbers from him are a little bit different. My numbers are:

48 61818a1 13p, his are also 48 en then something different (don`t have the exact numbers anymore) also an A and ends with 14p. I can imagine that his is 1 pitch bigger. I would like that because my engine is running 5700 WOT.

My propeller is also really stuck i can`t get it off. I`ve turn loose the bolt and the washer but it is stuck on the shaft. Anybody any advice on what to look for regarding the numbers and any tips for removing the stuck propeller?

Cheers,

Henk

 

[Maxz695]

Re: Prop mercury 500 thunderbolt

14 Pitch is 14 pitch the only thing is the diamiter may be different. Make sure your lower unit can handle a bigger prop. isn,t 5700 over rpm ing that engine a bit. maybe a 17 pitch would be better. Not sure but I think you should be around 5500 RPM. As for the prop being stuck Not good I had to carefully drill the thrustwasher and the rubber out of the prop then very very carefully chisel away the aluminum center shaft from the prop off the prop shaft without damaging the splines or the threads on the propshaft. The aluminum did split and break fairly easily after the rubber was removed. Take your time if this is necessary as you get 1 chance at this. if you mess it up. Big time trouble.New Propshaft $$$$ Cha Ching. Try every other means such as soaking it in oil puller etc before resorting to this action. By the way The stainless steel prop I drilled out is still in great condition and I put the newer type prop hub kit in it. Chances are an aluminum prop will be destroyed in this undertaking Good luck

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

Thanks for your reply! I`ll figure something out. Had contact with a dealer and he said it is a commun thing for older props to get stucks. I will try to pull it lose with a big puller with 3 ends and then centered at the axle so i don`t damage anyting.

Cheers,

Henk

 

[steelespike]

Re: Prop mercury 500 thunderbolt

When you pull it you may take the prop off the hub but that will give you an easy shot at the hub either with a puller or
some other technique.Before the new prop lube the shaft with light grease or heavy oil anything is better than nothing.

 

[etracer68]

Re: Prop mercury 500 thunderbolt

Going froma 13p to a 14p should put you right at about 5500 rpm.

As far as the stuck prop on the shaft is a mostly a lack of maintance, the most times when a lower unit leaks, are from the prop shaft seal. Fishing line and or other things can get around the shaft, and damage the seal. During winteriztion, or once a year the prop should be taken off, and re-lube the shaft, and inspect that there is noting that has gotten around the shaft or seal area.

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

Thanks for your replies. I just bought the motor last march. So dont now what the maintence history is.
I hope the prop will come loose. I spoke an 'expert' and he said the 2000 model has a different axle then my '78. Ill try an 14 pitch because I don't want to over rev my sweet engine. but i like to ski behind my boat.is that still possible with an 14p? Does the topspeed change much with a 1 size bigger pitch?

Cheers,

Henk

 

[jestor68]

Re: Prop mercury 500 thunderbolt

WOT rpm range for most "classic" Merc 50's (including your 1978) is 4800-5300 rpm.

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

So I'm definitely overreving. What pitch do you advice? Does this affect pulling power and accelerating?

 

[jestor68]

Re: Prop mercury 500 thunderbolt

So I'm definitely overreving. What pitch do you advice? Does this affect pulling power and accelerating?

Increasing pitch will slow your acceleration a bit, while increasing top speed a couple MPH. Whether it will adversely affect your ski pulling depends upon what type of skiing you do(2 skis or slalom ski) and what type skis you have, how much you weigh, etc.

If you only want one prop for everything, I'd stick with the 14" pitch. Running it at 5500 rpm will be OK, but you can control that with the throttle.

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

Thanks a lot I will stick to the 14p then. My weight is 80kgs and only 1 person skies behind the boat. I like to slalom and stuff but the boat handles that easily so 1 pitch up shouldn't provide big problems

 

[steelespike]

Re: Prop mercury 500 thunderbolt

I'm a little late on this but you should give us your wot rpm and speed by gps Or borrow a shop tach and confirm your rpm.
Also need to know about your boat and typical load.
A 13" prop doesn't seem small to me.
I have a 65 500 Not sure about the gear ratio compared to yours,Unfortunately I have very little run time so no particulars.
I'm second owner po was knowledgeable 18ft Crestliner utility with all up weight of about 900 lbs.
Presently has a 11" prop has 3 spares 2, 11" one 12".
Point is Tachs very often can be wrong it seems at this point we can't be sure you need a change.
A quick check indicates your gear ratio is 1.7:1 This Is a numerically low ratio prop pitch and diameter would be smaller compared to say a 50 Evinrude with a 2.42 ratio.I believe these usually run pitches around 15" in a typical 50hp application.
If you look up props here on iboats your 13" is slightly on the high side imo not likely to produce higher rpm unless your boat is light and fast. A 17" is the biggest listed here.

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

I'm a little late on this but you should give us your wot rpm and speed by gps Or borrow a shop tach and confirm your rpm.
Also need to know about your boat and typical load.
A 13" prop doesn't seem small to me.
I have a 65 500 Not sure about the gear ratio compared to yours,Unfortunately I have very little run time so no particulars.
I'm second owner po was knowledgeable 18ft Crestliner utility with all up weight of about 900 lbs.
Presently has a 11" prop has 3 spares 2, 11" one 12".
Point is Tachs very often can be wrong it seems at this point we can't be sure you need a change.
A quick check indicates your gear ratio is 1.7:1 This Is a numerically low ratio prop pitch and diameter would be smaller compared to say a 50 Evinrude with a 2.42 ratio.I believe these usually run pitches around 15" in a typical 50hp application.
If you look up props here on iboats your 13" is slightly on the high side imo not likely to produce higher rpm unless your boat is light and fast. A 17" is the biggest listed here.

Hello i added 2 photos of my boat. Don`t know the exact model but I think it is an almarine 400. Do you recognize the boat? Would be really helpfull =)

My boat does 5700 WOT at 49 km/h with only me on board. with 3 people also WOT 5700 rpm and 47 km/h. But the main focus is skiing with the boat

Hope you can help me.

cheers Henk

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

sorry the weight is around 300 kgs (don`t know the LBS)

 

[steelespike]

Re: Prop mercury 500 thunderbolt

The prop calculator says that at 5700 rpm guessing 10% slip you would be doing about 37 mph. your 49km is 30.5 mph.
Conversely 30.5 at 10% slip says about 4700. I think a tach check is in order before a prop change.
Also is your speed by gps? Gps would give us 2 true numbers to use, Gear ratio and speed.
You may be able to borrow a shop tach or get an induction tach.
Depending on your equipment I think your outfit weighs about 1100 lbs about 550 KG.

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

Hello Thx for the effory! Really appriciate al the replies.
The speed is in GPS measured by phone.
The weight maybe higher because the engine is also 80kg and a big battery of 20kg and a 30liter fuel tank. I also weigh 80 kgs so the 500 kg is a good guess! What your saying is that if my tachometer is wrong, what could be possible because I build it in later, I might even end up choosing a smaller pitch?

I will try to check the tacho. I know a guy who has one of those things.

Cheers,

Henk

 

[steelespike]

Re: Prop mercury 500 thunderbolt

Tachos usually have a setting on the back to match the stator poles.Yours could be set wrong.
Sometimes the switch contacts are dirty and operating the switch a few times will clean the contacts.
Keep in mind my 4700 rpm is an estimate Based On my 10% slip guess. But we do have 3 solid numbers ,your speed, the gear ratio and the prop size so 4700 is reasonable.
Apparently your happy with the performance so your prop may be right and the rpm might confirm at about 4800 the bottom of the rating.Sometimes the best speed is made with a prop that runs at a lower rpm.
If you can't reach the rpm with a typical load then you may have to drop an inch or two.
But try to confirm the rpm and we'll go from there.We may be able to improve your setup and gain a couple of hundred rpm.

 

[dutchman89]

Re: Prop mercury 500 thunderbolt

Sorry,

Didn`t checked the rpm`s if they are correct, but I have been able to remove my prop from the shaft! but now I have a question about that. It was really stuck and i ended up removing the hard way..

now i have everything except 1 pcs. Could you tell me if this have to come of or is this a part of the shaft? There was a big rubber surrounding this pcs. Please advice if this pcs have to come of?

Cheers,
Henk

 

[steelespike]

Re: Prop mercury 500 thunderbolt

Looks like the inner hub that is splined to the shaft and needs to come off.Soak it good with penetrating oil like PB blaster.
Rig a puller and apply some pressure.