Newbie Prop and WOT question

[Philster]

Re: Newbie Prop and WOT question

Glad we could help. Have you figured out how to check ratio?

Phil and I get snarky, but that's just at each other

Its keeps everyone on their game.

I'm expecting it to be a 1.5:1 ratio if that prop is 15P +/- a tweak from repair.

.

 

[svkb]

Re: Newbie Prop and WOT question

Its keeps everyone on their game.

I'm expecting it to be a 1.5:1 ratio if that prop is 15P +/- a tweak from repair.

.

If it is a taller ratio like 1.5:1, is that going to drastically affect my ability to prop it properly?

 

[QC]

Re: Newbie Prop and WOT question

Harder for sure, and not right, but there are options. Let's see what you find first. You really want to be in 17 - 21 range on most smaller boats.

 

[svkb]

Re: Newbie Prop and WOT question

Its keeps everyone on their game.

I'm expecting it to be a 1.5:1 ratio if that prop is 15P +/- a tweak from repair.

.

Well you were very close! I went out and had a look and low and behold I was imagining the 2.0 that I though was stamped on my lower unit. In fact it was stamped 1.62:1 so the lower unit has obviously been changed! I confirmed this by turning the engine. After one turn of the engine, the prop turned approx 2/3 of a turn.

I also checked the plugs, they were like brand new and gapped properly. I checked plug wires and found that the boot of one of them was split wide open, so that is obviously an issue! Checked the gap on the points and they were 0.019 and they are supposed to be 0.016, so I set that. The cap and rotor look brand new. I couldn't check the timing because (like an idiot) I left my boat keys at home before I went to the farm! :facepalm: I guess I have too many things on my mind!

Where is the fuel filter on this unit? Anybody know? I couldn't see anything inline, it looks like the bottom portion of the fuel pump comes off so there may be something in there, but I didn't take that off tonight. There is a clear fuel line that runs from the top of the carb back to the fuel pump, I don't think it's the fuel feed. There is a fair bit of sludge build up in that line

I found a bit of wood rot but it was very localized, it was (in automotive terms) in the lower left corner of the firewall. (not sure what that is called in the marine world) it was a very small corner and likely due to being in the bottom of the storage compartment where the previous owner stored his skis and life jackets! (underneath the rear bench seat). I checked the bilge again and it is bone dry. I tipped front of the boat up to see if anything drains.


Any more suggestions? Any ideas on what prop I should run with a 1.62:1 ratio to get correct WOT rpm and maximum speed?

 

[svkb]

Re: Newbie Prop and WOT question

Any more suggestions? Any ideas on what prop I should run with a 1.62:1 ratio to get correct WOT rpm and maximum speed?

Here's another newbie question! I saw the 1.62:1 on a white sticker on one of the flat portions on the outdrive, but when I started doing some internet searching, I found a website selling just lower units with a 1.62:1 ratio or 2.0:1 ratio. Is there a gear change in both the upper and lower units? I thought is was just the top. This is the website - http://www.seilermarine.com/outboard-recycle/mercruiser/mercruiser-alpha-gen2-drives.php

Or did I simply read the wrong numbers off the wrong part of my outdrive? As I said earlier, one turn of the engine equals approx 2/3 of a turn on the prop.

 

[fishrdan]

Re: Newbie Prop and WOT question

The upper unit has the gear ratio. I would look for a new/used upper as trying to prop it with the 1:62 ratio is going to be darn near impossible, you're at 3900 with a 15P and would need to drop 3-4" of pitch to put the engine at the top of it's WOT range,, 11 or 12P prop

SEI has new (china knock-off) uppers for something like $600.

BTW, I'm running a 18P 4 blade prop on my 2200+# 18'er with a 140HP Mercruiser, it turns 4500RPM at 33-34MPH, 1:98 drive ratio. (Every boat is different, those are my numbers)

 

[QC]

Re: Newbie Prop and WOT question

My understanding is the lowers are all the same and that the gear ratio is controlled by the upper. http://forums.iboats.com/showthread.php?t=461169

You should post those questions, ratio, fuel filter etc. independently in the Mercruiser section to make sure you're getting the best info. Sounds like the ratio is definitely off though.

Edit: What Dan said

 

[81 Checkmate]

Re: Newbie Prop and WOT question

Why Watson i think you have a clue! No wonder you get the LOW RPMS

As you all have suspected. Drive has been changed or reworked.

It could be posible that someone in the past blew the original and switch it out for a used one,but was unaware of the drive ratio.

That drive would be for a V-6!

I have an upper i bought from SEI 2 years ago and its still going strong + you get a 3 year waranty

Post over in I/O Form for your drive questions.

 

[svkb]

Re: Newbie Prop and WOT question

Why Watson i think you have a clue! No wonder you get the LOW RPMS

As you all have suspected. Drive has been changed or reworked.

It could be posible that someone in the past blew the original and switch it out for a used one,but was unaware of the drive ratio.

That drive would be for a V-6!

I have an upper i bought from SEI 2 years ago and its still going strong + you get a 3 year waranty

Post over in I/O Form for your drive questions.

Yes, the pieces appear to be coming together. First step though is making sure my engine is up to par. I found a couple issues yesterday for sure that need attention before I work on the gears and prop!

It's kinda discouraging though because this boat was purchased just to get our feet wet in the boating world and then upgrade in 5-6 years and now I have a (what I would consider) a major expense after only 3 times on the water! I guess thats how it goes with any recreational vehicle though! (I have a snowmobile and used to have sport bikes)

 

[svkb]

Re: Newbie Prop and WOT question

Yes, the pieces appear to be coming together. First step though is making sure my engine is up to par. I found a couple issues yesterday for sure that need attention before I work on the gears and prop!

It's kinda discouraging though because this boat was purchased just to get our feet wet in the boating world and then upgrade in 5-6 years and now I have a (what I would consider) a major expense after only 3 times on the water! I guess thats how it goes with any recreational vehicle though! (I have a snowmobile and used to have sport bikes)

Another question that I thought of (sorry for all the questions, I'm trying to learn)

Can you compensate for the tall gear ratio completely by going to a lower pitch prop, or is it still going to affect rpm? Basically what I'm asking is can you run the 1.62:1 gears I have now with a 14 or 15 pitch prop (it currently has 15) and get the same effect as the 2:1 with a 17 or 19 pitch? Would the taller gears make it more difficult due to the increased power it takes just to overcome the drag of turning a prop in water?