speedometer

[hoppy22]

I just purchased my first boat. It's a 1991 maxim 2100sc with the 4.3 i/o alpha 1 out board. Can some one point me in the direction to start looking to figure out why the speedo doesn't work. I am new to boats and not even sure how the speedo operates but I am good with tools and mechanically inclined. Thanks for any and all help.

 

[JB]

Re: speedometer

Hi, hoppy.

What you have can be called an outdrive, sterndrive or I/O. It cannot be called an outboard. Outboards are self contained engine and drive systems that mount on the boats transom. . .outboard of the hull.

A typical speedo has a forward facing hole in the drive unit that has a plastic tube connected. The tube runs up to your speedo, which operates on the pressure generated in the tube by the boats forward motion. I don't know that that is what you have, but it is a pretty good chance.

 

[jayhanig]

Re: speedometer

There's only three components to a speedometer: the gauge, the pitot (pronounced pee-doe), and the tubing that runs between the two. The pitot may be located near the bottom of your transom on the outside where it can stick out into the water flowing by it. On my boat, it's a little white plastic looking thing. I'd expect either the pitot is broken (or disconnected) or there's a break in the line before I'd think the gauge itself was broken.

http://www.iboats.com/Teleflex-Pitot-Tube/dm/*******.569641071--session_id.367056441--view_id.40246

 

[H20Rat]

Re: speedometer

There's only three components to a speedometer: the gauge, the pitot (pronounced pee-doe), and the tubing that runs between the two. The pitot may be located near the bottom of your transom on the outside where it can stick out into the water flowing by it.

Lots of boats don't have the pitot, the OP's most likely doesn't have one on that outdrive. Its built into the drive itself, there will be a little tiny fitting where the tube can attach to. Some newer outboards are now also coming with that feature built in, no additional pitot needed.

 

[Silly Seville]

Re: speedometer

the pitot (pronounced pee-doe)

Actually, it is pronounced pee-TOE...it is a French word.

 

[tpenfield]

Re: speedometer

1991 Alpha . . . probably has the built-in 'Pee-Toe' (that's the American spelling of the french word Pitot). I had to 'unclog' the one on my 1991 Bravo drive, which took a bit of work.

I did the normal 'poke a thin wire in the hole' stuff to no avail. Finally, I had to buy a really long 1/16" drill bit and carefully work it into the leading edge of the outdrive and then also into the fitting for the connecting tube that is above the ventilation plate. The maintenance manual said only to insert a drill a few inches, but that did not do the trick, so I kept feeding the drill bit (by hand) into the leading edge to about the depth where it should meet up with the vertical hole from the fitting. Presto !!! and I blew it out with my air gun.

Anyway, it finally cleared as the channel inside the outdrive had become completely clogged over the years. (it was a salt water sort of mineral build up) I noted that your boat/engine /outdrive is the same age as my boat, so the 'super clog' may be your issue. Each year, I recheck the innerds of the PeeToe and blow some antifouling paint through it. So far, so good.

 

[hoppy22]

Re: speedometer

Ok, thanks for the input, I won't be able to look at it til tomorrow but at least now I have an idea where to start.

 

[Beefer]

Re: speedometer

Get yourself a GPS, as even when working, speedos are historically inaccurate, and typically just a good estimate of the spped you are traveling over water (not ground).

 

[cyclops2]

Re: speedometer

Tpenfield has the right idea & way. If possible.

Remember ..he said... WORK THE LONG DRILL BIT IN USING.....YOUR HANDS ONLY. NO power drill.
I also have some small diameter 12" long drills.
I was chicken & lazy. had the marina mechanic do it. They only do non-outboards. Charged me $ 10.00. That included a free ride in my boat with his GPS.

 

[JimS123]

Re: speedometer

I often boat in a river with a very swift current. Thus, I need to know the water speed, not the ground speed. A GPS does me no good. For example, at one particularly narrow spot, the current is 16 mph. Going upstream at 16 mph my pitot show 16 mph, while the GPS shows zero! Burning a heck of a lot of gas for going zero....LOL.

A "good" pitot tube, pressure gauge type speedometer is typically accurate to + or - 1 mph if its functional. "Good" means Teleflex, Airguide or some others.

For a boat as old as yours, take the rubber hose off and replace it with a new one. When you reinstall it seal both ends so it doesn't leak water. Find the finest nichrome wire you can and feed it through the brass fitting on the pitot to be sure its clear. Don't use a drill or you will likely alter the accuracy. Better yet, just replace the pitot with a transom monted one -they only cost a coupleabucks. The instrument head on the dashboard rarely goes bad.

 

[tpenfield]

Re: speedometer

Yes, I found, with my boat, that the speedometer and the GPS were fairly close to each other in the mid-range (25 - 35 MPH) below that range the speedo was low and above the range the speedo was high . . . by a few mph (so about 5-10%)

 

[Oshkosh1]

Re: speedometer

Sometimes the tube from the speed-doe to the "pee-doe"(sorry!) will clog. Simply disconnect BOTH ends and using either your mouth or compressed air...blow into the tube from the speedometer end and ensure there is no muck clogging it. Also, (if equipped) check the pitot itself for damage from grounding. They're cheap and easy to replace if need be...around $10 or so.

 

[TilliamWe]

Re: speedometer

In case you check this before you go to the boat today, here's what the opening in the drive looks like and is located:

This is the pitot where it exits the anti-ventilation plate on the front of the drive:

 

[minx163]

Re: speedometer

1991 Alpha One Gen 2 would have built in petot with a quick a connect hose. check that first

http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=818183 91&ivar=images/COMMON/13834.png&inbr=1017&bnbr=50&bdesc=Bell+Housing



Buttttt!!!!!!!!!!!!!! If you are saying Alpha One pre gen 2 no internal petot there.Gen 2 started production in 1991, So i assume it's Gen2

That being said. the easiest way to check if it is tube and petot clog or the gage itself is to take the gage out of the dash .Disconect the hose a with small jewlers screw driver set by lightly prying the holes and opening the crimp on the clamp. once the hose has been removed blow through the hose from the gauge side. residuale water left in it should clear out. If it does not blow through freely then try compressed air. If it blows through freely right at the get go than the gage is most likly plugged. You could use the drill method to clear the hole in the gage but you need to use caution not to stuff and pack the contamination further inside or damage anything behond that.The gage set in that boat are probably relativley in expensive I would guess Teleflex..Ebay makes a great source for finding Era correct gages. when putting the tube back on the gage use a set of dikes to reclamp the crimp fiting

 

[hoppy22]

Re: speedometer

Had the chance to look at the boat today, I know why the speedo isnt working, but know Im more confused than ever. I found the hose that runs from the out drive to the gauge, it isnt hooked up to the outdrive put air to it and the speedo registered, so I know the gauge and tube are good. Now here is where the confusion starts. My boat is a 91,

I dont know if you can reed the serial or not but it is OD57 something, that range is supposed to be 91-95 gen 2 outdrive.
every thing I have read this is a gen 1? now Im confused, has the outdrive been changed and they used the gen 2 transom plate?
I found this hole in the bottom of the outdrive is this the petot?

the hose I found is just hanging there and is in the "cavity" the the single front bolt is that you have to remove to drop the lower unit and there is nothing there for it to connect to.

sorry for the poor picture the hose is the white plastic fitting in the upper right of the pic.


also when i put water to the 1/8th" hole in the front of the lower unit (on the nose of the bullet) I got water out by the shift bar and out by the prop I figured if that was the petot hole I would get water out of where ever that white fitting was supposed attach.

cant tell from the pic but the trim arms are held on by eclips not nuts on studs

 

[TilliamWe]

Re: speedometer

That hole is a drain, not the speedo. The speedo hole would be on the LEADING edge of the lower unit. Just like in the photo I posted above. The hose is attached to a fitting that pushes down into the hole in the anti-ventilation plate, and turns about 1/4 turn to lock in place. I think I see it in your photo.

 

[Don S]

Re: speedometer

You have an R drive (Not a Gen II drive) on an Alpha I Gen II transom shield. The last "470" built was in 84. The Gen II drives didn't start until 91.

There was no speedometer hook up on the earlier Alpha style drives until the Gen II.

It has always been thought that the older drives could not be used on the newer transom shields, maybe it was only the newer drives can't be used on the older transom shields ................ At this point, who knows.

 

[TilliamWe]

Re: speedometer

So what he means is that you have no place to hook up that speedo tube and fitting. Get a GPS at this point, it'll be easier.

 

[hoppy22]

Re: speedometer

I'm thinking an external pitot tube would be even fewer and easier.