Clogged speedometer inlet hole

[Oldskool]

Thanks in advance for any advise you can give. Last weekend my speedometer stopped working, right after having the upper half of the Alpha outdrive replaced. Thought it might be the pitot tube came loose, but not that lucky. Discovered today that the speedo water inlet hole is clogged. Thought it was just some of our famous Georgia clay, but nope, it appears to be some wood that has become lodged in there. Tried picking it out today, but only able to clear about 1/4 inch. I checked another drive on a boat next to mine and found that the hole goes into the drive housing about 2 inches or more before turning upward. I'm thinking that to remove this wood that I will need to VERY carefully and very slowly use a 1/32 or 1/16 inch drill bit and drill the wood out. Perhaps disconnect the pitot tube from the top of the drive unit and blow air from the top to push out any small pieces left behind. Any thoughts or ideas on how better to go at this? Man, what are the chances of something like this happening!

 

[Bt Doctur]

Re: Clogged speedometer inlet hole

what kind of drive?

 

[Oldskool]

Re: Clogged speedometer inlet hole

Mercruiser Alpha Gen 2

 

[FlyinGuy1017]

Re: Clogged speedometer inlet hole

Happens much more than you'd imagine! DON'T use a drillbit, I can almost promise the bit will break off in there. Also, any resizing of the hole will make it read (more) inaccurate. Start by blowing compressed air in the line (from the top side) and see if that'll blow it out. Make sure it's been out of the water for a while so the wood is dry.

Then again, it's a speedo! They're never correct and rarely work, as soon as you clear it out something else will get loged in there!!

Good luck and happy boating!

 

[Lodgepole]

Re: Clogged speedometer inlet hole

Clamp a drill bit in something you can turn by hand so you don't break it off or screw something up. The size of the hole is not what determines the accuracy of the spedo, its the pressure caused by foreward motion and the internal parts of the spedo itself. Clean out all you can and as stated above, let it dry and try to blow out the rest.

 

[cr2k]

Re: Clogged speedometer inlet hole

To those who claim that pitot speedos are inaccurate: Have you ever GPSed one? I did mine and it is within 2 mph. True below 10 mph they are kinda useless, but above 20 they are fairly good. Besides where are speed limits posted that require that kind of accuracy?

 

[achris]

Re: Clogged speedometer inlet hole

I have to agree completely with cr2k and Lodgepole. Use the drill in a hand chuck and do it slowly and carefully. And pitot speedos can be quite accurate. As also stated, the hole size has no bearing on accuracy.

But with the affordability and wide spread use of GPS today, why bother with a speedo? We have 2 main speed zones here, 5 knots and 8 knots. I know that for 5 knots, I need an engine speed of 1250rpm and for 8 knots, 2200rpm. After that all I need to know is if the speed I'm traveling at is safe for the weather conditions and comfortable for my passengers. Makes a speedo completely redundant.... And if I'm at WOT I'm too busy hanging on to look at the speedo....

Chris.....

 

[Philster]

Re: Clogged speedometer inlet hole

BE CAREFUL THERE:

Merc's Bravo manual says to use a 5/64 inch drill bit or piece of wire.

"Clean opening with a short piece of wire, if necessary. If obstruction can not be removed with wire, carefully reopen tube using a 5/64 in. (2mm) diameter drill bit. Do not drill beyond a depth of 2-7/16 in. (62mm)."

.

 

[zbnutcase]

Re: Clogged speedometer inlet hole

Those get clogged with wood all the time and are simple to drill out.

 

[Bama Boater]

Re: Clogged speedometer inlet hole

what kind of drive?

Does the drive determine the depth? the small drill bit I stuck in my Bravo III only goes in about 1/8 inch until it "bottoms out". Question is: is it bottoming out on debris or some internal engine component?

 

[spikedbat]

Re: Clogged speedometer inlet hole

Anybody have a pic of the hole (location) that we are discussing.
My speedo stopped working after the marina removed my lower unit.

thx

 

[iop]

Re: Clogged speedometer inlet hole

I gave up on mine a long time ago... with today's GPS systems who needs it??

 

[spikedbat]

Re: Clogged speedometer inlet hole

It just looks bad to have a dead gauge in the console.
No reason to really know the speed.

 

[Brewman61]

Re: Clogged speedometer inlet hole

To those who claim that pitot speedos are inaccurate: Have you ever GPSed one? I did mine and it is within 2 mph. True below 10 mph they are kinda useless, but above 20 they are fairly good. Besides where are speed limits posted that require that kind of accuracy?

I as well was pleasantly surprised when I compared my boat's speedo vs my gps. Pretty much within a few mph. It was more curiousity than anything.
We have a weekend/holidy speed limit of 45 mph, and a night speed limit of 20. And a relatively assertive water patrol equiped with stat of the art hand held laser radar. Don't think he'd qubble about a couple mph over, but it's good to know my speedo is good enough.

 

[achris]

Re: Clogged speedometer inlet hole

Anybody have a pic of the hole (location) that we are discussing.
My speedo stopped working after the marina removed my lower unit.

thx

Most likely they forgot to reconnect the tube on the lower unit.