Always small projects being whittled away at on the boat. Things like getting all the fans working (i.e. not squealing or vibrating), sealing a leaky skylight, and repairing a broken drawer. Also a few that are slightly more important. One of our lifeline stanchions nearly pulled right out of the boat so we drilled out the holes, epoxy filled them, and rebid the stanchion. Also discovered that our stanchions at the back of the boat were pulling out as well. These were screwed in right above the cockpit lockers, making it an easy enough repair by simply thru-bolting them instead. Sturdy as can be now.
Then today I finally began the process of repairing something that should have been done long ago—the tachometer. It hasn’t worked since day one on this boat and frankly I never much missed it. Until this last passage that is. When coming over from Mazatlan we seemed to burn way more fuel than I anticipated, and all I could determine was that I was running the engine at to high an RPM. I confirmed this when we motored north up and around the corner at a bit lower speed and burned far less. Anyway, all I accomplished today was to track down where the sending wire went after leaving the tachometer. At least I think I followed the right wire (it’s not always easy on this old boat). After winding its way through the boat it ended up here. And I don’t have a clue what that thing is. Anybody out there want to fill me in? I had expected to find a wire that ran somewhere in the neighborhood of the alternator, probably lying disconnected. Not to some random little piece on the opposite side of the engine.
17 Comments on “Projects”
Tachometers usually run off a sensor connected to the transmission. That does look like a sensor, but can’t tell if it is at the transmission. My boat (and my previous boat) doesn’t have a tachometer, so not sure if boat engines are set up different. But, it is either a bad sensor or faulty wiring….it wouldn’t hurt to change out both. Other than running it back through the boat….those things always bloody up my knuckles a bit. 🙂 Disclaimer, I am not a ‘gear head’ so double check my diagnosis.
there are a few ways that the engine can create a signal. first is the alternator. second is a camshaft position sensor, third, crankshaft position sensor. you can also have a sensor on the fuel pump. what you have there looks like an oil pressure sensor, but i could be wrong.
Not a marine repair guy but that looks like a sending unit. It is a mechanical electrical pulse generator that operates by moving a small rod up and down as a marker moves by on each rotation of the flywheel or crankshaft. If you grab a voltmeter the unit should create a pulse when the motor is running. If it is not then the unit is bad or the little push rod has worn down and will not actuate the sensor I would seriously doubt that the flywheel or crankshaft has and issue. If the sending unit is working then you know it is the wire or the gauge. I did a quick google about what I think is your motor (Ford Lehman 80hp) and this guy seems to be the most commonly talked about if you need parts http://www.bomacmarine.com/ the 80hp was basically a modified tractor motor so with the part number of the sending unit you may be able to pick it up in mexico at a tractor repair shop. good luck.
http://hydraulicspneumatics.com/site-files/hydraulicspneumatics.com/files/archive/www.hydraulicspneumatics.com/Content/Site200/Articles/04_01_2011/87208magneticpi_00000059841.jpg
sometimes the hall sensor becomes fouled and obstructs the magnetic field which generates the pulse which is read/displayed by the tach.
if you can clean it (the end) and/or then start the motor you should be able to meassure the output voltage…with vom. no output no tach. output bad wire or bad tach.the output votage is generated by gear teeth, the voltage is commonly ranges less than 1 to 1.6v
these are just tach basics 101 🙂
They came originally with a mechanical drive tachometer and those were usaually replaced with an electrical unit. That is the sending unit that replaced the mechanical cable (kind of like an old spedometer cable). Now you just need to determine what is bad, the gauge, the wires or the sending unit.
Two most common ways to pick up Diesel engine RPM are AC pulses from the dedicated alternator terminal, and a magnetic sensor on a bellhousing sensing the flywheel teeth.
The former is normally used for RPM gauges, while the latter is mostly found with engines controlled by ECU (a dedicated computer) – which you don’t have.
Is it possible you somehow mixed up the wires? They are all alike, when old.. What the pic shows looks more like a temperature or pressure sender..
The sending unit appears to be located consitant with the area of the gear train that drives your fuel injection pump, which could also be the gear that drives/generates the tach sensor. I would expect some gob of goo blocking the signal pick-up, after the previous years of no use.
Maybe some help here ?
http://trawler-beach-house.blogspot.com/2011/10/calibrating-our-ford-lehman-tachometers.html
Hmmm…It looks like a sending unit, but not on the flywheel or alternator. Fault could be the sending unit, the tach gauge or, mostly likely, corroded wires between the two. All 3 are probably original to the boat. I’m sure you can pick new ones up on the corner of any street there in Mexico, if not, you can always just raise those big white floppy things.
I think John is right and that is the way I would go. Maybe you can find a tractor part too. I found a tach sensing unit on amazon that may be like yours, and the link is below. Magic http://www.amazon.com/dp/B000KK91O6/ref=asc_df_B000KK91O62440057?smid=A2ZO16S61GUQY7&tag=shopzilla_mp_1223-20&linkCode=asn&creative=395105&creativeASIN=B000KK91O6
I think your engine is a ford lehman 4D254 aka 2712-e. I am pretty sure the photo is the Tach sensor here is a pdf copy of the owners manual http://bf494.co.uk/assets/Ford_Lehman.pdf on page 8 “N” appears to be the same location in the photo. Also here is the service manual for the motor http://bf494.co.uk/assets/Ford_2700_Range_Diesel_Engine_Workshop_Manual.pdf Great for your records.
Assuming the sending unit is bad after testing the following applies.
It appears that this engine came with both a mechanical and an electronic sending unit, yours obviously is electronic. If the motor to tach gauge is less than 12 feet you could switch back to a cable but I think you are over the distance. It looks like you will need to find a sending unit that has a 7/8″ #18 adapter nut which is the size the cable adapter needs to be.
I go with John’s response. It’s time, hopwever, that you obtained the Manual for your engine. Bet you can find one (or a used one) on line. It will save you this type of issue in the future. We boaters mostly do our own engine work (or should) so the Manual is really as essential as life preservers on a boat.
Rex is right about John being right.* Get a manual!
*Thank you, Mel Brooks.
Pat – We’re strongly considering your suggestion to head back north and get a boat, but until then I’m looking for a Sprinter Life mechanic. Mercedes Benz engine. Basic RV components. Afternoons and the occasional weekend. Good pay. Currently heading into Bolivia. (Meals and lodging not included). Are you interested? Let me know. -TREE
Man, if you’d just taken a VW instead of the Benzo you’d have your pick. 🙂
Who is this Mel Brooks guy?
Thanks for all the input. I’ve got it sorted now. It was indeed a tach sensor. Some sort of electronic converter for the original mechanical cable driven tach.
Also, I’ve got a manual! Lay off. 🙂 It’s dog eared, greasy, and full of notes. Sorry to have asked a question in which the answer could have been figured out with yet another perusal of it. Sheesh. 🙂
LOL no hate here just trying to get you what you needed to fix the issue. I figured you lost your manual to the sea or more likely a blue marker and a few mermaid drawings…. I have four I understand… hope you found a cheap tractor alternative to get it running again. sail safe and good luck on the black ops I was in Mexico for almost 6 months without a visa once, Oaxaca is a long way form the US so took some working to get it fixed…