Engine Hour Meters? Are They Accurate? Do We Even Want To Take The Time To Check?
Ya ever look at your dash or if not on your dash, see an hour meter? Well, we asked Dave VanNess of VanNess Engineering what the deal is. And were kinda surprised by the answer. They are not all that accurate. WHAT? Well, turns out they are set for a RPM of 1,725. Now that may be the average speed you travel. But does it count the hours of No Wake Zones, or that time you raced that Jet Ski…and lost? Well, turns out NO. Now of course once you think about it, it kinda makes sense. And of course someone shot on youtube a video of one working. You can watch the hours go by.
I will add that watching grass grow is more interesting.. No Really.. Look!
Really? That sucker is over an hour long! When did you figure that out.. 30 minutes into it? Well, if you had a good rebuilt hour meter from Mark Clawson from Clawson Classic Instrumentation, you may have been able to keep track. But when we spoke to Mark, he ilaberated on the subject even more.
“Matt, it’s actually WAY worse than 1725 RPM. I’ve seen some pretty random numbers occasionally. The Stewart Warner tachs used in Chris Crafts from 1957-70 were hardly ever printed with it but some did have 2,250 as the designated “hour”. AC had at least 1,725, 1,750, and here’s a few for you, how about 1,790 or 3,080!
Engine hours on mechanical tachs are directly driven off the cable with a 2 worm gear system. The faster the engine is running – the faster the hours rack up. So when your CC cruiser putts around the harbor barely above an idle it’ll take about three hours to get the same hour the ski buff is getting at full throttle. The latter of which is probably getting an hour in 45 minutes.
A few were produced with “revolutions per thousand” printed on the face. All of this is probably more meaningful to an aircraft guy as these indicate wear not time running. An engine hour is NOT a clock hour.”
Thanks Mark, SO? Confused? Care? I suppose its like anything. Its something to reference. But in the Woody Boater universe where we are exploring the most minute details. Hey 4500 stories and counting, and we still found something new here to talk about aint so bad. Or not! Thanks Mark Clawson and Dave VanNess for the inspiration.
Tach time vs key on time vs actual engine running time. It is not always clear which is best but it certainly varies depending on what you are using it for.
Next, is the tach appropriate for the boat? A 17xx tach time in Squirt would be near useless. She won’t plane at that rpm, 3600 might be pretty close though. On a flathead, 17xx may be perfect.
Finally, how reliable are they anyway? If you are trying to figure out how many hours are on the engine in the boat you are looking to buy, do you have faith that the meter has been hooked up and functioning for all of the past 6+ decades?
In the end, the only thing I have used one for is as a guide for when to change the oil on engine breakin. They work well enough for that and little more.
The only hour meter I care about is the one that tells me how long I’ve been quietly anchored somewhere enjoying a sandwich, a swim, and some time in the sun.
The Hobbs meter claims to work on 6-32 volts. When you change from 6 to 12 volts does it rack up the hours twice as fast? Does anyone besides Matt care?
Agree with m-fine on the real usefulness of “key-on-time” hour meters to tell when it’s oil change time. And yes, they can be disconnected to mask the true engine hours elapsed.
The one in my Lyman looks just like the one on today’s header. Looks nice on the helm station spinning and ticking away.
I would have posted an hour ago but the grass growing video was LONG!
HAHAHAAH! That grass growing is a killer!
Crap, now I have to cut the grass
“ilaberated”? Really? That’s not just Woody-spelling; it’s a new word. I congratulate you on your creativity. Awesome!
(It took me a few seconds to realize you meant “elaborated”.)
I will add it to the dictinary.
The idea of the “mean” engine hour (tachometer) is to reflect usage based on severity of use. Presumably, wide open is more stressful than idle. “Clock” hour reflects time ignition is turned on. I checked once or twice and each time the ignition switch was turned on the meter clocked 2 minutes minimum. So, every time the ignition switch was cycled (even if no start) two minutes were added to engine time on the electric hour meter. If you really want to “slice your peas” install both both, then try to interpret the meaning.
Hobbs meter in my boat only activates with ignition on. I put an hour of test time on the meter before I installed it, and it was dead nuts accurate. Not a new meter, but new old stock from the 1960s… Works fine. CQ
Sounds like the tach method is really quite accurate. The Cruiser puttsing around the harbor is putting very little stress on the engine while the ski boat is stressing it out hard. One of the hardest things on the engine is quick acceleration.
I love life at 8 knots!
Hour meters/Tachometer. They are fun to look at, but in reality are decoration. In this hobby when you buy a boat it is old. So the hour meter is the last thing you look at. As for the tach most boat owners can tell by the sound and feel of that engine what it and the boat are doing. Pay attention to the Oil Pressure and Temp. gauges they will tell you when problems are coming. Don’t we all change our oil at the end of every season anyway. Most of the boats that I have owned did not have a tach/hour meter on them, and I got across the water just fine having lots of fun.
I say the next article should be on oil pressure and temperature gauges. Mechanical ones versus electrical. Then ammeters versus voltage gauges. What fun the minutia on a cold winter’s day.
I have (2) hour meters on my boat similar to the small S/W’s you have pictured (they are some other brand that I don’t recall). They are activated with the ignition switch and are accurate when I have timed them against my watch. When my boat was in the yard being restored a worker left the ignition switches on and added 15-20 hours to the meters without the engines being run (this was before the boat was launched). I just made a note of this in my engine log.
The hours are very handy for keeping track of all service and maintenance work.
Install a 4 lb oil press switch in series with the Hobbs meter. Without oil press or eng running Hobbs meter won’t count hrs/min even if you accidentally leave ignition on. This way you will only count eng run time on Hobbs
Agree with your findings.
I just outfitted a new build with classic instrument speedo/tach with miles recorder.
The unit works off GPS and power from ignition. Easy to install and fun to see how many miles various place are on the lakes.
Classic instruments say it is very accurate.
Chris Craft service bulletin converting engine hours to miles.
Here is that doc opened up a bit to read easier
Here is my hour meter. SMILES PER HOUR!
electric hour meters on many boats will come on when the key is on… .Chris Craft had a 5lb oil pressure requirement to make the meter work … This prevented inaccurate engine hour time running up…. Modern boats don’t often have this but any time I install an electric hour meter it has the 5lb pressure switch . I want actual engine hours.