RPM minimum

Steve said:

"If one has weak clips holding your universals on the propeller shaft, it will come apart ..."


Or one or more of those clips may not have been well seated in the groove.

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The builder admitted there was a problem with the clips and sent replacement clips and shaft section. Fortunately, the failure happened at the home berth with the shaft section simply dropping (clunk!) rather than rattling and busting up things.

One good reason for having a proper boat blessing.

Marin,
I consider Ford a better source of information as they did design and build the engine and are a great manufacturer of engines. They should know ... however Ford wasn't privy to the fact that their engine was being used in boats so there was not a small load on the engine at idle. Idle in and out of gears on a boat w a hydraulic controlled transmission or on cars requires a different idle speed. But if Lehman specified an idle speed in gear it wouldn't be valid as boats vary greatly as to gears, reductions and props. I would probably run about 800 w 2500rpm at the pin. Especially if 800rpm was nice and smooth.

Mark,
I suspect your drive is not kosher. The universal joints may be trying to do something they weren't designed for. Do you have a thrust bearing? It was explained to me by an Aqua Drive rep why two universal joints aren't a viable drive system. I asked as I was about to make one up for my Albin. The plunging action/capability of the CV joint is necessary in their opinion ..... and they convinced me of that. It was some time ago and I can't remember the details. At this time you may talk to the builder, other owners and perhaps Aqua Drive about it.

There likely is something about your drive system that I'm unaware of. If so I'd be interested in an explaination as I may be able to do something like that on Willy. A flexable exhaust coupling is probably higher on my list at this time though. Actually just getting launched beats that. Decided to redo my fuel system before launch.

Eric, I suspect the Coot's propeller-shaft design is Sea Horse Marine's standard design for its steel boats. Haven't had an issue since the repair.

manyboats said:

I would probably run about 800 w 2500rpm at the pin..

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If you run a Lehman at 2,500 rpm you will not be running it for very long.

One or two minutes at 2500 w no negative observations should indicate the engine is performing as it should.

Bob Lowe on the GB owners forum has a great analogy. Would you take your heart right up to its absolute maximum rate and pressure periodically and hold it there for awhile to "see if it will fail?"

He feels it's the same with engines. If it's running fine at its normal power setting, there's nothing to be gained by maximizing the strain on it periodicaly just to see if it will fail. It just hastens the arrival of the day that it will. He is totally against the idea promoted by some to run an engine at max rpm under load periodically to see if it will do it.

As is everyone I've met with a credible history in the engine design, manufacturing, and servicing industries.

In the 16 years we've had our boat the engines (FL120s) have been above 1800 rpm exactly once, and that was to get rpm at WOT for the prop shop when we had our props reworked. Their normal cruise rpm is 1650, a setting at which they are very happy.

Depends on how an engine is load rated in some cases.

https://marine.cat.com/cda/layout?m=319656&x=7&id=914324

Saying running a Lehman once in a while at max rpm for 2-5 mins is going to some how cause it to die significantly sooner is silly IMO. As is the heart analogy.

Bob apparently has never had a cardiac stress tests.

Capt.Bill11 said:

Saying running a Lehman once in a while at max rpm for 2-5 mins is going to some how cause it to die significantly sooner is silly IMO.

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Ahh, but I learned about this engine (Ford Dorset aka FL120) from folks in the UK who built them and maintained them. Which means I know their entire sordid history as a total failure as a truck engine, which is what Ford of England designed it for in the late 1950s. In fact, Ford was within weeks of pulling the plug on the Dorset diesel assembly line when someone suggested using the engine for something else. That something else is what saved the engine from immediate oblivion.

In the course of learning about these engines, I learned their weak points and failure modes. Trust me, you do NOT want to run these engines at full power any more than you absolutely have to. For anything other than lower power, medium rpm, constant load applications, the Ford Dorset is a disaster waiting to happen. They have more failure modes than you can shake a stick at. In highway truck service, they rarely went more than 20,000 miles without needing major work which is why Ford had decided to scrap it. Absolutely terrible engine in higher rpm, high and constantly changing load load applications, which is the very definition of over-the-road truck service.

There is only one thing the engine proved to be suited for, and marine use is an offshoot of that.

BTW, one thing I learned is that never, EVER, let an FL120 overheat. Everyone I came to know over there who had anything to do with this engine said an overheat is the fastest and surest way to kill it dead. Talking to those guys in the UK is why we have a timer at the helm set for 5 minutes. Timer goes off ot remind us to check th engine gauges, and then we hit the button to start the timer again. I'm used to engine scans in an airplane, but it's too easy to get distracted on the water in a slow boat.

One or the other of our engines have started to overheat three times over the years. All due to cooling issues, nothing to do with the engines themselves. The first time was a failing coolant pump gasket on the delivery trip from Tacoma to Seattle after the boat came off the truck from California. The next two times were due to partial blockages in a raw water through-hull. On those occasions, it was our timer that brought the gradual temp increase to our attention long before it got high enough to be considered an actual overheat.

Keep an FL120 between 1500 and 1800 rpm with a moderate load on it and never let it overheat and the thing can go 12,000-14,000 hours in a boat assuming proper service and maintenance. Run it harder than that and the longevity comes down and the failure risk goes up.

Thanks Bill.

OK Marin let's just say WOT at rated rpm for normal engines and you the TF reader can decide wether or not a Ford 380 Lehman engine is normal.

But if it can't go WOT for 10 seconds there must be something wrong w it. And if there's something wrong w my engine I want to ...
A know about it
And
B. Fix it

Letting it lurk and fail unexpectedly is not the smart option IMO.

But your method seems to work for you.

Eric-- I'm not saying the FL120 can't go at WOT for 10 seconds without failing. I'm saying that running that engine at WOT takes something off it's overall TBO, and the more you run it that way, the shorter the TBO tends to become.

So if it's really necessary to run it at WOT or high power settings (from what the guys in the UK told me anything over 2,000 rpm is considered a high power setting for the thing), fine, do it. As I said, we needed to run at WOT under load to determine the rpm of each engine for the prop shop. But we didn't do it until the engines were thoroughly warmed up, and then we ran them at WOT just long enought to get everything stable and note the rpm of each engine.

But outside of things like that, we keep them in the recommended power band of 1500-1800 rpm.

For anyone else reading this, what I've been writing is applicable only to the FL120 because that's the only engine in the Lehman-marinized engine lineup I've learned about. I have no idea how, or even if, any of what I've written applies to the later Ford Dover engine (FL135). We don't have those engines so I have not taken the time to learn anything about them.

manyboats said:

Letting it lurk and fail unexpectedly is not the smart option IMO.

.

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So here's a question, Eric. You run your engine (whatever make and model) up to full WOT to make sure it doesn't fail. It doesn't, so you return to whatever your normal power setting is.

But how do you know the next time you run it to WOT it won't fail?

By running it up again, right?

So you do that, but now how do you know the NEXT time you run it up to WOT it won't fail?

So, like wondering if the dial tone on your phone is really working, you chase the thing forever. Until the day comes that you go to WOT and it DOES fail.

If you really need WOT--- to outrun something or to do a prop test or whatever--- you need it. At that point, it doesn't really make any difference if the thing passed your WOT test 100 times before, it only matters that it works now, right?

So why put all that stress and heat on the engine for no reason. Use WOT only when you actually need it, and keep your fingers crossed that it doesn't fail.

I don't believe the way to know if an engine is healthy is to run it up to WOT every now and then. You're running your engine every time you take your boat out, and it's always the same engine, right?

You're an experienced guy with a feel for machinery, so you know what your engine sounds like, what it smells like, how much it smokes or doesn't smoke, how long it takes to start when it's cold and when it's warm, what temperature the coolant normally is, what its normal vibration feels like, and so on.

When something starts to go amiss, the engine will tell you. It will sound a wee bit different, or there will be a vibration that wasn't there before, or it will take longer to start, or the idle won't be quite as smooth as it normally is, or there will be more smoke than usual or it will sound a little rough at x-rpm, or whatever

It will tell you visually, too. Maybe there's some coolant seeping around the pump gaskets or there's not as much water coming out the exhaust as you think there should be, or maybe the oil will look "a little funny."

On my honeymoon back in the mid-1980s, we took a floatplane up the Inside Passage into SE Alaska and up the Stikine River into the Coast Range and the BC interior for a few weeks. On the way home, I took off from the harbor at Prince Rupert, glanced down to pull the manifold pressure and rpm back to climb power, and the tachometer was sitting on zero. The engine was running just fine, but I turned around and landed and taxied back to the seaplane base at Seal Cove.

I called Bob Munro, the founder and owner of Kenmore Air Harbor (it was his plane), told him what had happened, and asked him if he wanted me to have the Seal Cove shop replace the tach cable, which I figured was what had failed. He said, "You know what the engine sounds like at cruise power, right?" I said yes, pretty much. "Well," he said, "just fly it home on the sound of the engine and we'll fix it when you get back." So I did.

Which is a major reason why, by the way, we don't run our boat from the flying bridge. I want to hear exactly what those engines sound like under my feet and if they so much as hiccup, I want to know it.

I suspect the engine manufacturers set the governors so that "maximum" RPM is less than that possible so to protect the engine. Seems that the "M" rating goes lower (longer sustainable time at maximum power) as the maximum RPM are lowered.

got to thinking about why idle speeds are what they are and in addition to being able to deliver the idle load I suspect that the jerking experienced at very low rpm has to do with injector timing.
Timing assumes a certain rotation speed and accounts for the millisecond of rotation to get the piston far enough in the rotation so that the injection does not result in trying to reverse the piston direction. If timing were set after top dead center idle could be slower. So idle speed is partially determined by injection timing which may be set in advance of top center for other reasons.. Just my present theory.

supertramp said:

What is the correct RpM standgas or minimum, 900 RpM are to much?
The engine are Ford Lehmann SP 135 natural.
_______________
Norbert

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To the original question, attached PDF is straight from my Ford Lehmann SP 135 manual: (see photo below)

I've adjusted my FL SP135 down to 650 rpm and she runs with a vibrating lope that knocks everything off the shelves. I've been keeping her at about 775 rpm and she runs much smoother...however the manual recommends against this. She was at 850 rpm several weeks ago before I made the adjustment.

As for the question on the cable, you may need to adjust that also. The cable may not have enough throw to reach a lower idle unless adjusted.

I'm not sure why the conflict on the photo from Marin? My manual is dated "July 1983" and the engine in Rekindle is 1987 so this should be accurate for my boat.
Jim

Marin wrote;
"So here's a question, Eric. You run your engine (whatever make and model) up to full WOT to make sure it doesn't fail.

No.

You run your engine briefly at WOT and full load to increase the odds of discovering any problems before they emerge unexpectedly at a bad time.

Any engine can fail at any time. The best thing to do is to minimize the failures and increase the odds of them happening under controlled circumstances.

manyboats said:

You run your engine briefly at WOT and full load to increase the odds of discovering any problems before they emerge unexpectedly at a bad time.

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So how do you know it won't fail the next time you run it up to WOT? Or won't fail the next time you start it, for that matter? You don't. So why bother to stress the engine for no real gain?

And what do you hope to find out by running it up to WOT for a few seconds. It either will or it won't. A few seconds at WOT isn't going to reveal any problem that regular running at cruise rpm won't reveal.

Personally, I put the "run it to full power periodically" in the shade-tree-mechanic myth category. I have never met a truly credible, experienced person in the engine manufacturing, servicing, or repair industry who recommended this practice. In fact, most of them have pooh-poohed it when I brought it up, calling it a silly idea that can potentially do more harm than good.

I know Bob Smith at American Diesel recommends this practice but he also recommends putting Marvel Mystery Oil in diesel fuel. He knows a ton about Lehmans but he's apparently just as prone to hanging on to a few old-time, bad ideas as anyone else.

I've mentioned in the past a friend in Hawaii who for many years, among other businesses, has run a small fleet of long-line tuna boats. These boats go out for a month or more at a time on a year round basis. All of them are powered by Volvo Penta diesels and the engines are never shut off from the day the boats leave the dock to the day they get back (unless they have to be shut down for a repair). His orders to his captains are NEVER to take the engines over 1500 rpm unless it's an emergency. No periodic run-ups to WOT, nothing. Fifteen hundred rpm is the most he ever wants those engines to see. And he gets really pissed off if he gets less than 30,000 hours out of one of these engines before they need an overhaul. That's about 4 years of nearly constant service in his application.

So sorry, Eric. I think it's a bogus idea.

BUT... I am not suggesting that you stop doing what you believe is the right thing to be doing or that I think less of you as a boater for your ideas. I would hope you know me better than that. You should run your boat in whatever manner you feel is the best way to run it, including the engine. I'm simply expressing my opinion about a subject that has come in this discussion.

markpierce said:

I suspect the engine manufacturers set the governors so that "maximum" RPM is less than that possible so to protect the engine. Seems that the "M" rating goes lower (longer sustainable time at maximum power) as the maximum RPM are lowered.

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Maximum RPM is an interesting concept. Maximum as it sits or as it can be made to run. We lived near Charlotte NC where you are surrounded by Nascar. Well, these guys get bored sometimes. I knew one of them to buy an old Correct Craft inboard that had a very nice engine initially and would run about 45 mph. Now he was upset at all these boats flying by. So they took it in the shop one week and did a Nascar racing type modification. Took it back out and turned over 7000 rpm, running 60+ mph and just passing their tormentors. Then the next week they returned it to stock.

Obviously engine builders have chosen to try to put their engines in a comfortable range.

What's all this about stress Marin?

Engines are designed to do everything I've talked about and more.

If you've got a weak engine and need to treat it like an old lady so be it. But the rest of us can run our engines fairly hard and the wear isn't worth talking about

I think most engines are rated to run at WOT for at least 30 minutes to an hour. And probably run 85 or 90% after that continuously.

But a lot of guys here have the Lehman. I don't know if they are really weak but if I had one I'd find out to my satisfaction and run accordingly .... like you do. Perhaps an extra water port on the back of the block and some kinky plumbing would solve the overheating problem? Just a thought. Then they could sell kits for others.

No need to stress yourself or your engines. Seems to me you're running hard enough to run warm enough and easy enough not to overheat or otherwise stress your engines too much. Just keep doi'n what you've been doing Marin.


BandB,
Actually I don't think rated rpm is maximum. Max would likely do damage or even total destruction. But if a diesel is set up right one can't get anywhere near maximum as the governor limits the max rpm to 2 or 300 over rated rpm. Been so long since I've run up against the govonor I can't remember what the rpm is. Should probably do it fairly soon. It would vary from engine to engine but one could probably run under propped and about 200rpm over rated w less than full load. Don't really know about that though.

Norbert mentioned
"I've adjusted my FL SP135 down to 650 rpm and she runs with a vibrating lope that knocks everything off the shelves. I've been keeping her at about 775 rpm and she runs much smoother...however the manual recommends against this. She was at 850 rpm several weeks ago before I made the adjustment."

Same here on the low idle speed. All the engine mounts and hardware fastening these to the stringers have been checked a few times and everything seems fine.
I like the 600 RPM or so the engines are set at when I'm slipping the BWVD's into gear, but the stove grates rattle so bad I can hardly take it. The shock load at a higher RPM shift surely causes more stress on the drive line.
So my approach is to start the FL135's at idle at the lower helm, after 30 seconds or so I ease the throttles up to about 8-900 RPM as the engines warm up.
Lines come off, from the upper helm I drop back to idle and then shift into gear.
At bridge openings, etc., with long idle times in neutral I have gotten into the habit of pulling the RPM back up to 800 or so. But I always drop back to low idle before shifting into gear. This seems to work well on our vessel. YRMV ?


1983 Present 42 Sundeck
Twin Lehman 135's

Lots of engines can't idle well at 600. The governors sort of go into this "starting mode" where a little droop means full rack, then slams back to zero fuel. That is what give the hunting or otherwise described instability. When that happens, you have little choice but to idle up to where things smooth out.

Cat 3208- can idle down to like 550
Cummins P7100- down to 500
CAV dis pump- usually 600
Lehman/Ford- not sure, some ok at 600, some not
Bosch/Nippon Denso- no way down to 600, best about 750
Bosch VE/Volvo- idle as low as 500, most of them

Those that are over propped may have trouble shifting into gear at 600rpm.

Smooth idle rpm should be your target for gear changes. I have Twin Disc 506 gearboxes. They have a good reputation and should last many thousands of hour before rebuild.

When I repowered we checked the chip screens in the gears and noticed some debris, so I decided that we did need to have the gearboxes taken apart after all. They had done just 1900 hours. Well, the guy rebuilding them said he had never seen a TD box in such poor condition after so few hours.

So what was the cause? The elderly PO and his sons all had trouble maneuvering in and out of their slip. Their habit was to use well above idle rpm and throw into gear, forward or reverse, in mild panic in order to avoid hitting stuff. They mostly succeeded - only 3 swim platform replacements that I'm aware of! But the TD gearbox paid a price in terms of lifespan.

Do as Marin and most other prudent captains suggest - pause in neutral, and only change gear at idle rpm. Or accept that a premature gearbox rebuild could well be in your future.

Very low RPM results in lots of motor vibration, especially for my boating pals who have plastic boats. 700 is the lowest I'll go on the JD4045, but 750/800 is better for the engine (my preference) but maybe not for the transmission and drive train when shifting gears.

manyboats said:

If you've got a weak engine and need to treat it like an old lady so be it. But the rest of us can run our engines fairly hard and the wear isn't worth talking about

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I don't know about other engines, only the Ford Dorset/FL120. And it is a "weak" engine if run hard. In typical boat service, where it sees 1500-1800 rpm, it will go a long, long time. But run harder than that and all its weaknesses can start to show up. These include a failure-prone in-line injection pump and a very weak head gasket setup, the reason for the fast failure if overheated. Number six cylinder is prone to overheating and scoring if run hard for longer periods of time. And there are other potential issues having to do with bearings, bushings, seals, and head warping.

The later FL135 may have none of these problems, I don't know. You would think Ford of England would have learned from the Dorset engine and so improved things with the Dover engine.

>I think most engines are rated to run at WOT for at least 30 minutes to an hour. And probably run 85 or 90% after that continuously. <

Most INDUSTRIAL engines can run at high RPM and load , in fact they prefer it.

Engines sourced from autos , small trucks and farm implements are far better at reduced throttle .

Some if the Northern Lights units may be an exception as they are sourced from earth moving equipment .

The engine converter should have 4 graphs of hp produced vs run time .

IF there is no 24/7 rating full throttle should be very limited .

JD specs for the higher, intermittent rating engines typically say that they can be operated continuously at 400 rpm below WOT. I've seen other brands state that for continuous operation do not exceed 85% of WOT. In all cases it is assumed that the engines are not overloaded eg highly overpropped in a marine context.

Modern diesels don't seem to have an issue with underloading. Sure, all manufacturers will all say do not idle for very long at all, but the JD dealer was telling me that provided I did the first 100 hours using break-in oil and kept 60-80% load for most of those hours ( follow da book) then I could subsequently run at quite low rpm for extended periods without issues. And he gave examples of commercial fishermen operating that way - continuous low rpm for over a week at a time. I found it a bit surprising, but can accept that electronically managed diesels and materials of construction have come a long way.

Still, I recall a Tony Athens comment on boatdiesel that about 600F on the pyrometer is a good minimum (and 900F at the top end) from a longevity point of view. With modern diesels the dealer can readily plug-in a laptop and download the operating history, so I intend to continue following these guidelines just in case of any warranty issue down the track. If I need to go slow to conserve fuel and cant keep 600F on the pyro then I'll turn off one engine and load up the other one so it will get to that load temp. Apparently I can 'free-wheel' the TD 506 gears for quite a number of hours without issue. Lubrication of course being the issue. So a fuel conservation strategy for extreme range would be to run on one engine at just enough rpm for 600F on the pyro, but change to the other engine every x hours. I have the magic 'x' number written down somewhere, just cant find it right now. IIRC it was at least 8. But it is gearbox specific.

I haven't searched, but I suspect that pyro readings for the Lehmans at high rpm and loads would quickly indicate why they don't last very long under those conditions.

Marin said:

BTW, one thing I learned is that never, EVER, let an FL120 overheat. Everyone I came to know over there who had anything to do with this engine said an overheat is the fastest and surest way to kill it dead. Talking to those guys in the UK is why we have a timer at the helm set for

Keep an FL120 between 1500 and 1800 rpm with a moderate load on it and never let it overheat and the thing can go 12,000-14,000 hours in a boat assuming proper service and maintenance. Run it harder than that and the longevity comes down and the failure risk goes up.

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All I can say is my 30+ years of experience with Lehman's is very different.

I have personally seen a 120 overheat to the point it locked up. Cooled it down, fired it up and away it went. No major damage. And no I was not the one that over heated it.

I have lost count of the Lehman's I have seen charterers over heat with no major issues afterwards. Some are still running to this day with no ill effects.

Running them day in day out at 1400-1800 is fine. In fact based on load that might be considered to low in many cases. But you're not really going to hurt anything by doing it. In fact running them day in and day out at 1900- 2000 shouldn't hurt them either. At those RPMs you're still 500-600 below max rated and could be at about 70% load or so.

Maybe others have seen all kinds of damage and loss of longevity to them from over heating, running above 1800, running up to max RPM for a couple of minutes. etc.
But I have not in my experience.

By load, do you mean the actual rate of fuel consumption as a percentage of maximum consumption?

Usually %load is figured by comparing gph at that rpm to gph at same rpm, but full power.

Sometimes when figuring the math, it is not clear at all how %load is figured. This is from evaluating computer controlled engines where gph and %load is displayed in real time.

I think most people think it's a percentage of rpm compared to max rpm but some probably are referring to the percentage of throttle deflection …. half of the way fwd = half throttle.

Fuel burned = work so load measurement needs to be directly connected to fuel burned.

Ski wrote:
"Usually %load is figured by comparing gph at that rpm to gph at same rpm, but full power."
Never thought of that but correct it is. However here we are usually talking about percentage of maximum power …. I think???
So when a boat is burning 5gph and at WOT (propped correctly) and burns 10gph at WOT it is at 50% load. It's "running your boat at 50% load or running your engine 1700rpm at 50% load.

With an over propped boat/engine that … "%load is figured by comparing gph at that rpm to gph at same rpm, but full power" … may not be reality as the injectors are injecting more fuel than the engine can use and some of the fuel injected is not doing work.