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Old 08-29-2014, 12:57 AM   #21
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If you are idling too high, your maneuvering speed is too high, so you end up shifting in and out of gear in order to keep the speed slow. Also, your rudder is nearly ineffective when you are in neutral so you have to keep shifting into gear to steer.

Also, your transmission type matters too. Velvet drives are all or nothing when you shift. Twin Discs can be eased into gear to ease the shock and this can be done at higher engine speeds.

Set up your boat where you like it. Like Ski says, doing 5 knots at idle is pointless and just wears everything out faster.
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Old 08-29-2014, 01:40 AM   #22
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RPM by it self does not communicate much info without knowing the gear and prop specs when discussing maneuvering.
I too am not a fan of high rpm shifting. The prop spinning while being shifted to the opposite direction is one reason.
Ski is correct that a six will idle smoothly down to lower rpm than a four. I wonder if high idle numbers were simply a copy of the idle speeds of the 4 cyl model if there was one.
The noticeable jerky slow idle of 4 cyl can't have good effect on dampers and transmissions. Slow a six to 500 rpm and it too gets jerky. The jerking can't make bearings happy either.
Modern engine have a bumper spring in the IP to reduce the need for high rpm when shifting.
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Old 08-29-2014, 02:36 PM   #23
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Many thanks to all for the interesting discussion

I have now found a operators manual from July 1983 of Lehmann Power:


" When properly serviced and after the initial " break in " period your engine should idle within a general range of 600 to 700 RPM; when new, idle may be somewhat higher. "


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Old 08-29-2014, 02:41 PM   #24
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Interesting. If that's a manual for the FL135 specifically, it seems they recommend an idle rpm that's lower than the idle rpm called out in the table of engine specs from Ford. 600-700 rpm seems to me to be preferable to the factory's 825-875.
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Old 08-29-2014, 03:24 PM   #25
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I never seen the 825-875 numbers before this. Only the 6-700 numbers.
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Old 08-29-2014, 04:27 PM   #26
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OK I may be off base on the slow idle. I had a Sumnercraft Express 29 that had a 120hp Sabre and it was supposed to be a "bluprinted" Ford 380 cu in engine that I was told was the same block or base engine as the 120 Lehman Ford. Never did confirm it and I wish I could remember the engine speeds I used. I do remember it topped out at 2500 (20 knots) .. right on specs but I don't recall the idle. If I had to guess I'd say 700. And if it had a flywheel and crankshaft weight with a compression ratio that resulted in smooth operation even 4or 500rpm may be appropriate. Like a diesel electric a very low idle speed is nice in tight quarters.

Something interesting about this conversation is that there's lots of talk about the BW gear suffering or sending "shocks" through the boat when put in gear. I have the same gear most of you do (BW) but w an 18" prop and the flywheel and crankshaft of a modern 107 cu in Mitsu. I have shifted into gear in the vicinity of 1200rpm w complete smoothness. But my gear was rebuilt and fitted w soft clutches and a hydraulic gear pump gear i/3 the standard size. So my shifting may be slow as a result. When I get the boat back in the water (week or two) I may try a 1500rpm shift and report back.

I certianly wouldn't regularly shift a boat into gear whereas there was a big clunk or shudder resulting. Nor would I idle at X amount rpm when 1 or 200 higher the engine was twice as smooth. Gears and damper plates take too much of a beating when the idle shudders significantly and a slight (1 or 200rpm) increase should be made. How many here have an idle of about 600 whose engine is much smoother at 800?

Thanks for the clarification on the two engines Marin.

And for an over propped boat idling as low as possible is preferable until or if the problem is rectified.
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Old 08-29-2014, 04:36 PM   #27
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If one has weak clips holding your universals on the propeller shaft, it will come apart ...

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Old 08-29-2014, 04:54 PM   #28
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"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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Old 08-29-2014, 05:36 PM   #29
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I never seen the 825-875 numbers before this. Only the 6-700 numbers.
Here you go. Straight from the horse's (Ford"s) mouth. Ninth line down, "Idling Speed."
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Old 08-29-2014, 05:46 PM   #30
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Here you go. Straight from the horse's (Ford"s) mouth. Ninth line down, "Idling Speed."
Thanks. Never seen that. But of course I never thought to look. As all the ones I've ever seen seemed to be set below that.
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Old 08-29-2014, 05:56 PM   #31
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Quote:
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"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.
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.

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Old 08-29-2014, 06:47 PM   #32
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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.
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Old 08-29-2014, 06:58 PM   #33
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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.
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Old 08-29-2014, 07:08 PM   #34
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I would probably run about 800 w 2500rpm at the pin..
If you run a Lehman at 2,500 rpm you will not be running it for very long.
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Old 08-29-2014, 07:23 PM   #35
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One or two minutes at 2500 w no negative observations should indicate the engine is performing as it should.
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Old 08-29-2014, 08:05 PM   #36
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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.
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Old 08-29-2014, 08:58 PM   #37
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Depends on how an engine is load rated in some cases.

https://marine.cat.com/cda/layout?m=...&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.
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Old 08-29-2014, 09:34 PM   #38
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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.

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.
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Old 08-29-2014, 10:24 PM   #39
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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.
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Old 08-29-2014, 10:49 PM   #40
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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.
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