Rough Idle on Grand Banks Ford Lehmans

I am close to buying a 1984 42ft Grand Banks with two 120 HP Ford Lehmans. During sea trial I noticed how "rough" the engines ran while in gear below 1000 rpm. So rough at 800 rpm that the drawers in dinette vibrated open. At 1000 rpm and above, engines run smooth and run cool. One person said, all Ford Lehmans are like that; the surveyor (not mechanic) said the rough idle is "highly abnormal"; another said may be need for valve adjustments and/or injector servicing. Don't have mechanic report yet but leaving survey, mechanic said his findings were minor. I remain very concerned about the rough idle. Could be a show stopper for me. Comments would be greatly appreciated!

Greetings,
Agree with surveyor "highly abnormal" for 120 Lehmans. Don't talk to the "all Ford Lehmans are like that" person any more!

(Jesse--- Sent you a Private Message with info on your question)

thanks for the feedback!

1984 was a long time ago , I would work with the owner on the cost of a compression check and having the injectors checked, rebuilt.

Rough Idling Ford Lehmans

FF, thanks for your reply. In addition to compression check and servicing injectors, I've had others suggest new engine mounts (though surveyor says mount's rubber is soft and mounts appear ok), and installing "drive savers". Engines have 4500 hrs but I am very concerned about the level of vibration.

JESSEDIVER49 said:

FF, thanks for your reply. In addition to compression check and servicing injectors, I've had others suggest new engine mounts (though surveyor says mount's rubber is soft and mounts appear ok), and installing "drive savers". Engines have 4500 hrs but I am very concerned about the level of vibration.

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Soft engine mounts aren't for all engines....Yanmar is one that does recommend them I'm pretty sure...not sure about Lehmans.

Old Cats preferred a relatively stiff engine mount.

Rough Idling Ford Lehmans

Thanks for the soft vs hard engine mount input. I am now being told by the Yacht sales guy that the engine mounts were replaced 4 yrs ago with an "improved design" and Sales guy says the rough idle is most likely an injector problem and an easy fix. He recommends having all injectors bench tested and repair/replace ones that are a problem and then consider valve adjustments.

As the Buyer, I'm thinking of requiring Seller to do that as a condition for the sale and if that smooths out the engine at idle, I'll buy the boat. If it doesn't solve the vibtation problem, decline.

What's the oil pressure doing at low revs? Is it dropping?

Does the engine also sound a bit rough?

I have a similar issue on one of my volvo's. I believe it is a dirty injector that is causing the engine to only fire on 5 cylinders at low revs hence the extra vibration. With revs above 1000, it is no problem.
I will whip them out for a service at the end of the season.

Might be the same issue.

I would be wary of the "Sales Guy" comments...he might actually know exactly what he is talking about...but in my experience...not likely enough to buy off on it without someone else chiming in.

I've been learning a lot about Lehmans for the last 3 years...NEVER have I heard anyone discussing engine mounts as an issue...other than normal swapping out...but no "redesign" recently.

His comments about the injectors and timing is good....I would have the current owner do it if these engines really are shaking that bad.

These guys have some answers for you...the only real input being on site would be a mech familiar with Lehmans.

http://americandieselcorp.com/

Decent amount of work the sales guys is saying, not sure the seller would be into doing all that, but I could be wrong, traditionally they down play an issue and take a couple bucks off hoping you'll bite.

Out of curiousity, does the vessel reach max RPM at WOT?

Hard to imagine a Grand Banks deal falling apart due to rough idling engines.

If the owner knows about it and doesn't want to have them smoother...either that IS normal and everyone else just thinks they are rough or the guy doesn't know and will fix them or he doesn't care and I'm skeptical of the whole boat then.

Good owners of higher end boats are usually proud of their boat and want you to be happy...granted some/many are clueless about the rest of their boat..but usually pretty sensitive about their engines.

If the owner won't make a minimal effort to solve the problem....I'd be looking at the buy as a near "engineless buy" price or walk.

Make your offer subject to your satisfactory resolution of the issue. The present owner will pay the cost of a good mechanic and an injector or two if he has a sale. Any Grand Banks buyer would require this. If it turns into something more difficult you can walk away.

JESSEDIVER49 said:

I am close to buying a 1984 42ft Grand Banks with two 120 HP Ford Lehmans. During sea trial I noticed how "rough" the engines ran while in gear below 1000 rpm. So rough at 800 rpm that the drawers in dinette vibrated open. At 1000 rpm and above, engines run smooth and run cool. One person said, all Ford Lehmans are like that; the surveyor (not mechanic) said the rough idle is "highly abnormal"; another said may be need for valve adjustments and/or injector servicing. Don't have mechanic report yet but leaving survey, mechanic said his findings were minor. I remain very concerned about the rough idle. Could be a show stopper for me. Comments would be greatly appreciated!

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There are definitely sweet spots in the Ford Lehman with regards to RPM. Could you isolate the problem to one or the other engine? Or did both do the exact same thing? It would be extraordinary for both engines to have the exact same problem, at the same time.

Just curious, have you heard the engines of other like boats?

Adelaide said:

There are definitely sweet spots in the Ford Lehman with regards to RPM. Could you isolate the problem to one or the other engine? Or did both do the exact same thing? It would be extraordinary for both engines to have the exact same problem, at the same time.
Just curious, have you heard the engines of other like boats?

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Good thought, narrow it down to one or the other engine; then, if owner will allow, loosen injector lines one at a time with that engine idling to find the offending cylinder (it's the one where the idle doen't get rougher when loosened). Then swap in an injector from the smooth engine to that cylinder. If then the engine idles correctly, you had a bad injector. If not you have a compression issue (valves maybe). Above is 1 hours work for a mechanic.

Brooksie said:

Good thought, narrow it down to one or the other engine; then, if owner will allow, loosen injector lines one at a time with that engine idling to find the offending cylinder (it's the one where the idle doen't get rougher when loosened). Then swap in an injector from the smooth engine to that cylinder. If then the engine idles correctly, you had a bad injector. If not you have a compression issue (valves maybe). Above is 1 hours work for a mechanic.

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Just by the sounds of his original post, and knowing the Ford Lehman engine, there is probably nothing wrong. Certain RPM's cause the boat to rattle, that's normal for a lot of diesel engines and the Lehman is no exception. I agree, if he finds a difference between the two engines, he could pay a knowledgeable Lehman mechanic to do exactly what you wrote for extra assurance and piece of mind.

Adelaide said:

Just by the sounds of his original post, and knowing the Ford Lehman engine, there is probably nothing wrong. Certain RPM's cause the boat to rattle, that's normal for a lot of diesel engines and the Lehman is no exception. I agree, if he finds a difference between the two engines, he could pay a knowledgeable Lehman mechanic to do exactly what you wrote for extra assurance and piece of mind.

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Adelaide makes a good point. Is it a rough idle or is a rattle that is set up due to the harmonics of the boat and engine.

i have a SP135 and at fully closed throttle, 600 rpms, it seems everything rattles on the boat, so after the first minute I raise the rpms to around 800 to 900 and it's as smooth as a baby's behind.

Never thought it was an engine issue, but more the whole system. I've had, have cars that have done exactly the same.

Good luck

I have a pair of the abive mentioned diesels and they shake under 800 rpms, especially under load. I had the injectors serviced and set the valves. No timeing adustments. They now run smoother and quieter and with less fuel out the exhaust into the water. They still rattle at 600 rpms. Softer mounts may help. 1000 and over they purr. Bob smith says to warm them up at 1000 rpm's. No need to rattle the dishes while they warm up. He also sells the soft mounts.

John

For most boats RPM is pure speculation , mechanical or electric tachs.

First borrow or buy a calibrating tack and find out the real numbers.

Wxx3 said:

Adelaide makes a good point. Is it a rough idle or is a rattle that is set up due to the harmonics of the boat and engine.

i have a SP135 and at fully closed throttle, 600 rpms, it seems everything rattles on the boat, so after the first minute I raise the rpms to around 800 to 900 and it's as smooth as a baby's behind.

Never thought it was an engine issue, but more the whole system. I've had, have cars that have done exactly the same.

Good luck

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And my FL120 does much the same - rough and rattley 500-700rpm, then smooths out and from ~1000 up 'sweet as'...as my son would say...

I have an American Diesel 136N which is a modified Ford Lehman diesel similar to the SP135. I don't know how much rattling is "too much", but mine too, has a rough idle at 1000 and below RPMs when cold. It rattles the galley dishes and stove grills. I might be due for an injector exchange, but boat has been running like a champ. I've got about 5000 hours.

Brooksie said:

Good thought, narrow it down to one or the other engine; then, if owner will allow, loosen injector lines one at a time with that engine idling to find the offending cylinder (it's the one where the idle doen't get rougher when loosened). Then swap in an injector from the smooth engine to that cylinder. If then the engine idles correctly, you had a bad injector. If not you have a compression issue (valves maybe). Above is 1 hours work for a mechanic.

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Great approach, I know the 135 Lehmans are a pretty big deal to swap.

Forkliftt said:

Great approach, I know the 135 Lehmans are a pretty big deal to swap.

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When I had t get water out of my cylinders...the mech felt he had to take the rocker arm off my 120 to get to the injectors...not sure now if that's necessary but if it is, not an hour task....

anyone pull the injectors on a 120 and NOT have to remove the rocker arm?

Rough Idle on GB 42 - Ford Lehmans

I do appreciate all the great inputs on this issue. I'm now off the fence and plan to move forward with the purchase.

JESSEDIVER49

JESSEDIVER49 said:

I do appreciate all the great inputs on this issue. I'm now off the fence and plan to move forward with the purchase.

JESSEDIVER49

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Enjoy your new boat congrats!

Call Bob or Brian Smith at American Diesel in Kilmarnock, VA. NOBODY knows more about the Lehman than this father and son team. They are the source of parts and information and are always pleased to talk about their Lehman engines. Good luck.

My 120's at low idle set up harmonics that vibrate everything... They do not idle rough. Just the vibration from the engines....just love em!
David

One thing that will cause a loud rattle at idle is a worn drive plate, usually a small increase in rpm & it will stop.

Taking off the valve train is just running up your bill...

Try and warm your engines at 1000+ rpm or better yet, in gear!

1 service your injectors at 1200 hours or when there is too much fuel and smoke in the water. "Too much" is for you to figure out.
2 adjust your valves too
3 torque your head bolts
4 change Simms pump oil at 50 hours without fail. Ziplocks are useful for this
5 install the American Diesel coolant tank very soon
6 burp the coolant valve on top of the block
7 check the raw water impeller and replace annually
8 buy a dozen heat exchanger zincs and a couple of caps and check them regularly
9 buy a new transmission cooler, install it and keep the old one for a spare
10 if you have an oil leak, it is 99% likely it's the lift pump gasket, even though it looks like it's the valve cover etc. Buy one and put it on and keep the old one for a spare.
11 toss the Simms pump drain tube, plug the hole and drill a small hole in the filler cap. This will stop a lot of mess.
12 likely, your dipstick will be marked wrong - measure the oil you put in then remark the stick
13 probably your engines and shafts are due for alignment - it's not hard but it will make everything smoother. Everything.
14 change the on-engine fuel filters unless you know for sure when they were done
15 if your drive-coupler plates rattle, they are shot and need changing. They won't fix themselves
16 never shift gears except at idle. Never.
17 change the oil in your transmission(s) too - it will make you happy.

The rattle of a Lehman is the best way to tell its running.