Rough Idle on Grand Banks Ford Lehmans

[Xsbank]

I meant to say fuel in the water, not oil - Marin corrected me.

I did mean to say that you should re torque the head bolts. I know this is only "required" on the turbo versions, however many of these engines are nearing 50 years old, they are rarely owned by the original owner, therefore many have been opened up and otherwise rebuilt or messed about with. The manual clearly calls for retorquing after the head has been off, after a few hours use, but many people do not do this task. Therefore, unless you have clear documentation that this has been done, a new owner should do this easy task. All it does is prevent an unnecessary head gasket failure...

The Lehman is basically such a simple, reliable engine, if it's running now it will likely continue to run for some years (given a heavy user might be 300 hours annually?) and give you lots of warning before it fails, therefore a feckless owner may not touch it until it blows. I happen to think that you should be kind to your engine, especially if you only have/had one and my little list is what I would do/have learned from babysitting one.

 

[expat]

XSbank, that's one of the best written simple basic service procedures I have seen, thanks.

 

[SomeSailor]

Mine are the same. Rattles at 600-800 RPM. Smooths out at 1000 or so and above. You learn what things need a strategic rag stuffed behind them.

 

[Rheal]

I recently purchased a 38' Permaglas trawler that has a 120HP Lehman and the engine runs rough below 1000 rpm. Would it cause a problem to run the engine for long periods of time below 1000 rpm or is there a solution to make it run smoother. Would like to be able to troll for salmon! Thanks.

 

[Ski in NC]

There are more than one kind of rough: One is from an engine problem like a misfire where not all six are hitting evenly. That's like a lump every six pulses. Engine in that case will sound uneven.

The other kind of rough is normal at low revs: The engine fires three times per rev, and each fire gives engine a shake. Lower revs make it more pronounced. If the mounts are stiff, this normal shake gets transmitted into hull structure and runs around the whole boat.

If your engine is running fine, but has low rpm shake getting into the boat, it does not really hurt anything, just annoying.

The fix is softer mounts. I have set up several with Barry mounts (the ones used on smaller Cummins) and they work very well. Soft enough to isolate vibes down to 5-600rpm, but stiff enough to keep alignment intact. Metallastic is another good mount, often seen on Volvos.

Swapping mounts is sometimes easy, but often the brackets and holes are not such that a direct swap can be made. New brackets, etc may need to be fab'd.

Mounts also must be very carefully selected. Each has a load rating and you have to match that so engine "floats". If weight per mount is estimated wrong, or wrong mounts selected, the mount will go beyond its limit of travel one way or the other and the engine won't "float". Vibes then still go through.

Done right, the improvement is remarkable.

 

[FF]

Here (SW FL) most injector shops will check injectors for free or about $5.00 each.

Rebuilding is in the $60 -$75 range each.

Removal and replacement is a low skill no problem task.

With the age of the engine rebuilt injectors would be required anyway.

However checking the valve adjustment should be done first .

If that doesnt smooth the idle , pull the injectors , check the compression , and have the injectors rebuilt.

With OK compression , if new injectors does not smooth the beast , the injection pump will need to be next to check.

The injection pump R&R can be complex , depending on the engine as re-timing may be needed..

 

[Marlinmike]

This alone should be a sticky for all to know/follow, great stuff:

Here (SW FL) most injector shops will check injectors for free or about $5.00 each.

Rebuilding is in the $60 -$75 range each.

Removal and replacement is a low skill no problem task.

With the age of the engine rebuilt injectors would be required anyway.

However checking the valve adjustment should be done first .

If that doesnt smooth the idle , pull the injectors , check the compression , and have the injectors rebuilt.

With OK compression , if new injectors does not smooth the beast , the injection pump will need to be next to check.

The injection pump R&R can be complex , depending on the engine as re-timing may be needed..

 

[av8r]

Ski
I changed mounts on one engine last year and I'm about to do the other. A PN and supplier for the Barry mounts for a FL 120 would be appreciated.

 

[Ski in NC]

Ski
I changed mounts on one engine last year and I'm about to do the other. A PN and supplier for the Barry mounts for a FL 120 would be appreciated.

Link to Barry: Barry Controls | Specialty Isolators | Marine Engine Mounts

There are downloads for the mount spec sheets. Need to know weight per mount. 27391-3 pretty typical for total engine and gear weight of 1400-2000lb. The smaller one is also useable on smaller engines.

 

[Xsbank]

Gentlemen, Lehmans rattle somewhere below 1000 r/m. If you are ever at a GB Rendezvous, when all the old dears start up on Sunday morning, not only can you not see your neighbour for the smoke but you had better have already said your goodbyes as the noise is, well, interesting.

You can do your injectors and adjust your valves and do your engine mounts and there will be some improvement but you will still have to pad up the Waterford and the bone China. Just increase the r/m until it stops. That's it.

 

[RT Firefly]

Greetings,
Mr. X. Short, sweet and to the point.

 

[av8r]

Ski
Thanks. Appreciate the input from someone who's actually done it.

 

[FF]

The balance of any engine , and its harmonic periods awe well known to the engine builder.

I suspect the Ford Econo Power engine were balanced TO have their noise under 1000 RPM as it is not common for farm implements to operate at idle.

Should someone be doing a TOTAL rebuild , after the crank is straightened go and have ALL the moving stuff balanced.

Front shive and damper, crank and flywheel, pistons weight matched and rods checked for straight and equal weights end for end.

This is done on most high performance engines , and will cost under 1/2 a boat buck.

The difference in SMOOOTH will be felt , esp if the usual operating RPM is known to the engine balance shop.

Bigger engines have a damper on the front of the crank, no Idea if Leman does , but these wear out or rot .

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[Ski in NC]

Idle shake of a in line six four stroke likely has nothing to do with balance of individual components. Always nice to have things in balance, but you will see no reduction in idle shake. Balance of those things shows up at high rev's where the inertial forces are much higher.

Straight six idle shake is simply due to the forces that come from compression and firing. It varies between engine brands due to the mass of the flywheels, mass of the block, mass of moving things like crank and other parts. All engines have it. The Ford seems to be no better or worse than others. What does vary is most Fords were installed with stiff mounts. They came from the factory with stiff mounts. That's why boats with Fords seem to rattle. Put the right mounts in, and the engine still shakes. But the boat does not rattle.

The Ford comes with a bonded-mass torsional damper, which does little to help idle shake. It is meant to damp torsional (twisting) vibrations at high speed. It provides little damping at idle. A viscous (fluid) type damper does help some with idle shake, but doubt one is available for that engine. Most Cat and Cummins do come from the factory with a viscous damper.