How can you tell if you aren't firing on 1-cylinder?

Hi All,

I am a want-to-be trawler owner looking a 40' Tawain trawler (Aquacraft Boat Corporation - previously misidentified in a survey as an Aquastar). I did a sea trial today on this boat which has a Model 6D-380 Lehman. The boat started right up (though the owner had been there all morning so perhaps ran it earlier). I have known several diesels in my life (Kubota tractor, diesel in a sailboat, and several diesel vehicles) - but have never seen one without glow plugs - is this ever a problem for anyone in colder climates? The boat seemed to run well but I kept feeling what I would describe as what felt like a little 'miss' ... I thought higher RPM's might even it out and it might have a little- but I kept sort of wondering if it was possible that one cylinder wasn't firing. The Lehman does have very high hours (6500+- it has done several trips to Alaska, around Vancouver Island, and frequent trips to the Queen Charlottes).

I have hired a mechanic to come look at the diesel, but the person I hired who seemed to know diesels has hurt himself and is sending the person who works under him. Are there ways to confirm if all cylinders are firing - something I should make sure this mechanic does? There was nothing 'distinct' it just that sort of feel/sound thing that just felt like something wasn't quite right - but of course I had never met this diesel before. Any ideas appreciated as this is a big commitment and rebuilding an engine right away would be well beyond my budget

Thanks for any suggestions/thoughts!

You can tell by cracking one injector line at a time while the engine is running at idle. If a cylinder is not firing you'll know it by whether it drops out as you crack the line.

Have some oil sorbs handy.

Capt Bill is correct, a couple of wrenches and you can tell. It's messy.

What kills Lehmans is overheating. It's usually number 6 cylinder that gets pooched. First of all, they all smoke when cold. Lots. Once it's warm, black smoke usually means the injectors need overhaul. Blue smoke usually means its wearing out, burning some oil, or it could mean the dipsticks were never re-marked and it got overfilled. When you do your sea trial, run it WOT for 5 minutes. That will tell you if the no 6 is good, it will tell you if the cooling system, heat exchangers etc. are in good shape.

If the worst happens, Industrial Engines in Annacis Island rebuilds them, long or short blocks. Or, if you can overhaul a '56 Chev straight 6, you will have no problems with doing the Lehman yourself. All the parts are still available, cheap at the above or at a tractor shop.

If you think the engine is shot, make an offset in the price?

The Lehman doesn't need glow plugs - those are usually something to do with emission controls and the Lehman has none. There is a cold start "button" you can press for a cold start but I never needed to use it on mine. In Victoria, the sea never freezes so the engine will always be above freezing too.

The Lehman is arguably the best trawler engine of modest (120) horsepower ever made. It had a checkered career before we started floating them but it excelled at generation and such agricultural use as combines.

It should start promptly when cold, warm it up at 1000 rpm or even better, in gear. It will never reach operating temperature at an idle. Better yet, start it and throw off the lines and go. Then the neighbours won't get annoyed at the smoke! You should witness Grand Banks Rendezvous in Roche Harbour when 120 boats, some with twins, all start up on Sunday morning...

Actually, a better answer would be to ask RT, there is some consensus here that he isn't. 8^)

AD,
Along with cracking the injector lines one at a time (watch your tach to be sure the engine slows as each line is cracked and speeds up when tightened), I would also remove the oil filler cap on the valve cover while running and watch for steam/ base pressure rising out. I have 135 Lehmans and don't show anything. If one cylinder is not contributing, and you see base pressure/ steam- this could indicate low compression on that missing cylinder. IF that were the case, it could possibly be the result of overheating.


1983 Present 42 Sundeck
Twin Lehman 135's

Greetings,
Mr. X. Keep it up pal. You'll soon be off my xmas list....And you don't wanna go there!

Thanks RT, just dropping a bit of bait on your pond! Good day to you!

I don't like the FL120 despite having had two of them for the last 17 years. But the absence of glow plugs is not an issue. They are provided with a cold start lever, on older boats like ours generally connected to a Teleflex cable and a pull knob on the instrument console. This disengages the limit stop in the fuel control in the injector pump and allows more fuel than normal to be fed to the injectors at startup. The instructions for using it are in the operator's manual. We have actually never used ours as it doesn't get that cold around here in the winter and we keep the engine room at 50 degrees or so during that time, so the engines start immediatey.

The typical quick way to determine if all cylinders are firing more or less correctly is to loosen (crack) each injector pipe coupling in turn while the engine is running. A change in engine sound and a slight drop in rpm indicates the cylinder is firing, no change indicates that it isn't. Make sure the engine surveyor does this.

It is said that the FL120 in typical recreational boat service is a 12,000 to 14,000 hour engine IF it is operated, serviced, and maintained properly during that time. I know of FL120s that have greatly exceeded those hours before needing a core overhaul and FL120s that didn't make it to 3,000 hours.

Another not so precise way to determine if your not firing on one cylinder is with a spray bottle of water. Get the engine up to temp and spray a mist on the exhaust manifold where it comes out of the block going from cylinder to cylinder. If there's a cylinder not firing the water will not evaporate nearly as fast as a cylinder that is firing.

Thanks all for your helpful information. I hadn't planned on going up for the mechanical inspection, but armed with this new information it might be helpful to be there and make sure the mechanic does all these things. I had asked about 'checking the oils' and he said that they can be sent to the lab, looking for metals and things, but without a baseline that it wasn't very useful information. So - I know he isn't planning on sampling it. There weren't a lot of mechanic choices unfortunately - and most specialized in outboards. At least this person is a diesel mechanic! I appreciate all the info!

While your mechanic is correct in that oil samples are most valuable for showing trends, I think he's doing you a disservice by not taking one. A one-time or first-time oil analysis can be the start of sampling for trends and it can give you a snapshot of the oil's and tne engine's condition.

Our engine surveyor took samples from both engines and the generator. The results were very useful to us even though there were no previous samples on file to compare them to.

A one time oil analysis can tell if there is antifreeze or salt water in the oil. Useful to know ;-).

David

A quick way to check is with a laser temperature gauge. Check each exhaust at the head and if one of them is colder or hotter than the others then that one has an issue.

Greetings,
Welcome aboard.

wwestman said:

A quick way to check is with a laser temperature gauge.

Click to expand...

Exactly. You don't need any wrenches. You don't even need to touch the engine. Get one of these (I got mine on sale, and with a coupon, for less than $30)...
Non-Contact Infrared Thermometer With Laser Targeting

Shoot the exhaust manifold where it connects to each cylinder. If one is not firing, it will be significantly cooler than the others.

(And once you have this thing you will find dozens of other uses for it!)

Another way to check (less messy) is to get a decent quality heat gauge and once the motor is up to temp, point the gauge at each injector individually. They should all read the same. Any cylinder that is not firing will be running at a much lower temp.

To: DenverdOn....sorry, I posted my reply before I read yours. You're right, either the exhaust manifold or injector will give the same results.

denverd0n said:

Exactly. You don't need any wrenches. You don't even need to touch the engine. Get one of these (I got mine on sale, and with a coupon, for less than $30)...
Non-Contact Infrared Thermometer With Laser Targeting

Shoot the exhaust manifold where it connects to each cylinder. If one is not firing, it will be significantly cooler than the others.

(And once you have this thing you will find dozens of other uses for it!)

Click to expand...

One of these is a fantastic investment, we bought one about 8 years ago and it's helped with more things then I can remember.

If the exhaust is above the waterline, it's simple. Take a piece of paper and put it over the exhaust pipe. the skipping cylinder will pull the paper in the exhaust pipe. works on all engines, regardless of vessel. Water in exhaust makes it a little harder.

You can even use a dollar bill...

Stu

Hi All,

Got a mechanical inspection and would be interested in opinions of this report. Doesn't seem bad for 6500 hours - but should I worry about more things in the near future.

This is what the report indicated:

Check over engine. It appears to be in fairly good shape. Was wet around top end, looks like V/C gasket leaking. Belts and hoses look good. Start up engine, check smoke (engine warm from owner running it earlier), a lot of smoke and appears to be blue in color. Check and record exhaust port temps: 1- 125, 2 - 122, 3- 124, 4- 141, 5- 127 6-145 degrees F. Coolant temp was 135 degrees F and RPM at 850, could not get RPM to go lower. Take boat out for a sea trial and ran up WOT RPM 2330 traveling at 8.6 knots. Coolant temp 186 degrees F, coolant started spraying out bottom of left hand side of exhaust manifold end cap. Dropped RPM and leak stopped, also rear cap has a wet spot on top of gaskets. Suggest resealing both, plus new thermostat and gasket on expansion tank and also replacing valve cover gasket. Noticed that it was wet at rear of head gasket though it may have been leaking - tasted liquid it did not taste like antifreeze, may be oil from V/C gasket. Tested 2 8D batteries #1 - 1247 Amp, #2 Battery - 1316 Amp, both batteries 1155 CCA, both tested good.

Following this the owner has replaced the blown gaskets and the valve cover gasket.

Thoughts? Does this seem pretty minor given the number of hours or would these sorts of issues suggest backing off the purchase or looking for a price reduction to cover future issues?? Apparently all cylinders were firing.

Thanks in advance for any thoughts!

AlaskaDreaming said:

Hi All,

Got a mechanical inspection and would be interested in opinions of this report. Doesn't seem bad for 6500 hours - but should I worry about more things in the near future.

This is what the report indicated:

Check over engine. It appears to be in fairly good shape. Was wet around top end, looks like V/C gasket leaking. Belts and hoses look good. Start up engine, check smoke (engine warm from owner running it earlier), a lot of smoke and appears to be blue in color. Check and record exhaust port temps: 1- 125, 2 - 122, 3- 124, 4- 141, 5- 127 6-145 degrees F. Coolant temp was 135 degrees F and RPM at 850, could not get RPM to go lower. Take boat out for a sea trial and ran up WOT RPM 2330 traveling at 8.6 knots. Coolant temp 186 degrees F, coolant started spraying out bottom of left hand side of exhaust manifold end cap. Dropped RPM and leak stopped, also rear cap has a wet spot on top of gaskets. Suggest resealing both, plus new thermostat and gasket on expansion tank and also replacing valve cover gasket. Noticed that it was wet at rear of head gasket though it may have been leaking - tasted liquid it did not taste like antifreeze, may be oil from V/C gasket. Tested 2 8D batteries #1 - 1247 Amp, #2 Battery - 1316 Amp, both batteries 1155 CCA, both tested good.

Following this the owner has replaced the blown gaskets and the valve cover gasket.

Thoughts? Does this seem pretty minor given the number of hours or would these sorts of issues suggest backing off the purchase or looking for a price reduction to cover future issues?? Apparently all cylinders were firing.

Thanks in advance for any thoughts!

Click to expand...

So the mechanic did not provide an indication of the overall condition of the engine? IMHO, you should ask for that. Isn't that what you paid him for? He seems to have done a decent job of highlighting the issues without telling you what needs to done to fix it.

I would be concerned about the blue smoke in particular.

Pointing a pyrometer at an injector isn't an accurate indication of the cylinder temp for several reasons, it is cooled by the fuel going through it, and second, the fuel lines lengths vary so the temp will pick up engine room temp (more on longer runs). The last is the accuracy of a non-contact temp sensor. Just because the laser is pointing at x, does not mean it is only sensing temperature at x. They often have a conical field of view, so distance tends to blend the temps of everything around the laser dot.

Dreaming,
How old is the report? Do I understand correctly that after the inspection the owner replaced the head and valve cover gaskets.

I received the report today- the inspection happened yesterday. As of this morning the mechanics went back and replaced the exhaust manifold gaskets and valve cover gasket. I am not sure whether the owner also replaced the thermostat at that time. I am about 2 hours from the boat and wasn't able to attend the mechanical. The surveyor comes tomorrow and I will attempt to get a chance to chat more with the mechanic. He did verbally give me a brief report - he said he wasn't concerned about the smoke, but did think that i should plan on having the injectors rebuilt within a few years - not sure what that is based on, so will try to get more infos. Not a great communicator via 'phone' so hopefully in person I will get more. There were very few choices for diesel mechanics for the inspection unfortunately.

Considering what the mechanic found and that the hoped for fixes have been made I would sure want to have the engine put through its paces again to see if the new gaskets, thermostat, etc. have made differences, particularly with the coolant spray from the rear of the manifold.

Any engine problem can be fixed, from replacing a belt to replacing the whole engine. The only variable is what the person who owns the engine is willing to do. I would not buy a boat with the engine issues you describe unless or until the problems were corrected properly OR.... if I decided I was willing to buy the boat with the engine as-is and deal with any problems on my dime. In the case of the latter, the price of the boat would have to reflect the risk I felt I was taking.

But in your situation, I would not buy the boat until the engine is run again to determine if what the current owner did has actually done anything. Then I'd know what I was dealing with and could make my decision on facts rather than suppositions, hope, and someone else's assurances.

The repairs were made by the mechanic who did the inspection and I will see the boat run again tomorrow as the surveyor will need to move it to have it lifted for bottom inspection. I will be able to talk directly with the mechanic then. The owner immediately had the mechanic make the fixes suggested at least the manifold gaskets ... Not 100% sure on the thermostat but more worried about the blue smoke as that might mean a rebuild isn't far away. That said the mechanic did not seem as concerned about that on our phone conversation but comments made here of course cause me to wonder. How would I know if the engine oil was overfilled and the dipstick not corrected as someone mentioned earlier?

Does it smoke all the time or just on startup and a few minutes after that and then clear up?

And?????

Checking with the mechanic and seeing/hearing it run again are good, but, to tell you the truth, just for piece of mind, I would get oil samples of the engine (s) and generator. This will tell you of any contamination of the basic wear metals. Should cost about 50 bucks each to get a full report. Contamination levels can tell you piston/ring/bearing wears and how soon before you have to get into the engine for what could be a major overhaul.

I saw an old discussion, about, how to check if motor is running on all cylinders. The answer was to crack the injector line. That works, but if you use a, hand held laser temp, reader, and point the laser beam at one exhaust outlet at a time while the engine is running, it will tell you more of the motors condition, by showing the difference in combustion temp, and a cylinder that don't run, is much cooler. And if one cyl, is hotter than the others , it may have a clogged injector,and is running to lean.