Help me trouble shoot my engine!

[weinie]

I adjusted the valve clearance and inspected the fuel timing.

The fuel timing was fine and i tightened up all the valves to spec. They were only loose by a couple of mm's or so.

However, everything under the rocker cover felt very gritty and rusty and I had to remove the screws and nuts to free them up and clean them so they would turn properly when i adjusted the valves. Yikes!

 

[weinie]

I've made the decision that I'm going to pull the engine out of the boat at the end of this season and rebuild it myself during the winter.
I must be really bored, insane, or both!

 

[anchorclanker]

It may not need a full rebuild, so much as a good freshening such as I suggested for Roger. For example, if the cylinders dont show wear, and mic out within spec, a honing with new rings would be more than sufficient.

Some of these little engines sit a lot more than they run, and lack of maintenance in boats has been an epidemic for centuries. As you said, access is difficult and getting you to check valves and timing took took convincing. Odds are that rocker cover hasnt been off in years and probably never. The rust is from years of neglect, lack of oil proper oil changes, and deferred maintenance.

However, it is not uncommon to see the top ends of overhead valve engines get a bit rusty such as your seeing. It does not always have any bearing on whats going on down below. As the engine cools, condensation collects at the top same as it would a pan lid on the stove. The bottom end will often be spotless.

You could simply remove the rocker shaft and clean it up well, put it back together and see how she goes. You already know it has good compression, an overhaul wont make it any better.

 

[weinie]

My father, who retired from practicing dentistry many years ago, has a unique aphorism for working in tight spaces. And despite working on the complete opposite end of the body, he would say working in a tight space is "like working in an a**hole"! And every time I am working on my engine, that, dare I say, image comes to mind.

Unfortunately, there is virtually no way to work on the top of the engine comfortably the way it is situated under the cockpit. There's only about 10 inches clearance. And forget looking down into the cylinders or removing the pistons. (I would have to drop the oil pan to do that, anyway).

Besides, once its all out, i can give it a nice caterpiller yellow paint job!

 

[anchorclanker]

Didnt know it was that tight, so its likely never had any maintenance, ever. Hopefully thats all it really needs.

 

[weinie]

Didnt know it was that tight, so its likely never had any maintenance, ever. Hopefully thats all it really needs.

Not my boat, but you can see that there is no clearance. The only other access is from an approximately 2 x 1 foot access window in the aft "cabin".

 

[David W]

I've made the decision that I'm going to pull the engine out of the boat at the end of this season and rebuild it myself during the winter.
I must be really bored, insane, or both!

This seems like an extreme approach for an engine that shows over 400 psi of compression. I honestly think a valve adjustment, clean injectors and a run through a tankful of fuel will make a difference.

 

[David W]

I adjusted the valve clearance and inspected the fuel timing.

The fuel timing was fine and i tightened up all the valves to spec. They were only loose by a couple of mm's or so.

However, everything under the rocker cover felt very gritty and rusty and I had to remove the screws and nuts to free them up and clean them so they would turn properly when i adjusted the valves. Yikes!

I've been re-reading this thread and there are a couple of things that aren't adding up for me:
Factory or near factory spec compression on a 1987 engine
Virtually all the suggestions thus far have not affected what seem to be minor issues; some soot on the transom but no visible smoke, and a questionable idle and max rpm (either 2600 to 2900 depending on which post)
Vibration at low speeds

And this post of tightening the valves up,to spec as they were only loose by a "couple of mm's or so"

If they valves were that loose, it would barely start, the transom would be covered in soot, and there is no way it would run up to virtually the factory max.
Vibration at low speeds? If it didn't vibrate, I would wonder what was wrong.

/Kevlar on/

 

[weinie]

I've been re-reading this thread and there are a couple of things that aren't adding up for me:
Factory or near factory spec compression on a 1987 engine
Virtually all the suggestions thus far have not affected what seem to be minor issues; some soot on the transom but no visible smoke, and a questionable idle and max rpm (either 2600 to 2900 depending on which post)
Vibration at low speeds

And this post of tightening the valves up,to spec as they were only loose by a "couple of mm's or so"

If they valves were that loose, it would barely start, the transom would be covered in soot, and there is no way it would run up to virtually the factory max.
Vibration at low speeds? If it didn't vibrate, I would wonder what was wrong.

/Kevlar on/

The valves were off by 1 -2 mms. And with the adjustment there was no change in performance. Whether 1 or 2 mms of increased valve clearance would cause that much loss of performance, I don't know.

From what I have been reading so far the vibrations may, perhaps be normal for this kind of engine. I do know my motor mounts are original and that the forward/starboard one looks like its lost its elasticity. Taking the engine out would definitely make changing the mounts easier anyway.

 

[David W]

The valves were off by 1 -2 mms. And with the adjustment there was no change in performance. Whether 1 or 2 mms of increased valve clearance would cause that much loss of performance, I don't know.

From what I have been reading so far the vibrations may, perhaps be normal for this kind of engine. I do know my motor mounts are original and that the forward/starboard one looks like its lost its elasticity. Taking the engine out would definitely make changing the mounts easier anyway.

From what I can find, the spec for the valve clearance on an M18 is .006 to .007 of an inch. That is a very small clearance as compared to even 1 mm which is .015 in, 2 mms is .07 in. That is a huge difference, and would have affected your performance much more than a 4-600 drop in max rpm (assume in neutral)

I'm just saying that any loss of performance seems minor compared to the efforts you appear to be taking. Since none of the very sound advice any of the posters have provided seems to have had any effect I'm not sure what you are looking for.

You did say that you are looking for perfection so perhaps a new engine or rebuilding yours though your self-admitted lack of mechanical experience would seem to make this a bad idea (assuming you are doing it yourself as there seems to be a reluctance to bring a competent mechanic to your boat)

Just saying that to a casual observer, something is off here.

 

[Jake N Eggs]

From what I can find, the spec for the valve clearance on an M18 is .006 to .007 of an inch. That is a very small clearance as compared to even 1 mm which is .015 in, 2 mms is .07 in. That is a huge difference, and would have affected your performance much more than a 4-600 drop in max rpm (assume in neutral)

I'm just saying that any loss of performance seems minor compared to the efforts you appear to be taking. Since none of the very sound advice any of the posters have provided seems to have had any effect I'm not sure what you are looking for.

You did say that you are looking for perfection so perhaps a new engine or rebuilding yours though your self-admitted lack of mechanical experience would seem to make this a bad idea (assuming you are doing it yourself as there seems to be a reluctance to bring a competent mechanic to your boat)

Just saying that to a casual observer, something is off here.

Just for the record, 1 mm = 0.040" making 2 mm = 0.080".

 

[Fred Villiard]

1mm=0.03937 inch
2mm=0.07874inch

Fred Villiard

 

[David W]

Yes sorry my bad, non-caffeinated math! Essentially 1mm is more than six times the factory clearance and 2 mm is about twelve times. I'm thinking this would have hampered performance as the valves would open late and less wide. Then there would be the excessive clatter.

Just saying, something seems off here.

 

[weinie]

Sorry guys, MY bad!

Units were thousandths of inch, not mm's.
As a college physics major, I'm ashamed!

 

[David W]

Weinie, was the valve clearance too tight or too loose?

Both are not good, but too tight would create a greater performance loss than too loose. In addition too tight also means the valves potentially didn't seat fully. On the intake side it's not as problematic but on the exhaust side it can result in a burned valve because the valve doesn't fully seat thus does does not transfer heat back to the head.

Too loose, not great. Too tight is worse.

 

[weinie]

Weinie, was the valve clearance too tight or too loose?

Both are not good, but too tight would create a greater performance loss than too loose. In addition too tight also means the valves potentially didn't seat fully. On the intake side it's not as problematic but on the exhaust side it can result in a burned valve because the valve doesn't fully seat thus does does not transfer heat back to the head.

Too loose, not great. Too tight is worse.

They were loose. And as I've stated before, I did not notice any increase in performance after the valve adjustment. And for the record, I did not hear any noticeable valve noise prior, which is one reason I put off the adjustment until now (that and the lack of access to the top of the engine).

 

[anchorclanker]

I think its time to start from scratch.

How does the engine run now, today. Does it idle any better? Initially you said it wouldnt idle under 1000 rpm. Any change?

Your initial post said it wouldnt idle and it wouldnt rev more than 2900 rpm.

Engines can be extremely frustrating when a person doesnt have good knowledge and experience with them. I know you have a degree in physics, but that doesnt make you a mechanic. They may be technically simple machines, on paper, but the myriad of strange problems they can cause have made the most brilliant and knowledgeable people pull their hair out, often the designers themselves.

And it becomes enormously difficult and frustrating if a person refuses to follow the proper order in troubleshooting. Lets do them now in the proper order;

Service and check primary fuel system and filters. Pass? Check.

Compression check. Pass? Check.

Check and/or adjust valves and injection timing. Correct? Check.

Checked and cleaned injectors? Replaced with new, but not checked. Check.

Checked and adjusted idle and no load speed? ? ? ? You do know this is part of the 500 hour maintenance including all the above?

Okay, so you did these all out of order, but they are all accomplished now (except the heart of your problem) and still no change, so whats left? The governor and injection pump. Before you go pulling the motor out, you should try to solve the problem now, rather than fight with it again later. If your thinking there is some major mechanical problem internally, causing your issue, I can assure you there is not.

An engine, any engine, gas or diesel piston engine, two or four stroke, Jet or turbine, need three things to run. Compression, fuel, and ignition. You have all three. It isnt knocking and has good oil pressure? Nothing major bad down below. It has good compression? Nothing major wrong between pistons or valves. We'll assume the injectors are correct, and you checked injection timing? There is only one thing left to check and its the governor/injection pump. If you dont deal with it now, youll be dealing with it later after its all pretty painted.

I would surmise that wear has taken place in the governor/injection pump/throttle control, which has allowed the rack to draw towards the low speed direction. This would have the effect of lowering the entire power band towards fuel cutoff. Lower idle (which would idle rougher/shake), lower max speed. So before you go crazy pulling it out, try adjusting the idle stop and max no load speed stop on the pump. Its probably never been checked or adjusted before either.

 

[anchorclanker]

which is one reason I put off the adjustment until now (that and the lack of access to the top of the engine).

Just an FYI, if not for yourself, for others reading. Valve wear does not always work to increase clearance. Seat wear of stem stretch can work to close up clearances. They can become so tight the valves start leaking compression and will burn the valves. This is why its so important to check them in some regular time frame. Lack of valve or tappet noise isnt always a good indication. In fact the opposite is a bit better, if your hearing them clack you at least know they arent tight. Loose is just noisy and reduces power some. Tights a killer.

 

[weinie]

Guys!

I am 100% in agreement with you!

I do believe, in fact, that I'm looking a problem with the "governor/injection pump/throttle control". And of course, if I were to rebuild the engine, I would most likely give the injection pump to the local professional anyway or just buy a new one (they are about $500 from an online tractor supply co.)

Just a couple of days ago, I was returning to the dock and my engine stalled when I throttled down. The idle was set at 1100rpm. I saw it slowly drop to 800, then 700, then 600 rpms before it died. There was no trouble when I left the dock and it's not like the rpms bob up and down when I'm cruising. (Well they did, but I replaced my tach and now that is fixed!)

And as I mentioned before, I had also adjusted the WOT screw on the engine to give me my max rpms, which it does just fine. The wire on the screw and Nigel Calder tell you not to do that, of course.

And believe me, I tried having "professional" mechanics take a look at it, but the one at my marina, who supposedly knows his s--t, has been blowing me off for weeks, and I get the idea he just doesn't like digging into engines anymore and would rather replace broken macerator pumps and cabinet hinges. The other diesel shop I called, who was highly recommended, now tell me to call back again after a month when they are less busy!

I wasn't planning on rebuilding the engine until I had the valve cover off and I saw how gritty and rusty looking the innards were. I really would have liked to remove them including the valves and valve springs to give them a good cleaning, but without having good access, I am hesitant to do this. And before you blame me for the mess, I've only owned this boat for just 2 years and have done at least 5 oil/filter changes since. And although this should not be a factor, the engine's just "looks" tired with all the old paint flaking off. From what I've been reading, there are two schools of thought on rebuilding an engine. Either leave well enough alone if there is no real trouble, or do it to prevent what MIGHT otherwise be inevitable trouble.

Let me just add, that given my inexperience, I highly value everyone's opinion here and if I was sure of myself, I wouldn't be posting my issues here! (And obviously, physics is not much of a help in diagnosing engine trouble, but screwing up units was definitely a common, but major screw up!)

 

[weinie]

So before you go crazy pulling it out, try adjusting the idle stop and max no load speed stop on the pump. Its probably never been checked or adjusted before either.

I was reading up about these the last few days and was going to play with them. My thought, however, was why they should NEED adjusting in the first place. Is it wear or a build up of dirt?

ETA: and why would BOTH screws need adjustment simultaneously? Seems to point to a governor problem except rpms are steady under way. Also, doesn't the idle stop spring and screw effectively do the same thing as the idle screw on the throttle?