Only getting 2100 RPM from CAT 3126

searaycruisn

searaycruisn

New Member
Nov 10, 2006
242
Old Saybrook, CT
Boat Info
2000 380 Sundancer
Engines
CAT 3126
I was crusing this weekend at my normal 2600 RPM when suddenly, the starboard engine lost about 600 RPM. I thought I had hit one of the throttles with my leg or something, because all of a sudden, the synch guage showed the engines were out of synch.

First thing I did was dive under the boat to make sure that I did not pick up a lobster pot. Next I changed the racor filter on that engine. I limped the boat into block island at 2100 RPM's at 17 knots.

Once at anchor, I replaced the secondary fuel filter on the boat.

I was able to get 2600 RPM when the boat was in neutral, but not when I put a load on it. Even disconnected the batteries to try to reset the computer. Checked all the fuel lines for a possible hole in the fuel line and air leak.

I was pretty much "tapped out" of ideas. Looked like a fuel starvation issue to me, but what else could I try? Other engine ran fine, so I do not think I picked up bad fuel.
 
Eric,

I think you have an injector seat leaking on either cylinder #5 or #6 on the engine that slows.

On a Cat engine, the injectors are fed from a fuel cavity in the head. If an injector seat leaks, it allows combustion gasses to escape into the fuel cavity and, since air is compressible, you are in essence, turning off all the cylinders after the injector which that is leaking. It is a simple problem and easy to fix, but, unfortunately, it takes a special reamer and specialized knowledge. Call your Cat dealer and schedule the service visit.........takes 4-6 hours.
 
You normally cruise at 2600RPM.....!!!!!:wow:.....BTW...your Bare Idle WOT should be around 3100RPM....it should be marked on your valve cover.
 
Last edited:
osd9 said:
You normally cruise at 2600RPM.....!!!!!:wow:.....BTW...your Bare Idle WOT should be around 3100RPM....it should be marked on your valve cover.
Click to expand...

Yikes! That's the first thing I noticed, I'm surprised that Frank let that one go.
 
Frank,

It is interesting that you mentioned an injector seat leaking. I heard a "valve tapping" sound on the engine that I was going to have the technician look into. The tapping is coming from the cylinder closest to the belts (front?) of the engine. Would that be cylinder number 5 or 6?

I have an appointment to have the boat looked at on Thursday morning.....will report back.

WOT under load on my boat is 2800 RPM's. I usually crise between 2400 - 2600 RPM's.
 
The tapping could be an air-bound injector or valve noise. When you call your Cat guy, tell him you want the overhead reset on the engine as a part of his repair..........if you don't know if the valves have been adjusted on both engines you need to do that now if you are over 250 hours.

Resetting the overheads retimes and adjusts the clearance on the valves and injectors and is about the only service need these engines have that you cannot do yourself. Resetting the valves will take care of the noise if its a loose valve adjustment and reseating the injectors will require readjusting them, so either way, its going to fix the noise.

I didn't mention his cruise speed because he can't turn but 2200 rpm anyway, besides, I figured some of you would bring that to Eric's attention. But, honestly, Cat engines can run a considerable amount of time at over-rated rpms before shortening the expected service life of an engine. While sustained cruise at over 2400 rpm isn't good, I really doubt that RPMs has anything to do with this particular problem.
 
The valves were adjusted at about 300 hours. The engines currently have about 585 hours on them.

Is adjusting the valves the same thing as "resetting the overheads"?
 
Took the boat for service. The fuel injector on cylinder #5 failed (exploded), causing the rocker arm to release the push rod (which was badly bent). The shop is recommending the removal of the head so that they can check for any damage in the lower part of the engine. They found small fragments of the fuel injector in the top of the engine, and they want to look for any additional fragments which may have travelled through the engine.

It is the opinion of the mechanic that when the propeller shaft broke on my boat (10 hours before), and the engine over reved (I think to about 3000 RPM's) that it floated the fuel injector, and caused the ultimate failure of the injector, and bending of the push rod.

I have notified the insurance company about a supplemental claim to my original broken shaft claim. They are waiting until they get an estimate from the shop, and speak to them about the situation before making a decision about covering the repair.

Any thoughts on the shop's conclusion about the connection betweent the broken shaft and the engine failure? The engines have under 600 hours on them.
 
I'll defer to Frank W, but 3000 RPM isn't really an over revving situation. These motors are speced to rev over 3100 Bare Idle...no load. The governor should limit that max RPM.
 
It is unusual, but I suppose it could happen. Follow the Cat guys recommendation. Little metal pieces down in an endine are not good. If a piston is damaged you need to find it now while you have t he insurance company "hooked up".

I'd also expect a battle with the claims adjuster on the engine work.

Resetting the overheads does refer to the valves but it also includes resetting the injectors since they are driven like the valves on Caterpillar's unit injection engines.
 
I have already authorized the shop to remove the head, and inspect the lower part of the engine.

I think the insurance company will play ball with me.

The claim for the broken shaft and new propellar ran close to $8k.
 
Received a call from the shop today.

The insurance company sent a surveyor down to the shop to inspect the engine. The surveyor agreed that with the rod bending the way it did, that it would have required a large amount of force, and that it is prudent to inspect the lower part (cam shaft etc.) of the engine for damage. He also agreed with the shop that the most efficient way to do the inspection is to pull the engine out of the boat, and remove the oil pan.

The shop feels that if there is any damage to the lower part of the engine, that the insurance company will authorize a replacement of the engine with a rebuilt engine from Caterpillar.

All along during this conversation, I am saying "at whose expense"? The shop manager assured me that the repair is authorized, and will be covered by the insurance company.

He indicated that the insurance company would prefer to replace the engine, rather than have the shop rebuild the current engine, because at that point, Caterpillar is now responsible for any future problems with that engine, not the shop, or the insurance company.
 
So...apparently the insurance company has agreed with your shop that the damage has resulted from the snapped shaft (covered cause of loss)?
 
Got a call from the shop yesturday. The engine is out of the boat, and they lowered the oil pan, and found metal in the lower part of the engine. At this point, the shop is contacting Caterpillar to find out what the options and costs are for a short block, long block, and complete rebuild.

The shop indicated that at this point they are 99% sure that the insurance company is paying for the repair. I called the claims adjuster a couple of days ago, just to check in, and he seemed distracted with other claims, and was not concentrating much on my situation. I left it with him that I would wait to hear from him, and so far have not. I get the feeling that the shop and the surveyor are working this out, and the insurance company is going to go along with the surveyor. Indications are good....so far.
 
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