Not getting max RPM's

Ripcat

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I've got twin Yanmar 4LHA's and just recently changed the primary fuel filters. They were pretty clogged, boats new to me and its now obvious that the previous owner wasn't a maintenance freak like I am. Anyway...not getting max rpm's out of starboard engine now...hits 3200 and that's it...port gives me 3400. Going to be changing the primary fuel filters tonight and pretty sure that's it but on my last fill, I noticed the starboard tank took 20 more gallons than the port did. Don't know if they are related but thought it was interesting. Starboard took more fuel but isn't getting max RPM's...HMMMM :confused:

Any thoughts?

Boats got some bottom growth but I would imagine that would affect both engines in the same manner so I've kinda ruled that out. Both throttle cables and Trans cables on port side were changed by previous owner but not starboard...could it be a cable adjustment thing?
 

plowin

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Cable adjustment would explain the rpm issue but not the fuel burn discrepancy. It would probably make sense to have the props checked, that is a possibility. How many hours? When, if ever, was the last time the injectors were pop tested and inspected for damaged tips? Any black smoke or soot
 

Ripcat

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I should've mentioned that the last time I went for WOT, maybe a month ago, they hit the 3400 mark fine. They each have 940 hours. No black smoke at all really...occasionally when i'm loaded and I put the hammer down there's a small amount of black smoke but under normal cruising there's none. I did clean the transom sunday and there was a small coating of black soot but barely noticeable unless you were an inch away.

As far as when the injectors were last dealt with...no idea but could ask the seller. When I had the engines surveyed prior to the purchase everything was checked and functioning properly.
 

djmarchand

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First check wot no load rpm. Should be about 3,600 for both engines. If lower on the starboard engine then that may be your problem. Adjust throttle so that it is at its stop at wot.

Then depending on the transmission, some have a slightly different gear ratio port and starboard to allow counter prop rotation. Boat builders put the same prop on both sides which causes one engine to work harder. If this is the case then repitch the starboard prop to let it rev up.

Finally if transmission ratio is the same on both sides, have props scanned to confirm they are the same pitch and adjust accordingly.

But before doing the later, take air cleaner off and spin the intake turbo by hand to make sure it is totally free with no rough spots. If there is any restriction, take off V-Clamp at exhaust turbo and look inside for rust- sure sign of seawater backing up damaging the turbo and maybe the engine.

David
 

Ripcat

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Good stuff fella's...thanks.

Dave,
Great idea of no load RPM check...can't believe I didn't think of it. I'll try that and see what I get. Just to be sure I understand what you mean, in neutral and go for WOT?

Fairly certain the engines aren't drinking the sea...I did a brand new wet exhaust system on each engine and even added a 3rd elbow downstream of the mixer to ensure a good down angle. There were no signs of it drinking water before I did this and I'd be shocked, and disappointed, if it was now. I will check though.

The other piece of info is that under cruising RPM's, around 2800, I get the same speed I always have...no difference in cruising...only at WOT.
 

djmarchand

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Ripcat:

Yes, in neutral and after warming the engine up, slam the throttle to the max and check rpms.

I would not think you have ingested water either. If the starboard engine will make 3,200 rpm then it is close. A seawater affected engine probably wouldn't get close to rated rpm in gear.

I agree that the fact that once both engines would turn 3,400 in gear indicates that the gears are the same and the props are right.

So maybe the throttle linkage shifted and isn't opening the last bit. Easy to check and easy to fix.

David
 

Dr Dude

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Last edited:

djmarchand

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The air cooler is a shell and tube heat exchanger. The shell is made from cast aluminum and the tubes are a bundle of cupronickel tubes. The raw water flows through the tubes and the air from the turbocharger flows outside the tubes on the shell side. So the air side is the shell side.

BillD implies a good point. The "air side" gets fouled with oil, soot and dust and can restrict air flow, leading to smoking and less power. If they have never been cleaned, read Tony Athens article at Yanmar Aftercooler Maintenance and clean them now. The article is for a Yanmar 6LY but the principles are the same for the 4LH. I wrote a posting to boatdiesel with a little more info an pics on cleaning a 6LY air cooler.

By the way air cooler, after cooler, intercooler are all synonyms for the same thing on a diesel- something that cools the air after it has been compressed in the air side of the turbo. The air can get up to 500 degrees before cooling.

David
 

captjohn

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If all this happened after you changed out filters the first thing I would do is change out both filters on the starboard engines, rule out a problem with the filter itself. If that doesn't do the trick try running both engines off of the starboard tank (switch over the return lines as well), see if they both start loosing RPM's (run them for 15 to 20 minutes), then switch over to the port tank (return line as well), rule out a clogged pickup or return line. Lets make sure your getting plenty of fuel to both engines before we start hauling the boat, cleaning the bottom, and checking props. As far as one engine burning more fuel that the other, could be normal if it's not excessive. I have yet to put the same amount of fuel in both tanks on any boat I've ever filled up, always some difference.
 

lobstercatcher

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I should've mentioned that the last time I went for WOT, maybe a month ago, they hit the 3400 mark fine. They each have 940 hours. No black smoke at all really...occasionally when i'm loaded and I put the hammer down there's a small amount of black smoke but under normal cruising there's none. I did clean the transom sunday and there was a small coating of black soot but barely noticeable unless you were an inch away.

As far as when the injectors were last dealt with...no idea but could ask the seller. When I had the engines surveyed prior to the purchase everything was checked and functioning properly.

Last month both engines got full rpm. Then the previous owner borrowed it and gave it back and did no maintenance while he borrowed it???? What a jerk they were .
 

Tuna Pursuit

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Bump on the WOT no load but I would disconnect the cable at the engine and do it by hand. Just went through it with my cummins. I needed new cables due to the groove at the engine end was worn from vibration. Also, are your tachs accurate?
 

pugsley

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perhaps something on the wheel? something wound tight might not give that much vibration.
 

Ripcat

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Wow...thanks for the education fellas. So much to learn!

A good list of things to check. Think I'll start with some of the simpler things and go down the list from there.

Thanks again
 

BillD

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Wow...thanks for the education fellas. So much to learn!

A good list of things to check. Think I'll start with some of the simpler things and go down the list from there.

Thanks again

Ripcat, a couple of last thoughts from me.

I assume you are "guessing" at the rpm numbers in your posts.:D

Analogue tachs are not always accurate and the drop in 200 rpms "overnight sort of speak" "could be" a simple electrical issue between the sender on the engine and the tach.

If this was my boat I'd start from scratch in the proper order. Accurate rpm numbers.

1. Buy or borrow a hand held photo tachometer..about $40 bucks online.
2. At the dock with the engines in neutral photo tach each engine @ WOT. The 4LHAs are "rated @ 3600"...no load WOT should be well over 3700..maybe 3800. Don't worry, the engines are governed and will not blow up.
3. Assume the engines spin up to 3700 + WOT no load..skip to #5
4. If the engines do not reach at least 3600 @ WOT check the throttle cables for "full throw" on the engine fuel pump lever, no binding etc.
5. OK, the engines can reach over 3600 @ dock no load WOT using the photo tach....all set for sea trials.
6. Take out the boat and get the WOTs both engines with photo tach. If you can't reach @ least 3600 with the boat full of fuel, water, gear and people NOW start looking for the "problem/issue".

Read, this article a couple of times. Get accurate rpm data.
It will ALL make sense.


Understanding Low Power Troubleshooting

Good luck, we are here to help :D

Bill D
 

Ripcat

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Great read...thanks BillD. Heading down to the boat tonight to see about the no load WOT...and will go from there. And yes, the tachs were checked before it was shipped from NC to NH but since then my temp gauge on the stbd side has fallen off by about 10% so it wouldn't surprise me if the tach was off too. I'll confirm that though.

Really appreciate the guidance and help. I always thought of myself as mechanically inclined, my first vehicle was a 1964 Chevy Pickup with a small block that I built entirely myself from the chassis up. When it came to the engine, my dad bought a book on rebuilding the small block chevy (305), handed it to me and that's exactly what I did one winter. That said, I have NO experience with diesel engines but have done a lot of reading, own every manual Yanmar makes for the 4LHA and luckily have DEBF to guide me in the right direction!

Thanks again guys....
 

BillD

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Great read...thanks BillD. Heading down to the boat tonight to see about the no load WOT...and will go from there. And yes, the tachs were checked before it was shipped from NC to NH but since then my temp gauge on the stbd side has fallen off by about 10% so it wouldn't surprise me if the tach was off too. I'll confirm that though.

Really appreciate the guidance and help. I always thought of myself as mechanically inclined, my first vehicle was a 1964 Chevy Pickup with a small block that I built entirely myself from the chassis up. When it came to the engine, my dad bought a book on rebuilding the small block chevy (305), handed it to me and that's exactly what I did one winter. That said, I have NO experience with diesel engines but have done a lot of reading, own every manual Yanmar makes for the 4LHA and luckily have DEBF to guide me in the right direction!

Rip,

You have a very good pr. of base engines. The Yanmar 4LHAs were one of the BEST engines Yanmar ever produced and are no longer produced.

If Yanmar had a RECON program similar to Cummins, Yanmar would sell the 4LHAs by the 100s for repowers of older hulls.

Remember, when you say the "tachs were checked" @ survey...were they checked "with a photo tach" ?? that's key and that is your starting point to get this issue resolved....accurate rpms !!!!
 

captainlarry84

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Photo taching is a must. Based on the fact that fuel burn is up on one motor and the RPMs are down. It sounds to me like a bent propeller.
 

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