Missing 60 rpms at no-load wot?

[tobnpr]

I had not checked no-load rpms for quite a while, did it yesterday at the dock. Stbd engine turned 3045, port would only turn up to 2940 (Aetna tachs). Had previously turned up to the 3000 min. spec'd.

Do you think I should be concerned about the "missing" 60 rpms, and if so, is this a governor adjustment?

 

[Lazy Daze]

I can't answer your question, but... How easy is it to swap your tachs?

 

[earthmover17]

I had not checked no-load rpms for quite a while, did it yesterday at the dock. Stbd engine turned 3045, port would only turn up to 2940 (Aetna tachs). Had previously turned up to the 3000 min. spec'd.

Do you think I should be concerned about the "missing" 60 rpms, and if so, is this a governor adjustment?

First you need to throw your calculator away. Your difference is 105 RPM.
I would see what WOT is at load (if the seas ever lay down up here).
I would start looking around for what's going on. You know enough to start troubleshooting. I would look at airflow first and then progress to fuel etc.

Jack

 

[fwebster]

Try it again after a long run to see if it clears itself.

Assuming there is no intake air restriction, I would be looking for a carbon deposit on an injector based on the age of your engines. It doesn't take much to change an atomized pattern into a spray with droplets which can make a cylinder burn the fuel charge incompletely burn a fuel charge.

 

[osd9]

Basic I know, but did you first confirm full throw on your governor? Remove the cable and check the cable hasn't stretched. Also, is one motor slaved from a Synchronzier? If so, try diconnecting the synch, or, try Bare Idle Speed test with the synch on.

 

[osd9]

........ Stbd engine turned 3045, port would only turn up to 2940 (Aetna tachs). Had previously turned up to the 3000 min. spec'd......?

First you need to throw your calculator away. Your difference is 105 RPM......

I think we'll have to check your reading glasses prescription first.....:grin:

His Port motor is only spec'd at 3000RPMs....each motor has it's own Bare Idle Speed spec....they are not all the same.

 

[tobnpr]

Thanks guys.

Like Jack said, 'tis the season- weather's finally cooled off, but we've got twenty knot winds thru the weekend. Guess I'll take her out and open it up as Frank's suggested, doing a little 'surfing' down the ICW and see what happens.

I noticed some excessive brown smoke in the exhaust last time out (not black or gray) and had a pretty sooty transom by the end of the day. The foam air cleaner elements were pretty oily, so I changed them out as well as the Racor elements before this check. Since it's not reaching no-load rpms I suspect Frank may be correct (surprise!).

If I find out anything that might be beneficial to anyone I'll pass it along.

 

[earthmover17]

I think we'll have to check your reading glasses prescription first.....:grin:

His Port motor is only spec'd at 3000RPMs....each motor has it's own Bare Idle Speed spec....they are not all the same.

Bottom line is I know a lotta guys with diesel engines in their boats and the only time there is a difference in RPM's at WOT between engines something's not right. And it's not just Cats.
My engines when running right, run within 15 Rpm's of each other. Starboard runs slightly less as it runs the power steering pump.
I am lucky as I have the load function on my gauges. Run both engines up to a certain Rpm and check the load. They should be identical. If not there is an issue.
Just defending my reading glasses.

Jack

 

[osd9]

Your defense is weak. The OP is not talking about WOT 'under load' He's talking about Bare Idle Speed....the max rpms that the motor is spec'd for 'in neutral'.....'no load'.

You still timay need to up the optical power to +2.5......:grin:

 

[tobnpr]

Turned out to be an easy fix.
I called my mechanic today. He said clean bottom, no smoke meant it was most likely a simple adjustment as the throttle probably wasn't getting "full throw" and not hitting the stop. Funny, Dom said the same thing shoulda listened to you first...

Walked out back, opened the hatch and checked. Sure enough, with the throttle to the pin there was still around 1/4-1/2" to the stop. Turns out the "ball and socket" linkage is pretty worn and sloppy. No danger of it falling out, but I'll probably replace them just to be safe. Unhooked it and lengthed it a bit with the adjustment screws, throttle would now hit the stop @ wot.

Fired it up and voila...3085 rpm, well above spec.

Moral of the story- even if you basically know jack about diesels, always start with the simple stuff first (and it sure helps to have a great mechanic...)