Rev limiter 1900 SCR3 - Maxum Boat Owners Club

martynj19 · 05-23-2016, 12:32 AM

Hi guys , does the 4.3 carb v6 have a rev limiter ? Also what are the effects on a marine engine if, as an example travelling at 50knts the engine was over revved or the boat left the water briefly?

Thx Marty

mmwjr · 05-23-2016, 03:01 AM

What year is the engine?

The prop coming out of the water will allow the rpms to kick up but for a very short period that should not cause an issue.

What did you expierence?

martynj19 · 05-23-2016, 03:40 AM

Hi Mike,

It was our first outing in the bay ( Moreton) on Friday, nice trip over to Moreton island, no dramas going out. On our return we were 3/4 way back travelling at about 50 ish and there was a loss of power and lots of noise from the stern area (sounded like clattering) , it happened very quickly. We stopped the boat , no audible alarms , all gauges reading normal. Had a look underneath at leg and prop (all good). Started engine again . ticked over fine , tried F/R , then powered up back on plane all way home , all normal never missed a beat. I know its difficult trying to describe , but I was thinking water in fuel briefly? or misfire?. btw its a 2006 engine

Marty

mmwjr · 05-23-2016, 03:44 AM

Marty what rpm is the engine turning at 50 mph?

martynj19 · 05-23-2016, 03:53 AM

To be honest , I didnt check , my son in law was driving and we are still finding our way around the boat , we were constantly checking the gauges for temps and oil pressure. GPS was saying one thing on speed and dial was saying something else , it shook us up a bit , as we are new to boating etc , we will check out rpm when we take it out again. There was only the 2 of us on the boat.

Marty

mmwjr · 05-23-2016, 12:37 PM

OK to my knowledge there is no rev limiter but a knock sensor that is triggered will retard the timing. Clattering noise is not a good thing.

The WOT (wide open throttle) for this engine is around 4400-4800 and should only be operated in this range for short burst as the engine is not designed to run there under normal conditions. I suspect doing 50 mph you were at or near WOT. A boat is much different than a car, a car moves under rolling resistance but a boat is always under high load pushing through water which is very dense. It's like going uphill pulling a heavy load all the time.

martynj19 · 05-23-2016, 10:19 PM

I will certainly be more observant when we go out next , Is there anything to look for around the shift mechanism? Would high speed or slamming cause it to jump in and out of gear? All the linkages seem tight and in place , I will check everything thoroughly at the weekend. As you know , it it very difficult to pinpoint something when not hearing or feeling it yourself, and I thank you again for your help.
Martyn

mmwjr · 05-23-2016, 10:58 PM

hard to say. Look for signs of rubber behind the engine as the coupler may have let go but this ussually stays broke and will not get above 2000 rpm before slipping again.

BTY did you notice what the tach was reading when this occurred? Rpms drop or shot up?

martynj19 · 05-24-2016, 04:23 AM

All happened very quickly , made a big noise , he throttled off and killed the engine , I looked over the swim deck thinking the prop had destroyed itself, then lifted the cowling. Inspected engine , bilge , fluid levels and then started it up , ticked over sweet as, and ran all the way home took about 30 mins with no dramas. The prop looks fine nothing bent turns, freely . Thx

shrew · 05-24-2016, 02:30 PM

Quote:

Originally Posted by martynj19

All happened very quickly , made a big noise , he throttled off and killed the engine.

How quickly did the engine get shut down? More importantly, how fast were you going? most importantly, did you shutdown before the wake caught up to you? That is a great way to dump a bunch of water in the engine through the risers and manifolds. The exhaust pressure is needed to prevent this.

When stuff like this occurs, putting the drive into neutral is important. Short of a fuel system rupture and fire, wait until you come to stop and then shut the engine off.

martynj19 · 05-24-2016, 11:11 PM

Cant remember whether the noise was still there when I told him to turn off engine or the engine may have died before we had stopped. Thx for advice on not switching off when wake is still advancing. If you are travelling fast and the safety switch is pulled (accidently or on purpose), is that something that can cause engine dmage if wake passes back on risers? I think there are "check" flaps which are supposed to minimise or prevent this ? (thats if they are operational of course.) Just spoken to son in law , and he reckons we were running about 3000 rpm at 40 mph , what effect does a slug of water in fuel line have when running a marine engine? Would that "knock" "bang " etc , it did feel as though it missed on a couple or more cylinders , but not being used to boat engines its difficult to pin down. Much appreciated for advice and comments. Thx Marty

mmwjr · 05-25-2016, 03:27 AM

Any abrupt slowing down whether kill switch or pulling the throttle back may result in the wake flowing back through the exhaust and can find its way into the engine. Yes there are flappers that will minimize this.

Hard to believe water caused your issue. Water or dirt in the fuel will cause the engine to sputter and potential not run at all but not make any noise. A boat gas engine will suffer the same issues as a car engine as far as problems that make them not run good. However a boat engine is subject to water issues much more. Also issues with the water cooled exhaust system.

shrew · 05-25-2016, 03:27 PM

I don't think water caused the issue. I was concerned with the potential ramifications of quickly shutting down the engine when the issue occurred. Like making a bad situation potentially worse.

Did you take a look at the prop? you could have hit submerged debris, like a water soaked log.

martynj19 · 05-25-2016, 10:13 PM

I have attached this photo of the leg , I am mainly looking at the position of the forward /reverse shaft connection , would I expect to see this inline with the centre line of the leg so to speak? The shift lever at the helm is in the neutral position.

Thx Marty

mmwjr · 05-25-2016, 10:57 PM

The shift shoe should be facing forward when the shifter is in forward gear.

martynj19 · 05-25-2016, 11:11 PM

Thx Mike , is there an equal amount of travel ie if it was in reverse would the shoe be pointing to the right (as we are looking at it in photo? )

mmwjr · 05-25-2016, 11:17 PM

Quote:

Originally Posted by martynj19

Thx Mike , is there an equal amount of travel ie if it was in reverse would the shoe be pointing to the right (as we are looking at it in photo? )

Don't know. I just know to pull the drive the shifter has to be in forward so the shift shoe and shift shaft are facing forward so everything is inline to allow the drive to pull straight back off and on to install.

martynj19 · 05-25-2016, 11:24 PM

Son in law is taking boat out today and over weekend , all inshore stuff , I won't be there

, so we will see how it goes when he is back. I didnt get chance to check stern leg oil condition , I am leaning toward the noise being made by it jumping or slipping out of gear. need more investigation I suppose.
Marty

mmwjr · 05-25-2016, 11:28 PM

Keep us posted on what you discover.

martynj19 · 05-30-2016, 08:57 AM

Son in law , used the boat over the weekend , absolutely no issues , ran great , a couple of fast runs, the rest cruising. No noises etc. When he brought it back I noticed that the "shift assist" rod/spring assembly had seperated (see photo). This was like this when we first picked the boat up. At the time I just shifted it back into what I thought was the correct alignment. I did not undo anything or make any adjustments, just popped it back together. It has obviously come apart again , but it would have to move quite a bit to do this. I am now presuming that something is not right with the shift adjustments for it to come adrift?

Marty