Engines out of synch

[rondds]

Two pictures tell the whole story. Since I've gotten this boat (Summer 2004), the engines have a synch problem. At lower RPM, they are audibly in synch, the tachs are in synch and the synch gauge reads straight up. At higher RPM (around 2600), if I use the synch gauge and tachs, the engines are audibly OUT of synch (the chug chug sound). So I generally cruise with the following readings...

WHEN THIS PIC WAS SHOT, TACHS AND SYNCH GAUGES appear to be out of synch, but engines are synched to the ear...

Floscan readings at the above rpm...

Just some background - This has always been an issue from day one. I have done two tuneups since, replaced the tachs, the floscan gauges and the floscan senders. The fact that the port engine burns more gas is confirmed at fill-up. The Floscans are DEAD ON BALLS accurate, also confirmed at fill-up time. Exhaust system is all new.

One theory is that the timing is off - I have never checked the timing on port engine - the starboard had heads off two years ago so the timing was set when replaced. This did not change anything. BUT why does it run synched at lower RPM. A friend suggested that as RPM increases, a module controls the timing and maybe the module is misbehaving.

You may note in the first picture, there is a checkbook register on the dash - I keep a log of consumption all season long based on the Floscan totalizers. There is a stark difference in consumption as you can see by the Floscans - stbd burns 18-20% less than port.

A great man here on CSR told me a few years back to stop worrying and go boating, which I DO. The boat runs otherwise flawlessly. This just bugs me.

 

[mistercomputerman]

When great men talk, wise men listen...

 

[RollerCoastr]

So the tachs, the flowscans, the sync gauge and the actual fuel burn all agree with each other, but disagree with your ears. Are you sure they're actually out of sync when your ears tell you so?

 

[rcknecht]

Ron, I have heard that the engine that turns the counter rotating prop usually burns more. Having one engine that burns more than the other is common... As far as the sync issue... Does your engine have an anti-knock sensor? It if does that adjusts the timing to avoid knocking from low octane fuel.. As the engine works harder at the higher RPMs, the spark might be retarding to avoid knocking... If it retards too much, you will burn rich, and your fuel burn for that engine will be greater. Also with the incomplete burn on one engine may affect the harmonic sound you are hearing between the engines...

 

[Half Fast]

So the tachs, the flowscans, the sync gauge and the actual fuel burn all agree with each other, but disagree with your ears. Are you sure they're actually out of sync when your ears tell you so?

Except there is nothing like a good set of ears to dial in sync. Plus the burn difference seems like its more than could be accounted for by the 100 or so rpm difference on the tachs. That is a significant difference he's got working there.

I vote for just go boating while letting them continue to make sweet music together, gauges and fuel consumption be damned.

 

[rondds]

Absolutely sure my ears are hearing correctly. I've had other boaters on board and had them listen as well.

Rod, not sure my old '89s have a knock sensor (?) If the problem you describe did exist, would I ever hear a knock or would I get "run-on" when shutting down? ;Cause I have never had a problem in taht department.

These engines are designed to run on 86 octane fuel but I've never used anything less than 87 - and even that was on a rare occasion when I had no choice. BTW, this has been an issue well before the onslaught of E10. E 10 has had no effect on this difference and I put the prescribed amount of Startron in at each gas-up, whether it makes any difference or not is probably debatable.

 

[RollerCoastr]

Yeah - I'm generally with you on not doubting the ol' human ear, but I've also seen people plow along at the wrong speed, wrong trim "cuz it just sounds right", so I wanted to throw it out there.

I see more than a 100 rpm delta: Each hash mark is 200 RPM. Port reads 3400. Stbd reads just over 3200 and the sync gauge suggests that it's even wider.

As much as I like the "just go boating" idea, would be too much for me to overlook.

 

[Bugsy24]

I didn't know GCM sold 86 octane... you Cheapo you!

 

[rondds]

3400 and 3250 to be exact (as exact as can be with analog).

Yeah, it's bothersome but it doesn't stop me from using the boat. Just don't know what to do about it. I should probably start with checking timing on the port engine.

Oh yeah, did I mention the props were redone by a PropScan shop? no difference.

Marshall, GCM sells 89. I've never used anything less than 87, and that was only at Shore Point in Toms River (maybe twice).

 

[expressboy]

what about the props?.. if one had a slightly different pitch or diameter it might throw the " in sync " sound off at the same rpm on the gauge as the props to be in sync would be at a different rpm ( thus throwing the tach's and sync gauge off).. Possibly a re size prior to your ownership?
EXPRESSBOY

 

[rondds]

Expressboy, in anticipation of that question, I put a post up 1 minute before you did!

 

[rcknecht]

Ok... the marina switched your port prop with your neighbors 370. Now you have a slight difference in your prop size and pitch...

 

[rondds]

Ok... the marina switched your port prop with your neighbors 370

You may be right! Stranger things have happened!

 

[Bugsy24]

Do I sense a little Hostility to "Obnoxious Posts"?

 

[mistercomputerman]

Naw...

His marina really might have done that. He put in an order to have his cutlass bearings changed. They changed the cutlass bearings...on someone else's boat and sent him the bill.

So, they could have put someone else's props on when they finally got around to changing his cutlass bearings.

 

[rondds]

His marina really might have done that

How true. Besides, Rod is incapable of doing ANYTHING obnoxious!

 

[fc3]

Well, you could check the engines at running RPM with an optical timing light. That would confirm or repudiate the sync and tachometers. Then you might want to check your WOT RPM. Since the tachs are suspect, you either need to use a different tach or confirm that the tachs are accurate. Then you can move to the next step. You don't have enough data, yet.

Best regards,
Frank

 

[Bugsy24]

Naw...

His marina really might have done that. He put in an order to have his cutlass bearings changed. They changed the cutlass bearings...on someone else's boat and sent him the bill.

So, they could have put someone else's props on when they finally got around to changing his cutlass bearings.

Don't say that I'm actually going to move to "His" Marina in April!!!!

 

[Bugsy24]

How true. Besides, Rod is incapable of doing ANYTHING obnoxious!

Rod, is an MMA Graduate.... anything they do is OBNOXIOUS! :grin:

 

[rondds]

Frank
I have just such a tach but haven't gotten around to running that test. At least I'd be able to confirm the accuracy of the analog tachs at that point.

Regarding WOT, I have done that several times and I believe I maxed out at 4400rpm on both. If the engines were in or out of sync during that test I couldn't tell you - It was so loud I don't think I'd have been able to tell anyway.