Strange Change on RPM's - any ideas?

[LBI4fun]

My Smart shows a single display with both port and starboard displayed, each has a line that moves with the drive. I have clibrated it and still see it a bit faster on the port just like the dial display.

 

[toofast]

My madness continues...

Last night turned warmer again and little wind, so I decided to take a friend and do some more research.

First of all the drives measured almost perfect...the STBD drive does seem to trim down a bit quicker, but all fluids are fine, so I can only assume it always worked that way. So I can eliminate the drive trim issues as what effects my RPM issue.

We did some more engine work...and my buddy knows a thing or two about motors...and he concluded that the engines appear to be running perfectly. We ran them both up to about 2,000 RPMs in neutral...and no missing, no sputtering, and perfect sync. So I am now starting to feel the engines are fine.

No the real test...bay was calm, so we headed out...at the first run, we did notice some strong vibrations in the 1500-2500 rpm range. But once on plane, they seem to go away. Of course the STBD engine is still lagging behind. So we stop, and this time just run up the PORT engine to 2500 RPMs, smooth as silk. Ok, now we run up the STBD engine alone...and man, there is a pretty strong vibration again. Yet once past a certain RPM it seems to go away.

So we dive in the water again, and inspect the PROPS....they appear perfect...HOWEVER my vibration must be coming from the outdrive or props (and I recently had the outdrive serviced)

Anyways...quick questions.

1) If I had a damaged prop, would the vibration go away at higher RPMs?
2) Has anyone ever changed BIII props in the water, I can change on land no problem?is it doable in the water?
3) Is there any reason I can?t swap PORT and STBD props to see if the vibration follows the props?
4) If the props turn out to be ok, any ideas as to what might be causing this vibration issue through the mid range rpm?s?
Thanks again!

 

[V1rowT8]

TF,

Yes, one can experience vibrations at a given RPM which are not noticeable at different RPM's. Harmonics and resonances are often involved, but at a level I do not fully understand. Vibration in general is certainly bad for materials though, potentially leading to parts fatigue and premature failure. For this reason alone, your scenario is important to resolve in the near term.

As you know, I have different drives than yours, but I too experienced mid-band vibration a while back. In my case, my wheels were ever so slightly fouled, and as soon as I cleaned them, the vibration went away. I did not have the RPM disparity though. In your case, it sounds like your props are clean as a whistle, which is puzzling. I suppose it's possible you came in contact with something which slightly altered one of the blades, but was minor enough for you not to have felt while underway. Who knows.

Good luck getting to the bottom of it. Swapping wheels sounds like a reasonable next step.

 

[CoolChange]

Toofast;
The best way to check your wheels and know for sure is take them to a prop shop and have them check the balance.

You mentioned you had the drives serviced recently. Did the vibration and RPM loss start then? Did they pull the drives? The alignment of the universal joint in that drive is very critical. After you verify your props are good you might want to run the engine at different trim angles in the vibration zone and see if anything changes. If it does, I would suspect U Joint issues.

Also, one more thing, if the vibration was accompanied by "roaring" sound, I would defiantly have you props checked. Oh yea, I can't remember if those props have to be aligned a certain way when installed, but it might be a question worth asking.

 

[toofast]

Toofast;
The best way to check your wheels and know for sure is take them to a prop shop and have them check the balance.

You mentioned you had the drives serviced recently. Did the vibration and RPM loss start then? Did they pull the drives? The alignment of the universal joint in that drive is very critical. After you verify your props are good you might want to run the engine at different trim angles in the vibration zone and see if anything changes. If it does, I would suspect U Joint issues.

Also, one more thing, if the vibration was accompanied by "roaring" sound, I would defiantly have you props checked. Oh yea, I can't remember if those props have to be aligned a certain way when installed, but it might be a question worth asking.

I don't think the vibration started when the drives were serviced...although it may have...but I doubt it. They did not pull the drives, just replaced the lowers.

I was thinking alignment and u-joints, but crap I have 70 hours on the brand new boat....

I wanted to swap props to see if it goes away...and yes they need to go on a certain way...in a cloverleaf pattern.

 

[CMac]

I have swapped props in the water on my previous boat with the Blll. I was in the water and very nervous about it though, don't want to loose anything. The props are not side specific, however, I did here someone tell once that there is an alighnment procedure. The props are counter rotating, so I'm not sure where any alighnment would come in, I would think one point would cross paths with another inner prop to outer prop. I guess I would possition them the same and keep it all the same when putting them back on.

 

[selpel]

Toofast;
The best way to check your wheels and know for sure is take them to a prop shop and have them check the balance.

You mentioned you had the drives serviced recently. Did the vibration and RPM loss start then? Did they pull the drives? The alignment of the universal joint in that drive is very critical. After you verify your props are good you might want to run the engine at different trim angles in the vibration zone and see if anything changes. If it does, I would suspect U Joint issues.

Also, one more thing, if the vibration was accompanied by "roaring" sound, I would defiantly have you props checked. Oh yea, I can't remember if those props have to be aligned a certain way when installed, but it might be a question worth asking.

I don't think the vibration started when the drives were serviced...although it may have...but I doubt it. They did not pull the drives, just replaced the lowers.

I was thinking alignment and u-joints, but crap I have 70 hours on the brand new boat....

I wanted to swap props to see if it goes away...and yes they need to go on a certain way...in a cloverleaf pattern.

I agree that a prop swap would be the next step.....but....... don`t count out engine alignment. Although you have only 70hrs. on your boat this doesn't mean that your motors have`nt settled a bit and the engine coupler is NOT aligned with the gimbal bearing. The engine coupler on the flywheel on your motor has a metal splined sleeve in it surrounded by rubber. If the motor has settled at the front the steel splined sleeve will twist to allow the output shaft to past through the gimbal bearing. This will load the output shaft and cause premature spline wear and could cause a vibration at certain RPM`s
Here at the LOTO we recommend the drives be pull once a year or every 100hrs. to check the engine alignment and make sure we DO NOT have coupler spline wear that may cause a problem in the near future............. 8)

 

[Seas-The-Day]

That is good advice, Steve. My last Formula (2002 330 SS) was less than 100 hrs old and one engine did go out of alignment and it wrecked a coupler. However, the sound that drew my attention was a very faint clicking while I was idling thru a marina. I do not recall any other noise or vibration while cruising.

 

[toofast]

For safety's sake, I just bought a alignment tool...I will just do it myself...I can't stand that the marina charges so much and you never know how accurate a job they do.

I will also try to swap props this weekend and see if that makes a difference...

It's always fun!

 

[selpel]

For safety's sake, I just bought a alignment tool...I will just do it myself...I can't stand that the marina charges so much and you never know how accurate a job they do.

I will also try to swap props this weekend and see if that makes a difference...

It's always fun!

That's a great idea...............When you start to check the alignment make sure to turn the motor over a couple of times during the process. Warning do not turn it over with the alignment tool in the coupler. The reasoning for this is to make sure the spline sleeve is straight at different positions on the couplers clock. Example 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock.

Also if you have a problem knowing if it is done right ask the marina to let you watch how it is done the first time, that also puts the ball in their court to complete the job in a timely fashion. It will also show you what has to be done when you start doing it yourself.

The rotation thing is something I did when I turn wrenches on boats before going into sales so not everyone may do this, but if you are standing there you may ask them to try it, and make sure it fits like it is suppose to.............. 8) 8)

 

[castines]

another trick we used was to put plenty of grease on the alignment tool.. then insert the tool. remove the tool and sometimes you could see splines in the grease on one area of the tool and not the other.

 

[Seas-The-Day]

Ok. So, I was hanging out at my dock and there is this guy with a 42' Apache with twin 1050 HPs. He has done a lot of racing and does his own work. I ran the "Lagging Stbd" issue by him to see if he had any ideas.

You know what he said?

He has the same problem. His Stbd lags also!

He had a buddy with him who drag races cars and is pretty handy around engines. None of us could come up with anything we have not already in this thread. We agreed, the next step is probably a compression test and leak down test.

But, wht always Stbd ??? Interesting!

 

[CMac]

I had to go back and reread your first post because I was thinking 20 or 40 rpm difference, like mine is sometimes, might be normall under different circumstances, but 200 rpm is big.

Is it still that much different after all the things done and checked?

Does sound like a dead cylinder to me. I heard that the 496's eat plugs too.

We used to check exhaust manifolds, on our dragsters, for equal temp with a probe. Just a thought. But it sounds like you've covered all that.

Seems to soon on an '08 for out drive, but I would suspect the props.

I bent one fin on one inside prop, trapped wood between cav plate, and it just ended any idea of planing out. It wasn't very visible to the eye.

 

[toofast]

I think I am starting to sound like a broken record

This weekend I managed to swap the props while the boat is in the water...just for the record doable, but a bit un fun!

Anyways, props look perfect, but you never know...so once changed I took her out for another test run.

Well, same thing again...STBD engine is 200-400 RPM difference. At mid-range it is 200 RPM off, at WOT I can only get about 4200 RPM out of my STBD, while my PORT is spinning 4600.

So we know for SURE it is not the props...

So back to the drawing board....

This time I decided to do a few test runs with the engine hatch up...while I had a buddy driving. Believe it not, I am switching my thoughts...for sure the vibration on the STBD is still there...but it feels like an engine miss. Strange thing (or not so strange) is the engine appears to ONLY be missing under a load...or at least that is when you can feel it. I could visually see the STBD engine "shaking" under load, while the PORT was gently singing along...

After I get to cruise, the missing seems to go away, but it must be affecting the performance.

Guess I finally need to get my engines scanned and then get a compression/leak down test.

Bummer...I thought these 496's were rock solid....more as the story unfolds.

 

[castines]

Did you try new plugs yet? you could also have a bad coil. coils will break down under load.

you can check to see what cyclinder or plug/wire/coil may be the issue. while at idle, remove 1 plug wire at a time to see if the cyclinder drops out and engine idles rougher. if you remove a wire and no difference in the enging idle then that is usually the susupect cycliner/plug/wire. you need to listen close and feel for the difference when you remove the wires.

Be careful, I have been bitten many times by the spark . if you cant get to the plug to take off the wire go to the coil for that cycliner.

good luck!

PS. my dad got me really good when i was young. we were working on the lawn mower. he had the spark plug out, asked me to hold the wire and check for spark and he pulled on the rope! Eeeyowww! you have no idea how fast a mower spins with no plug in it i climed up on top of a large tool box and was afraid to go near the lawn mower.

 

[toofast]

Did you try new plugs yet? you could also have a bad coil. coils will break down under load.

I did not try new plugs, as they all looked good...but maybe that is the better next step. I could also swap out the coil with the port engine...maybe that will tell me something. I just hated to change all the plugs when they looked perfect...also because Seas did this without fixing his issue, I thought it didn't make sense.

But as well all know, boating issue seldom make sense...

 

[castines]

i am pretty sure there is 8 coils per engine, or maybe a pack of 4 per side of the block. the days of one coil for 8 plugs are gone.

 

[castines]

Did you try new plugs yet? you could also have a bad coil. coils will break down under load.

you can check to see what cyclinder or plug/wire/coil may be the issue. while at idle, remove 1 plug wire at a time to see if the cyclinder drops out and engine idles rougher. if you remove a wire and no difference in the enging idle then that is usually the susupect cycliner/plug/wire. you need to listen close and feel for the difference when you remove the wires.

Be careful, I have been bitten many times by the spark . if you cant get to the plug to take off the wire go to the coil for that cycliner.

good luck!

PS. my dad got me really good when i was young. we were working on the lawn mower. he had the spark plug out, asked me to hold the wire and check for spark and he pulled on the rope! Eeeyowww! you have no idea how fast a mower spins with no plug in it i climed up on top of a large tool box and was afraid to go near the lawn mower.

one more thing, if you find a cyclinder that does not make a difference when removing the wire, and then change the plug, wire and or coil and still does not make a difference then you can look into other things. at this point they could be rings, valves etc....

 

[CMac]

You can use a simple old timing lite to check power to the plug. Clip it to each wire as close to the plug as possible to see it blink per fire.

Bet it's a plug, they can look good, but be failing intermittently.

 

[toofast]

You can use a simple old timing lite to check power to the plug. Clip it to each wire as close to the plug as possible to see it blink per fire.

Bet it's a plug, they can look good, but be failing intermittently.

Dumb question...will the timing light catch a bad plug, or only if it is completely "dead" i.e. getting no spark? Just curious if I should invest in that, or simply just replace every plug, even though when I pulled them before they all "looked" good.