How much vibration is normal for a full stringer BBC boat?

« **on:** May 25, 2015, 08:55:14 PM »

So I'm new to jet boats, just recently got the engine into the boat, took it out this weekend and holy hell... I can feel the thing vibrate the hell out of the boat at RPM. I should mention my previous boating experiences have always been with standard SBC/Alpha1 combo's that were quiet and smooth. Am I trippin' here or is there something going on?

It's a full stringer spectra 18 jet.

« **Reply #1 on:** May 25, 2015, 10:02:07 PM »

Definitely something going on! Start with the usual, verify that you have the correct balancer and flexplate for your engine. Im assuming that it is a 454, which is externally balanced. Both the balancer and flexplate should have counterweights.

If correct, you should have a dowel pin installed in the crankshaft flange, however nobody ever does. This dowel pin performes two functions: 1. It takes the loading of the flexplate/flywheel (in a car) or the PTO in a boat off of the bolts so the bolts only job is retention. 2. It polarizes the clocking of the flexplate/flywheel so that the counterweight is installed in the correct location. If the dowel pin is not installed, the flexplate can be incorrectly installed in 60-degree increments. I have my money on this option.

Next possibility is that the drive line is either assembled incorrectly or is on the verge of failure. Verify that all is well with your U-joints.

Another possibility is that you have a rock lodged in your impeller causing an imbalance.

There is no reason why you can't have Cadillac smoothness compared to an outdrive, being there is only one moving part. You can always let the camshaft rattle your fillings loose should you choose.

Cheers,

Joe

« **Reply #2 on:** May 25, 2015, 10:09:17 PM »

Chad89GT had an excellent post describing the difference in internally and externally counter weighted balancers (dampers) and flywheel/flex plates with pictures to illustrate.

http://www.socaljetboats.com/index.php?topic=23240.0

Quote from: Chad89GT on April 27, 2015, 07:28:13 PM

BBCs and SBCs follow the same basic balancing convention... all are internal except the biggest one. IE: 454 BBC and 400 SBC are externally balanced.

I've seen people replace a 396 with a 454 and reuse the 396 damper and flexplate. Major vibrations!

If you're sure it's a 396 definitely check both the damper and flexplate/flywheel for a weight. There should be none on either.

Flywheel comparison:

Flexplate comparison (size isn't always different, it was the only pic I could find):

If the balance of the flywheel and damper are OK you could have bad U-Joints or a misaligned drive shaft. There are threads on that topic here, search should bring some up.

http://www.socaljetboats.com/index.php?topic=23240.0

« **Reply #3 on:** May 25, 2015, 10:43:02 PM »

OK some great info here to go off. From what I understand the guy who built the motor said the machine shop balanced the entire rotating assembly with the balancer. It's an 8" balancer. I know the flywheel does in fact have a dowel , but I don't know the history of it, or if it was with the motor when balanced.

However the alignment of the PTO/ujoints may very well be off. Looking at it f from the top is definitely not in line, but I assumed it would probably be fine since it's a double cardan joint. I haven't measured though to see if they're on the same plane.

« **Reply #4 on:** May 25, 2015, 10:45:00 PM »

Just heard from my buddy that the flywheel was indeed sent with the entire rotating assembly to be balanced.

« **Reply #5 on:** May 25, 2015, 11:08:57 PM »

Make sure the flywheel is on the right way as well!!!

Sent from McIntyer park

« **Reply #6 on:** May 25, 2015, 11:49:39 PM »

Quote from: crazyjim on May 25, 2015, 10:43:02 PM

However the alignment of the PTO/ujoints may very well be off. Looking at it f from the top is definitely not in line, but I assumed it would probably be fine since it's a double cardan joint. I haven't measured though to see if they're on the same plane.

Would be a bearing cap is pushing out, allowing the shaft to move off center. The alignment looking off could be an illusion, regardless, you don't want it to come apart at speed.

You might also check the condition of the rubber in your damper, if it has allowed the outer ring to slip, that could be the problem.

Otherwise, did the engine have good power? Did it pull strong on the water. Everything seems OK except for the vibration?

If not the flywheel or damper, I would try running it with the drive line removed next (for a very short time). Don't take it to the lake, just long enough to isolate the problem. If you try to drive it that way, it will kill the bearings and could break the crankshaft. Make sure the flywheel is torqued.

« **Reply #7 on:** May 26, 2015, 07:59:53 AM »

Jim, I had the same problem with my Omega. Mine ended up having the incorrect flywheel since it's a 396.

A rock or something lodged in your impeller would cause a vibration but it would also slow the boat wayyyyy down.

Take your PTO off and start the engine and see if the vibration goes away. That will tell you if it's in the engine or pump.

« **Reply #8 on:** May 26, 2015, 11:28:25 AM »

Ok so it looks like I'm really going to focus my attention on the driveline. I don't believe it's the balancer or the flywheel, since it was all balanced together right before last summer, and the motor has MAYBE 10-15 hours on it since it was built. This is of course assuming the motor was balanced correctly, but I've heard good things about this machine shop.

The boat pulled strong, took the spectra up to 58 without really stretching it out too much since it was the first weekend after getting it back together. I couldn't imagine anything being in the pump and running this heavy pig at almost 60.

I'll try to get some pictures of the driveline angle and see if it looks correct to anybody.

« **Reply #9 on:** May 26, 2015, 12:14:58 PM »

It don't take much at all stuck in that pump to make it do some weird chit?? But pull the drive shaft and you will no for sure in about 10 minutes! If you have already had 10 or 15 hours on the motor with no vibration? Unless you slung the weight off the back of the flywheel they just don't mysteriously all off a sudden unbalance and still run good? Check the counter weight on the flywheel... And like someone mentioned the outer hub on the balancer and make sure it's not getting ready to come say hi? But pulling the drive shaft will tell you motor or pump...

Sent from my iPhone using SoCal Jet Boats

« **Reply #10 on:** May 27, 2015, 12:12:24 AM »

So I just bought the boat from my buddy's brother. He's the one with time on the boat/motor. I've done about 2 laps total in the boat because I was chasing a fuel issue which turns out to just be dirty tanks. According to my buddy, the boat has always had a nasty vibration since his brother installed the motor. I'm assuming he just didn't know what he was doing, you can see that the motor isn't perfectly square, it's kicked off to the side in the front, so sort of diagonal to the pump. Is the fix for this to re-rig the boat? I can't say that I have any clue what I'd be doing either, and would hate to buy a new motor mount kit just to have it end up being wrong again.

Can the current mounts be used and just moved? Do I need to buy an entire new motor mount set? Anybody you guys can recommend or anybody here feel like helping tackle this in the future? Thanks for the help guys, gonna try to run the motor without the driveline connected this week, but I can't for the life of me figure out a good way to disconnect the driveline. The front flange that's hooked to the PTO is inside the bellhousing quite a ways, and the slip yoke on the drive has maybe 1/4" that it can slide in...

« **Reply #11 on:** May 27, 2015, 01:02:15 AM »

You probably got a 3-point mount.

Do something first. Pull the plugs and turn the engine over by hand. Got a bad feeling all of a sudden. As you turn the engine, feel for binding of the drive line. If you do feel binding, cut apart your oil filter, looking for traces of destroyed thrust bearing.

Do that before you start it again!

« **Reply #12 on:** May 27, 2015, 02:00:14 AM »

Quote from: Flusher on May 27, 2015, 01:02:15 AM

You probably got a 3-point mount.

Do something first. Pull the plugs and turn the engine over by hand. Got a bad feeling all of a sudden. As you turn the engine, feel for binding of the drive line. If you do feel binding, cut apart your oil filter, looking for traces of destroyed thrust bearing.

Do that before you start it again!

You sir... I don't like the things you're saying to me...

I'm just going to pray to God that's not my issue. But I'll try that first before I pull the driveline.

It's a 4 point mount (I believe). Here's a shot of one of the front mounts:

And the rear bellhousing/mount:

While I was out there, I snapped a picture of the driveline angle, it looks WAY more than a degree or two off, which is what's leading me to believe this is the culprit. The more I read about driveline angles on the forum, the more it looks off...

TOP:

SIDE:

« **Reply #13 on:** May 27, 2015, 02:12:02 AM »

Yes, 4-point.

From the pictures, there is no sign of impact on the drive line. Also, please check that you have a minimum of 3/16" clearance between where the yoke bottoms out on the snap ring on the shaft, just in front of the thrust bearing.

Yes, you can make all the mounts work again.

« **Reply #14 on:** May 27, 2015, 02:25:57 AM »

Quote from: Flusher on May 27, 2015, 02:12:02 AM

Yes, 4-point.

From the pictures, there is no sign of impact on the drive line. Also, please check that you have a minimum of 3/16" clearance between where the yoke bottoms out on the snap ring on the shaft, just in front of the thrust bearing.

Yes, you can make all the mounts work again.

Ok, so we're in agreement that it's more than likely an alignment issue? I was also going to ask about the grease being flung everywhere, which is what I'm assuming led you to ask about the yoke? Is that a bearing cap seal that needs to be replaced? I know the yoke doesn't have much travel in it, but I'm almost certain it's at least 3/16", I'll check that tomorrow when I'm in there, am I basically checking from the back of the yoke to the snapring on the shaft? Thanks a bunch for all the help, I'm trying to stay positive here but it's becoming a nightmare relatively quickly.

« **Reply #15 on:** May 27, 2015, 02:31:58 AM »

No worries brotherman, we will get it sorted out.

Check the clearance when you unbolt the drive line. See how far the drive line slides back. If not at all, it is pounding on the crankshaft and the crank thrust bearing (#5 main).

« **Reply #16 on:** May 27, 2015, 02:47:30 AM »

Thanks dude! I'll report back in the morning with what I find.

« **Reply #17 on:** May 27, 2015, 06:50:51 AM »

Disconnect drive an move it around. If its got some binding, replace bearings. unbolt rear feet an pull the pass side off to hollow out the holes just a bit an ad a spacer(1/8" piece of aluminum or what you need) to driver side. That should move the drive over enough without to much labor. Goal is to have angle between .5-3* while keeping the crankshaft an pump shaft parallel. Your pump shaft could be bent but hopefully its just a minor fix.

« **Reply #18 on:** May 28, 2015, 05:43:01 PM »

Disconnect the driveshaft and run the engine, if no vibration fix the mount issue, if its still there the engine balance is wrong. At our shop we etch the balance number on the crank, flywheel and balancer, whether internally or externally balanced. Our balance card also indicates internal or external balance. Any good shop should do this and have the info immediately available by phone. TIMINATOR

« **Reply #19 on:** May 29, 2015, 06:56:13 AM »

Quote from: crazyjim on May 27, 2015, 02:25:57 AM

Ok, so we're in agreement that it's more than likely an alignment issue? I was also going to ask about the grease being flung everywhere, which is what I'm assuming led you to ask about the yoke? Is that a bearing cap seal that needs to be replaced? I know the yoke doesn't have much travel in it, but I'm almost certain it's at least 3/16", I'll check that tomorrow when I'm in there, am I basically checking from the back of the yoke to the snapring on the shaft? Thanks a bunch for all the help, I'm trying to stay positive here but it's becoming a nightmare relatively quickly.

I am not sure what the easiest way to prove this without some proper tools, but. ...

A driveline alignment issue will shake things in an axial direction (front to back). Or simply cannot generate more vibration radially (up down, side to side).

A balance issue will shake things radially, mostly vertically.

Start the engine and use your fingers to see if you can trek if it is shaking harder front to back or more vertically.

This will answer the question immediately. The engine still needs to come out, but at least you would know what your chasing.

X2 on pulling the drive shaft and hitting the key.

GT

« **Reply #20 on:** May 29, 2015, 07:16:30 AM »

Hey Jim, it's odd that the motor is not in there straight. I'd think whoever originally rigged the boat did it right, and then something got changed when the motor was pulled.

Maybe the bellhousing feet got swapped from side to side?
Maybe someone used wrong holes in stringers?
Maybe you have those weird rubber mounts on the side of the engine and the rubber is deteriorated?
Maybe Vicky cursed you?

« **Reply #21 on:** May 15, 2016, 09:48:00 PM »

Quote from: Your Mom on May 27, 2015, 06:50:51 AM

Disconnect drive an move it around. If its got some binding, replace bearings. unbolt rear feet an pull the pass side off to hollow out the holes just a bit an ad a spacer(1/8" piece of aluminum or what you need) to driver side. That should move the drive over enough without to much labor. Goal is to have angle between .5-3* while keeping the crankshaft an pump shaft parallel. Your pump shaft could be bent but hopefully its just a minor fix.

What is the best way to get this angle of .5-3° while keeping everything straight??
Having a problem after pulling my motor and installing a new/used housing with shaft and putting my motor back in after a rebuild. Started the motor and it has crazy vibration through the boat.
Any help would be appreciated.

Sent from my iPhone using SoCal Jet Boats

« **Reply #22 on:** May 15, 2016, 09:54:37 PM »

Quote from: 77Galaxie on May 15, 2016, 09:48:00 PM

What is the best way to get this angle of .5-3° while keeping everything straight??
Having a problem after pulling my motor and installing a new/used housing with shaft and putting my motor back in after a rebuild. Started the motor and it has crazy vibration through the boat.
Any help would be appreciated.

Sent from my iPhone using SoCal Jet Boats

I would recommend starting your own thread.

Show what you have going on.

GT

crazyjim

Flusher

Flusher

crazyjim

crazyjim

jyeager

Flusher

philofab

crazyjim

Blue2184

crazyjim

Flusher

crazyjim

Flusher

crazyjim

Flusher

crazyjim

Your Mom

TIMINATOR

GT Jets

philofab

77Galaxie

GT Jets