Bad vibration/knock underway

Hey guys, haven't been in here in a while, back with problems unfortunately.

Boat: 1989 Ski Nautique, PCM LH 351, 1.23:1 trans, acme 470 prop. Owned since 2010, and has been a great running boat for years.

Last year this engine developed a bad oil leak from the rear intake China wall seal, so naturally I decided to replace that. Other than oil leak, boat was running fine in October when it came out of the water. Manifold was replaced with new gaskets, and I added a DUI distributor as well to replace my worn out stock unit. Anyway, it seems to run great on the trailer, idle is good, throttle response is snappy, so I thought all was well. On the water yesterday there is a horrible vibration starting just off idle and getting worse as rpms come up, eventually sounding like a full on knock, almost sounds like something is smacking the hull. The engine pitches fore and aft up til around 1500 rpm and then settles down, but the vibration just gets worse and louder. It is not subtle.

Things that have been checked this far:

Firing order: ohmed out plug wires and verified everything is correct. Firing order on tag is 13726548, CCW around the distributor, cylinder 1 is left bank closest to the front, cylinder 5 is right bank front. I actually even tried the other 302 firing order as a troubleshooting step just in case someone put a 302 cam in it before I bought it.

Distributor clocking: rotor points at #1 plug wire at TDC on compression stroke of #1. Compression stroke verified by finger in the plug hole and turning over with a wrench on the crank pulley. Timing set with a light at idle at 10deg btdc and advances smoothly as revs come up.

Compression test: solid readings of 150-170 on all cylinders. More variation than spec, but not bad enough to cause alarm.

Prop appears to be just as clean and nice as when I installed it years ago, lapped to shaft, still tight on the taper. It was smooth in October on the last run of the year and has been on the trailer in a heated garage since, so I don't think anything happened to it or the propshaft. Shaft is a 5 year old ARE double taper.

Plugs: Autolite 24 platniums gapped at .050, brand new with distributor install. Wires are new Taylor spiral pros. Plugs are dark black with sooty residue, not sure if running excessively rich, or a sign of too much idleing on the trailer. Plugs have about 1hr of trailer run time and 15min on water time.

Oil: hasn't been changed yet since manifold install, but is clean with no signs of water in oil. 20w50 VR1.

Oil pressure on the gauge is 50-60psi, same place it has been for as long as I've owned the boat. Temp runs about 160, no signs of overheating.

The vibration is excessive, and the knocking sound is loud, but does not appear to be coming from the motor. My first thought was we had picked up something on the prop that was hitting the hull at speed. No signs on the hull of any contact, and it would be obvious, cause the bottom of the hull is embarrassingly filthy.

Anyway, thoughts on something new to check? I'm stumped. Boat seems to run excellent on the trailer with no load. Thanks!

You’re saying all the right things but I would look at the firing order again.

Damper plate is likely original. Will they make the whole boat shake and knock like this? It is very violent.

I'll put a set of fresh eyes on the plug wires again today and verify the order again. Yes, cylinder one is towards the driver side on the front.

Yes, ballast resistor is gone, I put a relay on a 10ga wire to the dissy, straight from the main engine breaker, good full voltage to the dissy.

Now that I'm thinking about the DUI power wire, is it possible that the relay is clicking on and off causing it to miss and run like crap? Maybe I should jumper the relay out of the equation for a brief run, just to rule it out. And yes, cyl 1 is closest to the driver, also stamped 1 on the intake manifold casting.

Usually when your damper goes, it gets really noisy (metallic grating noises) and the boat quits moving as the springs come apart.

Key words would be "metallic grating noises"

It can make noises in neutral too since the engine is turning and the damper plate is turning but the female splines on the damper(which are engaged with the male splines on the transmission) aren't turning or are slipping due to the broken springs.

Yes, when not in gear, it runs fine. Idles great, revs to 3500 no problems, haven't pushed it faster than that in neutral. Timing advances normally up to 30-35ish degrees total at 3000.

Just to make sure everyone is on the same page, cylinder 1 is front of motor, by driver's seat. Opposite side of fuel pump. Number 5 is on front on fuel pump side.

This really feels like an ignition issue, but it doesn't make complete sense. Firing order is 100% right. I even swapped 3 and 5, 4 and 7, to try to early 302 firing order, and that resulted in lots of backfiring and wouldn't idle, so I am confident that I have the correct 351w order.   I even traced the old wires back to verify firing order on the old dissy before I pulled it out. Wires are brand new Taylor, don't hear any arcing around them. Cap and rotor seem ok. I think I will pull all my plugs and check spark at the gap next, just to rule out bad plugs.

Plugs are very black and sooty, could a stuck choke, blown powervalve, or something else in the carb cause it to run rich enough to miss this badly?

All parts and repairs were made this past couple of weeks. It ran great but was leaking oil badly in October.

It seems to be starting to run worse on the trailer now, and the exhaust smells really strongly of fuel. How rich would something have to be to stop firing on multiple cylinders under load?

1989SN2001 wrote: Plugs are very black and sooty, could a stuck choke, blown powervalve, or something else in the carb cause it to run rich enough to miss this badly?

It seems like you did your homework before the install

Most likely with any of these things you listed (stuck choke, blown power valve), it'll idle like crap.

Have you looked down the throats on the carburetor while it's running?

A new set of plugs would be helpful about now since they're not gonna get any better and will probably get worse unless you get the problem figured out.

A simple thing would be to disconnect the tach wire and see if there's any change.

And bypass your relay like you mentioned.

It's a new distributor, and the problem came about after the manifold and distributor install You wouldn't be the first guy to get a bad one.

If you're baffled, undo what you did and put the old distributor back in and see how it runs to eliminate that variable.or go to your favorite parts store and get a GM 4 pin HEI module and replace the one in the new distributor with that. They're pretty cheap and easy to swap Or a coil too for a GM HEI distributor. They'll be good spares if they're not the problem.

And don't worry about the rotor rotation Mr McD mentioned, if it was wrong the thing wouldn't run at all and that would be a good thing because the oil pump would be turning the wrong way and you'd have no flow or pressure   

Agree with Ken, didn't catch that all the repairs & new distributor had been installed very recently. That would be my first step at this stage - reinstall the old one, complete with the old cap & rotor to see if this problem still exists. I have bought more than a couple parts for various cars, boats, etc. and had them come out of the box defective. Seems like I remember a thread several months ago (or so) where a guy did get a bad distributor and went through heck trying to figure it out. Eliminating the cap & rotor one at a time is a good idea as well, new or not.

You might want to refresh the carb while you have it off. Could be dirt in the needle valve too.

Wow, yes that is BADLY out of alignment. I'd advise not running the boat till you get it aligned - I've read on the forum that this much of a misalignment can actually damage the shaft and/ or transmission. as far as how it got that way in the last 4 years there may be a few possibilities.   I find it difficult to believe that the isolators would cause such a drastic difference, but I suppose it's possible - Pete knows, I'm sure.   So my first question is how are your stringers?   I don't know much about your era of boat but I thought I noticed somewhere that the mounts were bolted directly to the stringers. And with the well documented stringer issues of the 70's and 70's boats..... Hopefully not, but I thought I'd throw it out there as something to check since it should be an easy visual confirmation.
I haven't replaced just the mounts, but was in fact going to do this before I ended up pulling the entire thing for a new long block. It shouldn't be too difficult, if necessary. Seems like there's a reasonable amount of room to get around in your era of boat.

As I recall, 89 would have an aluminium engine cradle, so you might want to check that for cracks & such.

Today I got the alignment a lot closer, but didn't have time to really dial it in. Using feelers, I'm within .007 or so, a lot better than where it was before. There is a slight run-out in the face of the coupling on the shaft, .003-.004, so it's hard to gauge how good the alignment is and how much is shaft runout. It is a newer ARE double taper shaft, so I will pop it loose from the taper and reinstall it to see if it maybe finds a better home. If not, I will pull the shaft and have it trued up at a machine shop. Either way it is world's better than it was before. I can spin the prop with one finger again and it will continue to turn another 1/4 turn from momentum when I spin it fast.

The motor mounts straighted back up when I released the pinch bolts and started turning the jack nuts.   The rubber seems pretty solid, so I think I may put off changing the bushings for another time. After it goes in the water for the season, I will spend a day getting the alignment spot on again.

Anyway, now that I'm so much closer on the alignment, the vibration is completely gone. The boat pulls harder than it ever has, not sure if it's because of the carb finally being set up right or the ignition upgrade. With the acme 470 prop the boat would usually do about 4500-4600 RPM and about 43mph on the GPS. Didn't clock it with GPS tonight, but it was turning about 4800, so I expect that it picked up one or two mph on the top end. Mid range throttle response is much improved to. It's finally running like it should and I'm thrilled.

Is 4800 a little fast for this motor? We primarily wakeboard with this boat and run 750-900lbs of ballast, so I love the low end grunt with the 470, but maybe now with the engine running right I can step to a slightly less aggressive prop and still get the stump pulling low end that we like. We do occasionally put the boom on and do some short line footing, but not usually for more than a few 3-4 minute bursts. It doesn't see much slalom action anymore either. Thoughts?

Thanks again for all of the assistance!

Congratulations, glad you are getting it ironed out.
4,800 RPM is not too fast. My GT40 would run up to 5,200 RPM when I had the 224 prop on it. I would not be concerned and just enjoy how well it is running.
When you are moving the engine around trying to find the sweet spot for alignment first look at the prop shaft and feel where it wants to locate, there is a sweet spot where it will rotate freely and be centered in the strut. It may not be centered in the log but being centered in the strut is most important. You will need to lift it some at the engine side to find where the sweet spot is.
Once you know where it is take a small block of 2x4 maybe 3-4" long, cut a V in the top of it to cradle the shaft. Rest it on the bottom of your boat with the V facing up. Slide it back under the shaft until the weight of the shaft starts to rest in the V. Once the shaft is in the sweet spot and the block is holding the front at that spot adjust the engine to match this point. Now the engine and shaft are both in line with the sweet spot.

Pete, I am sorry, on my ARE install I failed to lap the engine side of the shaft, I only lapped the prop to the shaft. All has been great for 4 seasons now but now you got me thinking.

Pete,

I didn't pull the prop, but I put a dial indicator on the pilot at the very end of the shaft behind the prop after the threads and found a TIR of .004. I know this isn't as good as actually checking the taper portion, but I think this is close enough to within spec that I don't need to dig any further. Pulling the prop off a shaft that has been properly lapped can be a real hassle.

TIR in the middle of the shaft, just aft of the log, while connected to the trans is a little bit worse at .008. Again, this isn't great, but I don't think it warrants taking the shaft out and to a shop. As smoothly as it is running and as easy as the shaft is to turn, I think I'm going to put it in the water and get it aligned as best I can and run this season with it. I'm sure there are plenty of boats out there that are much much worse than this one. I'll also be checking that alignment monthly now that I've seen how much it can change over a couple of seasons.

I don't think I'm in the "going to kill my trans output shaft bearing in a few hours" range anymore. Besides, its likely been running the past 3 or 4 seasons much much worse than this.