1992 alpha one gen II & 4.3L vibration at mid-RPMs

[Falcon-]

I finally got my new (to me) boat in the ocean and have been figuring out how she handles. My one concern is that there is an obvious vibration when in gear between 1500 and 2200 RPM. I also get vibration to a lesser extent in neutral at from 1400rpm to 1700rpm - I am assuming this is the same thing just showing itself differently when not under load. The vibration is not evident at higher RPM operation, nor at lower RPMs (though perhaps the idle or near-idle roughness simply hides it).

The prop is a 3-blade stainless and has no nicks or other visible damage.

My first guess was an alignment issues between sterndrive and motor, but I was doing a search here and saw a post that referred to a lack of a "balance shaft" on these engines (http://forums.iboats.com/showthread.php?t=326667). I do not know enough to tell if this could be related to my vibration issue.

Before I pull the boat out of the water is there something I can do now to narrow the cause down? Are there other possibilities I should be looking for as the cause?

Thanks

- Sean

 

[swordfish25]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

Possiably you have a bad U joint. You can pull the drive off and check. Make sure you grease it and put spline grease on the splines when you put it back on. The water pump is in the lower unit, so you can start it and check for vibration while it is off. Do not run it too long as it will get hot. Good luck

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

swordfish25

I had the drive off just before I got the boat in the water to replace the bellows, shift cable, water tube, impeller, and oil seal below the water pump. At that time I re-greased and looked at the ujoints - they looked good to my untrained eyes (no rust, moved well in the hand). I pump'ed em full of grease till the old grease squeezed out, and greased up the splines as well before re-inserting. It was relatively easy to get the sterndrive on/off so at the time, given I did not have an alignment bar, I assumed I had good alignment.... (I have since acquired an alignment bar from ebay but have not had the sterndrive off again). I also found the bearing seemed to turn fine when I reached in and turned it by hand, and saw no rust or other obvious damage on that either.

All that being said it appears to me that the sterndrive had not been taken apart like this for a long time - perhaps since new.... 17 years is a long time, even at low usage hours, so who knows!

If the ujoint was bad, what would would I look for to tell?

 

[dubs283]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

I assumed I had good alignment...

thats a problem

start with pulling the drive and checking the alignment

then with the drive still off you can check if the neutral vibration has any changes. okay to run the motor for up to a minute without water supply, not gonna hurt anything

if the vibration is still there, you can bet its a motor issue and need to troubleshoot there

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

Ok, I will haul the boat out as soon as I can and pull the drive - while I have it off can I get some recommendations on checking the ujoints? They visually looked fine when I had the drive off a couple weeks ago (no rust, etc), but I am very much not an expert.

 

[dubs283]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

if the u-joints are not rusty and have good movement in all directions (no stiffness) and are not sloppy (ends loose or wobbly), they are probably okay

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

dubs - thanks, from that description it sounds like mine are doing fine, or they where 4.1 engine hours ago (that being the total time since I put it in the water).

How about the Balance Shaft mentioned in that other thread - how much vibration does that cause? This vibration is not of the subtle "is that really there?" type....

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

Update: I got the boat out of the water today, ran with the prop off to see if I could visually see any wobble - none visible, and pulled the sterndrive and checked alignment with the alignment tool. Alignment was perfect with no adjustments needed. (I also drained some oil - looked clear, not milky)

Should I be concluding that my vibration issue is due to a lack of balance shaft on my model/year? If that is the case, I am guessing I want to avoid running at those mid-RPM speeds when possible, right?

 

[quattro II]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

Hey Falcon, searched you thread because I have the same motor and issue in my 93 baja. feel its worse in neutral, around 1700 rpm. wondering if you have any conclusions. John, first boat, pretty stoked

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

alas no one gave me an answer, however from my reading of another thread the lack of balance shaft *should* cause vibration centered at 1700rpm, so that SOUNDS correct anyway, and the fact that both of our engines do the same compounds that.

I have made it a habit to run at above or below the vibration-inducing speeds and things seem fine. For *my* boat/prop setup I find running at or just below 3000 rpm is smooth and a good cruising speed (22knots).

Enjoy your new boat!!

 

[quattro II]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

Hey Falcon, found some more info on our issue, pretty sure you have a balance shaft engine, to find out compare your engine ser# against the Merc manuals in the adults only forum to find out. Bal engines started in 92. Do you have a 2 or 4brl carb? Even if you have a 2brl this issue could still be the culprit. Check out my post on the following thread and see if it could also be affecting your ride. If you need send me you ser# and I can let you know. John
http://forums.iboats.com/showthread.php?t=314464

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

quattro II: Thanks for the info! I will dig up the serial number and see if we can confirm balance shaft or not. I had not considered a carb issues as a possible culprit. Mine is I believe the two-barral carb version.

 

[Bronc Rider]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

I have no idea if you have a balance shaft in your engine. I have had two non-balance shaft 4.3's and I want to say the vibrations would go away above 1100 rpm. I know for sure there was no vibration at mid or high rpm's. Do you have a way of posting a video? Have you checked the engine mounts/lag bolts?

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

The engine mounts seem nice and solid to me. Yes I can post a video, but given as it is blowing 25knots and pouring rain right now it may be a bit before I get out there and actually *record* one!

That is very interesting that your pre-balance shaft engines reduce their vibrations after 1100rpm - that is certainly a different RPM range then I am seeing.

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

quattro II - I was finally able to get at the engine and check the SN, but I am really not sure what I am looking for in the manual to determine if I do or do not have a balance-shaft version. The engine serial number is 0D835726.

 

[180shabah]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

Based on your S/N, looks like you are pre-balance shaft. 16-1800RPM is right where these engine realy "shake". Doesn't sound like anything out of the ordinary.

 

[Falcon-]

Re: 1992 alpha one gen II & 4.3L vibration at mid-RPMs

180shabah

Thanks! Good to get a solid answer on the existence of the balance shaft.