5.7(350) BAD Vibration under 1000rpm

[Franzel311]

Hello everyone from Iboats! Winter has Finally come to an end it seems in the Northeast and It's time to start thinking about boating.
I need some advise! I put a early modle 5.7 350 two piece rear main seal engine in my 1990 201 Liberator last season the engine runs great but it shakes bad!...at idle it is fine,then as you raise the rpm'a it starts to shake around 700/750 rpm then gets a lot worse as it comes to the 800's then starts to settle as you get to 1,000 rpm's and after that it's smooth as silk any ideas on what it could be? I got the timing right on the money I pulled the drive back off and rechecked the alignment of the drive to coupler and that's good the motor mounts seem good I played with the carburetor settings then took it off and had it rebuilt put it back on and to no avail still shaking i can make it worse as I play with the carb. settings but it only gets so good and then stops getting better I'm at a total lose I think I'm going to have to bring the boat into my shop over the weekend and start yanking the motor out again and start all over...I want to b able to be in the water by mid April so theirs no time to waist...if any one has any ideas on what it could be I would really appreciate it...thanks iboat world!!!!!

 

[Bondo]

Hello everyone from Iboats! Winter has Finally come to an end it seems in the Northeast and It's time to start thinking about boating.
I need some advise! I put a early modle 5.7 350 two piece rear main seal engine in my 1990 201 Liberator last season the engine runs great but it shakes bad!...at idle it is fine,then as you raise the rpm'a it starts to shake around 700/750 rpm then gets a lot worse as it comes to the 800's then starts to settle as you get to 1,000 rpm's and after that it's smooth as silk any ideas on what it could be? I got the timing right on the money I pulled the drive back off and rechecked the alignment of the drive to coupler and that's good the motor mounts seem good I played with the carburetor settings then took it off and had it rebuilt put it back on and to no avail still shaking i can make it worse as I play with the carb. settings but it only gets so good and then stops getting better I'm at a total lose I think I'm going to have to bring the boat into my shop over the weekend and start yanking the motor out again and start all over...I want to b able to be in the water by mid April so theirs no time to waist...if any one has any ideas on what it could be I would really appreciate it...thanks iboat world!!!!!

Ayuh,.... Is the firin' order Correct,..??

Are All the cylinders Firin',..??

 

[Franzel311]

Ahoy Mr. Bondo I was hoping you were going to jump In to this thread you gave me a lot of good advise a couple months back about a 383 stroker swap into this boat but I wasn't able to do the project over the winter so I'm going to run the same motor this season again....so hear is the deal with this engine it's a long story but I'll try to keep it as short as I can...it is a mid 70's(I believe) chevy block 2 piece rear main seal, the marine mechanic I worked for when I was younger built this motor acouple years back for his boat, no major mods just a little matching in parts and some head work just enouf to give a little pep and reliability...but when he went out on his own and opened up his own small marina his work truck engine wasn't up to the task of towing all the time so the engine he built for the boat ended up in his work truck and after his business was doing well enouf he bought a new truck and I bought the old one just for the engine to put in my Libby so it has all marine parts in it stainless steal head gasket's, brass freeze out plugs marine cam, pistons and heads set up for quench/squist-but don't know the numbers, 4 bolt main crank Ect...it was built for his 20ft Mariah) I ran the truck b4 I did the swap and the motor ran great, it was smooth and powerfull...he had all the mercruiser parts to make the engine a complete marine motor but my Libby is set up OMC. so that didn't do me any good and my parts were good I just needed the block so I stripped down the new engine to a long block double checked that all other parts were realy marine parts, they were so I cleaned, checked each OMC part and installed, some stuff had to be modified others didn't fit at all the flywheel and coupler was off a newer 5.7 one piece rear main seal engine and I'm useing an older block with a two piece rear main seal so the wheel n coupler was totally different, I found a mercruiser flywheel and coupler in the marinas spare parts closet that bolt patterns lined up to the 2 piece crank so I installed them had to modify the the bell housing some because of the split fire ignition system (after reading up on that ignition system I opted to get rid of it all togeather and go with the Mallory system that's more like the merc system) so then I was able to grind all the spit fire ignition system mounting points off the bell housing and then the bigger flywheel and coupler was able to fit under the OMC bell.. and it all lined up well I checked the measurement from the end of the splines on the shaft of the drive to the end of the inside splines of the coupler once mounted to the motor and even tho the flywheel and coupler were different styles and makes OMC vs. Mercruiser the measurements were excatly the same from drive to motor...so after all that and then the wiring mess of changing the split fire ing to the Mallory ing it was smooth sailing I got the engine mounted lined up to the drive witch I quadrupl check ran all new fuel lines, wires, and switches double checked EVERYTHING again Ran water to her and VERRRUUUM she fired right up!....but had an extremely violent vibration from 600 rpm to about 1,100 rpm then went away and ran great from there up so I took the drive off again checked the alignment, it was good checked the U joints there good reinstalled the drive n then played with timing I spent hours on the phone with Mallory (boy let me tell ya there customer service is impressive!!!they realy went above and beyond trying to help me out) so we got the timing right on firing order is correct it did clean up a little bit with the shaking but not totally gone(I don't remember at what it's set at but the marine machanic checked it with his timing light n said it was good to) so then I started playing with the carberator and it was pretty bad so I had it rebuilt, installed and that helped some but it's still there, from the 7's to the 900'srpm range after 1,000rpms it's smooth as silk but it's not terrible nothing like it was but it's not right and it makes me nutz...I would say in comparison it would be like one blade on a stainless prob being bent how you get that shutter vibration around 15 mph as you plane off it comes on then fades away but it's at just over idle and goes away just after u bump the throttle and stays smooth all the way to WOT

 

[Franzel311]

And I did a running drop test had the engine runing at 600rpm and pulled each plug wire and the motor kicked out on each wire pulled...pulled plugs and all r nice n brown/black

 

[NHGuy]

Pull off the drive, run water straight to the engine and start it. If it still shakes you could have the wrong flywheel for your rotating assembly. If that's the case get the flywheel from the truck setup and figure it out for your drive.

 

[Dogdave]

Just a thought, how are the bushings in the distributor? Mine had a shake at idle and my lower bushing was shot in the dist. Cam lobe going flat?

 

[Fun Times]

Does it vibrate on land or water or both? If on land, try pulling the drive and see if you still have the vibration.

I'm thinking "maybe" with all the possible mismatched parts of the flywheel, coupler, stern drive input shafts between years and models that they may not be matching up correctly causing unseen visual/measuring problems. Edit: I just saw NHGuy post above, I didn't mean to copy his advice.:redface:

Below is some info to consider looking into should you start to find the drive/coupler items to be the/a problem.
http://bluewatermarinesvc.com/html/mercruiser_fyi.html
https://www.perfprotech.com/blog/articles/alpha1-alpha2-sterndrives
http://forums.iboats.com/forum/boat...l-pressure-and-temperature-alarms#post9256087

Also just to be sure, be sure there is no forward and reverse crankshaft end play by hand.

Hope you find it, good luck.

 

[Bondo]

Pull off the drive, run water straight to the engine and start it. If it still shakes you could have the wrong flywheel for your rotating assembly. If that's the case get the flywheel from the truck setup and figure it out for your drive.

Ayuh,.... I have to Agree,.... It sounds like it went from a 12" flywheel, to a 14" flywheel, which shouldn't be a problem, but most certainly could be the issue,...

 

[Franzel311]

Hi guys sorry it took so long to get back to this I have been insainly busy at work...
So yes it does shake on land to...I like that flywheel idea it was the same size flywheel that I put on just the bolt pattern was diff going from the one piece rear main seal to the two piece seal I just grabed what ever fit I figured they would b the same but after reading your posts I did alittle research into it and the older two piece rear main seal engines require a balanced fly wheel and I have no idea what I put on it so either this weekend or next I'll get it in the shop pull the drive start it c what happnes and if still shaking then it pull the engine n c what flywheel iv got on there n go from there
THANKS ALOT TO ALL OF YOU It would have been a lot of head banging against the wall trying to figure this outi never would have thought it would have been the wheel... I get back n let you know how it turned out