motor vibration through the hull-real tough question

[f_inscreenname]

I have a 19'boat with a chrysler 360 with a volvo 270 outdrive.At diffrent RPM levels (1200 to 1400 and 3200 to 3800) I get a vibration thru the hull. More herd not realy felt but humm....humm....humm...humm... I have had many boats and they didnt do that (I must admit they were outboards or mercruisers). Everything is new. The motor complete rebuild and balanced. Had a problem with the pilot bearing,the crank was never drilled for one so I ground a bearing down to fit the hole that was there (dont ask how I did it but I think it came out right. The bell housing shaft sliped right in. No resistance at all).Motor was just installed.A couple of people said to line up the motor you must line up the tabs on the bell housing and on the transom shield but there isnt any on mine I have 2 bell housings and the second one dosent have tabs eather. So I measured from the stringer to the top of the exhust mani. Is there a better way? The bell housing on the boat was completly rebuilt. New U-joints in the outdrive. New bushings in the pins that hold the outdrive to the shield. I dont know what else to do. Is this normal? Like I said I had a few boats and they have never did this. noticable

 

[MGuckin]

Re: motor vibration through the hull-real tough question

I remembered reading about your project and I did a search for it. http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=009979 <br />Might help with determining solution if it is known what you have and have not done.<br />Just my thoughts.<br />I would imagine that some vibration would be considered normal, especially with a homemade pilot bearing. <br />If the hole in the crank was never bored on center, how did you determine that it would not be off-balance and that it was actually cast on center? <br />If bearing is not in the center, it would cause a misalignment (out of balance) from the pilot to the motor, which could cause a telegraphed vibration thru everything and pre-mature wear.

 

[DJ]

Re: motor vibration through the hull-real tough question

Screenname,<br /><br />You have a harmonic imbalance going on. Evidenced by the vibration repeating itself at decreasing spread between rpm's.<br /><br />I am not familiar with you set up, here is what I would try/look for.<br /><br />1. Does your engine have a harmonic balancer?<br />2. Unhook the accessory drive belts one at a time and run the engine BREIFLY to see if the vibration is there at 1200. An alternator or water pump can set up vibrations like this.<br />3. Are your exhaust manifolds grounded (touching) anything on the hull that is not insulated by rubber?<br />4. Loosen the engine from the bell housing-completely. Retighten, does the vibration change or move in rpm's? If so, I believe you have an alignment problem.

 

[MGuckin]

Re: motor vibration through the hull-real tough question

djohns19,<br />I thought of the harmonic balancer also, but I figured, in as much as this is a new rebuilt high performance motor, that it was a balanced assembly.

 

[DJ]

Re: motor vibration through the hull-real tough question

Mike,<br /><br />As I mentioned, I'm not familiar with this set up. But, in light of that, if the engine had a balancer on it before the rebuild, it needs one after. Almost every engine needs a balancer to dampen combustion spikes. Even a balanced one. All the balancing does is removes most of the rotational imbalance and balances the piston and rod weight.<br /><br />The more I think about this, I believe he has an alignment problem. Loosening up the engine and retightening may tell him something.

 

[MGuckin]

Re: motor vibration through the hull-real tough question

Agreed. Especially with the homemade pilot bearing. Isolating the motor from the drive and trying it sounds like a good idea. Thought of mounts too.<br />Hopefully it is a minor problem.<br />I am curious and gonna check back for comments but for now, it is time to go fishin.

 

[f_inscreenname]

Re: motor vibration through the hull-real tough question

Mopar 360s are externaly balanced motor. Everything was balanced befor the motor was put together.Hum balancer and flywheel. Like I said the bell housing shaft sliped right in (it has to go through a vibration and into the pilot bearing the drive shaft goes through a fixed bearing in the outdrive side) it would have to be stright or it would not go in. The shaft dose not move inside the the pilot bearing at any time so wouldnt the vibration be there all the time if it was not right? If the hole in the crank was never bored on center it should vibrate all the time??? A update; Took it out today.Ran great,vibration sound less. I guess I will run it till I brake something.