Possible unbalanced U Joint assembly -- yoke - input shaft - u joints -

Brought the boat to the marina mechanic, Started it up on the trailer for him. The noise is definately louder. he said sounds like a u-joint rattling and it got louder as i turned the wheel. The input shaft that was replaced was a complete new Sierra assembly. Maybe there is a difference between Sierra and Mercruiser. I decided to replace what was bad on my oem assembly. I just purchased a new oem yoke coupler and 2 new oem merc u-joints. Put it all back together.. One thing i noticed ..On the Sierra assembly before installation it seemed tighter than the merc assembly i just rebuilt. You maybe be right...something wrong with the Sierra unbalance or out of round etc
Next update after i change the input shaft assembly
Thanks

Hopefully I am not jumping the gun here --- but you do not have to say anymore Sierra assembly, It prob is an unbalanced assembly on top of and I am not kidding about that with Sierra. I have seen that before and more than once.. Also will add even seen where people with Volvo Penta SX outdrives change U joints only and the assembly becomes totally unbalanced. Thru OEM Volvo they do not sell the U joints alone you have to buy the the whole assembly even if it is one u joint bad a dealer going thru Volvo still has to buy the complete assembly. Their assemblies are completely balanced. Volvo --- thru them. Just saying

If you said that to begin with -- ( its a Sierra assembly ) I would have said swap that all back out to Merc assembly and see what happens. I would have done the whole assembly with Merc as it comes all together as well. .

It makes sense...The mechanic that was working on this suggested Sierra because it was 1/2 the price of the merc assembly...Live and Learn.. Hopefully this is the problem and hopefully if it is unbalanced it hasn't messed up anything else in the drive. So now i am waiting for my new mechanic to fit me in to change the input shaft. I will keep you updated. Thanks for the explanation

Mechanic installed the Merc. OEM input shaft today..He said everything was squeaky clean inside the drive. Oil was clean (Amsoil Marine gear lube). Nothing unusual found.He put the drive back on the boat and i started it up on the hose....Same noise still there. he did mention that Bravos Rattle.....Ok I Give Up!
Anyone in need for a complete Sierra input shaft for bravo 1 with 10 hours on it......

Thanks for all the help here.

Hope he pressure tested the outdrive after he put it all back together. The upper input shaft seal could have been compromised from an imbalance assembly.

So are you saying it is better but not 100 percent currently ? How much better is it ?

Its the same no change. He did pressure test it. I noticed a few scratches or marks on the center yoke and he also said he noticed that also but there is nothing in the area that can rub on that..The boot...?

How about trying another complete known good drive on the problem side? If noise persists then its from transom forward if noise goes away you know its drive associated.

Great idea, with all the work you have gone through already just swap your drives and see if the noise moves.

You might also want to do a cylinder balance test. Rough idle could cause a gear noise.

I agree with all...The mechanic mentioned that when an engine is running at idle it actually slows down and speeds up based on the compression stroke that can cause a rattling...First for me but at this point I would believe anything.. SO.. I will swap the drives ( what a pain in the _ _ _ _ )
Thanks for every ones input