Mercruiser rattle noise at high RPM

[Jiminthekeys]

I've been trying to narrow this problem down and there was a previous post. Old now and not getting any more replies. What I have done so far is new ujoints, gimbal bearing, plugs, full tune up, set timing to *2ATDC new fuel filters all the way around, new 90Octane marine fuel, checked everything I could really think of and the problem although less apparent then before readjusting timing is still there.

Here is a better video of my problem.

 

[thumpar]

No video. What motor/drive are you working with. 2ATDC doesn't sound right for any engine. Most mercs are 6-8 BTDC at idle.

 

[Jiminthekeys]

It's a 2007 Mercruiser 3.0 with the TKS carb and alpha 1 gen2 drive. 2*ATDC is what the manual states as well as my flame arrestor sticker.

 

[Jiminthekeys]

https://www.youtube.com/watch?v=ynQu4lZr1PA&list=UUI-SdFRliVkw8VxchzHdPUg

 

[tinkerguy70]

I do all of my own work (thanks to the wonderful folks here at iboats forum!), but I'm no boat mechanic, it sure sounds to me like something loose making that rattling noise. I don't think it's anything mechanical, but perhaps a loose fitting spark arrestor, heat shield, belt driven accessory, or something like that.
It could even be something as simple as a slightly loose bolt with a rattling washer under it somewhere on the engine. Even the smallest things can sometimes make a lot of noise when vibrated in the right way.
I know this has been bothering you for a while, but I think if you keep looking around back there, you're going to eventually find something loose that's making that noise.

 

[Jiminthekeys]

No Title

A Mercruiser tech from just answer web site suggested I may have a blown head gasket or a city carb after he told me to do a compression test. What do you guys think? Below are my numbers and a picture of my plugs (fairly new with only a few trips on them) below. Plugs are 4,3,2,1 from left to right.

#1 180psi
#2 162 psi
#3 160 psi
#4 170psi

 

[tinkerguy70]

With those numbers, I don't think so. Leaky valves maybe, but not a head gasket.
I don't see any pics of plugs so it's hard to tell about that.

From what I can tell of the videos, your engine is running well aside from the noise. To me, it doesn't sound like anything seriously wrong other than something rattling.
I'm going to watch your video again, but I think you're looking in the wrong place for that noise.

 

[Jiminthekeys]

No Title

Sorry. Not sure why the photo didn't post. I'll try again here. The tech said the plugs look steam cleaned and the center cylinders where lower which is why he suspected a blown head gasket. He did recommend a carb rebuild first then head gasket if the plugs are still white and clean and sound is still there.

 

[Jiminthekeys]

https://www.flickr.com/photos/126361946@N06/

 

[Jiminthekeys]

Any thoughts? I talked to a merc tech at a local service center today when I was looking for carb rebuild parts and showed him the pick and told him about the pressure numbers. He didm 't seem to see an issue with either but suggested to retard timing a degree at a time and see if the issue goes away it could be that or just a dirty carb. Any thoughts here??

 

[tinkerguy70]

Any thoughts? I talked to a merc tech at a local service center today when I was looking for carb rebuild parts and showed him the pick and told him about the pressure numbers. He didm 't seem to see an issue with either but suggested to retard timing a degree at a time and see if the issue goes away it could be that or just a dirty carb. Any thoughts here??

I think that would be a very good idea!
Your compression test is OK, a general rule is no more than 10% between lowest and highest p.s.i. readings. I think you're OK on the head gasket too. In my experience, when you have a blown head gasket, there is usually little to no compression on one or more cylinders,

 

[Jiminthekeys]

Took the boat out and had a friend drive to produce the noise. To me with my head down in the engine compartment it definitely seems to be coming from somewhere near the bottom of the engine (maybe flywheel area). My friend seems to think the same as well. argh... I just keep spinning in circles over this issue. I've put my hand on everything on the motor or attached to the motor and nothing is lose or seems out of the norm. Maybe the coupler has a lose bold or something? I don't know.... I guess only one way to find that out...

 

[UNSUREBOATGUY]

Maybe remove the flywheel dust cover and give it a run with that removed to see if it might be the cause of the noise?

 

[Jiminthekeys]

I'll try that

 

[Jiminthekeys]

Problem turned out to be a bad power steering pump. I replaced the pump with a remaned gm pump from auto zone and problem solved.