Mercruiser 5.7L Engine Knock - when accelerating - incident likely caused this

[Searay205]

Back in the good ole days with leaded gas i saw carbon build up on intake valves. You needed a chisel and hammer to bust it off . All this intake cleaner in my opinion does ZERO. Carbon eventually turns into diamonds with enough heat and pressure. If the intake cleaner solved the problem then you didn't have one related to fouling. I do agree with the one post if you don't know the difference between a carburetor and fuel injection abort mission before you really screw it up.

 

[minn_darren]

Searay/Lou/Scott, HA!! Agreed! I know enough about engines (and youtube videos) to make myself dangerous. I am having a guy come out on Thursday to assess. I really just wanted some info and backing so I can direct the tech and not get screwed. I'll let you know what it is/was. The knocking/pinging only happens under heavy load or if I gradually get the RPMs up. Once I back off, it runs perfect. Starts perfect, idles perfect, revs in neutral perfect.

 

[minn_darren]

Just had a guy out to look at the boat. He doesn't think it's engine related at all and thinks it's the gimbel bearing. Stated around 1200-1500.00. Does that sound reasonable?

 

[jaybird7]

odd because part of the noise sounds very similar to a situation i had on my 5.7 a few years ago and i fixed it. mine was considerably worse than yours but makes me suspect the same cause. going to try to post the video for you to see/listen to. turns out being 47 seconds file is too big to attach. perhaps email? maybe i can upload to youtube...also it happened when i tried pulling a water skier the first time too...weird

try this youtube link but keep in mind mine was much more pronounced than what i hear in your video.

https://youtu.be/aDrpN2diMeU

 

[minn_darren]

Jaybird, I was able to see/hear the video on youtube. YES! Sounds almost identical. If you rev'd it in neutral was it still fine? Was it only that way under load? Looks like when you run it slow the sound would go away, which is the same as mine. Yes, yours sounds a bit worse but does sound identical....what was the fix?!

 

[jaybird7]

yeah unfortunately i didn’t get more video at the time but it was quiet and smooth with no load on it. i don’t recall if it was smooth in neutral because it’s been a few years but the knock was so similar i felt yours is probably the same thing only smaller. i ended up doing a compression test (you can buy the tester pretty cheap) and confirming i had cylinders with low to NO compression. pulled the heads and found a blown head gasket AND part of the head gasket was stuck in a valve keeping it open. my guess would be you have a small tear in part of a head gasket and it quite possibly is stuck in a valve too. compression test all cylinders would help confirm. i had the heads resurfaced at a shop for around 225 bucks bought new head gaskets, cleaned everything up and put it back together myself. boom she’s been great since and was on her yesterday. now i’m back here with a fuel pump issue... please let me know what you find when you do...good luck dude

 

[Searay205]

some gimbal bearing can be greased externally. there a zerk fitting on the gimbal housing. pump it with grease and see if noise changes if it does you got your problem

 

[Rick Stephens]

If you brought the boat in to me, I would change a gimbal bearing in under 2 hours. Max. And I don't do em for a living. $700 an hour is a total ripoff or ignorance.

 

[minn_darren]

Rick, He charges 100.00/hour ....says it will take him all day. I am seeing videos that look relatively easy. Do I need to change the bellows too or can I simply leave them alone. I checked them and they look really good

Thanks JAyBird! I sent him your video and your comments...we'll see what he says...

 

[Rick Stephens]

Rick, He charges 100.00/hour ....says it will take him all day. I am seeing videos that look relatively easy. Do I need to change the bellows too or can I simply leave them alone. I checked them and they look really good

Thanks JAyBird! I sent him your video and your comments...we'll see what he says...

With the right tools, no reason to touch bellows. All day is not a mechanic. Must drink a lot of beer. I suppose with enough beer I could take all day too.

 

[jaybird7]

no offense to your mechanic but i’d be checking things myself too before letting him do anything and charging you 100 hr. compression tester is 30 bucks at auto stores. unless you know for a fact this guy is good at what he does although i think you said you don’t have much mechanical experience right? a simple compression test and 30 bucks for the tester isn’t bad. they’re good to have. i am not a boat mechanic i just do things myself and learn as i go. but i have a hard time believing its the gimbal bearing. too coincidental that it’s under load and the issue started after putting a heavy load on the engine. you’d wanna check the exhaust flappers too if it ended up being the head gasket. mine was gone and i have to wonder if that contributed to the issue too. the quick stop when pulling a skier and rush of water with no exhaust flappers ? more experienced boat dudes may know that one.

 

[minn_darren]

LOL! I agree, especially looking at how easy it looks. Couple of questions, some of the gimbel bearings looked like they had grease holes and others did not. This is a 2002 so I am guessing it will have a grease hole. Should I buy a gimbel with a grease hole or does it not matter either way? Also, is there typically a gasket that I will need to replace on the hole housing? Finally, should I grease everything when I put it back together (bolts, spine, etc...)? Thanks!

 

[minn_darren]

Jaybird, thanks very much for the advice. Yes, I will likely do the compression test too. You are right. Can't hurt. I really am unsure if this guy knows enough based on the 5 min he spent looking. Maybe, but it's probably best I do some more due diligence

 

[Searay205]

You need to step back and find a quality boat repairmen. You are literally throwing darts at a board. Tell him he changes gimbal bearing and it don't fix issue he don't get paid.

 

[TanTan32]

Do the compression test!!! I just went through the same thing, same noise. I was mind blown:boom:Just could"nt understand how it could run so good and have a blown head gasket. Took me a whole hour to figure it out.

 

[jaybird7]

minn_darren do you have any updates on your situation? It’s best when others report back and let ppl know what the issue was for reference when others may be searching posts for similar issues. perhaps you haven’t gotten to diagnosing or fixing it yet but figured i’d check in.

 

[minn_darren]

Still getting it worked on. Had a guy lined up for a month out and he flaked on me. Have an appt on Wed, Sept 9th

 

[minn_darren]

Hey All, I took it to two mechanics and the results are as follows: Compression showed the two inside cylinders (4 and 6) at 30 and the two outside cylinders (2 and 8) at 180. This is only on the drivers side (v8). Nothing done on the other side. Leakdown test showed intake valves on cylinders 4 and 6 is leaking possibly due to bent condition. They added:

"Will need to be re ringed and honed with a new valve replacement..possibly a head or replace the entire engine"

NOT the news I wanted. I spoke with him and he was stating that it might be more cost effective to just buy a new engine. I am not convinced.

Any thoughts on this?

Thank you,
Darren

 

[minn_darren]

Hey All, I took it to two mechanics and the results are as follows: Compression showed the two inside cylinders (4 and 6) at 30 and the two outside cylinders (2 and 8) at 180. This is only on the drivers side (v8). Nothing done on the other side. Leakdown test showed intake valves on cylinders 4 and 6 is leaking possibly due to bent condition. They added:

"Will need to be re ringed and honed with a new valve replacement..possibly a head or replace the entire engine"

NOT the news I wanted. I spoke with him and he was stating that it might be more cost effective to just buy a new engine. I am not convinced.

Any thoughts on this?

Thank you,
Darren

To close this out...sorry It took so long...was the head gasket that needed to be replaced