Mercruiser 170 Knock?!

[TheCubDriver]

OK you guys have all been extremely helpful in rebuilding this engine! One more question. After starting the engine I seem to hear a ever so slight knock, I dont know if its just me or is this normal for these older motors? Here is a link to it on YouTube http://www.youtube.com/watch?v=3b7ltUhnaXI I've ran it out on the lake without the engine cover and it seems noticeable, but I want to know from the pros if you hear it? It seems to have plenty of power, and runs strong. I just don't want to go out and have it blow up on me pulling skiers.

-Jake

 

[90stingray]

Re: Mercruiser 170 Knock?!

Hard to tell... kinda sounds like a slight rod knock but could just be the exhaust slobbering along. Did you plastigauge the crank and rods?

 

[dubs283]

Re: Mercruiser 170 Knock?!

all i hear is exhaust

 

[Fordiesel69]

Re: Mercruiser 170 Knock?!

I can hear the knock thru the video and all I can offer is lower end. It could be cam, or rods, not sure.

 

[solar7647]

Re: Mercruiser 170 Knock?!

It hard to tell, there is an odd sound there but it could just be bouncing on the floor. Did you do anything with the cam, litters or pistons during your rebuild? Did you charge the oil system before starting, did you set timing?

This is a vid of a 3.7 I did last year to compare to, started it same as yours on the garage floor you can tell there's a difference.

http://www.youtube.com/watch?v=ldeUvKat94Y&feature=youtube_gdata_player

 

[krjohnson76]

Re: Mercruiser 170 Knock?!

I have a similar knock on my 4cyl 3.0L OMC......did you figure it out??

 

[TheCubDriver]

Re: Mercruiser 170 Knock?!

I did nothing but inspect the rods, cam, and lower unit. It all looked fine and tight when I had it apart. Hopefully I'll get another video of it out on the lake. Like I said it runs fine, so I'm going to run it a little bit keeping my ears open.

 

[solar7647]

Re: Mercruiser 170 Knock?!

You know what I had a similar sound when I fist got my 3.7l a few years back, it ended up being the cover of the flywheel that is under the engine be hide the oil pan, it got a little bent and was allowing the flywheel to make contact with it. You check tha before installing it.

Good luck

 

[TheCubDriver]

Re: Mercruiser 170 Knock?!

hmmm... it didn't seem to make contact when I turned it over. It also looked good. I'll look closer and listen to see if the knock is coming from there. That would be a great piece of mind if that was the issue!

 

[solar7647]

Re: Mercruiser 170 Knock?!

You can always use the old screw driver handle trick, put your ear on the handle and the head on the engine and keep movin it till you find the spot were it's loudest

 

[TheCubDriver]

Re: Mercruiser 170 Knock?!

OK, sorry this took so long to put up. http://www.youtube.com/watch?v=0uNzC2Z90ZE I put on a new set of plug wires as well. You can hear the knock at idle, I've had a couple people tell me it sounds like a wrist pin?!

 

[dubs283]

Re: Mercruiser 170 Knock?!

i can't tell you what that is

the only way you are going to have a definite chance of locating the source is to get the boat on the water and put a load on the engine

that way you can get close with a stethescope and really pinpoint the knock location

 

[TheCubDriver]

Re: Mercruiser 170 Knock?!

Does anyone else have a video of a Mercruiser 470 running? Something to compare it too.

 

[dubs283]

Re: Mercruiser 170 Knock?!

Does anyone else have a video of a Mercruiser 470 running? Something to compare it too.

and what is that going to do for you??

let you see how someone elses engine runs??

keep in mind it is YOUR engine that has the issue, looking at other peoples engines isn't going to solve your problem

if you have to see another 470 running, search youtube - lots of 470 videos there

 

[TheCubDriver]

Re: Mercruiser 170 Knock?!

dubs,

Thanks for the advice. I've looked all over YouTube and it almost sounds like most of the motors have the same sound. This is why I'm looking for someone who has clean sounding one. If I hear one that sounds similar, I'm not going to worry about pulling my engine again. It's looking like I'm going to have too, so I want to exaust every resource before I do so.

 

[dubs283]

Re: Mercruiser 170 Knock?!

also, it is important to note that your engine under normal conditions should run like a tractor - its just the design of the engine

just get it on the water and check for noises because your boat (and everybody else's) isn't designed to be opertaed on land with the muffs

if there is a major issue you will definitely know once you are on the water and have a load on the engine

 

[TheCubDriver]

Re: Mercruiser 170 Knock?!

I guess I forgot to mention that I put it in the water a few weeks back. The sound almost goes away at 3,000 RPM and I think if I had the cover on the engine I wouldn't even hear it. It comes up with plenty of power and runs great.

-Jake

 

[stonyloam]

Re: Mercruiser 170 Knock?!

Can you feel it if you place your hand on the engine?

 

[TheCubDriver]

Re: Mercruiser 170 Knock?!

There is a slight tap when I put my hand on the valve cover

 

[dubs283]

Re: Mercruiser 170 Knock?!

There is a slight tap when I put my hand on the valve cover

collapsed lifter??

what are you using for engine oil??

did you replace the lifters with the re-build??