Intermittent "knock" in 1969 mercruiser 160 inline six

[rpeter46]

Hello,
I have a 1969 mercruiser 160. I took it out for the first time this year yesterday. The motor runs like a top. After about 40 minutes into a ride, at about 2500rpm the motor started making a "knocking" sound. I shut it down immediately. I looked at the oil for water or gas intusion and didn't find anything. It appeared to still be full. After I let it cool down, I decided to fire it back up and just putt-putt back home downstream. The knock was immediately there again. However, running between 600 and 1100 RPM the knock is intermittent. It does not sound like a lifter tapping. It sounds like a KNOCK. It sounds like upper motor, though.
After reading some posts about another identical sounding problem a couple years ago. I started thinking about this post.
http://forums.iboats.com/showthread.php?t=47167

The motor stills runs like a top, no hesitation, all six cylinders running well, just the intermittent "knocking". Although it knocks more than it doesn't.

I pulled the fuel pump and the spring is not broken, but seems 'a little weak'. I suspect that it is original to the boat. I know-I should probably just replace it now. But I don't like just blindly throwing new parts at a problem. What do you guys think? Is this probably the right first step?

http://forums.iboats.com/showthread.php?t=46972

If I do replace the pump, and it doesn't fix it, what are steps 2 and 3?

Illerad- does this look like same symptoms and same suggested remedy?

Thank you to anyone who takes the time to read, think about it, and post.

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

BTW- Can any of you suggest the best brand of replacement fuel pump? I'm afraid to buy Sierra(you often get what you pay for)?

Bad and good experiences welcome on this one.

 

[windsors03cobra]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Mine kind of knocks all the time, not a rod knock or a bad knock more of a a I'm 30 years old and my roots go back 70, I may sound a bit like a diesel and may not be the most powerful but I'll do this for another 30 years kind of noise.
I just run it and call it my inboard diesel. Mine is kind of a low pitched thuding noise most notable during low rev operations. It putts around great and also goes fine when I need it. Been very happy.

I just replaced my 33 year old original pump with a sierra and yea that was a load of crap. All the 1/8 npt ports were undersize and I probably was only able to turn my fitting in 3 turns. Made in Taiwan and cost $125.
I plugged the ports on my 33 years old Carter pump and put it in the box and tossed it under my boat seat, just in case.
I was fearful of the old pump stranding me on the water, with the old rubber compounds and new ethanol crap and just old age.

Heres mine starting and idling, albeit cold.
http://www.youtube.com/watch?v=hgzYAC4__hg

 

[zbnutcase]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Never had a prob with a Sierra pump yet, and have installed many of them. And welcome to pipe threads, thats how their SUPPOSED to be.

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Well, I can't quite live with that kind of knock. It's bad enough that my wife heard it right away. I guess that I'll start with the fuel pump, and pray that it solves the issue. I REALLY can't tell you how much I don't want to tear into the motor...

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Allright. Just installed the direct replacement fuel pump from the local mercruiser dealer. Problem NOT solved. Any ideas??? It's the intermittent part that is crazy. There's no timing chain, so that's not a factor, right?

Frustrated in St. Clair, MI...

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

anyone???

 

[windsors03cobra]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

How much oil pressure ya got ?
Sounds like you got a classic rod knock if its that bad. Probably a G to rebuild the short block.

 

[RJLeuwen]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Are you SURE the knock is in the engine and not in the outdrive?

RJ

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

RJLeuwen-
The knock is there regardless of drive engagement. Would that be enough to rule it out?

Windsors03cobra-
I was told if it was a typical wristpin rodknock that it would be constant, and not intermittent. The sound is not constant, and comes and goes. I just don't want to tear down for exploratory surgery. I also haven't given it any good reasons to knock!
In addition, it doesn't seem to be lower motor. It definitely sounds like upper engine.
Thanks. I'm not trying to shoot down any suggestions, so please keep up the questions. I want to fix this thing!:redface:

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Windsors03cobra-
Sorry I missed a question 40-50lbs of oil pressure.

Thanks

 

[Bravo]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

have you adjusted the valves, or is it more of a deep knock?

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Bravo,
I did not adjust valves-it doesn't sound or act like valve clatter or lifter noise. Sounds like more of a knock, but doesn't sound like lower end.

 

[Bravo]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

I think your best bet is to see about getting the fuel pump replaced. Remember that the fuel pump lever rides on the cam, which is in the middle of the block. You can try something though. Take a prybar or a long screwdriver, and with the engine running, press the bar against several different places on the engine while having the other end against your ear. This allows the sound to travel like a doctor's stethoscope and maybe you can pinpoint the sound better.

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Bravo,
I did the fuel pump already. No luck. Still sounds the same. I will try the big screwdriver or small prybar trick. Thanks.

 

[Bravo]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Just make sure you press it tightly to the center of your ear... works great.

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Bravo-
Thanks for the advise. As soon as the rain relents, I'm going out there...

 

[Bravo]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

I was also thinking that maybe you should pull the valve cover off and have a look see at the valvetrain. It might be surpprising as what you can find. I've seen broken and weak springs that make a knocking noise, flattened pushrods etc. The gaskets are about $10 at most parts stores around here. You could possibly have a loose coupler or flywheel too. Not so common, but I guess anything is possible. There is definatley something wrong, the trick is to find it. Worst case scenario would be to yank the motor and start poking around. Thats how I finally found the interior crack in my L6 160 merc. I didn't wanna believe it but with the advice of fellow members, I located my problem. Just gotta find a doner block now... Dangit.

 

[rpeter46]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

Too bad you live all the way in GA. I have a spare inline 6. That is if I don't need it now!

 

[windsors03cobra]

Re: Intermittent "knock" in 1969 mercruiser 160 inline six

That oil pressure sounds nice, is that hot oil pressure ?
Any idea on the compression ? or hours on the engine ?
I think taking the valve cover off is a good idea too, you can look at the valve train and see some of the inside of the engine. Make sure its oiling up there.