Mercruiser 3.7 "Clacking"

[brodie123]

Hi All;

Mercruiser 3.7L L4

Engine is "clacking" when I go 2000 rpm or above and increases with RPM. Below doesn't make any clacking. It seems like it's coming from the top end. It's not running as smooth at lower rpm as it did before. Runs ok at around 1500 for around 1/2 hr and then worsens and eventually stalls and will not re-start unless it sits for an hour and then is fine again for a while.

It does this under load or in neutral. I tried moving the timing around but that had no affect. (fingers crossed it's not a cylinder)

My guess is I have a bad hydraulic lifter and the reason it stalls is because it's probably flooding itself.

My plan is to replace all the hydraulic lifters and go from there. Before I do that, I wanted to post this and see if I am on the right track.

Thoughts?

 

[floater212]

my first thought is a bad rocker or bent rod. I buddy of mine had a 4cyl. merc. years ago and it did just that, clacking, took to dealer and they said new motor under warranty, great, they had it for the last 2 months of use and then decided to replace rod and rocker, 20 minute job. there went that year of boating.

 

[chris mig]

I agree with floater. had a 351 Cleveland do that before and freaked me out, [was a pretty fresh rebuild] and was just bent push rod clankind around.Pull that valve cover and check before doing anything

 

[brodie123]

I get the push rod, but how would you detect a bad rocker?

 

[chris mig]

I am guessing push rod all the way, but the cup on the rocker can wear out causing the rod to be loose.
visual inspection first, if all looks good, than pull one rocker at a time and pull rod check for bends and inspect rockers. You can also carefully with cover unbolted but in place start motor and slowly lift and look and listen keep rags handy for oil spillage
have done this on a car I know its a bit different with the boat and all as far as bilge

 

[brodie123]

Hi All;

I pulled the lifters. The rods all look straight as could be. No unusual wear on the rockers that I can see.

some of the lifters (3) had a different wear pattern than the others. The 3 looked like a bunch of circles within each other. Could this be caused by hopping?

I really need help on the next steps here.

thanks in advance.

 

[brodie123]

I should add that the 3 I am referring to, the circles are more pronounced than the others. 2 of the 8 had a 'very' minor spotted center.

 

[philbullet]

I had a 3.7 /470 for a while in my boat with a 3" heat exchanger and it always ran hotter than the one with a 4" heat exchanger that I have right now.
The one with the 3" ex. Chan. Always made more noisy even when I baby it which was always.lol