1985 mercruiser 3.0L 4 cylinder has a pecking/knocking sound

[jimbojonesmc]

Any thoughts would be great. 1985 mercruiser 3.0 4 cylinder has a internal pecking/knocking sound coming from The front of engine around the timing gear cover after engine warms up on muffs or on water.
Constant sound never goes away…knocks at idle… knocks going up to a higher rpm …knocks at high rpm and knocks Coming back down to a idle. Does not sound like a rod or main. I have checked the following
Fuel pump (new)…valve adjustment…ignition timing...spark plugs...rocker arms...changed oil...distributor…push rods…lifters…have removed belt and to confirm it’s not the water pump or alternator. Engine has 135 lbs compression in all cylenders and 35 lbs oil pressure at a idle. Runs like new except for this knock.
I’m thinking cam end play or timing gears…any ideas??? OBTW this boat new to me so i have no clue
when it started making this noise.
Jim

 

[scottn83]

Re: 1985 mercruiser 3.0L 4 cylinder has a pecking/knocking sound

From the things you have checked i would guess you have also checked the rocker arm adj. But if not you might try this. Pull the valve cover off tighten until the rod doesnt move then loosen until the rod will just move then tighten one turn. I believe that is the way mercruiser manual has you do this adj from my memory.

 

[Silvertip]

Re: 1985 mercruiser 3.0L 4 cylinder has a pecking/knocking sound

The man says the noise is coming from the front of the engine in the vicinity fo the timing cover and that he has also checked valve adjustment. Yes -- the timing gears can get a bit sloppy and make that exact noise.

 

[achris]

Re: 1985 mercruiser 3.0L 4 cylinder has a pecking/knocking sound

Could it be a slack timing chain, flicking on the timing cover?

 

[jimbojonesmc]

Re: 1985 mercruiser 3.0L 4 cylinder has a pecking/knocking sound

Well did some exploratory surgery and Silvertip was almost dead on. Again i find a fiber timing gear
that should be made from metal...will never understand that...anyway which is not looking its best
and here is the real kicker...pull the cam from motor and check the end play which is suppose to be
1-5 thousands and i find 22 thousands. the back of the cam gear is chewed up causing the extra play.
Rest of cam looks good so ordered timing set. OBTW if u have a 140 engine a mid 70s to late 60s chevy
2.5,2.3 4 cyl and a 250 in line 6 cyl uses the same timing set...Chevy monza,nova,camaro,vega,or chevy II
and a few others...get it from your local parts store and save yourself a boat load of money. And opt for
the metal gears instead of the fiber. I'm just glad the cam bearings looked good as i really didn't want to pull
the engine out. And yes there's no way of knowing if this is really whats causing the knock until i put her
back together but it sure looks that way. Thanks for the comments and ill post back after its back together
with the outcome.

 

[achris]

Re: 1985 mercruiser 3.0L 4 cylinder has a pecking/knocking sound

Could it be a slack timing chain, flicking on the timing cover?

Timing gears, no chain... :facepalm: What was I thinking!!!

 

[Silvertip]

Re: 1985 mercruiser 3.0L 4 cylinder has a pecking/knocking sound

Well did some exploratory surgery and Silvertip was almost dead on. Again i find a fiber timing gear
that should be made from metal...will never understand that...anyway which is not looking its best
and here is the real kicker...pull the cam from motor and check the end play which is suppose to be
1-5 thousands and i find 22 thousands. the back of the cam gear is chewed up causing the extra play.
Rest of cam looks good so ordered timing set. OBTW if u have a 140 engine a mid 70s to late 60s chevy
2.5,2.3 4 cyl and a 250 in line 6 cyl uses the same timing set...Chevy monza,nova,camaro,vega,or chevy II
and a few others...get it from your local parts store and save yourself a boat load of money. And opt for
the metal gears instead of the fiber. I'm just glad the cam bearings looked good as i really didn't want to pull
the engine out. And yes there's no way of knowing if this is really whats causing the knock until i put her
back together but it sure looks that way. Thanks for the comments and ill post back after its back together
with the outcome.

Very wrong on your suggested sources for timing sets. The Vega was an overhead cam engine and uses a timing belt. There was no 2.3 engine in the chevy line-up that uses a two-gear setup. The 4 banger marine engine is a two gear setup -- no timing chain. As for why the gear is fiber -- well it was to reduce noise. Go figure. You can actually buy a metal gear set but it will be much noisier.

 

[SSTKO81]

How did this exploratory surgery work out? I've run into a similar front end knock/chirp on my 140 and wonder if it's the same deal?

 

[GA_Boater]

Over 5 years old and the OP disappeared.

Closed.