3.0L GM Mercruiser Engine Tap/Knock?

[dino941]

Its hard to explain a noise but here is the video with the noise....What is it??

http://www.youtube.com/watch?v=xfkfkAcw1jM

 

[lilb]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

sounds like a lifter tick to me. Could just need to tighten the rocker arm nuts to spec or a lifter could have collapsed

 

[a70eliminator]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Sounds more like a clanking rod. To determine if this is a rod problem pull the spark plug wire one at time if it's a loose piston rod the clanking will go away when you disable that cylinder, if it's valve train the tapping will remain audible.

 

[joey maneri]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

definitly sounds like a lifter. does it have oil presure?

 

[lilb]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

that was going to be my next question joey. Ialso hade the same noise coming from my merc 3.0. one of the rocker arm nuts was stripped out replaced the bad one and the noise went away

 

[a70eliminator]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Nothing hard about pulling a valve cover.

 

[Gary H NC]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Nothing hard about pulling a valve cover.

My thoughts exactly....sounds valve train related to me too.

Welcome to Iboats too...

 

[Bondo]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Quote:
Originally Posted by a70eliminator
Nothing hard about pulling a valve cover.

My thoughts exactly....sounds valve train related to me too.

Welcome to Iboats too...

Ayuh,.... I concurr.....

 

[dino941]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Thank you all very much for the welcome, fast responses and comments..I am going to get a better look at everything tomorrow after-noon. I did pull plug wires one by one and sound was still audible (So its looking like the valve train)..There is oil pressure..

I will do a compression test tomorrow just to make sure the pistons-block is ok. Then will take a look under the valve cover to see if it is a loose nut/stripped nut. I will update the thread with the results tomorrow evening...

 

[cr2k]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Might try running some Rislone in the engine or Mac's #13 if you can find it. Either will loosen any sticky lifters.

I very much agree its valve train related.

 

[dino941]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Compression is good 142-150....The tapping is coming from the #4 cylinder area..It sounds like a bent push rod slapping around..perhaps a stuck or collapses lifter..

None of the rocker arms/nuts are loose...Valve cover is off

The Next step?

Should I pull off rocker arms first check for bent push rods..
does anyone know the torque for the rocker arm bolts..I (ordered) have not got my shop manual yet ....Must the rocker/rods be on the compression stroke or does not it matter while I dissasemble & inspect push rods....take on and off the rocker arms ect...

Or should I just (forget everything in the last paragraph and) pull off the head....to check the lifters as well as the push rods..

 

[vegasphotoman]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

theres a side plate on the 3.0 you can yank...thats the only access to the lifters....pulling the head off they are still inside the motor a good 4 to 6 inches down.....I bet you could event replace lifter by pulling valvetrain rockers/pushrods and side plate to access.

check the #4 rockers for PLAY....there should be just a smidge of play....there is no torque its about the free play....even with hydraulic lifters.....hydraulic cam fords have torqued rockers, that much I know. Chevy based... are a little bit different as outlined above

crank the motor around a few times to see when teh rocker is loose, should have a little tiny bit of freeplay....otherwise just tighten that rocker arm nut up till that freeplay is 99% gone and should take care of tapping sound, if not the lifter is bad/collapsed

 

[vegasphotoman]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

you might find this thread helpful
http://forums.iboats.com/showthread.php?t=364237

Install pushrods, making sure they seat onto the lifters, my engine required valve adjustment as such, tighten rocker arms until there was just a little bit of play (very little bit), crank engine around so cam lobes are on the low side, re checking over and over till all the valve rockers were adjusted.

see the gold color bolt (that was holding the coil pack on) just below that is the side cover to access the lifters

here you can see the holes in the block where the pushrods go down to the lifters, also you can see the side access plate...replace the gasket on this if you take it off. if you use any silicone be sparing

 

[vegasphotoman]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

I just watched the video...definatly lifter rocker related....

 

[lowkee]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Wow, you could eat off those pistons! If you had that on a Seafoam ad, I'd buy a can

 

[vegasphotoman]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

yeah they were clean clean clean.....SEA FOAM! lol
naw I didnt use any....

it was just ran hard by me...musta cleaned up the tops! there was very little carbon buildup on em

 

[dino941]

Re: 3.0L GM Mercruiser - Rocker Nut Torque spec??

Re: 3.0L GM Mercruiser - Rocker Nut Torque spec??

Thanks Vegas....I dont want to take the head off ; if its not necessary...

I will try removing the side cover to replace the lifters....If necessary..

I will turning the cam and seeing if there is play in the #4 rocker...

Anyone know the rocker nut torque spec??

Im downloading the manual now and I have a hard copy coming in the mail...

 

[Gary H NC]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Are all the rocker arms snug? Or does the ones for the #4 piston have a lot of slop in it?

 

[dino941]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

Are all the rocker arms snug? Or does the ones for the #4 piston have a lot of slop in it?

All seem snug now as the engine is but dont I need to rotate the engine to the compression stroke to check the rocker arm...


I found the spec its 40 ft lbs torque for rocker arm bolts...

 

[Silvertip]

Re: 3.0L GM Mercruiser Engine Tap/Knock?

You are not listening! There is NO torque on the rocker arm nuts. There are two ways to ADJUST valve lash on a hydraulic lifter with adjustable rockers which is what you have. With the engine running, back off the nut until the lifter clatters. Slowly tighten the nut in 1/4 turn increments until it just quits clattering. Then turn the nut another 3/4 turn. This is obviously a messy operation as oil comes up the push rod to lubricate the rocker arm and valves. Throw a towel over the rockers you are not adjusting or use clips made for this purpose. Aluminum foil wrapped over the hole in the rocker works as well. On a non-running engine the process is similar. Rotate the engine so the lifter is on the base circle of the cam. Valve fully closed (rocker arm all the way up). Loosen the nut, and then rotate the push rod while slowly tightening the nut. When you being to feel resistance on the push rod, do the 3/4 turn thing. Done. WARNING: Torquing the nuts will bend push rods and perhaps have a valve(s) contact a piston. If you don't know what you are doing have someone do this who does.