HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

[Skipster1]

IT WON'T GO AWAY???!!!<br />This is the same noise I've had from the beginning. It sounds like a loose pushrod. I adjusted them .... the noise remained.<br />So I replaced all pushrods and hydraulic lifters. (Even tho none of the rods were bent .... and none of the rods or lifters showed ANY signs of wear.)<br />Previous owner mentioned that the noise always was there but it quiets down after a bit of running.<br />I AM NOT going out into the Gulf of Mexico with that noise threatening my engine.<br />I ran Mystery Oil thru the system to clean out crud in the oil system. Then drained it and put in new 20-50 weight Valvoline. Put in new plugs.<br />Set the timing to 10 degrees before TDC .... <br />Used the "dry method" (engine not running) to get the pushrods tightened down precisely and tightened the rocker arm nut down 3/4 of a turn after the pushrod was tight (at lash?????).<br />No luck.<br />Two mechanics have listened and agreed it is coming from the top, front of the engine and it sounded like a loose pushrod.????????????????<br />Jeez...... <br />One old shade-tree mechanic suggested it was "spark plug knock' from using 87 octane gas instead of 89 octane. Would it make that loud of a noise??????? I had some 87 octane gas in the tank but now have added some Octane Booster and will see if the knock gets quieter. <br />But I don't think that is the problem. The noise is too loud????<br />I have been after this noise for over a month - out there in 90 degree heat - trying everything suggested and the noise is still there????<br />PUHLEEZ HELP!<br />Skip

 

[Formula1974]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Dont know anything about boat engines but I have seen a car engine that had a button on a spring on the front of the cam that came loose or went bad or something and it knocked like crazy. Maybe someone will pipe in with what the correct term is I dont know if your motor has this or not. This was a few years ago and I cant remember the specifics but this button thing kept the cam pushed back or something and when it was loose it would allow the cam some back and forth action and it would knock. just a thought

 

[Dunaruna]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Skiph, just thinking out loud, <br /><br />You've virtually confirmed (previous posts & mpeg) that its front & top. Noise can travel and sometimes be deceptive. Maybe cam thrust bearing or timing gears? <br /><br />Maybe its time to dig a little deeper and remove the timing case.<br /><br />As I said, just thinking out loud. Dunno.<br /><br />Aldo

 

[Skipster1]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

I dunno either Chief. The engine simply starts and runs too well. I'll keep that in mind but, for now, I am thinking it is something else.<br />Would using 87 octane (this engine is supposed to be run on 89) cause a loud knock?<br />Also, when I pulled the plugs to run compression tests I probed the cylinder with a magnet, hoping to find a piece of metal that might be rattling around inside causing the noise.<br />No luck, but I did notice I was pulling up some black stuff out of each cylinder.<br />Could that be an excessive carbon buildup that might cause the knock?????<br />Any thoughts??????

 

[Rickles]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Yes carbon build up can cause a knock but it usually sounds low like a rod or main.If your sure it's up top i'd pull the head to see if something is stuck in the head or top of a piston.I had a 165 last spring that got a piece of metal from somewhere. we never did figure out where it came from.Also check the heat tube to the carb.It passes through the manifold and comes out on the bottom.A leak can sound like a lifter tick.Hope this helps you out.

 

[Rainmaker]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Skip,<br />During your previous post on this subject I mentioned a rocker stud might be pulling out of the head as you adjust the valve clearance. Have you checked this. These studs are just pressed in and have been known to pull out. You will never get the valve lash right if the stud pulss out as you tighten the nut.<br /><br />I had this same problem on my old 165. Replacement screw-in studs are available.

 

[FreeBeeTony]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Don't overlook the circulating pumg. I have heard that sometimes the bearing wears and the "impeller" hits the outside of the #1 cylinder.

 

[Skipster1]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Okay... Rainmaker: I have been looking at those rocker studs and didn't notice anything. I now will make some measurements to precisely compare. Your notion makes a lotta sense so I will follow thru, thanks.<br />FreeBeeTony: By circulating pump do you mean the oil pump? Sorry if this is a dumb question, I'm not a pro and don't know all the "correct terminology"<br />Thanks,<br />Skip

 

[llerrad]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Just another thought, 165 6cyl same as the 250 chev 6cyl. there was a common condition with the spring on the fuel pump breaking (getting weak) and the lever would knock on the cam when actuated.

 

[Skipster1]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Hey llerad.....thanks. Wouldn't the fuel pressure drop off under those conditions?<br />I only ask because I have good fuel pressure and the engine does run very good?<br />Thanks,<br />Skip

 

[llerrad]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

No the diaphram spring maintains function but the leaver spring takes out any gap in the leaver to cam plunger. It only takes a small lash to rap loud. This could be just one cheap common problem to check before you go deep into the engine.

 

[steve n carol]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Skippy, llerrad gotta a good thought! my friends Mopar has a soiid push rod that actuates the fuel pump. He only found this out after he rebuilt the bottom end! whadayathink? can this be heard w/ a steathascope? (never had to spell that word in my life!)

 

[Boatist]

Re: HELP! The knocking noise , on my 165hp Mercruiser 6 cyl IL

Skiph<br />Last time I had what I swore was a bad lifter / tappit I worked 12 hours on top with no change. Pulled the pan and found one of the rod bearing halfs had turned inside the other rod bearing.<br /><br />Things to do. Start by pulling one plug wire at a time and see if can find cylinder. If that does not help try pulling one plug at a time. Remove vlave cover and with a clean rag push down on each rocker are to put more pressure on each lifter. If it a lifter rocker arm or push rod the noise will change when you get to the bad one. If it is bottom will be no change. Pulling the plug will still help find the bad rod bearing. If you still think it is a bad upperend pull the pushrods and take out the plug. That will stop rocker arm noise for that cylinder. You need to isolate the noise before you can fix it.<br /><br />Do a compression check and look for one cylinder that is different.