3.0L engine tapping or knocking

[taylorsfields]

I just practically stole a 1980-something 3.0L mercruiser inline 4 for $150. It hadnt been started in about 2 years, but sat covered in the boat under the engine hood/cover.

I pulled the motor from the boat and set about getting it running. I found that the valves were rusted in the position they were set in before the boat was parked, so I threw on a 2.5L head from a running motor with a cracked block.

With these new heads in, it runs nicely, but only after I threw the 2.5L distributor on also.

Basically where I'm at, the motor starts easily and runs well but makes a tapping noise, like a push rod wants to go through the valve cover, and the oil pressure fluctuates.

I was concerned about the oil pressure but when I pull the filter off and crank it it throws oil about 2 feet. looks like plenty of pressure so i switched oil pressure switches and still reading is low sometimes, sometimes none.

I'm going crazy and hope someone can decipher this novel I've just written. This is my first post on this forum, but i've been reading for quite some time.

Thanks,
Taylor

 

[Howard Sterndrive]

Re: 3.0L engine tapping or knocking

sounds like the engine has a bad bearing somewhere. If you take a long screw driver and put the handle to your ear, and the other end against various places on the block you might be able to hear if it's a particular main or a cam bearing gone, or a hydraulic lifter collapsing etc etc. Or, use a mechanic's stethoscope (about $15 at an auto parts store)

I would cut open a filter to look for bearing material and if I saw anything alarming in the pleats probably just buy an oil pan gasket and pop the rod and main caps off and do a visual on the bearings.

 

[PatrickBoyle]

Re: 3.0L engine tapping or knocking

Sounds like a problem with the bottom end. Oil pressure is not created by the oil pump, it's created by the bearing clearances in the crankshaft. If you're oil pressure is low and/or fluctuating, you've got bearing issues.

 

[Bondo]

Re: 3.0L engine tapping or knocking

I just practically stole a 1980-something 3.0L mercruiser inline 4 for $150. It hadnt been started in about 2 years, but sat covered in the boat under the engine hood/cover.

I pulled the motor from the boat and set about getting it running. I found that the valves were rusted in the position they were set in before the boat was parked, so I threw on a 2.5L head from a running motor with a cracked block.

With these new heads in, it runs nicely, but only after I threw the 2.5L distributor on also.

Basically where I'm at, the motor starts easily and runs well but makes a tapping noise, like a push rod wants to go through the valve cover, and the oil pressure fluctuates.

I was concerned about the oil pressure but when I pull the filter off and crank it it throws oil about 2 feet. looks like plenty of pressure so i switched oil pressure switches and still reading is low sometimes, sometimes none.

I'm going crazy and hope someone can decipher this novel I've just written. This is my first post on this forum, but i've been reading for quite some time.

Thanks,
Taylor

Ayuh,.... Did ya adjust the valves after ya swapped the head,..??

 

[Silvertip]

Re: 3.0L engine tapping or knocking

Install a mechanical gauge and check oil pressure. If the tapping is coming from up top of the engine it is valve/rocker noise. If it is rather deep sounding thud type knock farther down on the engine it is likely rod or main bearing know. Other possibilities are piston slap from piston skirts that have collapsed, or even a broken spring in the mechanical fuel pump. Yes -- engines have been torn down for bearing replacement because that noise can mimic a bad bearing. Noise at the top of the engine signifies worn rocker arms/pivot balls or lifters that have not been properly adjusted.

 

[taylorsfields]

Re: 3.0L engine tapping or knocking

Thanks everyone for the fast replies.

I went ahead and lapped all the valves and got the old head working nicely, but guess what? Still knocking.

The oil pressure is back up to a constant 20 (psi ?) on the gauge. all I can deduce is that the oil passages were different on the 2.5 head vs the 3.0 head. either that or the years must have been different enough (i was told they were both 1986-89s, but who knows) to through it off.

While the head was off, I inspected the pistons and on the 3rd piston, there are visible marks where the intake valve was hitting it.

Howard Sterndrive, you mentioned something about the hydraulic lifter collapsing - could that cause a noise like this and indentation in the 3rd piston only?

Bond - o : I was under the impression that with these valves being hydraulic there was no adjustment... if there is that could very well be an issue. The only thing that mystifies is that it still does it with the original head in...

I think i might remove the valve lifters on the 3rds cylinder and see what I get.. any reason not to do this for a short period of time? other than it being a pia?

Thanks everyone

Taylor

 

[taylorsfields]

Re: 3.0L engine tapping or knocking

silvertip : i thought it might have been the fuel pump also, so i unbolted it and fired it up with it off for a few seconds and it still made the same noise. i'm hoping it is just a hydraulic lifter or something else i can replace with the motor in the boat. I really dont want to pull the motor again...

if anyone has some tips about adjusting the valves if possible or replacing / testing the hydraulic valve parts i would greatly appreciate it.

Thanks

Taylor

 

[Silvertip]

Re: 3.0L engine tapping or knocking

hydraulic lifters on that engine must be adjusted. Until you do that you have a problem. And if you simply cranked the pivot nuts down the valves could hit a piston which accounts for the noise. You should now be looking for bent push rods. Ohhh the value of a service manual.

 

[taylorsfields]

Re: 3.0L engine tapping or knocking

i downloaded the manual and adjusted as per instructed. still made the noise. Went and replaced all the hydrualic lifters and it seemed to be alright for about 30 seconds and then it started again.

This is killing me, im about ready to give up on it. The one thing i found today was that if it slows down enough, like just enough rpm to stay running (below normal idle) it doesnt make the noise. It also doesn't make it while cranking.

What are the odds this is oil pump related? i think i may have lost pressure again but without a physics pressure gauge I cannot check.

Has anyone else heard a noise like what i'm describing? If anyone is close enough I'd even pay them to check it out! I'm in RI.

 

[Silvertip]

Re: 3.0L engine tapping or knocking

You need an accurate measure of oil pressure. That happens wirh a mechanical gauge. A spun bearing can be causing fluctuating oil pressure. Tou haven't answered whether the noise is high or low in the engine. Diagnose rather than replacing parts hoping you get lucky.

 

[taylorsfields]

Re: 3.0L engine tapping or knocking

Which bearing could cause this? I found a set containing the main bearings as well as the rod bearings for under $50.

The noise is hard to pinpoint. I've had the stethoscope out and tried to locate it. From what I can tell it sounds like it is closest to the front #1 or #2 cylinder (bow) about half way up the motor. It's hard to say though, the iron block seems to carry the sound. It's definitely more prominent towards the front of the motor.

Thanks for the input

Taylor

 

[Bondo]

Re: 3.0L engine tapping or knocking

Which bearing could cause this? I found a set containing the main bearings as well as the rod bearings for under $50.

The noise is hard to pinpoint. I've had the stethoscope out and tried to locate it. From what I can tell it sounds like it is closest to the front #1 or #2 cylinder (bow) about half way up the motor. It's hard to say though, the iron block seems to carry the sound. It's definitely more prominent towards the front of the motor.

Thanks for the input

Taylor

Ayuh,... Rod, 'n Main bearin's run on a film of oil,...
If 1 or more is damaged, the crankshaft needs turning, 'n a matched bearin' shell is used...

 

[Silvertip]

Re: 3.0L engine tapping or knocking

I would suggest you stop spending money on parts that you don't need -- at least until you've proven they are needed. Those 4-bangers do not have a timing chain but rather timing gears that have been known to make a knocking noise. That would NOT account for fluctuating oil pressure but it is at the front of the engine and when bad, can cause the knocking. You cannot tell if you have a spun bearing unless you pull the oil pan, the rod and main bearing caps, the bearings and do an inspection. If a bearing is spun, the crank needs to be turned and undersized bearings installed. Does your "absolute steal" still sound like a "steal"? Perhaps the "deal" you got was due to the fact that the seller actually knew what the problem was! So far we have no idea if you have run a compression/lead down test, done a true oil pressure check using a mechanical gauge, whether the lifters have been properly adjusted, whether you have bent push rods or valves because of improper assembly, etc. You admitted there was evidence of piston crown damage so that would confirm improper assembly. So again, stop buying parts. Its time to do DIAGNOSTICS. To check for a rod knock you can start the engine and pull off one spark plug wire at a time. If the noise goes away or lessens, you have found the bad cylinder. You then need to determine if it is a collapsed piston skirt, wrist pin wear, or rod bearing. If not, that leaves bad cam bearings, worn timing gear or a main bearing/thrust (cranksaft end play) problem. Confirmation of any of these issues involves engine tear down and a thorough mechanical inspection against engine specs. That requires various measurement tools to check cylinder bore diameter, taper, piston skirts, rod and main bearing journal condition and diameter, wrist pin wear etc. I suspect this is all beyond your capability and likely you do not have the tools to do these checks. An engine builder can make this survey for you but it will come at a cost. You asked if this could be an oil pump problem. Oil pumps are usually NOT the cause of low or fluctuating oil pressure. Wide bearing clearances or spun bearings cause that. That is not to say it definitely is not an oil pump problem. A malfunctioning oil pressure relief valve in the oil pump could be an issue but highly unlikely. Another potential problem is that the oil pump pickup tube may have come loose. The pickup is pressed into the oil pump housing and due to vibration or ???? may have worked loose. Again, you need to pull the oil pan to have a look.
Unless you know what you are doing when dealing with the engine internals, you best follow the process outlined in the service manual for engine disassembly and you had best mark bearing caps for orientation and cylinder as they must go back together in the same way they were removed. I'm of course curious of the outcome but I've given as much help as I can here. I'm done here.

 

[taylorsfields]

Re: 3.0L engine tapping or knocking

silertip: Thanks for the info. I really appreciate the help. I pulled the motor and threw it on the stand. Pulled the oil pan, and found very thin flakes of what appears to be steel. I had a few people inspect the crankshaft, and after some deliberation I went ahead and ordered a set of std size rod and main bearings. impossibly it looked like the crank was in near perfect shape while the bearings took the abuse. The crank was smooth as glass and came up nice and round according to the caliper.

As for the fluctuating oil pressure, there was a nice 1/2" of sludge sitting in the bottom of the oil pan - not to mention the small scraps of metal...

Ill most likely clean the oil pump inside and out with the parts washer I just bought for the rebuild and reuse it.

While i'm waiting for the bearings to get here, I'm planning on pulling the head, header/intake manifold, etc and clean and blow each oil passage.

Should I use a moly assembly lube or just regular motor oil?

 

[taylorsfields]

Re: 3.0L engine tapping or knocking

to summarize everything that happened in case someone else has this issue:

I believe the 1/2" of sludge blocked the oil pump and ruined the #1 and #2 cylinder rod and main bearings.

The bearings were definitely shot.

new set going in soon

good luck everyone and thanks for the help