What is this noise?

[Lyle29464]

Re: What is this noise?

My first test would be compression. I think that will tell where the problem is. I would never run an engine that has a noise like that.

 

[fossill]

Re: What is this noise?

If its a lifter, remove the valve covers, start it up and put some pressure on each rocker arm on the push rod end to find the noisy one. Use some common sense though so you dont get hurt. Was one of my tricks when I worked in the automotive repair trade.
If it's actually knocking from below, I'd say your engine has had it and you're looking at some major coin to fix or get a long block, unless you just plan on patching it up.

 

[ENSIGN]

Re: What is this noise?

Sounds like a rod bearing,disconnect one plug wire at a time and see if the noise lessens.

 

[dg512055]

Re: What is this noise?

I had a buddy with a 4-wheeler once that I rebuilt with new rings,etc. It ran fine for awhile and one day he cranked it over to start and it produced a similar noise,only it did not start (single cylinder). After another teardown and further investigation, the old gas in the tank was the problem. It coated the valve stems with a tar-like substance. The coating would let the valves work when hot, but when it cooled off, it was much harder. The next cold engine crank stuck one of the intake valves open and the piston hit it. This is the same thing with your boat engine. Ran fine previously, then the next cold engine crank produces scary sounds. If you are certain that all the VALVES are moving through their travel range, this is not the trouble.

DG

 

[kwoolard]

Re: What is this noise?

Well at least I know what cylinder it is, cold compression readings are in:

1 - 175___________2 - 180
3 - 155___________4 - 175
5 - 160___________6 - 160
7 - 165___________8 - 0

DG, just by looking at the number 8 cylinder rocker arms and valve stems while cranking, they are moving normal. I haven't put a dial indicator on them.

I will try and do a leak down test tomorrow to see if it is valve related. Wish I had one of those bore-scopes? Either way it looks like the intake is at least coming off.

How do the other compression readings look? The plug tips and exhaust passages were real sooty with carbon, not sure if the compression readings could be higher because of carbon on the piston.

 

[superpop]

Re: What is this noise?

I would pull it and drop in a new block based on those numbers. They are too far apart unless you are not doing the compression test right. Should be no more than about 5% difference in compression between all cylinders.

 

[vegasphotoman]

Re: What is this noise?

That aint no lifter

Id bet $100 its = a Rod knock or piston slap....way too deep of a sound for lifter
maybye a rod cap nut came loose (I had that happen to me on a perfectly running motor, all sudden similar noise! very sudden)
was yours that sudden?

That loose rod cap would be a good thing, easy fix! no cost except pan gasket and oil...problem is its IN A BOAT and hard to get to all the stuff

perhaps drain the oil, unbolt and lower the oil pan and see if you can look at all the rod cap (using a mirror) have a pal rotate the motor by hand or you may find the nut in the bottom of the pan....mighta bent the cap, HOPE NOT!
mebbe just loose (a good thing) torque should be about 25lbs if I remember right on a v8...

I worked over 10 years as a ford dealer mechanic and have seen alot (I did heavy line work) motors and manual trannys etc all day long

(dont run it no more!!!!!!!) doing damage to it...

1500 rpms is too high for idle if thats what yours is set at BTW

 

[mdlee]

Re: What is this noise?

I think a bad valve would lead to lowe compression. A lower end knock would not lead to a compression of 0 unless there was a prob with the piston or the rings. It sounds like you have a valve prob on the # 8cyl. the backfireing may be gas coming back into the intake on the exaust stroke. Or vice versa. I THINK

 

[vegasphotoman]

Re: What is this noise?

Well at least I know what cylinder it is, cold compression readings are in:

1 - 175___________2 - 180
3 - 155___________4 - 175
5 - 160___________6 - 160
7 - 165___________8 - 0

DG, just by looking at the number 8 cylinder rocker arms and valve stems while cranking, they are moving normal. I haven't put a dial indicator on them.

I will try and do a leak down test tomorrow to see if it is valve related. Wish I had one of those bore-scopes? Either way it looks like the intake is at least coming off.

How do the other compression readings look? The plug tips and exhaust passages were real sooty with carbon, not sure if the compression readings could be higher because of carbon on the piston.

DOH missed that post! lol
yup ........serious it is!

let us know what ya find when yu have the engine out

 

[fishinpa]

Re: What is this noise?

Well at least I know what cylinder it is, cold compression readings are in:

1 - 175___________2 - 180
3 - 155___________4 - 175
5 - 160___________6 - 160
7 - 165___________8 - 0

DG, just by looking at the number 8 cylinder rocker arms and valve stems while cranking, they are moving normal. I haven't put a dial indicator on them.

I will try and do a leak down test tomorrow to see if it is valve related. Wish I had one of those bore-scopes? Either way it looks like the intake is at least coming off.

How do the other compression readings look? The plug tips and exhaust passages were real sooty with carbon, not sure if the compression readings could be higher because of carbon on the piston.

ok we have now have comp readings !

so put the air to #8 cylinder / if it comes out / Intake /Exhaust or both ,its more than likely the valve or valves/are not closing -
or the valve may be broken . spark plug was not beat up physically on the end so chances are the valves are may still be somewhat intact!

if you get air out the dipstick tube /or thru the bottom end in any way -then you have a hole in #8 piston /or have pretty well destroyed that piston .

If you get air out the intake and exhaust - loosen the nuts on the #8 rockers and check comp on that cylinder again!


fish

 

[Lone Duck]

Re: What is this noise?

ok we have now have comp readings !

so put the air to #8 cylinder / if it comes out / Intake /Exhaust or both ,its more than likely the valve or valves/are not closing -
or the valve may be broken . spark plug was not beat up physically on the end so chances are the valves are may still be somewhat intact!

if you get air out the dipstick tube /or thru the bottom end in any way -then you have a hole in #8 piston /or have pretty well destroyed that piston .

If you get air out the intake and exhaust - loosen the nuts on the #8 rockers and check comp on that cylinder again!


fish

YUP!!

 

[Grumman59]

Re: What is this noise?

Well, the valves must be closing and are unlikely to be bent, otherwise there would be a very loose rocker.

Are you sure the #8 piston is actually moving? It might have cracked in two or the rod could even have broken. I'm sure a leak down test will show all leakage to the crankcase on that cylinder.

The 40lbs oil pressure you mentioned would seem to indicate that it's not a rod cap or bearing problem.

 

[fishinpa]

Re: What is this noise?

OK Heres a pic for ya

Head appears in good shape, all rockers moved up and down nice looked Normal; from atop!

Mind ya now this motor had no compression in #3 cylinder.
Zero none absolutely 0 psi.

Care to see the bottom of this head ?

Can Crazy things happen ?


fish

 

[fishinpa]

Re: What is this noise?

So if ya dont see the missing part , ya just look in the big Hole below! lol

Notice the custom piston crown ?
How about that nice big D shape there where it was kissin the head !

It even has a nice curved shaped from being inserted into the piston at speed ! lol


fish

 

[Grumman59]

Re: What is this noise?

Fish, I had that exact same thing on a European GM 4-banger. The valve head looked as if it had been torched off, melted, but in my case it hit the piston to the side, breaking the piston and seizing the engine solid.

That was back when leaded gas was getting hard to find and I always wondered if unleaded gas had something to do with it.

In your case, that rocker must have had zero clearance, due to the springs pushing the valve stem up higher than normal.

 

[kwoolard]

Re: What is this noise?

That's look bad!!

I am being optimistic and hoping it is a valve that is not seating completely, but noticed that during the compression test on that cylinder I didn't even get a pulse of pressure reading on the gauge, I fear the worst

 

[Bondo]

Re: What is this noise?

I am being optimistic and hoping it is a valve that is not seating completely, but noticed that during the compression test on that cylinder I didn't even get a pulse of pressure reading on the gauge, I fear the worst

Ayuh,.... So go pull the Head,... Enquiring minds want to Know...

 

[FreeBeeTony]

Re: What is this noise?

I agree, what are you waiting for?

 

[kwoolard]

Re: What is this noise?

......just waiting for this nightmare to be over with....somebody pinch me

I'll have it off before the weekend is over.

 

[victorc1]

Re: What is this noise?

Cool you found the problem, lets fix it