my engine sounds like a sledge hammer convention

[poor rich]

Backgound first... my engine is a 256 flat head, out of what I cant say.
even with my new exaust my truck seames loud, had a slight tick, and low compresion in front cilinder, expected a burnt valve.
Last night wife sent me to the store, (she was to busey baking cookies, no lie) I got to the light, when I pulled away something went terribly wrong. Bangs and knocking like Ive never heard before, but no smoke, no steam, no oil leak. I limped it home, and spent the night drinking heavly. Thinking about how much damage a broken connecting rod might do.
Tonight ...first I took a compression check, front still 50 psi, all others strangely have gone UP 10 to 25 psi,
Next I started it and imediatly shut it off, it sounded like an old diesel started on a cold day. connecting rod not broken just piston hitting the head?
Next idea... drain the oil look for chunks, none found.
Because of the amount of sluge that was in the oil filter when I bought the truck I knew the pan was going to get cleaned out sooner or later so, sooner it is. but everything looks good from below.
Well... if it looks good from below, then I must have a piston hitting the head.
So off with the head...Now Im dumfounded. other than the burnt front exaust valve that I expected, theres not a mark on any of the pistons or the head.
could I have skiped a timming gear, chain, belt, just what does it have anyway?
Is it possible for the oil pump to make such a racket?
Is it possible Im not smart enough to figure this out? Not likely.
Is it possible Im to proud to ask for advice? not a chance.
Help me please! Or I'll be forced to keep disassembling my engine!

[rixm37]

could be the connecting rod bearings. I don't believe it is possible for the pistons to hit the head they just bearly come up to the top of the cylinder bore. Sounds like its the bottom end somewhere.

[Drew M.]

First off, connecting rod bearings don't suddenly go bad at near idle speed. Also, if the bearing suddenly went bad - the oil pressure would plummet. You did not mention oil pressure, so I assume it stayed constant.

For giggles, rotate the crank each direction while watching the pistons and valve. Do the pistons have the same amount of slop in the bearings - they all move right? Valves- all move right? - if not check for broken camshaft.

Cylinder bores - spin the crank and examine the clyinder walls for wrist pin scraps in case one got loose.

While spinning crank, does it spin smoothly, stiffen up in a certain place/lots of resistance or spin too easy in an area?

Debris in the crankcase - you said nothing was seen - did you put a magnet in the old oil to find brken bits? The oil should not look like metallic paint for a paint job. There will be sludge in the pan from your description - it may hold broken parts from pouring out with the oil. Search for debris with one of those tiny magnets on the tip of a telescoping rod. Finally, the 265 oil pan has a slight lip at the oil drain hole that prevents debris from escaping - put your finger in the hole and feel around for debris - hopefully there is none.

Keep us informed.
-Drew M.

[Carter]

With the oil pan removed, take a small hammer and tap the crank and note the sound, then tap each of the connecting rod bearing caps and compare the sound to that made by tapping the crank. The bearing cap sounds should be the same as when the crank is struck, solid with sort of a ringing sound much like a bell, if the bearings are good. Repeat several times, tap the crank then the caps to be sure of what you are hearing. Bad bearings sound noticeably different than good ones. Try the same process on the main bearing caps next and note the sound made. Like the rod bearings, the sound of a worn out one is much different. Instead of a solid ringing the bad bearings produce more of a dead thud sound. This is a quick and less that perfect way to ck. for worn or spun main or rod bearing shells. This might save a lot of time pulling everything apart to only find everything is OK with the lower end but is no substitute for measureing or plasti-gauging everything. It's just a guide to focus your attention on possible failures.

[MSeriesRebuild]

Your compression readings are not good at all.

[poor rich]

Charles, yes your right my compresion is not the best but each time Ive tested it got better, last test with engine cold it was between 125psi to 145psi excepting the one that I knew had a bad valve.

Carter I will try taping as you recomend, this sounds simple and logical.

Drew I did turn the crank, didnt notice sticking or loose turning, looked at the cilinders just to see how bad they looked, but Ill try again with this in mind.
The sludge in the bottom of the oil pan was thick as vasoline, the first thing I did was check for grit, chunks, and shavings, didnt feel anything, i can try a magnet.
thanks guys for the help, Ill keep you up to date

[VROD02]

low end noise from my exp. is a slower process than what you have said, since nothing seems to be blown up or apart. Like Charles said your comp #'s are terrible! How did you aquire them anyway? Look into your camshaft and timing chain or belt. I've had them slip esp. after leaving a red light like you said. I think you would have heard bearings coming on slowly.

[TRACTORg25]

I am quite surpprised that no one has mentioned possible jump timing. A worn distributer drive gear or cam gear could result in mistimed engine which could show up as a knocking, skipping, dieseling or other noise. Also check your distributer cap for cracking or tracking. Tracking is a build up of conductive material between each contact on the cap and as the rotor spins it can arc across the build up resulting in firing two or more cylinders. Though usually if this happens you will see some smoke.

[TRACTORg25]

one other thing that I have seen before is a broke crankshaft usually ringht at the end of a main jurnel. You can check this by locking the flywheel with a pry bar and using a socket wrench on the front crankshaft bolt try to rotate back and forth. You you not be able to do so. If you are able to move any continue to rotate back and forth while looking from the bottom and see if you can locate where the break is. Most of the time I find them at the next to the last main or the very last main jurnel.

[poor rich]

Crankshaft, berrings, connecting rods all sounded good to my untrained ear.
Using the fan to turn the engine it felt reasonably stiff, not loose or sloppy or binding, I couldnt see or feel any scraches.
most logical at this point seams timming. Keeping in mind I have the drain pan and head off the engine is there any way to test the timming without further dissasembly?

[MSeriesRebuild]

Crankshaft, berrings, connecting rods all sounded good to my untrained ear.
Using the fan to turn the engine it felt reasonably stiff, not loose or sloppy or binding, I couldnt see or feel any scraches.
most logical at this point seams timming. Keeping in mind I have the drain pan and head off the engine is there any way to test the timming without further dissasembly?

Yes you can check it easily since the head is off. The firing order is 1-5-3-6-2-4. With the pointer lined up with the DC mark on the crank pulley, either #1 or #6 piston will be at TDC on the compression stroke. The other will be up on the exhaust stroke. Determine which piston is up on the compression stroke by observing the valves. Both valves will be fully closed when on the compression stroke, the one that is on the exhaust stroke, the exhaust valve will still be slightly open when the piston is fully up. If #1 is on compression, bar the engine over 1/3 of a revolution, the DC mark on the pulley will be at 4 o/clock. #5 will now be fully up on compression, observe if both valves on #5 are fully closed. Bar it over until the DC mark is at the 8 o/clock position, #3 should be up now with both valves closed. Bar it to the 12 o/clock position so the DC mark is again lined up with the pointer, #6 should be up with both valves closed. Bar it again to the 4 o/clock position, #2 should be up with both valves closed. Bar it now to the 8 o/clock position, #4 will be up with both valves closed. If you started with #6 being on the compression stroke, the same thing should occur only the sequence will be 6-2-4-1-5-3. If the valves aren't behaving as I've described when the pistons are at the top of the compression stroke, you definitely have a timing issue. Could be a loose chain that has allowed the sprocket to jump, a broken cam, or any number of other related issues. You should be able to determine if a wrist pin is loose at the same time by observing the action of the pistons.

[poor rich]

charles I'm at a total loss. Is there a diffrence between the drive pully on the diffrent size engines? specificaly would there be a diffrence in the location of the timming notch on the pully?
I started by turning the engine so cil. 1 was at TDC, then turned the engine several revolutions, it looks like the valves time correct. So I next wondered about the spark, I turned on the ignition and it looks like the spark might come to soon. So I reset the engine to #1@ TDC, I figured I would hook up a timming light and test this more acuratly.
Then things get weard. the V notch on the pully is no where near the timming marks. The V notch is aprox. at 2 oclock. There are 6 bolts that hold the pully on, had the previous or current hack mechanic not gotten the pully back on in the right position this would make sence... So I pulled the radiator, pulled the bolts on the pully and turned it Then I discovered the bolt pattern is not semetrical and only lines up where the pully was set.
Is there 1 key that locates the timming gear and pully hub in place that might have sheared ?
eather way I think ill be calling you on monday to figure what to do next.

[k8icu]

poor rich,

I hate to ask this, but have you RTFM (Read the Field Manual, Read the Fine Manual, Read the Friggen Manual etc.)

I ask this because the manuals that the army spent lots of your tax dollars on or depending on your age your fathers or grandfathers tax dollars on is full of good information. It takes a little dective work to go between the different manuals like a -20 -30 and the realted parts manuals, but if nothing else they will allow you to double check the timing and how it is suppose to be.

The manual may help by giving you a visual to look at while looking at the motor.

Just a thought.

[TRACTORg25]

Front crankshaft pulleys are secured in two manners that I know of. 1) Woodruff key. 2) Blind spline. These engines use the woodruff key. It is possible that the key may have sheared but I would bet that the camshaft gear key is the one failed and not the crank. The camshaft key is a lot smaller than the one on the crankshaft. Also you may have a sheared distributer drive. Most are roll pin. Over time any wear in this area will result in a sheared roll pin and thus jump timing.

[MSeriesRebuild]

charles I'm at a total loss. Is there a diffrence between the drive pully on the diffrent size engines? specificaly would there be a diffrence in the location of the timming notch on the pully?
I started by turning the engine so cil. 1 was at TDC, then turned the engine several revolutions, it looks like the valves time correct. So I next wondered about the spark, I turned on the ignition and it looks like the spark might come to soon. So I reset the engine to #1@ TDC, I figured I would hook up a timming light and test this more acuratly.
Then things get weard. the V notch on the pully is no where near the timming marks. The V notch is aprox. at 2 oclock. There are 6 bolts that hold the pully on, had the previous or current hack mechanic not gotten the pully back on in the right position this would make sence... So I pulled the radiator, pulled the bolts on the pully and turned it Then I discovered the bolt pattern is not semetrical and only lines up where the pully was set.
Is there 1 key that locates the timming gear and pully hub in place that might have sheared ?
eather way I think ill be calling you on monday to figure what to do next.

You mention a "V" notch in the pulley, all I've seen has numbers & degree lines imprinted into the pulley flange & thus line up with the pointer. Seems like I do recall some having a "V" notch at a different location on the pulley, but was not relavant to correct timing. Does your pulley not have numbers & a DC mark on it? If you don't see these, you may need to do some sanding on the pulley flange, it is possible you could be aligning the pointer with the wrong reference mark.