When cold, my 351m has a slight clunking noise in the block towards the front at idle. With higher RPMs I don't hear it. It's mostly half speed relative to the RPMs, but sometimes I'll hear faster noises. When the engine is well warm at idle, the noise is barely heard. Oil pressure is about 60 psi cold and 25 psi warm at idle. The engine has 71k miles.

So far, I removed every plug one at a time to try and discern piston slap - didn't make any difference as far as I could tell. Also ruled out water pump and power steering pump by removing the belt. I'm tempted to remove the fuel pump and see if that makes any difference. Don't think it's lifter noise as I can hear some of that 'ticking' through the headers.

Likely I'm heading towards pulling the oil pan. Short of any obvious visible damage I may find, what's the best path forward to inspect the crank/rod bearings for being out of spec?

 

To answer the question, use Plastigage. It gives a very accurate reading of bearing clearance, although it is messy to use it under an engine due to the dripping oil. I think if I were doing it I'd change oil and run it a bit to get rid of the black, smelly stuff to make the job as pleasant as possible.

But, I'm not sure that's where the problem is. I'd bet the timing chain is loose and what you are hearing is the slack coming and going as the engine runs roughly when cold. So, pull the fuel pump and check the chain by rocking the crank just enough to take the slack out - which you can feel with a screwdriver.

 

You can also pull the dizzy cap and watch the bug while you turn the engine back and forth with a breaker bar. If there is a lot of slop you might need a chain, I forget how many degrees is bad.

 

. Prolly just the timing chain... with only 71K miles (if accurate), I'd just ignore it till about 150K or so...


. But if you have replacement Chinesium distributor cap that fits poorly, you may have the rotor contact hitting inside the cap...

 

Thanks everyone for the good ideas. A loose timing chain sounds like the next place to look. When it was cold the other day, I turned off the choke and it was really clunking at 650 RPM and running rough. But when well warm it idles at 600 RPM with little noise. This is more appealing than working in dripping oil! I'll keep you posted on what I find . . .

 

. Bearing noises get worse when warmed up...

 

Pulled the fuel pump off today. With a homemade measuring stick, the deflection is right at 1/2". Seems I recall reading somewhere this is the maximum allowed. Likely it's a little worse as I don't think I can fully measure it through the fuel pump mounting hole given where my stick touches the chain. Looks like a new timing chain set is in my future. Any recommendations?

 

I doubt where the engine stopped put all the slack on one side. So if you got 1/2" then there is probably more. And that does mean it is time for a replacement.

I don't have a recommendation for a brand, but a good brand double-row roller would be more than you need. A Cloyes, or similar would be excellent.

 

I agree, I turned the crank to try and tighten one side, but without being able to see, it's likely greater than 1/2". Time to do some shopping . . .

 

Advanced Auto had 20% off when I bought my double roller!! Had to buy it on line to get the discount.



Has 4 degrees before, straight up and after key ways,

 

Thanks! I'll look there as well. Did you have to change your fuel pump eccentric? I happened to look at the Edelbrock timing set and it states one needs to convert from a 2-piece eccentric to a 1-piece. Is this case in general?

 

Nope just bolted everything Straight up! Just make sure you look at the correct set, advanced auto has 351W and 351C sets both under H code vehicles.

 

Finally got the timing chain and gears replaced with an Edelbrock set. It made a difference in reducing the knocking sound when the engine is cold. Pretty easy swap other than installing the timing cover without dropping the oil pan. Still a bit of noise so I might look at the bearings over the break.

 

Glad it helped on the noise. Did you notice any difference in power?

 

Not that I could tell. The chain/gears I replaced was at 0 degrees. Not knowing whether the cam is original (a PO added an Edelbrock intake), I also installed the new chain/gears at 0 degrees. I do think it idles smoother. Since I have a data logger plumbed into the tach I can check this against data I have.