The Stovebolt Site Forums The Shop Area Engine Shop Newly rebuilt 261 making noise

Just finished a complete overhaul on a 261 its got 45 lbs oil pressure but developed a knock soon after cam break-in. It was magnafluxed, bored .080, reconditioned rods with ARP bolts, Clevite bearings,.010/.010 crank, balanced, block decked .030, 848 head milled .050, new milling oil pump, new valves, seats springs and keepers, Patrick's solid cam, Clifford water heated 4 barrel maniford with 500 cfm edlebrock, fenton headers, electric fan,PCV system, full flow spin on filter, custom power steering pump bracket and lots of chrome.

I changed the break-in oil yesterday and found shinny metal flakes in the filter and a small amount of residue on the magnetic drain plug. The engine was assembled with edlebrock assembly lube and the oil pump was primed prior to start-up. The engine has about 100 miles on it.

The knock gets worse as the engine heats and the oil pressure drops to about 25 lbs. The knock does not change as plugs are individually grounded, so I assume it is a main bearing or cam bearing problem. Idle vacuum is a steady 20". Bearings were set up at .003 by the crank grinder, I wanted .0015-.002 but settled for what they gave me. I advanced the cam timing 4 degrees. I'm pulling the engine this weekend. Any ideas what went wrong inside? Do you think I should totally disassemble and clean the engine if I find an isolated bearing failure?

Did you break in the cam properly,sustained 2000-2500rpm for 15 -20 minutes? You may have wiped a lobe.Not uncommon for this to happen.

Yes, I also used some additional Lucas oil additive per Patricks advise.

Main bearings make a fairly heavy thumping/clunking sound when loose, which may get louder under load. Main bearing noise also tends to be more noticable at low speed, under acceleration. From your description, it doesn't sound like rod bearing noise- you can't short out the noise. What happens as you accelerate and decelerate the engine, up to about 1500 RPM, and return to idle? Piston noise tends to be more noticable at low engine speed, but often disappears after temperature increases, so it doesn't sound like piston noise. Also, piston noise is usually a light tapping sound more noticable at light acceleration. The decreasing oil pressure and increasing noise as the engine warms up go with main bearing trouble. A worn cam lobe would give you a loud tappet and shiney metal in the oil, but wouldn't affect the oil pressure. The oil pressure numbers you gave seem low, but I don't remember specifically what what is normal. Cold engine should have something higher than 45 PSI, I think, although that might be all right with the engine warm at idle speed.

My guess is that you have a disassembly job in your near future. If you find a bearing failure or worn cam lobe, flushing the engine oil circuit probably is a good idea.

Harvester

Do you think it would be a good idea to check compression in each cyclinder to verify cam lobe condition prior to engine removal? Wouldn't a cyclinder with a flat lobe stand out like a sore thumb?

Wags,

The people above have far better knowledge than I do about engine rebuilds. I rebuilt a 261 in 1972 and am still running it. I did not change out the original "higer-lift" camshaft.

I think that there is an oil pressure release mechanism (in or near the oil pump) that cuts in at 45 psi - I'll check a Shop Manual tonight.

What type of oil did you use during the initial run-in?

Good luck, and please keep us informed of what you find.

Tim

Tim

I used 5 quarts Valvoline 10-30 and 1 quart of Lucus oil additive.

I'll post the results the first of next week. I'm just sick about this problem. If the cam went flat, I am contemplating installing one of Cliffords hydraulic grind. I've used one of these on a 235 and really liked it.

A compression check would be reasonable to perform before disassembly, and would show low compression if an intake lobe is worn, but normal compression is quite possible with a worn exhaust lobe. Also, with a worn exhaust lobe, the compression gauge sometimes will show an extra pressure pulse during the first couple of crankshaft turns of the test- although that occurance is not entirely predictable. Worn lobes would cause tappet noise with solid lifters, and wouldn't explain the worsening noise as the engine warms up. I wouldn't argue against a compression check before disassembly- all information is helpful in this case, but the description of the noise seems to indicate something other than camshaft trouble- to my mind...

Harvester

I'm wondering if the .003 clearance for the mains and rods caused this failure?

I was thinking .003" is a little loose, but I don't think that would cause your trouble. I'll see if I can find the original specs for your engine. Or maybe someone else has them readily available.

Harvester

Loose main bearings can make a deep clunking sound, and certainly show up as reduced oil pressure, but in my experience, they won't throw "shiny metal pieces" which would be trapped in a filter.

The sloughed off tin/babbitt coating would be dull and probably not magnetic. Is it too late to take a mechanics stethoscope and find out where this sound is coming from. It could be much less catastrophic than you think it is.

Stuart

From my recent experiance, it sounds like the problem I had with a scored crankshaft and bearings in the firetruck. I had the deep clunking sound and little metal(shinny) slivers in my oil pan and filter.

261 new main bearing clearance: .001" - .003"
261 used main bearing clearance: .001" - .0045"

You might also have spun a cam bearing or it just wasn't installed right. The cam bearings have to be clocked right or the next one won't get oil.

I wouldn't run it any more before finding out where that metal came from.

Thanks for all your suggustions. I'm pulling the engine tommorrow and will post the problems Monday. I now remember when I disassembled the 261 that was sitting on a pile of stovebolts in an old Flagstaff junkyard for who knows how many years, that the #4 cam bearing was lunched.

Maybe it spun in the block and wouldn't hold the new cam bearing in place. These bearings were installed by the engine machinest and before I installed the cam I verified the oil galley holes were showing through the bearing openings.

If this is the case (A spun cam bearing) I assume the block is toast.

For the record, I don't think .003" for the rod bearing on a 261 is correct, definitely not. The mains could be set at that but not the rods.

From the 1960 & 1954 Shop Manuals:

261 connecting rod lower bearing, clearance on diameter:
New: .001" - .003"
Used: .001" - .004"

261 upper bearing:
clearance to piston pin boss: .015" minimum

Lots of clearance opinions here. I believe the sweet spot for these bearings is .0025"- .003" and agree with what the builder did. .003" won't make noise and will provide sufficient oil pressure. A used crankshaft can easily have .001" out of round or taper that is not detected by the person measuring it. Set with .001" clearance this condition will burn.

I stand corrected and surprised. I guess my 40 year memory bank is slipping!

Tim,

I'm just guessing here, but .015 is huge! Did you drop a zero...maybe .0015.(one and 1/2 thousandths) Is the the wrist pin clearance you are talking about.

Stuart

Stuart,

I agree with you about the .015" seeming to be too large. Maybe the piston pin "boss" is not what I (we?) think it is?

Here are all the entries (same in both 54 & 60)

Connecting Rods, Upper Bearing - Locked on Pin
Clearance on Piston Pin Boss - .015" Min.

Piston Pin Fit - Slip
Max taper - .0002"

?????

Tim

Just throwing a different idea out there, I once had a fresh motor make a knocking noise, we tore it down checked all the bearings, no problems.Turned out to be a valve, you could grab the valve and wiggle it around, sounded just like a bearing knock.I took the head back to the machine shop and they fixed it in 1/2 an hour.It was v8 though.

what kind of rings did you use? i remember my father and uncle telling me stories about using "chrome rings", they were supposed to last longer and give better compression, but seemed to want to come apart and flake on break in. they stopped using them soon after. if it were a ring issue that would explain the oil pressure variance as well as the difference in the knock, based on rpm and load.

I think the clearance of .015" referred to is to the minimum the piston must be able to move side to side so binding doesn't occur. If you have only .005" clearance here but you have .007" of crank end play rubbing will occur.

Curt B.,

Thanks for the interpretation - it sounds quite reasonable. I'll look tonight to see if there is mention of side-to-side movement.

Tim