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Bad Knock in New Rebuild


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Our 48 V-12 finally started, something good for the stay at home order.  However, it sounds terrible.  https://soundcloud.com/user-17353757/20200408-102737a.  Sine the recording, I fixed a couple mis-firing spark plugs and installed a mechanical oil pressure gauge, and put in fresh oil.  Helped a bit, but there is still a knock about each revolution. 

Engine was rebuilt with solid, adjustable lifters on re-ground camshaft.  Used a Melling M-15 oil pump.  Put a pipe plug in the rear oil spring chamber, and thinking that some oil was still needed for the lifters drilled 1/16 holes in the plug and through the bottom of the front spring chamber as well as in the front plug so the timing chain would get some oil.  Also put in a full flow oil filter by drilling a return hole in the rear of the engine and putting a plug between the filter out and filter in lines.

 

Pressure gauge reads about 20 lbs, I think it should be more.  Seems to be good volume of oil flow.  Still does not run well, idles too fast.  Any suggestions before we pull the pan?

Abe

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Before you pull things apart listen all over with a mechanic's stethoscope. If you have a fan belt on remove it to eliminate sounds that don't come from the engine internally. I once had a piston that expanded with warm up and caused noise. It was hard to find without the scope pinpointing the area of knock.

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Stop!!              pull plugs, look for impact-- poss pull head.. did you lose any bolts or nuts??

chk compression listen for which side.. top or bottom... sounds like upper to me..

dont run it any more..

 

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Oil pressure seems low and you modified the oil galleys. Can you put it back to stock to ensure the mains are getting sufficient oil? It may not be pressurizing the entire system if it's too easy for it to bypass and go straight through the filter or into the front cover where you drilled a hole for the timing chain. I might also see if there's a stock oil pump you could put in there instead, just in case the aftermarket pump isn't doing its job properly. You've made some significant modifications and when rebuilding a vintage engine, it's always best to do it 100% stock so diagnostics are easier. Do the modifications later after you're sure everything else is healthy.

 

Idle is not related to the knock, so don't worry about that--that's just tuning. Address the knock first and foremost so you don't hurt anything.

 

I once thought I was improving the oiling system on my '29 Cadillac by using a bigger fitting to feed the oil filter, but instead it had the effect of totally killing oil pressure. I put the older, smaller fitting back in and voila! Back to normal.

 

Put it back to stock and see what happens.

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I had a problem with my 47 rebuild that resulted in low oil pressure and knocking because the crank bearings were the wrong size. Oil flowed too easily and had to replace crank and bearings. So diagnosis is key before damage results.

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Is the knock coming from both sides? It sounds like there is more than one source of the noise. It could be piston to plug interference, but it sounds more like something is hitting the head. Does the knock appear when you crank the engine with the starter and the ignition off? That could happen if there is a foreign object in the engine.

 

If the plugs look OK, and it doesn't knock with the starter, run it just long enough to isolate the sound to one or both sides and upper engine or lower end, and do NOT run it above idle speed.

 

My engine sounded like that when I had Egge pistons that the wrist pins were not accurately located, the pistons on a couple of cylinders were hitting the head and other pistons did not come up as high in the cylinders as the should have.

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Too big of an overbore and pistons could hit the head gasket. This has happened, when an engine warmed up and the chamfer went above the block. Quiet on start-up then knock came as the engine warmed.

Edited by JFranklin (see edit history)
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The plot thickens.  Knock seems worse in lower parts of motor, but is pretty loud everywhere.  Noise occurs with fan belt on or off, but not wen cranking with the starter with ignition off.  Compression is quite low in cylinder no. 8.  I'm suspecting something serious. Bore is 0.060 over.   Hmmm.

Abe

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Open her up, heads off, inlet manifold, do a good check then drop pan. Happy Daze! Change back to new Melling m15 pump. Connecting  FULL Flow filter to oil outlet will lower oil pressure. A BI-PASS Filter is usually fitted there it restricts flow, has restrictor inside. Oil to bearings is pumped direct from pump  doesn't  go thru filter first like  modern motors. You need to be sure to fit oil pressure relief  valve up front.  Sounds like you  have clearance problems and lack of oil pressure. Stay Home and stay focused.  Cheers.

Edited by 38ShortopConv. (see edit history)
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If you continue to run it you will tear it up. Stop, and pull it out and all the way down. There’s no free lunch, engine noises never get better and they never go away, until the point it scatters itself all over the pavement.

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Start by pulling the intake and head with the low compression reading and look for signs of something hitting the head, like a loose or bent valve. Check to make sure that all of the horseshoe clips are properly seated in the guide groove.

 

.060" over size is a larger bore that Lincoln originally provided pistons for, but I doubt that it is large enough for the pistons to hit the firing ring on the head gasket. Your engine may tend to run hot. I hope that the machine shop did a sonic test to make sure that there were no casting voids. Lincoln only provided oversize piston up to .040".

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  • 1 month later...

I put a used engine in a truck one time and had a similar sound. In moving around the engine had been resting on the oil pan. The oil pan had mushroomed out a bit on the sides. The crank throws were hitting on the pan bottom. In that instance my fix was to start the truck and lie under it with two ball pien hammers and tap the sides of the oil pan until the "belly" came out.

Worked fine after that.

Bernie

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The V12 Engine Rebuild Manual cautions to assure all stamped rod and cap numbers 1-12 are assembled facing the front of the engine.  If not, it will cause a clatter or loud racket, depending upon how many are backward.  You are describing this as a knock, so this may not be the problem, but a long-shot possible cause.

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Posted (edited)

Yes, I read some years ago in an early  issue  of LZ magazine that same situation but don't have the mag. any more and wasn't sure how you tell if the rods are back to front. Didn't post! Now we know. Thanks  40 Zephyrsedan.
Worth checking before you put that pan back  on Abe.!! 

Edited by 38ShortopConv. (see edit history)
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Got rear bearing cap off, looks like lots of oil was getting to it.  I'll check the rest,  We did plastigage the mains, all were in spec.  However, we did find a suspicious bung someone had welded about 1/3 way down the front part of the pan, likely for a breather or maybe a dip stick.  I've ground it pretty close to flush, hopefully won't hit a crank throw.  Also been polishing chambers in aluminum heads. 

The Melling M-15 pump is also out, will look over but seems OK at first look.  The rear oil slingers have been replaced with a Ford seal, so I don't anticipate the need for a drain pipe in the big hole on the rear cap that now leads to the Ford seal chamber.  A smaller hole in the bearing cap leads to the rear main to drain oil that goes that way.  Drain pipe was in the way of Melling pump pick up tube.

Still need to scrape the old head gaskets off the block, tedious job as head studs won't come out.  Going to try a neoprene edge seal on the rear lip of the pan that hits the rear bearing cap. 

Abe

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The title of the thread is loud knock. That means you need to find it. Doesn’t seem from what you have been through so far that you have ID the knock.

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The purpose of the pipe coming from the rear main is to direct the excess oil coming from the rear main back into the oil pan. The need for it is not eliminated when you use the rear rope seals in place of the slinger seal. Without it, you could end up with the oil leaking out and contaminating the clutch. Using a high volume Melling pump could aggravate the situation.

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I think we can identify the problem.  When I put the M-15 oil pump back in, the pickup tube and screen look like they've been through a war zone.  There is a flat spot on the top of the tube where the rear crankshaft counterweight has been hitting and bending the bottom of the screen housing on bottom of the oil pan.  It's a Mac's screen and pickup that are supposed to fit the M-15 pump.  Maybe the Ford V-8 doesn't have such a large counterweight.  Constant banging each revolution might also reduce oil and oil pressure.

Now for a little heating and tube bending.  Also make sure the pump is not rotated clockwise toward the counterweight.  I tapped the oil drain hole fin the rear bearing cap for 1/4 npt, to install a street elbow to get drain away from the pickup tube.

I appreciate the advice guys.  The bearing caps are numbered with arrows toward the front, so they are fine. 

Abe

oil pickup tube.jpg

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I hope the modified  drain pipe clears  side of  pan, time will tell.  Apparently  the original drainpipe reaches right down into   oil  to avoid  crank/web counterweight  flicking excessive oil onto cylinder bores  promoting oil burning.  Theres  always someone coming up with  somthing  isnt  there. Happy Dazes. Roy 

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  • 4 weeks later...

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