The Stovebolt Site Forums The Shop Area Engine Shop just rebuilt - now an engine knock

:confused: OK, so I have driven my 235 88 miles into the break-in period. Now there is a knock coming from the engine. I've read various threads you guys have posted on the subject. The knock is definately more noticable when the engine is warmed up, and really seems to be most noticiable when accelerating. took off plug wires one by one while idling and reving the throttle with left hand. could not assign knock to any one piston. I did not install new cam or cam shaft but did use all new bearings. I torqued all the bearings using plastiguage w/ 0.001 clearance. My oil pressure on this '54 HP engine is great. I re-used piston rods and pistons,but installed new bearings and rings. When re-installing end cap on one of the rods, nut wouldn't tighten up to required torque and became "stripped". The only solution I came up with was to re'thread with tap-die set, install new steel nut and lock washer. I was then able to reach the required torque (about 40 pounds) and thus re-installed and re-assembled everything. My question is where should I start looking for this knock...is it too early to drop the oil pan. I am sure everything was torqued correctly, but now I'm afraid my decision to alter the piston end rod cap is haunting me somehow. Is an individual rod availalbe for my engine, or what should I do ? Sorry so long....just trying to give all info possible.

dublenaught,

Sorry to hear about your problem. Were the rods and mains mic'd by a machinist, deemed OK, and the appropriate inserts installed..how 'professional' was the rebuild?

From my experience, a rod bearing usually knocks when NOT under acceleration as the forces created will load the clearances up and negate the problem. If you rev the engine at a standstill, a rod will usually rattle as throttle is let loose and the engine coasts to a idle.

A main bearing usually will make noise under load, but it is a deep, hollow thumping. A broken piston can mimic a rod bearing but will be more tinny sounding.

Your idea of pulling a plug wire to ID the offending cylinder should have produced some type of difference if it were a rod bearing.

If your crank wasn't ground and matching inserts supplied, it's sort of a crap-shoot. The lock washer episode on the rod cap bolt doesn't sound encouraging either. Maybe someone will be along to give you a better answer. Good luck.

Stuart

dublenaught,

Before I went nuts taking the engine apart, I would grab a rubber hose, or mechanics stethoscope and give the engine a going over. If you can pinpoint the location of the noise first, it might save you some headache. It might be a lifter banging on the rocker lube tube or something just as silly. Try to find what it is first.

Stuart

Too loose a piston will create "piston slap". What was the clearance of the pistons in the bore?

I think if the rod cap nut and stud were questionable, I think I would drop the pan to confirm one way or another.

All of the other posts are good points. I also would look to a loose piston pin causing this knock if in fact the pistons and pins were not replaced in the rebuild. No insult intended, but I assume that you know that rod caps must be installed on the rod they came off of and in the correct direction relative to the rod.

I have confidence in the machine work, as that was done by a competent professional in a well equipped shop. I believe I was given all the appropriate oversized inserts. Things went together very tight. Atomarc....it's interesting you mention a lifter/rod as the culprit, because I did not replace those. However, the sound wasn't there before I pulled the engine. If the harmonic balancer has slipped slipping on the shaft or is loose then maybe that could be the problem. don't know which I hate to do worse, Drop the oil pan or pull that darn radiator cage.

J D, was the cylinder ridge at the top of the bore cut (removed)?
Doug

don,t forget the fuel pump....doc

Yes, also are you shure the flywheel bolts are tight/clutch etc I have seen people disassemble a engine to find loose flywheel bolts. It sounds just like a rod knock. ck to make shure fan/generator/waterpump is also not hitting something. I would ck all other causes before tearing back down.

My buddy totally rebuilt my 305E v-6 and it had a funny knocking-clicking noise too, but with the stethoscope routine found out it was the fuel pump making the noise.
Got a new pump, no more noise.
Ted.

I use a piece of 3/8" or so vinyl hose to listen. I hold one end to my ear and point the other end at the area I want to listen to. I find it is extremely directional and very handy for sorting out noises.

I'll get my wife's stethescope and take a listen....for the record, no the cylinder ridge was not severe and not removed....and I dont know what the clearance was (the machinest does)...this sound was never there before the rebuild, thus I am left to conclude it is either a result of the new parts fitting, or re-assembly. Some of you mention a flywheel bolt....do you mean a loose bolt ?? or one that has fallen completely out? This noise sounds like a good old fashion deep drone of a knock - not a "ting" or "cling"....I'm going to Hilton Head now....will tackle this thing when I get back and let you all know what I turn up.

J D, The ridge was left from the previous rings 'stopping point'. Now with new rings & crank bearings the new rings will be right at the edge of the ridge at TDC, almost guaranteed bumping into it. Keep in mind the new bearings, having closer clearances, will 'raise' the crank higher, ever so slightly. The old ring top ring edge wore down a small amount, along with the cylinder wear. You install new rings, they are unworn & so the top edge is just a couple thousandths 'higher'. Then, with heat, you get rod elongation. Thats why the ridge should ALWAYS be removed. Normally the bores are honed, at least with a 'glaze breaker' to provide a proper surface finish to seal & seat the new rings. This in itself requires cutting the ridge. If not done, at the very least you can destroy the sealing edge of the new rings, & possibly crack a piston groove land. Doug

Doug, Excellent point.

Never thought about how new rings, new rod bearings and new crank bearings would raise the height of the top ring on each piston, and possibly run into the old "ring ridge". Interesting!

JD, When you get back from Hilton Head, pull the oil pan before that re-thread, stripped nut and/or bolt haunts you.

Did you try to torque, a different nut before you did the re-thread? Sometimes a nut will not torque because the bolt is weak and twisting within itself, gettin ready to snap.

Re-threading a connecting rod bolt doesn't sound like a good thing to do. Never did it, but I would think you could replace just the bolt.

if you didn,t remove the ridge you should do that now as it will damage piston also replace the rod bolt...doc

does anyone sell just the rod cap bolts ???

Check out the bolts sold by ARP, the racing engine parts supplier. I don't know if your specific engine will be covered, but they sell a wide variety of bolts, and they're much stronger than original-equipment parts. When I'm building a "claimer" race engine with stock rods, I always switch to ARP bolts.
Jerry

My FLAPS carries connecting rod bolts

Did you resolve the knock?

To help listen take the fan belt off. with the engine reasonably cold it won't try to over heat for some time, that's the time you have to locate the knock

Grigg

wifes stethescope revealed a knock in the 4th cylinder. I held it on the push rod cover. OK, the oil pan is off.....no metallic pieces, nothing obvious in the oil. Drip, drip, drip.....will wait tonight....after all, tomorro it should cool to 102 here in charlotte. so guys, what should I try and wiggle....what should I look for around the crack that would correlate with a rear cylinder knock...will it be obvious ?????

You probably can't see or feel anything that will confirm the knock.

Was this the rod with the bolt in question?
Either way, re check the bearing clearence on the #4 rod, and the one with the bad bolt after you replace it with a good bolt.

You may be able to check the clearence between piston and bore with a feeler gauge, use the service manual as a guide / instructions.

from a machinist point of view i am a little concerned about the tap and die set. did you
go up a size or just re tap the holes? if you re tapped the holes all you did was reform some half loose metal to get a torque by friction that broke loose when the engine started.

philip - the "tapping" I did was to the piston rod end cap bolt. The reason for this was because once I started putting things back together, the nut would not tighten to the required torque....just spinning and spinning....stripped, I guess you would say. So I took a tap/die, cut NEW threads into the rod cap bolt, and fitted with an ordinary common-day nut and lock washer. It tightened after that. I know it was risky, but I didn't know what elese to do - now I'm being told that those piston rod bolts are actually replacable. I"m going to check it all out tonight after the drippping is done.

The dripping won't be done for about a month...

You must replace that bolt and nut, and no lockwasher. To leave them here is just asking for trouble. A rod bolt is one of those fasteners where you can't take any chances.

Lockwashers don't belong inside an engine. They are prone to breaking, then you have two pieces of metal in your oil pan and a loose fastener.

On a modern engine it is recommended / required that you replace the rod bolts. They stretch with the initial torque and don't do the job as well the second time around.

I don't think it's necessary to replace all the rod bolts in a 235, but it would be a good idea.

Grigg

I've inspected the rod end caps and bolts. Despite the dreaded lockwasher and home-altered remedy, the cap nuts are tight. I don't see any problems that are obvious. the number 4 and 5 both have quite a bit of lateral play....that is, they slide quite easily on the crankshaft from side to side. Obviously, I can't really check the bearing clearance unless I pull one of the caps and use the plastigauge. Does anyone know how much lateral play I should have here ??? How easy should the rods slide on the crankshaft when moved from side to side....could this be my "knock" ???

Yes It could be. take your time and look around very closely. You might find metal shavings in the bottom of the oil pan. I did...

I would like to mention I have the exact sound coming from the firetruck. This morning, I dropped the oil pan. I had lateral movement on all rod end caps except one. I removed one just to look at the crankshaft bearings and crankshaft. It was scored very badly. I called oneof my mechanic buddies to take a look and he agrees with me, the motor has to come back out...

New pictures with oil pan dropped: http://rides.webshots.com/photo/2388959750080243953GXqkUO

Don't over look the rockers, lifters, pushrods, valve springs, and fuel pump. Just hearing the knock at or around #4 doesn't mean its in the bottom end.
Side to side shouldn't knock unless the crank is moving around alot. Check the crank thrust bearing, see if you can pry the whole crank forwards or backwards in the block. Also check the flywheel bolts very close. They only have to be a little loose to make a lot of noisy. Any chance the lock washer pushed the rod nut farther out on the bolt letting it hit somewhere? Pull the plugs and spin the motor with the starter, give it 12volts so it really goes, you might hear or see something.

At this point, you only have a few choices, pull it out for a tear down, or tear it apart as much as you can till you find it. Eather way, you are looking at more gaskets and some time.

Joe

I am going to replace the bolts and throw away my re-threads. I am also going to get some plastigauge and spot check a coupleof the connecting rod bearings to see clearance. the crank was really tight...can't believe a problem there. why is everone telling me to check flywheel bolts? I have to drop the transmission to do this. bolts would make a clanging noise - not a knock.....just playing devils advocate, I guess

Good idea and plan. Make sure when you spot check the connecting rod bearings, you look for the shiny wear indications. If you got it apart, might as well check anything that is loose.

No need to drop the trans to check the flywheel bolts. Just rock the frywheel back and forth while holding the crank. You would be suprized what kind of noise the bolts make. A automatic trans flywheel wheel or flex plate will be a higher pitched knock them a heavy manual trans clutch flywheel combination. Then engine will not idle smooth on its own, it needs the weight of the flywheel to smooth it out. If the bolts are loose, you will hear it banging against them as its running. A loose balancer will make a similer noisy. Joe

You may have an epiphany about the cause of the problem, but I've found that slow and systematic really does work. First engine I rebuilt I put the main bearing caps on backwards. All of them. That engine sure felt tight.

Don't dis a flywheel bolt problem. I bought an engine from another Big Bolter, and it didn't look like it had ever been apart, although it did look like it had a lot of miles on it. I would be surprised if the flywheel bolts had more than 20 ft/lbs of torque on them. I'm surprised that didn't come apart before it left the factory.

It certainly isn't going to hurt to Plastigage the rod and main bearings, but I think that if the clearance has gotten large enough to make the engine knock, you would be able to see it.

I've recently dealt with ARP about fasteners for 235s. The engineer I talked to sent me a nice spreadsheet to fill in with every conceivable fastener specification required. What you need is interchange information. Is your rod bolt the same as was used in a 1964 Chevrolet 327? There are certainly lots of those around, for cheap. I wish I had the answer to that question, but I'm going to have to find out about mine the hard way. I'll post my findings if I don't die of old age before I finish the re-build.

pull & check the main cap farthest from the pump also

sometimes a fulepump will make a knock you should have used locktite on that one rod stud dont drive it till you pull the pan a look it over

Just taking a look back at Deserdog Doug and oilrag Tom's post on 03 August on this issue (which I have yet to resolve). While, yes it is true that adding new, "thicker" rod bearings will send the top of the piston just a little higher, thus hitting the old ridge, isn't it also equally true that adding new crankshaft main bearings would compensate for the difference by "pushing" the crankshaft LOWER??? Thus, now the entire crank/piston assembly is just about back at the same location, thus relatively speaking, the pistons should stop at the ridge.....it makes sense to me. By the way, the guy at the machine shop told me that the bores needed honing only.

Any clues as to what is really causing your knock?

I can't believe that a "professional" wouldn't cut the ridge before he took the pistons out. Just my $.02 worth. Don

the cylinders were honed. Nothing more was needed. The engine was already bored .060 ......probably when grandpa had it rebuilt in the 1970's. For those who are interested, I am awaiting the arrival of new rod bolts so I can seal this rascal back up and get rid of that lock washer. I'll check the clearances when I pull the caps.

If the top of the cylinder had a ridge big enough for rings to hit and make noisy, you got way more problems then you think!!! Also, you would hear all six, not just one of them.

Change out the rod bolt, and see what happens.
When it comes time to start her back up, get a few people around so they can pinpoint the problem area as well as you. Joe

Again,
Run it without a fan belt at start up, without the noise from the fan, generator, and water pump you can hear a lot better.

Grigg