Knock / Tap at idle in oil pan area.

EagleTalonTim · 04-02-2011, 05:41 PM

Well, there are a number of things this could be, but before I go breaking loose the rods, I want to get some feedback on what someone may suspect this is. Unfortunately, I did not get a video of this sound since I wanted to get into the oil pan before dark.

Here is the problem I am experiencing.... For the past 3 or 4 days, I started hearing a slight tapping sound that was not steady in the engine area when sitting at a stop light. The sound only happens at about 900 rpm...no higher, no lower. Higher RPM, everything is normal, idle rpm (750) the sound is not there. As soon as I press the gas a slight bit, the tapping sound shows up but is still not a consistent tap. I jacked the car up this evening and tested to see if the transmission was my issue. When I got under the car and had a friend rev the engine a bit, the sound was clearly coming from the oil pan close to the #3 cylinder. So far, I have drained the oil which is perfectly normal and actually in need of a change (no flakes or shavings), dropped the oil pan, and rotated the crank around so I could see if the rods had slack in them. All the rods have about 1/64 or 1/32 of an inch play side to side from left to right. I can't really tell if there is up and down slack since the pistons don't move as easy. I can tell that when I push up on the rod caps, the oil around it gets "thicker" and when I let go, the oil seems to suck back into the bearings.

I just replaced the bearings about 10,000 miles ago with ACL bearings fit to stock specs. I do not have a micrometer, so checking specs is really hard to do. Of course, I did break in the bearings like stated in several rebuild forums by driving 500 miles and changing the oil and taking it easy on it. Currently, I am running 20psi with an EVO III 16g and never go over 6k RPM. The oil pump was BRAND new and was put on right before winter and before the bearings were put in. So, if anyone has and ideas on what to check for or if the slack in the rods is ok, please help! This is my only vehicle and I really need to get it going again soon.

iugrad92turbo · 04-02-2011, 06:03 PM

I would pull oil pan and look around and check it out.

rlacasse1 · 04-02-2011, 06:09 PM

Did you grab ahold of the rods and move them around to see if one felt abnormally loose. Usually you can tell when one has a bad bearing cause it will have an enormous amount of play.

And just so you know, the next time you put bearings in you can use some Plastigauge. You can buy it at any part store, that way you don't need a micrometer to check if everything is in spec.

EagleTalonTim · 04-02-2011, 06:09 PM

I have already done that. That is what I listed in my first post.

Quote:

Originally Posted by rlacasse1

Did you grab ahold of the rods and move them around to see if one felt abnormally loose. Usually you can tell when one has a bad bearing cause it will have an enormous amount of play.

And just so you know, the next time you put bearings in you can use some Plastigauge. You can buy it at any part store, that way you don't need a micrometer to check if everything is in spec.

The rods all seem to have the same amount of play. The side to side play is what I was wondering about and would that cause a loud tapping noise at idle? The in and out play is hard to tell without disconnecting the piston from the rod and moving it. I have turned the crank over a few times with a 1/2 in breaker bar and moved it back and forth to see if any of them had play, but I really could not tell. I guess my best bet is to go ahead and pull the rod bearings and see how they look?

*ADDED* I asked my local parts store guy if they had any Plastigauge and he looked at me like I was an idiot. So...I guess I need to order some online.

rlacasse1 · 04-02-2011, 06:16 PM

Some side to side play is ok. There should be some, if there wasn't the rods would get jacked up from rubbing on each other. And no, it wouldn't cause any tapping.

What you should do is reach up and grab a cap and try moving it up and down and back and forth. Don't just spin the crank to see. You need to grab the cap and move it.

You don't have to unbolt anything or take the pistons off the rods (which is impossible without pulling the rods anyways).

So yeah just reach up, grab a rod cap and see if there is alot of play, or none.

I wouldn't pull it apart until you know for sure.

EagleTalonTim · 04-02-2011, 09:22 PM

From what I could tell when I tried to move the rods, they are pretty solid. I just can't think what would cause the loud tapping sound at 900 RPM which sounds like it is inside the oil pan. Nothing else is around it except the transmission. All the torque converter bolts are tight as well. Would a cracked flywheel make that noise?

I really don't want to have to pull the transmission to check if the flywheel is cracked and I don't know any symptoms that I could check for if it was cracked. I do have an extra one in case I need to replace it though.

bradselph · 04-03-2011, 08:57 AM

A crack flywheel could cause a weird tapping noise.

I been threw 3 crack flywheels on my 383 and they all sound like a click/tapping noise.

EagleTalonTim · 04-03-2011, 09:48 AM

I fully inspected the rods this morning and they all fell solid except for the slight side to side play which apparently is normal. I did find 2 very small pieces of metal in the bottom of the pan, but they are to small to even worry about. I also checked the flywheel for visible cracks or uncommon wear which there is none. Like I stated before, what else would cause a tapping sound that is NOT consistent only at 900 RPM and coming from the lower area of the engine?

I am putting the oil pan back on and filling it back up with fresh oil. If the sound gets worse, maybe I can pin point it later. Guess this is one of those "drive it till she blows" kind of problems.

lil corb · 03-12-2012, 04:04 AM

Bringing this back up because I have the exact same problem. Only 900 rpms too. Knock doesn't get any louder with revs either. Motor is brand new less than 100 miles, a\f ratio has been in check since motor was first turned over. Haven't been at wot yet and I'm running bradd penn break in oil.

Specs are weisco pistons, manly rods, acl bearings, arp main and head studs, fp2 cams, bse kit, new water pump, timing components, front case with gears, quartermaster twin disc, shep stage 3 tranny. No significant degrees being pulled from knock (.4 to .7) around 2200rpms. I do have avid 75a really stiff mounts. Oil pressure is a little higher at 25psi at idle because of bse. Engine was professionally built.

Any ideas?