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Discussion Starter #1
How wide should the conecting rod's big end bearing shells be in relation to the rod itself?

I am still working on locating a clattery noise I don't like from the engine of our GTV6. I had found a worn camshaft and was hopeful replacing it (and the tappets) would solve the issue. It is better. The constant clatter I described as like a baseball card in bicycle spokes is gone. But there is still a noise that makes me think of a rod knock.

The knock or rap is present on acceleration and much less on decelleration. I suspect the noisy camshaft masked this noise earlier. Ignition timing is correct and it does not sound like pinging.

So, as curiosity mounted, I decided to drop the bottom half of the sump to see if I could discern any issues with the rod bearings. I can detect no looseness/movement about the circumference of the journals but I can move each rod side to side a fraction of an inch. Enough that I can make them 'click' against the sides of the crank. There is no discernable movement of the crank itself in the main journals.

The big ends of #2 & #5 are easy to access with the bottom half of the sump removed. Those bearings look fine. The crank journals look fine. But I did notice something confusing to me. The rod bearing shells are narrower than the rod's width. In other engines I've worked on the bearing shells are always as wide as the rod. I assume if the bearing shells were as wide as the rod then the rod would tend to stay centered in the journal due to the small radius at the sides of the journal.

Could this be the source of the clattery noise? Should I just turn up the radio?
 

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Discussion Starter #2
So, to answer my own question - partly - I found this thread with the following photo in the 164 section.



That is what the bearing shells look like in our GTV6. Narrower than the rod width.

Still doesn't explain the noise I am hearing.
 

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Although I'm not a V6 guy, I've built a lot of various engines over the years and these look OK to me. It is normal to have longitudinal movement. An engine with, for instance, 1.5 thousandths of a clearance between the bearing and journal may also allow .012" - .025" end play. If the journals are true, there won't be any significant movement. If the journals are not true (aligned with the crank), the rod will slap forward and backward with every rotation, but you would also see accelerated wear in such a case. I doubt this is the source of your noise, based upon this picture. Of course, you can have a failed rod bearing on one of the other cylinders, which could be your noise.
 

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Rod Bearing

Hi Ghnl

You said

“But there is still a noise that makes me think of a rod knock.”

Over the years I've found that if it sounds like rod knock, it probably is rod knock. On all the Alfa V6s that I've seen with rod bearing failure(three engines) it has happened on the first rod journal (pistons #1 and #4), so I wouldn't draw much comfort that rods bearing #2 and #5 look good. Furthermore I'm assuming that when you said the rod bearings looked good you meant the lower portion? It's the upper potion that get the most wear.

You can do this test. Get a mechanics stethoscope and listen to the engine (after it's fully warmed up) on various locations around the top of the engine while somebody else lightly accelerates it. Do this until you have a good measure of how the engine sounds.

Now do the same on the bottom of the engine, either with a lift or with the car on jack-stands. If the lower half of the engine is nosier than the top, then the engine has to come out.

Although the labor to pull the engine is considerable, a lower end rebuild is fairly inexpensive as long as it is performed before the crank is destroyed by a failed rod bearing.

If you do have a failed bearing on the first rod journal it will eventually destroy the entire engine. I've seen this happen on a maintenance neglected Milano 2.5 engine.

More Rod Stuff

Generally small side to side motion of the rods is not a problem, excessive up and down motion is the problem.

Crankshaft and rod issues are not generally resolvable with the engine in the car. You can remove rod caps #2 and #5, by taking off the lower sump cover. You will then need to re-tighten them with a torque wrench. This is a critical setting and working beneath the car and upside down is not an ideal way to torque this bolt.

Heavier oil (50 weight) will reduce lower end noise and should definitely be used if your bearing were built on the lose end of the spectrum (many race engines are built this way). However, heavy oil may simply mask a problem until real damage has been done.

Hope this helps
 

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Discussion Starter #5
Thanks. It does help. So, may I presume that the bearing shells shown in the picture above* are 'normal'. And that they would not be expected to be as wide as the rod itself?

I realize that only looking at #2 & #5 did not prove anything. I did push the rod/piston up enough to get a look at the other half of the bearing - again nothing terrible seen in the two I checked. I did reach around to wiggle the other big end bearings but only noticed the sideways movement - no up/down movement discernable. Which also does not rule out anything...

I have listened around with my mechanic's stethescope. The loudest location is in the valley of the vee, in the vicinity of #2 & #5 but audible towards #1 & #4 and #3 & #6, too. Not much help either I fear...

I am not opposed to pulling the engine. I'm just trying to get a diagnosis before going too far in the wrong direction.

* the picture above is not from my engine - I stole it out of the 164 section while searching for info about the bearing shells.
 

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Hi

Yes the bearing shells in the picture above are normal. If the engine isn't noisier in the pan then it may not be a rod problem. It could be piston slap. Supposedly you can tell the difference between piston slap and rod noise by listening but I've never been able to. It's also possible that you have a slightly bent valve that is banging against it's seat. What are your compression numbers?
 

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Discussion Starter #7
My experience is that piston slap is more of a ringing noise.

Compression is 170 psi in #1, 165 psi in 2-6, leak down 2%-3%. Cam timing marks align, timing belt has ~ 7,500 miles on it, tensioner checked and adjusted. Ignition timing 4.5 degrees BTDC at idle (950 rpm) with vacuum hoses attached. Oil pressure 75 psi cold, drops to 60 psi warm (>2000 rpm) and ~ 20 psi at idle. Doesn't burn oil, doesn't leak oil.

If it was burning oil, leaking oil, showed low oil pressure, etc I'd be ready to yank it out and rebuild it.

Thanks for your thoughts - keep 'em coming!
 

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Hmm 165 psi (+) compression all around, no noise in the bottom end doesn't use oil. Sound like a good motor to me. Maybe you should just turn up the radio.

How did you resolve your noisy cam issue? Did you replace both cams? I'd investigate that area. Maybe a cam follower is out of round or something has come lose?

Bye
 

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Discussion Starter #9
I replaced both cams with good used stock cams (using the cam followers that they had been mated with). Re-shimmed the intakes to 0.018" - 0.019" clearance. Adjusted the exhausts to 0.009".

Before: I had started the engine with the cam cover off to watch & listen. There was an obvious loud clatter/clicking from the vicinity of both #5 & #6 (idle speed).

After: (engine idling with cam cover off to watch & listen) what I consider normal flat tappet lifter noise. Plenty of oil flowing. I hoped I was all set.

I suspect the knocking clattery noise was there before but masked by the noisy cam/lifter.
 

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I had an old MGA that had a funny noise. Upon disassembly I found a broken piston pin.

You might send an oil analysis to one of the many shops that do such things and get a report. They make much more sense if you've had them done over the years and have a trend line, but if they note a spike in iron, for instance, it might indicate a rocking piston that is wearing the cylinder walls. You'll get quite a metallurgical indication well before loss of compression.
 

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Discussion Starter #11
Hi On all the Alfa V6s that I've seen with rod bearing failure (three engines) it has happened on the first rod journal (pistons #1 and #4), so I wouldn't draw much comfort that rods bearing #2 and #5 look good.
Looks like it is engine removal time. I dropped the lower half of the sump (again) and removed the oil pump to get at the #1 & #4 rod bearings. They aren't the worse I've ever seen but it appears I have located a problem. Hopefully it is the problem...

(The mark going across the #1 bearing is a reflection.)
 

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Rod bearings

Eric, just for a point of reference , plastigage and record your big end to crank journal clearances to see where they compare with nominal wear limits. Is this a high mileage motor?
 

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Eric, did you resolve this issue by replacing the bearings?

I've got a noise that happens only when warm and its at about 2-3K RPM...a couple of mechanics believe it to be a rod bearing. I'm planning to pull the engine soon for this, but was curious what happened with your issue.

Thanks,

Hector
 

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Discussion Starter #15
No, I still have the noise. It has not changed in any noticeable amount by installing new big end bearings. The engine runs fine, it doesn't burn or leak oil so I am loathe to yank it out but also curious to find out what it is.

If you find an answer let us know.
 

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I can't help other than to say my father classic raced a BMW 2002Tii for many years and he was always annoyed with this noise in the engine. He could never get rid of it, but it ran really well and was a good loose old engine.

When he sold it the next owner replaced the block and pistons ... noise went away. It was piston slap. I though would not pull an otherwise perfectly working engine because of piston slap ... doesn't hurt to have a loose free revving engine.
Pete
 

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Eric, sorry to hear you still have the noise after the work you did. Looks like I won't know until I look at the bearings.

I think piston slap happens when the engine is cold, so in my case its definitely not it because the sound only happens after the engine has been at operating temp for a liitle while.

I've looked at quite a few postings on this topic (mostly on the gtv6 board) and a few say its no big deal, they've run it that way for years...others say its just a matter of time. My engine seems to run great otherwise, but I'd hate to ruin the crankshaft when I could've prevented that by changing the bearings. Better safe than sorry...
 

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Looks like it is engine removal time. I dropped the lower half of the sump (again) and removed the oil pump to get at the #1 & #4 rod bearings. They aren't the worse I've ever seen but it appears I have located a problem. Hopefully it is the problem...

(The mark going across the #1 bearing is a reflection.)
What's wrong with these bearings?? I would expect there to be some "polish" on a bearing but in hindsight I'm not a mechanic and I really don't know anything so.... Should a good bearing always retain it's grey coating ?

Might the offset wear on the bearing suggests rod is skewif on the power stroke (offset is on the top bearing?); perhaps worn little end resulting in piston slap

I making stuff up :D and pictures don't follow quotes (why?)
 

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I get what I call piston slap when engines are hot not cold. We had one 92 146L that was really nosiy at hot idle in summer time but noise went away once engine at high idle or under power.
 
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