Another rod bearing question

[pccorrig1]

I've been reading through the forum posts related to rod bearing questions, but can't find any followup posts to see if the suggested fixes solved the problem or not. And many ultimately drift off topic, which makes for interesting reading and some interesting gems of knowledge.

My '94 ATX, 161K, not modified, not raced, reasonably maintained over the 11 yrs that I owned it, has a knocking sound on the #1 cylinder. I've been using my stethescope to narrow it down, and it is loudest when I have the probe on the #1 spark plug boot. I'm suspecting the rod bearings.

Here's my question: if the rod bearing is worn or has spun, is it likely that the crank journal is damaged, which would then cause new bearings to fail within a short period of time?

I know some of you guys and gals have replaced rod bearings. What does it look like in there? What has been your experience

Thanks from an old, gray haired grand father, who still enjoys his SHO, and isn't afraid to get his hands dirty.

 

[Devin]

You have to look at it. First off you can see if you've worn through the copper on the actual bearings and then look at the journals themselves to damage. If you want to be precise you'll want to plastigage the bearings and make sure the clearance is within spec.

This bearing shows copper, but is okay.



These bearings aren't.



This crank is not okay.

 

[rubydist]

If the rod bearing has spun, you would have a loud knocking noise, and the odds that the rod and crank are damaged are 100%.

If the bearing has worn, there is a very good chance that the journal is okay, but you won't know until you take it apart and examine it carefully.

 

[bubba]

Not to go off-topic, but could there be a chance that the cam lobe could be pitted? causing a tick?.... but I sure the rods bearings are going though

 

[1995SHO9]

Where are you in pa? I go from Harrisburg to Carlisle, if you needed a hand, I could come out maybe?

 

[SHO_91]

Plasti-gage

If you're sure that the crank journals are okay (i.e. no spun bearings), it's rather unnecessary to plasti-gage the clearance. Let's say, it IS out of spec, what could you do about it? Nothing, short of re-grinding the crank. Even though, I've never heard about that kind of crank wear with the SHO motor.

Plus, in order to plasti-gage the clearance, you'd have to tighten the rod bolts to spec, loosen them again, and then tighten them again to spec, which puts undue stress on them (they stretch). From what I heard, they are meant to only be tightened a few times...last thing you'd want is a broken rod bolt @ 7000 rpm.

 

[SuperHO]

i can show you pictures of what happens when that occurs...

 

[pccorrig1]

You have to look at it. First off you can see if you've worn through the copper on the actual bearings and then look at the journals themselves to damage. If you want to be precise you'll want to plastigage the bearings and make sure the clearance is within spec.

This bearing shows copper, but is okay.



These bearings aren't.



This crank is not okay.

Thanks for taking the time to post these great photos, as they will be very helpful if I decide to drop the pan and take a look. But I fear the worst, and might check out one of those used engines currently up on eBay. So far, no one there can confirm the claimed mileage, so they may not be any better than what I have now.

 

[pccorrig1]

If the rod bearing has spun, you would have a loud knocking noise, and the odds that the rod and crank are damaged are 100%.

If the bearing has worn, there is a very good chance that the journal is okay, but you won't know until you take it apart and examine it carefully.

Rudydist, I began this "repair" thinking I had the dreaded crank cancer, and bought a used crank pulley sprocket from you. After getting it apart, I found that was not the case, crank bolt was tightly torqued, and no wear on the slot, key, or sprocket. But I put yours on, because it was cleaner than my original.

What I did find was a separating inertia ring on the dampener pulley, and replacing that with a new one eliminated most of the original knocking sound.

But not all - there is stilll some bearly audible after startup, but clearly there when probing around the top on my engine with a stethescope.

Thanks for your input...pc

 

[pccorrig1]

Not to go off-topic, but could there be a chance that the cam lobe could be pitted? causing a tick?.... but I sure the rods bearings are going though

I had the top apart in May, thinking I had bad cam chain tensioners. I also bought a set of heads on eBay just to get the tensioners before beginning that project.

But the cams were perfect, no pitting at all, not like the cam photos posted somewhere here on the forum. And there was nothing visibly wrong with the tensioners either. I measured a shallow .002" groove on the tensioner contact face, and .003" on the set I bought. I could not measure any difference on the timing chains, so reassembled with the original parts, new cam seals, new CPS, and still have what sounds like the chain making contact with the rear cam cover below 2000RPM.

 

[pccorrig1]

Where are you in pa? I go from Harrisburg to Carlisle, if you needed a hand, I could come out maybe?

I'm just outside of NE Philly in Lower Bucks.

Thanks for the offer.

 

[SuperHO]

sounds like you have the same issue i do...rod bearings are worn. RCM sells em for cheap, and it's only about a 3 hour job if you're reasonably mechanically inclined. just make sure to torque the rod caps properly.

 

[pccorrig1]

If you're sure that the crank journals are okay (i.e. no spun bearings), it's rather unnecessary to plasti-gage the clearance. Let's say, it IS out of spec, what could you do about it? Nothing, short of re-grinding the crank. Even though, I've never heard about that kind of crank wear with the SHO motor.

Plus, in order to plasti-gage the clearance, you'd have to tighten the rod bolts to spec, loosen them again, and then tighten them again to spec, which puts undue stress on them (they stretch). From what I heard, they are meant to only be tightened a few times...last thing you'd want is a broken rod bolt @ 7000 rpm.

I thought about plastigage, but tend to agree with you. Without pulling the engine and crank, essentially to do a full rebuild, the measurement is useless. If the journal is in good condition and won't damage a replacement bearing, that's as good as it gets IMO. Knowing the exact journal diameter, whether or not it has a taper or is minutely out of round doesn't buy me anything. But if I decide to go ahead and pull the pan, I'll probably plastigage it anyway, just to confirm my belief that this is an original, unground crank, and know what the journal-bearing clearances are.

 

[93rev2sev]

I think you would be wise to check the timing belt tensioner before tearing off the oil pan.

I'd bet $5 that's your problem. Rod bearings don't make noise for very long.

 

[pccorrig1]

sounds like you have the same issue i do...rod bearings are worn. RCM sells em for cheap, and it's only about a 3 hour job if you're reasonably mechanically inclined. just make sure to torque the rod caps properly.

It will take me more than 3 hours just to get the car jacked up, and clean off 15 years of engine crud from leaky gaskets and seals.

Regretfully, I've gotten older, slower, have to take frequent breaks, and can't always find the tools that are right in front of me.

But I still like working on my own cars, and have accumulated alot of tools over the 44years of car ownership. Never paid a mechanic for any repair on my SHO in 11 years.
PA requires annual emission and safety inspection, so I have to keep on my mechanics good side, and let him do basic repairs on my wifes Mountainer.

 

[bubba]

That's good to know, I would check everything before busting that pan off though. Sounds like it should be a quick repair though

I had the top apart in May, thinking I had bad cam chain tensioners. I also bought a set of heads on eBay just to get the tensioners before beginning that project.

But the cams were perfect, no pitting at all, not like the cam photos posted somewhere here on the forum. And there was nothing visibly wrong with the tensioners either. I measured a shallow .002" groove on the tensioner contact face, and .003" on the set I bought. I could not measure any difference on the timing chains, so reassembled with the original parts, new cam seals, new CPS, and still have what sounds like the chain making contact with the rear cam cover below 2000RPM.

 

[pccorrig1]

I think you would be wise to check the timing belt tensioner before tearing off the oil pan.

I'd bet $5 that's your problem. Rod bearings don't make noise for very long.

I had the timing belt and tensioner off last month, thinking I had crank cancer. Did not. Seemed to be OK. Had to put the tensioner in a vise to retract the piston, was tight. Tensioner pulley bearing smooth, no sign of immenent failure.

Grandpa to grandpa, what makes you think that?

 

[SuperHO]

I think you would be wise to check the timing belt tensioner before tearing off the oil pan.

I'd bet $5 that's your problem. Rod bearings don't make noise for very long.

i'm gonna have to disagree with that last statement...mine's been knocking a wee bit on cold startups for a couple of weeks now...which is why i'll be ordering bearings in about 20 minutes. however, my old 3.0 that i ventilated knocked for a solid three months of me beating it like a rented mule, and it finally gave up on life after multiple trips to 140...and i have witnesses. oh yeah, and when it started knocking, i yanked off the oil pan and confirmed it had indeed eaten a bearing and tore the **** outta the crank.

 

[SHO_91]

I thought about plastigage, but tend to agree with you. Without pulling the engine and crank, essentially to do a full rebuild, the measurement is useless. If the journal is in good condition and won't damage a replacement bearing, that's as good as it gets IMO. Knowing the exact journal diameter, whether or not it has a taper or is minutely out of round doesn't buy me anything. But if I decide to go ahead and pull the pan, I'll probably plastigage it anyway, just to confirm my belief that this is an original, unground crank, and know what the journal-bearing clearances are.

I believe that undersized rod bearings are marked as such (.25, .50, or .75 mm under), stamped on the outside of the bearing. It's really small lettering, so you might have to clean them up well and use a magnifying glass. If there is no indication that yours are undersized, then you have an original, unground crank and can save yourself the hassle of plasti-gaging. If, however, you have undersized bearings in there, then I'd probably plasti-gage one bearing with the same (new) undersize bearing that came out of the engine. Here is the excerpt from the SHO Engine Book (download from http://alfitz.com) regarding the clearance of the rod bearings to the crank:

Clearance to Crankshaft
Desired 0024-0.056mm (0.0009-0.0022 in.)
Allowable 0.08mm (0.0031 in.)

 

[pccorrig1]

This is great!!!

I have a complete set of Helms, but this is SHO specific, and explains things.

Thanks again!