Main Bearings Replacing
Thread Starter
Advanced
Joined: Oct 2019
Posts: 62
Likes: 2
From: Kissimmee, FL
I would like it to be either one of those, but I'm not hearing the sound from there; hearing it under the left side under the valve covers. Not a "click click" though, as I was hoping maybe a valve loosened up, but a knock. I replaced the alternator about 6 months ago; no issue there and the tensioner also seems fine. Granted, this has not been confirmed by a mechanic. I'm just going by my research having compared the sound I'm hearing to "spun bearing" clips on YouTube.
Sure would like this to not be a spun bearing, but as the oil pump has been acting irregularly for the last 4 months (that was the next replacement in my restoration), it seems likely that a bearing has gone bad.
Sure would like this to not be a spun bearing, but as the oil pump has been acting irregularly for the last 4 months (that was the next replacement in my restoration), it seems likely that a bearing has gone bad.
Race Director
Joined: Apr 2003
Posts: 17,697
Likes: 1,666
From: moraga ca
I would like it to be either one of those, but I'm not hearing the sound from there; hearing it under the left side under the valve covers. Not a "click click" though, as I was hoping maybe a valve loosened up, but a knock. I replaced the alternator about 6 months ago; no issue there and the tensioner also seems fine. Granted, this has not been confirmed by a mechanic. I'm just going by my research having compared the sound I'm hearing to "spun bearing" clips on YouTube.
Sure would like this to not be a spun bearing, but as the oil pump has been acting irregularly for the last 4 months (that was the next replacement in my restoration), it seems likely that a bearing has gone bad.
Sure would like this to not be a spun bearing, but as the oil pump has been acting irregularly for the last 4 months (that was the next replacement in my restoration), it seems likely that a bearing has gone bad.
Le Mans Master
Joined: Feb 2005
Posts: 6,475
Likes: 564
From: Clearwater Florida
..... If you have spun a bearing you are not going to get away with simply replacing the bad bearing ... you will need to take the crank to a machine shop to have them grind the crank smooth again and replace the damaged connecting rod ... that is , if its a bad rod bearing ... if its a main bearing that has spun it gets more interesting ... either way , the engine comes out of the car ... time to consider another short block .....
Thread Starter
Advanced
Joined: Oct 2019
Posts: 62
Likes: 2
From: Kissimmee, FL
..... If you have spun a bearing you are not going to get away with simply replacing the bad bearing ... you will need to take the crank to a machine shop to have them grind the crank smooth again and replace the damaged connecting rod ... that is , if its a bad rod bearing ... if its a main bearing that has spun it gets more interesting ... either way , the engine comes out of the car ... time to consider another short block .....
Melting Slicks
Joined: May 2014
Posts: 2,876
Likes: 588
From: New Port Richey FL
Before jumping to conclusions, pull the pan pull some caps and look for the grooves that was mentioned in a previous post if they are there plan a complete rebuild. If the crank is smooth Not Blue Stained. Clean up the crank and Plasi Gauge test all surfaces for fit of the old set if exssive fit new bearings, also look at piston skirts for cracking.
if an automatic look at the Flex Plate for cracking or Loose Bolts Before pulling the pan.
. But in the long run it is best to overhaul if you are having a inside Engine problem.
if an automatic look at the Flex Plate for cracking or Loose Bolts Before pulling the pan.
. But in the long run it is best to overhaul if you are having a inside Engine problem.
Last edited by s carter; Jan 17, 2021 at 12:32 AM.
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Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Some good points made. Cut the filter with shears or something that doesn't produce shavings (i.e. don't use a dremel). I'd also say throw on a mechanical oil pressure gauge, and run it with the belt off (won't hurt it to idle for a little bit with no belt) to rule out accessories.
I don't think the dual mass flywheel was introduced until '89 with the ZF6.
I've replaced bearings on my 1990, and it wasn't too bad. I have a whole thread on it, but I knew nothing back then so it's a lot of me just being dumb. I've summarized the important parts:
I don't think the dual mass flywheel was introduced until '89 with the ZF6.
I've replaced bearings on my 1990, and it wasn't too bad. I have a whole thread on it, but I knew nothing back then so it's a lot of me just being dumb. I've summarized the important parts:
- Disconnect the battery. You'll be working by the starter, and you do NOT want to short it to the frame through a tool. Not that I'd know.
- Take off the front crossmember braces. Two 18mm nuts on the front crossmember, and a couple of smaller bolts on each frame rail (terminology?).
- Take off the metal oil cooler line that runs under the pan. Hopefully you don't have one - this part was pretty annoying. I don't recall the specifics, but taking off a hose connection that has had 25 years to weld together is no fun.
- For some reason I'm thinking I had to take off the starter? Should be pretty apparent if it's in the way.
- Unbolt the pan. Pretty straightforward. There are a few studs, which in my case came out with the nut. No biggie.
- Throw a breaker bar on the crank pulley and rotate it so the pan will slide out between the crank and the front crossmember. It would be nice to have some help for this; I remember it taking a bit of tweaking to get it past the counterweights.
- Take off the windage tray if you have one. I ended up needing a 5/8" crowsfoot adapter because the standoffs on the bolts were so long. You can take them off with a wrench if you're strong, but you'll need the crowsfoot to put them back on with a torque wrench.
- Replace one set of bearings at a time. Do not remove multiple main caps at once. This increases strain on the crank and gives the possibility of mixing the caps up.
- Note the orientation of the main cap.
- Take the main cap *most* of the way off, then gently tap it side to side till it works loose. If you take the bolts all the way out, you're gonna end up dropping the main cap right on your face/the concrete. Bad either way.
- Might want to plastigage the old bearings just to have a frame of reference. Your call.
- Remove the old bearings. Easy enough for the shell in the cap, but the one in the block is a little tricky. You can either make a flexible shim to tap it out with a hammer, or you can make a small pin (I think I make one out of a nail) to put in the crank's oil hole and roll the bearing out by rotating the crank. I first tried the former, but I ended up doing the latter.
- Install the new bearings. Make sure they're tang-to-tang.
- Plastigage the new bearings. This is a must. Google the proper clearance here.
- Some people will say you should replace the main cap bolts. Up to you; this is only 100% necessary if the bolts are torque-to-yield (mine weren't).
- Torque the bolts to spec. If using a crowsfoot, make sure it is perpendicular (90°) to your torque wrench so you're not changing the length of the lever arm.
- Check the endplay of your crank. Google this.
- Some people would say you should replace the oil pump. I did, but I'm not sure it was really that beneficial.
- Put everything back together.
- If you have an oil cooler, it's going to have a bunch of crud trapped in it. I tried and tried and tried to flush mine, and it just kept dumping crap out the other end. If I had to do it again, I'd flush it with a solvent (probably gasoline) rather than motor oil or send it to a sonic cleaning company.
Last edited by C4ProjectCar; Jan 17, 2021 at 12:02 PM.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,216
From: Park City Utah
Good idea, right here. Way less work to diagnose. ALSO, run the engine and kill one cylinder at a time by pulling or better, grounding w/a test light, one spark plug wire at a time. If you have a spun bearing, the knocking sound will change or go away when you get to the cylinder affected. If a crank bearing, sound will change when you get to a cylinder next to the main bearing.
Car a stick of auto? On an auto, a cracked flex plate will make a knocking sound that is very similar to a bad bearing sound. Easy to drop the dust cover and look.
Car a stick of auto? On an auto, a cracked flex plate will make a knocking sound that is very similar to a bad bearing sound. Easy to drop the dust cover and look.
Instructor
Joined: Aug 2024
Posts: 107
Likes: 71
Some good points made. Cut the filter with shears or something that doesn't produce shavings (i.e. don't use a dremel). I'd also say throw on a mechanical oil pressure gauge, and run it with the belt off (won't hurt it to idle for a little bit with no belt) to rule out accessories.
I don't think the dual mass flywheel was introduced until '89 with the ZF6.
I've replaced bearings on my 1990, and it wasn't too bad. I have a whole thread on it, but I knew nothing back then so it's a lot of me just being dumb. I've summarized the important parts:
I don't think the dual mass flywheel was introduced until '89 with the ZF6.
I've replaced bearings on my 1990, and it wasn't too bad. I have a whole thread on it, but I knew nothing back then so it's a lot of me just being dumb. I've summarized the important parts:
- Disconnect the battery. You'll be working by the starter, and you do NOT want to short it to the frame through a tool. Not that I'd know.
- Take off the front crossmember braces. Two 18mm nuts on the front crossmember, and a couple of smaller bolts on each frame rail (terminology?).
- Take off the metal oil cooler line that runs under the pan. Hopefully you don't have one - this part was pretty annoying. I don't recall the specifics, but taking off a hose connection that has had 25 years to weld together is no fun.
- For some reason I'm thinking I had to take off the starter? Should be pretty apparent if it's in the way.
- Unbolt the pan. Pretty straightforward. There are a few studs, which in my case came out with the nut. No biggie.
- Throw a breaker bar on the crank pulley and rotate it so the pan will slide out between the crank and the front crossmember. It would be nice to have some help for this; I remember it taking a bit of tweaking to get it past the counterweights.
- Take off the windage tray if you have one. I ended up needing a 5/8" crowsfoot adapter because the standoffs on the bolts were so long. You can take them off with a wrench if you're strong, but you'll need the crowsfoot to put them back on with a torque wrench.
- Replace one set of bearings at a time. Do not remove multiple main caps at once. This increases strain on the crank and gives the possibility of mixing the caps up.
- Note the orientation of the main cap.
- Take the main cap *most* of the way off, then gently tap it side to side till it works loose. If you take the bolts all the way out, you're gonna end up dropping the main cap right on your face/the concrete. Bad either way.
- Might want to plastigage the old bearings just to have a frame of reference. Your call.
- Remove the old bearings. Easy enough for the shell in the cap, but the one in the block is a little tricky. You can either make a flexible shim to tap it out with a hammer, or you can make a small pin (I think I make one out of a nail) to put in the crank's oil hole and roll the bearing out by rotating the crank. I first tried the former, but I ended up doing the latter.
- Install the new bearings. Make sure they're tang-to-tang.
- Plastigage the new bearings. This is a must. Google the proper clearance here.
- Some people will say you should replace the main cap bolts. Up to you; this is only 100% necessary if the bolts are torque-to-yield (mine weren't).
- Torque the bolts to spec. If using a crowsfoot, make sure it is perpendicular (90°) to your torque wrench so you're not changing the length of the lever arm.
- Check the endplay of your crank. Google this.
- Some people would say you should replace the oil pump. I did, but I'm not sure it was really that beneficial.
- Put everything back together.
- If you have an oil cooler, it's going to have a bunch of crud trapped in it. I tried and tried and tried to flush mine, and it just kept dumping crap out the other end. If I had to do it again, I'd flush it with a solvent (probably gasoline) rather than motor oil or send it to a sonic cleaning company.
Melting Slicks
Joined: Nov 2016
Posts: 2,193
Likes: 3,020
From: So Cal
2023 C4 of the Year Finalist - Unmodified
Instructor
Joined: Aug 2024
Posts: 107
Likes: 71
The engine sits on pads from the crossmember. The braces are below these pads. The engine stays put, sitting on the pads. << I know this is true for the late crossmember used with ZR-1/LT5 and the LT1/LT4 because I've had the braces off of both of these. I'm not sure about the earlier L98, because I haven't had the braces off an L98 car.
1992 LT1
My 1996 LT4
My 1996 LT4
Melting Slicks
Joined: Nov 2016
Posts: 2,193
Likes: 3,020
From: So Cal
2023 C4 of the Year Finalist - Unmodified
L98 with KC4 oil coolers have the pipe under the oil pan. They also have the air tube to the rear cat converter visible to the inside of the exhaust pipe. LTx don't have oil coolers or air pipes. L98 have different braces and crossmember than LTx, including LT5.
Last edited by IHBD; Dec 30, 2024 at 08:47 PM.
