L98 Rod Bearings
Thread Starter
Heel & Toe
Joined: Oct 2018
Posts: 24
Likes: 0
L98 Rod Bearings
I just picked up my first Vette. 87'. The guy I bought it from thought he blew the motor. As it turns out it was a bit fo piston slap in cylinder one. Easy fix, right?
The question I have is that bearing in #1 is about 0.040 thick. #2 is 0.0605 thick. Both caps read the same ID, but I can't get my caliper to get a good reading on the crank (looks like 2.085 OD, hard to reach with a 6" caliper). It's obvious that #1 spun, no scoring (got lucky), but what size bearing should I get?
Thanks in advance,
MrN
The question I have is that bearing in #1 is about 0.040 thick. #2 is 0.0605 thick. Both caps read the same ID, but I can't get my caliper to get a good reading on the crank (looks like 2.085 OD, hard to reach with a 6" caliper). It's obvious that #1 spun, no scoring (got lucky), but what size bearing should I get?
Thanks in advance,
MrN
Melting Slicks
Joined: Jan 2014
Posts: 2,192
Likes: 381
From: Lunenburg MA
The crank needs to come out and get checked if it spun a bearing. Also the rod that spun needs to get resized. The bearings should all be the same thickness unless the factory chose a couple thousands over. It would be marked on the back of the shell if that's the case. I know it's tempting to do it quick and cheap, but you'll most likely be sorry if you do.
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
The crank needs to come out and get checked if it spun a bearing. Also the rod that spun needs to get resized. The bearings should all be the same thickness unless the factory chose a couple thousands over. It would be marked on the back of the shell if that's the case. I know it's tempting to do it quick and cheap, but you'll most likely be sorry if you do.
Le Mans Master
Joined: Feb 2005
Posts: 6,485
Likes: 566
From: Clearwater Florida
The crank needs to come out and get checked if it spun a bearing. Also the rod that spun needs to get resized. The bearings should all be the same thickness unless the factory chose a couple thousands over. It would be marked on the back of the shell if that's the case. I know it's tempting to do it quick and cheap, but you'll most likely be sorry if you do.
…. You can't just put a new bearing in after one has spun … the crank needs to be machined and ALL the rods need to be checked … it might be cheaper in the long run to get another short block … it will definitely be a quicker way to get the car back on the road again …..
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
The stock rod journal is 2.0893-2.0998. So spinning removed atleast .0043 off journal. Standard .001 and .002 could be used or mixed to clearance as a " band-aid" You really need a crank kit ( remanufactured crank with matched bearings) both rods on that journal should be reconditioned or replaced. When bearing spins it builds alot of heat. Some of that heat is transferred to the adjoining rod, sometimes it will fail shortly afterwards. Another thing to check in cylinder walls debris from failed bearing can pit cylinder(s). A earlier suggested a short block or crate engine could be a cost effective option for a long term repair.
Thread Starter
Heel & Toe
Joined: Oct 2018
Posts: 24
Likes: 0
The stock rod journal is 2.0893-2.0998. So spinning removed atleast .0043 off journal. Standard .001 and .002 could be used or mixed to clearance as a " band-aid" You really need a crank kit ( remanufactured crank with matched bearings) both rods on that journal should be reconditioned or replaced. When bearing spins it builds alot of heat. Some of that heat is transferred to the adjoining rod, sometimes it will fail shortly afterwards. Another thing to check in cylinder walls debris from failed bearing can pit cylinder(s). A earlier suggested a short block or crate engine could be a cost effective option for a long term repair.
MrN
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Thread Starter
Heel & Toe
Joined: Oct 2018
Posts: 24
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I checked. There is a lip between 1 & 2. Looks like the spun bearing wore 0.070. That seems crazy to me, but it is what it is. #1 on crank is reading 2.030 and #2 position is reading 2.100. However I checked rods and caps and they are good. Looks like I need a crank and bearings. Good thing this is a long term project 😁.
MrN
MrN
Last edited by MrNobody; Oct 3, 2018 at 09:09 AM.
Race Director
Joined: Feb 2008
Posts: 19,691
Likes: 322
From: Alexandria VA
First step: Quit using calipers. You really need to use micrometers for this situation; get yourself a nice set that can read in tenths (of a thousandth).
Second, crank MUST come out. Have it checked and best case, get away with a simple polish.
Third, none of this will solve your piston slap issue. That’s caused by the bores/piston being out.
For reference, on the last motor I did (LT4), which I pretty much did everything except a line bore (ran on the loose side), it was about $2500 including a decent set of new pistons. This included:
Punching 0.030” over w/ hone.
Polish crank
Installing new cam bearings
Hot tank
Checking the deck surface (didn’t redo)
Completely re-doing the heads including shimming the springs
Balancing w/ the FW.
Rod reconditioning
Pressing in the pins for the new pistons.
ARP for the rods.
You can see that unless you’re building the motor for a specific reason (mine is built to get beat on at the track), it may be easier to just buy a shortblock. You really need to be checking your journal sizes with the calipers. FYI, plastigage is pretty much worthless. You also need to get some rod/crank bearings. You’ll install and torque everything to spec. You then need to use a dial bore gauge (and your mic(s)) to get where you want to be.
Second, crank MUST come out. Have it checked and best case, get away with a simple polish.
Third, none of this will solve your piston slap issue. That’s caused by the bores/piston being out.
For reference, on the last motor I did (LT4), which I pretty much did everything except a line bore (ran on the loose side), it was about $2500 including a decent set of new pistons. This included:
Punching 0.030” over w/ hone.
Polish crank
Installing new cam bearings
Hot tank
Checking the deck surface (didn’t redo)
Completely re-doing the heads including shimming the springs
Balancing w/ the FW.
Rod reconditioning
Pressing in the pins for the new pistons.
ARP for the rods.
You can see that unless you’re building the motor for a specific reason (mine is built to get beat on at the track), it may be easier to just buy a shortblock. You really need to be checking your journal sizes with the calipers. FYI, plastigage is pretty much worthless. You also need to get some rod/crank bearings. You’ll install and torque everything to spec. You then need to use a dial bore gauge (and your mic(s)) to get where you want to be.
Last edited by RandomTask; Oct 4, 2018 at 10:23 AM.
Thread Starter
Heel & Toe
Joined: Oct 2018
Posts: 24
Likes: 0
UPDATE: Motor is out...I don't know that the previous owner changed the oil before he spun a bearing. Once I got inside of the motor, the oil was horrible. Also, all the other bearings looked like they could go at anytime. There was some serious contamination and deep scratches in the bearings.
Fingers crossed for a big commission check this month so I can get everything done before spring.
MrN
Fingers crossed for a big commission check this month so I can get everything done before spring.
MrN
Instructor
Joined: Apr 2018
Posts: 125
Likes: 20
Question for Random Task: It was my understanding that LT4 rods were not able to be reconditioned due to fracture design at the splitline...is this untrue or did you use different ones. I am going to be digging into my LT4 this winter I hope....
Thanks!
Thanks!
Safety Car
Joined: Apr 2005
Posts: 3,624
Likes: 431
From: Dale City VA
Now the GM LT1/4 and Vortec PM rods are not cracked cap. They use a thru bolt (not a cap screw) to align the rod cap and rod big end just like the old 1053 forged SBC rods and the bolts can be pressed out, the rod cap and rod big end parting lines machined flat and the rod bored or honed back to the factory housing bore ID and use regular rod bearings.
With the cost of new ARP rod bolts, $70 and the cost of rebuilding the rods, about $20 per rod.... I wouldn't recommend anyone to waste that kind of money on them.
Will
Last edited by rklessdriver; Oct 18, 2018 at 11:29 AM.