MrNobody

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

jv9999

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.

aklim

I'd just get a crate motor. I really don't like different sized bearings.

C409

….. …. 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 …..

Kevova

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.

MrNobody

Thanks. I appreciate the input. Money is more important than time. With that being said, I want it done right.

MrN

MrNobody

The bearing spun on when the car shut off and parked (supposedly). I pulled #2 as well and it was clean and smooth. I am going to get a difference caliper or mic to verify my readings (just for education). Everything thing looked clean and all the debris was in the pan as far as I can tell.

MrN

mickey5

Is the journal tolerance spread really .0105 (2.0893-2.0998)?

mtwoolford

look at the back side of the bearing shell; it should be stamped "STD"; ."001 OS", ".010 OS" etc.; that's the clue you're looking for.

Kevova

right out of the FSM. Alot more than I expected.

MrNobody

RandomTask

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.

MrNobody

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

C4Newb

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!

rklessdriver

The cracked cap PM rods can be rebuilt..... but you bore the big end oversize to do so and they require special oversize OD rod bearing shells. Availability of these oversize bearing shells is very limited in some applications.

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