Easy, quick engine question

Since I'm replacing the oil pump in my '87, I figured I'd go ahead & swap out the main & rod bearings. I ordered up a set and got started tearing down this morning. I got the main cap off & noticed that the bearing in it is labeled .010, the ones I got are standard size.

I pulled a rod cap off & it has a bunch of numbers on it but nothing that comprehends to .010.

Question is this. Is it safe to assume that since the mains are oversized, the rods are the same size? I have already re-ordered the bearings but wanted to make sure first. The engine is still in the jeep, just the oil pan is off.

Thanx,
Brad.

Bradzuki said:

Since I'm replacing the oil pump in my '87, I figured I'd go ahead & swap out the main & rod bearings. I ordered up a set and got started tearing down this morning. I got the main cap off & noticed that the bearing in it is labeled .010, the ones I got are standard size.

I pulled a rod cap off & it has a bunch of numbers on it but nothing that comprehends to .010.

Question is this. Is it safe to assume that since the mains are oversized, the rods are the same size? I have already re-ordered the bearings but wanted to make sure first. The engine is still in the jeep, just the oil pan is off.

Thanx,
Brad.

Click to expand...

No, it's not. Cranks can be re-ground to -.001", -.010", -.020", and -.030" as a rule, but how much they are undersized is going to depend entirely on what flaws want fixing. Get a micrometer and measure the thing, next time BEFORE you order bearings!

Also, if the mains are not significantly flawed but the rods have deep striations (for instance,) it's possible to get a crank reground -.001"/-.020". I've seen some odd stuff in buying crank kits, which is why I'll MEASURE the crank before I order bearings, or just get a full crank kit (which should come with bearings in the proper size.)

5-90

As 5-90 stated, the Main and Rod journals can be ground to distinctly different values than "Standard". To ensure to get the correct bearings, you will need to measure each journal to ensure you get the proper bearings.

Ron

Are you replacing the bearings as preventative maintenance just because you happen to have the oil pan off?!?!? If there's no problem with them, just put them back in and torque the caps properly.

If you need to replace your bearings, pull the engine, put it on a stand, yank the crank, and then measure everything with a micrometer.

Look on the right side of the block, near the distributor. If you have non-standard bearings, there will be some letter codes. You should see a small boss, probably with a recessed, square-drive pipe plug in it. The codes should be stamped in the boss, above the plug.

B = All bores 0.010" oversize

M = Main bearings 0,010" undersized

P = Rod bearings 0.010" undersized

C = Cam bearing bores 0.010" oversize

No, it is NOT safe to assume that if the mains are .010 undersize the rods will be the same. But the factory did send out engines with those non-standard sizes, always 0.010" off from standard. If you find the codes on the block, you should be safe to assume that you're the first person to be changing anything and you can order according to what the codes tell you the factory used.

Ok, thanks for the info. I was only changing the bearings because I had the pan dropped. I went ahead and changed all the mains but left the rods in after checking each one.

I did swap out one of the rod bearings with one of the new ones. I put some plasti-gauge on it and re-torqued it back down. It barely even touched the plasti-gauge, so I had .003 or more oil clearance. Since I didn't know what size I needed, I just put the old rod bearings back in.

Actually I did have another reason for at least looking at all the bearings. In the last week or so I've noticed a knocking sound. I thought it may be a bearing, so I figured while I had the pan down I would check them. All the bearings look fine but I've still got the knock. It's coming from the back, where the motor & trans. meet. Since I know it's not the motor, now I shift my attention to the transmission. Is there anything that would make a knocking sound in the front of the trans.? Torque converter maybe? The jeep runs & drives fine, but the knock is getting louder & happening more often. I'd like to find out what it is before I get left on the side of the road.

Thanks for any suggestions,
Brad.

Ok. Just got back from the local trans. shop. Guy there says it sounds like the flex plate has a crack in it. Does that sound right? Anyone ever have that problem? They want $250 just to drop the trans, not counting fixing whats wrong. I've got to get this fixed, already got reservations @ Crawfords for the Tellico run. Less than 2 weeks to get it fixed.

Brad.

Bradzuki said:

Ok. Just got back from the local trans. shop. Guy there says it sounds like the flex plate has a crack in it. Does that sound right? Anyone ever have that problem? They want $250 just to drop the trans, not counting fixing whats wrong. I've got to get this fixed, already got reservations @ Crawfords for the Tellico run. Less than 2 weeks to get it fixed.

Brad.

Click to expand...

Loosening bolts are a pretty common problem. You can check that without dropping anything. If you're lucky it may not be cracked. A search here might help. Or just wait until 5-90 checks back; I think he's dealt with this one.

Matthew Currie said:

Loosening bolts are a pretty common problem. You can check that without dropping anything. If you're lucky it may not be cracked. A search here might help. Or just wait until 5-90 checks back; I think he's dealt with this one.

Click to expand...

Yeah - a couple times.

First, check the four bolts holding the torque converter to the flexplate - they may be easily accessed by removing the inspection cover at the bottom front of the bellhousing, and manually rotating the flexplate with a screwdriver or somesuch. There are FOUR, and I have found it helpful to take some chalk when checking them, and make a mark AFTER I know it's torqued. I also remove the bolts (if it's the first time I'm doing it - no chalk residue) and apply LocTite #242 to the threads. I don't have the torque specs handy, I'm at school.

If all the torque converter bolts check out, grab a stout flatblade screwdriver and a good, bright flashlight. You'll want to watch the ENGINE side of the flexplate while you pry the flexplate AWAY from the engine - not too much, but enough to show cracks (which usually happen around the hub.) It's easiest if you check at each TC bolt - since you might be 180* away from the crack and miss it entirely otherwise.

If the flexplate is cracked, a new one is required. If you've got RENIX, you will NEED a RENIX flexplate, since the sensor trigger notches are different between RENIX and HO (so are the sensors, but that's another story.)

Also, if you remove the flexplate, replacing the retaining bolts is indicated. I don't know the part number for OEMR offhand, but they're threaded 1/2"-20, and 1/2" long. ARP makes a kit for Pontiac flexplates that works neatly - that's what I use as a replacement (I don't like for critical fasteners to fail...)

5-90