I'm considering changing out my rear main seal, due to suspicions of leakage. I have the engine out right now with tranny and everything off of it, so it's a good time. Is there anything in particular I should know, watch out for, etc.? I have never done this job. It's on a 383 stroker.
Thanks, Patricia

If it's a late model block it's a one piece seal, goes in around the crank from the back side. Use a little loctite on the outer surface and drive it on straight with a suitable sized seal driver. If it's an early block it's a 2 piece seal, the rear bearing cap must be removed and the seal worked around the upper bearing. The bearing cap must be installed with a little RTV sealant, but you must be very careful not to get any RTV on the seal itself. Usually the seal kits have detailed instructions on how to install and where to place the RTV. There are also some little strip things included in the kit that aid in working the seal around so it's not damaged. The smallest little nick will probably come back and haunt you. The hardest part will be removing the old upper seal half, you might need to get a little puller that is sort of like a cork screw. It threads into the edge of the seal so you can pull it around and out. Be sure to re-torque the bearing cap using the proper procedure. ARP bolts are torque to yield and it's a 3 step process to get them properly tightened. Factory bolts are not torque to yield. Normally an engine builder would include the ARP bolts in an engine like this.

It's a 2-piece rear main. I'm actually not sure if it's leaking; my pan and valve covers were definitely leaking, but I don't know if the rear main seal may also have been leaking. I do know that the 4-speed I had in the car had an out-of-round input shaft, which we did not realize until it had been with that engine for 5000 miles, plus it was speedshifted some. So, out of prevention I'm thinking of swapping it now while it's easy. However, if I were to leave it in the hopes it's okay, what kind of job would it be to swap it out later? One source I read mentioned needing to remove the bellhousing's dust cover, while the other source said nothing of it. I will be installing a Lakewood scattershield which is, of course, 1-piece with no dust cover to remove, so it would mean tranny and clutch removal IF it's true you have to normally remove the dust cover. Is that the case, or can the job be done merely removing pan and pump?
Thanks, Patricia/'75 w/aftermarket crate 383

It's certainly a LOT easier to do with the engine out of the car, especially if it's on a stand. Sounds like the car was run pretty hard, might not be a bad idea to have an engine builder mike out the bearings and crank to make sure everything is allright. How many miles and what was the oil pressure like? Any grit or metal laying around the inside of the oil pan? How about crank end-play? any noticeable end play could be problems.

It's a new engine; it only has 5k miles on it. All those miles were with the 4-speed in it which we later found out (after continuous issues with popping out of gear) to have an out-of-round input shaft. I bought the tranny as a rebuilt unit to replace the sad original; he figures the tranny must have come out of a car that had a bang-up. The case showed no damage but that input was messed up.
Yes, there would be a little bit of metallic sludge on the magnetic drain plug on oil changes, but then perhaps some of that is from breaking in? Engine ran like a champ. I did play with it a bit, such as revving to 5k rpm and popping the clutch for some fun take-offs, plust some speed-shifting, but I didn't do it very much. Mostly it was around-town driving. It leaked like a sieve, but I found the oil pan bolts to be way too loose and the cork gasket was soaked. I changed it to a silicone 1 piece and I swapped out the valve cover gaskets, too. I just really want the thing to be dry so it doens't leak all over my new susp.

I would at least check for any crankshaft end play and see how the rear main looks while you have it apart. Might not hurt to look at the front main as well as it is farthest from the oil pump. You wouldn't think there could be very much wrong with a 5,000 mile engine, but a whole lot of things can happen.

Is it possible to describe in a few words how to check crankshaft endplay? And what do I look for with regard to bearing condition? I'm not familiar with the guts of a motor just yet. My main concern is that this engine lasts about 5 years for me, after which time I ought to have $ for something more interesting. So I'm not overly worried about really high mileage on this one.

Any play that you can actually see and feel while forcing the crank end for end is reject. Look for any unusual wear marks on the bearing and crank bearing surfaces whil you have the bearing caps off. Any wear marks would at least be an indication you will need to go farther and get an engine builder to measure things out. Those bearings should be barely broke in with only 5,000 miles.

|UPDATED|1/21/2004 4:37:25 AM (AZT)|/UPDATED|

Big Fish:

A little clarification here. What does ARP stand for and please define "yield" and the three step process for torqing the bolts...Thanks.

Mike

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Mike

First, if you loosen all of the crank main bearing caps, just a few turns of the bolts, then pull on the crank away from the block, the top of the rear main pulls out very easily. A bit of motor oil on the new one and it slips back in easily. Of course you need to retorque all of the main bolts.

Three step. First run all of the bolts down, and make sure the caps are seated. Then tighten the bolts down to about 1/2 of the torque spec. Then step to about 3/4 of the torque spec. Now tighten to full torque spec. Retorque and double check. I know that's more than three, but it will assure everything is correct. I always do any torque in this manner.

Remember do each part in a pattern. Don't torque one cap or one bolt all the way then go on to the next. Do every bolt one step before doing any of the next ones. Then do all the next step on every bolt, etc. If you don't keep it even, you could create a failure even when the final torque is reached. Don't overtorque. Even if you loosen the bolts and retorque the bearing , or in some case gaskets, can be overcrushed and will never be correct.

Ken Styer

ARP is a manufacturer of high quality fasteners used mainly in racing engines. Their fasteners are made to stretch ("YIELD") at full torque. This keeps better holding pressure against whatever application they are used for. Ken gave a great description of how to torque standard "factory" bolts and fasteners. Find out if you have the ARP bolts and if so, please post here and I will type up the procedure for torquing them, it's somewhat lengthy.

Since I've got a non-stock 383 stroker, do I follow torque recommendations for a 400, since I have a 400 crank? Actually, I don't know if a 400 was a stock motor in a Vette, so I'm not sure where I find proper torque value for my 400 crank...?

Patricia/75

Since it's a 350 block, I would use the specs for the 350.

Why would you consider not changing a $5 oil seal when you have the motor apart? You wouldn't want to pull the motor or pan again to do it later.
Make sure you put A LITTLE sealer on the ends of the new seal, and on the rear bearing cap/block surface.
Joe

The procedure for torque to yield bolt depend on the very specfic bolt. Not just the size. All bolts stretch when tightened. When loosed, they return to their original shape. The is the elastic properties of the bolt. If it does not return, it will stretch again, weaken, and fail. The reason we torque the bolts is to get it in the correct range, but more so, to determine the clamping force of the bolt. How hard it's twisted really does not matter, except that the only way we can determine how hard it is clamping.

Torque to yeild bolts are different. They are tightened to the point of passing the elastic point of the bolt. It stretches, and does not return. As it starts to stretch, it "Yields" or will only clamp so hard. As we turn it more, it will maintain the same clamp force until we go to far, stretch it too much, and it gets weak. This very exact amount of plastic stretch gives us a very exact of clamping force. Much more accurate than a standard bolt and torque.

These bolts are usually tightened to a given torque to make an initial adjustment, then turned a given number of turns so it will stretch and clamp properly. This varies with each design bolt and application. Go by the mfg of the bolt, and their procedure.

The advantage, much better, more accurate. Disadvantage, only one or two uses, then throw it away and get new ones.

Ken Styer

Should I use Loctite blue (242) on the bearing cap bolts when changing out the rear main seal?

If my torque wrench is not perfectly calibrated (probably isn't), I suppose there could be some torque variance between the rear main bearing cap I work with and the other bearing caps the mfg. torqued (and which I would not touch). For instance, if the rear main cap ends up being a few ft*lb tighter or looser than all the others due to wrench calibration differences, would it wear that bearing out faster than the others or put extra strain on it? The alternative would be to loosen all bearing caps and re-torque them all with my one wrench so they'd all be identicle. Should I bother to do that? I don't have a feeling for how touchy these things are.

Thanks, Patricia/'75 with 383 that probably isn't leaking but whose seal may have been abused by an out-of-round tranny input shaft for 5k miles

I would rather see you use a torque wrench you can trust. Have yours calibrated, or test it compared to a known accurate one.
If the bolts are too loose, the bearing caps will not properly crush the bearing, and it will spin and fail. If the bolts are too tight the bearing may overcrush and not have enough clearance, and wear out quickly. Locktite on the bolts will not affect the bearing crush. This is a fairly exact requirement with out much "fudge factor". If you are more than 10% off you may have a failure. Better to be less than 5% off. If your torque wrench is off, loosening all the caps and retightening will only create the problem at all the bearings, instead of just one.

Ken Styer

I wouldn't mess with the other bearing caps unless you decide to remove all of them to allow a little clearance for installation of the rear main seal. Loctite certainly can't hurt, make sure you get the studs and nuts really clean to get the stuff to take.

Ken, thanks for explaining about the caps' torque being critical. I did not know whether the cap's torque or whether the cap-to-block mating surface dictated the bearing's tightness. I was hoping the cap's "parting line" that butts against the block was what set the bearing tightness and the bolts' torque was merely a matter of the cap not coming loose. I'm glad you clarified it's the caps' torque which dictates the bearing's tightness.

Now I'm curious: When rebuilding an engine do you ever re-machine the area of the crank that sits against the bearings (like if the crank got damaged with a bearing failure)? If so, doesn't that tweak with the bearing's tighteness when you use standard cap bolt torque?

BigFish thanks for your help; I'll plan on using 242.

Man, maybe I should leave my seal alone; I didn't realize I could mess up a bearing if something went wrong or if my wrench isn't perfectly calibrated. I'll have to stew about this one.

Don't stew about it. Take your time. The most important thing is to assemble everything CLEAN. Dirt will ruin the job. Just borrow a good torque wrench and compare it to yours. Mine acutally reads about 10% off, and I compensate for that when I do the work. You'll do fine. And it is easier to install the rear main seal if you loosen all of the caps. The crank will lift a bit, and allow the seal to go in easier. Just torque them back when you are done.

As for a repair to the block the machinist do what is called line bore. The bearing caps are bolted back in place. The the block and caps are bored in a stright line and even size. When putting the crank back in a "oversized" bearing is used. This means the outer wall of the bearing is a larger size, to make up for the metal cut from the block. If the crankshaft itself is machined to make a better surface, the bearings are "undersized". The inner measurement is smaller to match the crank size. Both work very well, and many sizes are available. This does not match new spec, but is just as good. Many crate motors are engines that have had a problem when made, and have had that corrected with different size bearings and or pistons. Not a thing wrong with them, they just don't match OEM spec in the new car.

Ken Styer

Ken, I went out and bought myself a "Real" torque wrench today-a Proto. I think I can trust it right out of the box. I had suspicions my older Craftsman wrench may have needed calibration. Thanks for the help, Patricia