Cliff Harris

I had an oil leak that seemed to be coming from the front of the engine. I couldn't be sure if it was coming from the front main seal or from the front of the oil pan.

About 10 years prior to this the outer ring of my harmonic balancer came loose and walked into the front of the timing chain cover, grinding a hole in it. I patched it with JB Weld because I didn't want to pull the oil pan to replace it. That patch might also be the source of an oil leak.

I decided to replace the timing chain cover and the water pump (since it was 116K miles old and I would have to remove it anyway). While I was in there I thought it would be a good idea to replace the timing chain (since it also was 116K miles old).

The instructions on how to remove and replace these items are described in the FSM (Factory Service Manual) in several places. I found that some of the steps shown in the FSM are not necessary.

The job can be divided into two sections: removing the oil pan and removing the components on the front of the engine. You must remove the oil pan to get the timing chain cover off because they interlock. That's not 100% true, and I have heard of people removing the timing chain cover without removing the oil pan but I wouldn't do it that way. I have also heard of people loosening the oil pan bolts and dropping the pan slightly so that the timing chain cover can be removed. I think this would result in dirt getting into the oil pan so I didn't want to do it that way. The basic procedure here is remove -- clean -- replace. For brevity, I will describe how I deviated from the FSM procedure. These notes apply to what I found while I was working on my 1986 Corvette. Obviously variations seen in other years will affect the procedure.

Removing the oil pan
The procedure is on page 6A1-16 in the 1986 FSM.
Step 4 says to disconnect the transmission oil cooler lines. There is not enough room to do this because the clearance between the transmission and the transmission tunnel is too small to get a wrench on the cooler line flare nuts. I believe they put in this step to make it easier to get the flywheel cover off. I have taken it off several times by pushing the cooler lines out of the way, and that's what I did this time.
Step 5 says to disconnect the catalytic converter AIR pipe clamps at the manifold and exhaust pipe. I did not disconnect the AIR pipe at the manifold. I did remove the clamp on the exhaust pipe because the AIR pipe interferes with access to one of the starter mounting bolts.
Step 6 says to disconnect the wires at the starter. I did disconnect the positive battery cable but couldn't easily get to the solenoid wire so I left it in place. In retrospect, I don't think it's necessary to remove any wires.
Step 8 says to remove the starter. I did not do this because the solenoid wire was still attached and the trans cooler lines were in the way. The starter sits nicely on top of the trans cooler lines and the AIR pipe so it doesn't really need to be removed. It DOES need to be unbolted because there is not enough room to access the pan bolts with the starter in place.
Step 9 says to remove the oil filter. I did this but I don't recomend it. Oil will drip out continuously while you're working, which is very inconvenient. There is plenty of room to access the oil pan bolts, so I don't see the need to do this.
Step 10 says to disconnect the oil cooler line at the block. I did this because I wanted to remove the oil cooler just to see what it looks like and to replace the gasket. I don't think this step is necessary.
Step 14 says to remove the front crossmember braces. I did not do this and had no problems with clearance. I did find that one mounting nut was loose.
Step 16 says "Rotate crankshaft". They don't tell you where to rotate it TO. My engine just happened to be at TDC on cylinder #1 when I took it apart and I found that I could get the oil pan off without rotating the crankshaft.
Step 17 is Remove oil pan. I don't recommend this, as oil will drip from everywhere. I dropped the pan down a couple of inches to allow the timing chain cover to be removed. I was surprised to find that the oil pan gasket was a one-piece unit. I thought that technology came much later.

Removing the timing chain cover
From page 6A1-13 in the 1986 FSM.
A note here: loosen the water pump pulley bolts before removing the serpentine belt. It's a lot easier with the belt holding the pulley in place. If you're going to reuse the water pump then you don't need to do this.
Step 1 says to remove the torsional damper. I have always called it a harmonic balancer. I have had a Proto 4005 "harmonic balancer puller" for many years, but the bolt was too long and interfered with the steering rack pipes. I bought a Lisle 45500 "harmonic balancer puller", which has a shorter bolt and it worked fine for me. One thing to watch out for is to NOT use the tapered part that goes into the corresponding part of the crankshaft. You WILL mess up the harmonic balancer bolt threads if you do this. I suggest a flat washer between the tapered part and the crankshaft. The Lisle puller has a flat piece that presses against the end of the crank, so it avoids this problem.
Step 3 says to remove the AIR pump pulley. I did not do this.
Step 6 says to remove the AIR pump. I did not do this.
They don't mention the serpentine belt tensioner, but I removed it. That may not be necessary, but I think it would interfere with the A/C accumulator.
Step 8 says to remove the rear A/C compressor braces. I only saw one brace and I did not remove it. I did remove the bolt that goes through the brace and the AC compressor.
There is one A/C compressor mounting bolt that I could not remove because it hit the valve cover. I loosened it and left it in place.
Step 9 is remove lower A/C compressor mounting bolt. This bolt is hidden underneath the compressor pulley and is very difficult to see. It is a Torx T-40 bolt. I found the hole to be full of grease and dirt, so it's important to clean out the hole before attempting to remove it to prevent stripping the hole. This is an interesting bolt, because there is a flat ground into the head. Without that flat part you will not be able to get the bolt out because it will hit the A/C compressor pulley. You will have to turn the bolt so the flat faces the pulley to get it out.
Step 13 is remove AIR hose at right exhaust manifold. I did not do this.
They don't mention the AIR solenoids and valves, but they ("it" if you have an '89 or newer) must be removed.
Step 14 says to remove the compressor mounting bracket. This is rather difficult, as the fuel lines and the catalytic converter AIR pipe run up through it and the compressor is very heavy and quite tightly tied in place by the refrigerant lines, which aren't very flexible. Working the bracket off the water pump studs was also a challenge.
Step 15 says to remove the upper AIR pump bracket and power steering reservoir. I did not do this.
Step 16 says to remove the lower AIR pump bracket. I did not do this.
Step 19 says to remove the water pump. I found that I could not get a socket on the lower bolt on the driver's side because the power steering pump pulley was in the way so I used a wrench on that bolt.

Removing the timing chain
An extra couple of steps here that will make things easier later. Before removing the timing chain, make sure the timing marks on the crankshaft gear and the cam gear are lined up EXACTLY. Make sure there is a little slack in the timing chain on BOTH sides. This will make it much easier to mount the cam gear.

Now for the pictures. Here is the reason I was replacing my timing chain cover. A 10 year old repair (that actually worked out quite well). You can see where the harmonic balancer outer ring was rubbing against the cover. If you look closely you can see the shiny area where the oil was running down from the front main seal.



A little slack in the old timing chain. The new chain had some slack in it too, so I'm not really sure the old one was all that bad. The slack will affect the cam timing a tiny bit and the ignition timing will also be off a little. The important part is the driving side between the crank and the cam sprocket (which was tight in this picture). It effectively divides the slack in half.



These marks MUST line up perfectly. I once put together an engine and somehow got the cam gear off by one tooth. It ran OK but didn't have anywhere near the power it should have.



I recently found out that the timing mark on the harmonic balancer does NOT line up with the keyway in the crankshaft. From my research I have found out that it varies from 2° to 10° to 50°, depending on year. For our L98s, we're at 10° and the timing mark lines up with the edge of one of the ribs, as shown here with the rule aligned with the rib. This is how you can tell if your harmonic balancer outer ring has shifted.



I decided to replace the oil cooler hoses "while I was in there". I was surprised to find the original one was molded in one piece.



I took off the oil cooler because I wanted to replace the gasket. The center "bolt" has a snap ring on it to hold it in place. I thought it was strange that there is no snap ring groove. It just grabs the bolt and is held with spring tension. The oil cooler construction is interesting. It has a stack of "washers" with holes in them that cause the oil to flow through the cooler in a convoluted path.



Several things are going on here. I painted my new Stewart water pump with POR-15 to help keep it clean. The shaft on the pump was too long and the water pump pulley did not fit. I had to cut 3/8" off the shaft.
The new GM timing chain cover did not come with a timing tab, so I had to buy an aftermarket one that is attached by a couple of the timing cover bolts.
I put a timing tape on the harmonic balancer for future reference. A LOT cheaper than having it machined. I hope the tape holds up.
The harmonic balancer does not appear to be installed all the way onto the crank (because it isn't at this point) and that was also true after I got it tightened down. The pulley ended up in the right place, so it's obviously OK. I think the aftermarket timing tab is too skinny to give the correct geometry. I have a theory that the rear of the harmonic balancer should line up with the hole(s) in the timing tab (my old one did, and I have seen several photos where it did). This is an indicator that the outer ring hasn't shifted toward the timing chain cover (they always seem to go in that direction -- good thing).
What I'm showing here is the method for installing the harmonic balancer. The stock harmonic balancer bolt is too short to draw the harmonic balancer onto the crank. I bought a longer bolt with the same threads and used a stack of washers to pull it on. In this picture it is about 1/4" away from its home position.

84wuzmy1st

When I read stuff like this I feel like a got a hold of the Half-Blood Prince version of the FSM.

Great info, thanks for posting it up.

MrWillys

It is my understanding that the 10* off keyway mark on the harmonic balancer was used from 69 through 91. 68 and older lined up with the keyway.

The picture you show seems a bit odd, so I went and looked at mine. My balancer is about a 1/2 from the timing cover, and my bolt on timing tab comes to within 1/4" of the front of the balancer. The tab could simply be being made by different manufacturers.

Also, there's two bolt holes near the bottom of the block on the passenger side. The upper one sometimes gets drilled through to the mechanical fuel pump shaft hole, and may leak oil. It is always good practice to put a 3/8"x5/8" in this hole to avoid possible leakage.

Cliff Harris

I saw a post on another forum from a guy who had the harmonic balancer with the timing mark at 50° (his timing tab was at the top of the timing chain cover in the middle -- he didn't mention what kind of vehicle it was). Somebody said GM moved it because the accessories get in the way of seeing the timing mark in what we think of as the "normal" position.

That timing tab is a Mr. Gasket 4592. I bought a GM timing cover and it came without a timing tab. I have never seen a GM timing tab as a piece by itself, though you would think they would be needed if the covers don't have them. It really bothered me that the harmonic balancer didn't seem to be all the way on, but all the pulleys line up and I've been driving it and the belt has stayed on. I remember thinking that maybe the balancer was hitting the key for the crank timing chain sprocket, as it was sticking up a little. I remember when I took it apart the rear of the balancer was right in the middle of the timing tab hole, like this one:



I took another look just now and it appears that the timing tab is not parallel with the cover. It appears to be bent toward (and almost touching) the cover. I haven't looked at the timing yet, so I don't know how that might be affected.

From what I recall, there was no bolt in that hole. Whatever, I've had this car since 1985 and it's never leaked from there so I think I'm OK. There is a corresponding pair of holes on the driver's side. I have a vague recollection that very early Corvettes had motor mounts bolted to those holes.