Intel's Ronler Acres Plant

Silicon Forest

Sunday, August 21, 2011

Chrysler Sebring 2.7 Liter V6 Assembly Notes

Installing the Camshafts and Timing Chains

Installing the timing chains was fraught with terror. I had two friends who did valve jobs on expensive overhead cam engines and both of them had to do the job over. Both of them did the job with the engine in the car, and they figured that if you didn't move the crank while you had the engine apart, it would still be in the right place when they put it back together. If both cases they were wrong. Once they had their engines assembled and turned them over, the mis-timed valves impacted the pistons and they all got bent.

This engine has dual over head cams, that is two camshafts per bank of cylinders. Two banks of cylinders means a total of four camshafts. Each pair of camshafts has a chain connecting them. The intake camshafts have a second sprocket that is driven by a chain from the crankshaft. So we have two separate situations that need to be coordinated.

Before we start putting anything together, we turn the crank so the mark on the crank aligns with the mark on the block. Normally I would expect this to put piston number one at top dead center, but not here! Shoot, none of the pistons are at top dead center. Oh! Clever devils! I see what they have done. With the crank in this position, all of the pistons are at least an inch down in their bores. So no matter what we do with heads and valves, there is no way the valves are going to impact the pistons. So we just need to not move the crank until we get the timing chains all installed.

Timing each pair of camshafts in a single head is not two difficult. Two of the links are marked and the sprockets on the camshafts are marked as well. Simply line up the marks and then mount the camshafts in the heads.

Now we can install the main timing chain and the large camshaft sprockets. This is a bit tricky. As I recall, the chain is draped over the rear sprocket and then dropped through the hole in the head. Then the front sprocket is inserted in the chain and fed upwards through the hole in its' corresponding head. Or maybe it’s the other way around. Whatever. Now the sprockets can be slipped on the camshafts where they are free to rotate. Now we can adjust the timing marks on this chain and these sprockets so they all line up.

Now we have a problem. The two camshafts in each head are in their proper relation to each other, and the main timing chain and all its' sprockets are all coordinated, but we still haven't connected the camshaft sprockets to the camshafts. This is done with a pair of bolts in each one. Unfortunately, with all the timing marks where they are supposed to be, the bolt holes do not line up. How effed up is that? The bolt holes are diametrically opposed, so the sprockets can be bolted to the cams in either of two positions. Either position will work mechanically because the crank makes one complete turn for each half turn of the cams. So icrank cannot tell if the cam is 180 degrees off. However, there is also the ignition timing to consider. Or what if we get one cam right and the other 180 degrees off? We might have a very rumbly engine.

In any case, the bolt holes were not that far off, and they were both off the same amount and in the same direction, so I simply went with the closer position. One problem is that one cam did not want to stay lined up. It was at a point where at least one of the cams was on the tip. As soon as you put it in position, the valve springs would cause it to move. The camshafts have square recesses to accomodate a square drive socket wrench extension, with that and a pry bar, you can rotate the cam into position and hold it there while you put the bolts in. A rachet won't work. As soon as you get to the position, the springs grab the cam and twist it away. Happens in both directions, hence my conclusion that it must right on the tip of the cam.

Installing the Crankshaft Pulley and Seal

Installing the crankshaft pulley and seal was a bit tricky. The pulley mounts on the end of the crank. The seal rides on a surface just behind the pulley, and slightly larger in diameter. The surface of the crank between these two area is beveled, so by turning the seal while pushing it will go right on. Unfortunately, the seal has to be mounted in the timing cover first, and the protrusions on the cover preclude any rotation while mounting it. If you just push the cover and seal into position, the edge of the seal will catch on the beveled lip on the crank and flip inside out. Somehow I imagine it will not seal effectively like that. Chrysler has a special tool for installing the crankshaft seal. I really don't want to buy one. I can't imagine ever having any other use for it. Besides, as specialized as it is, I am not even sure where I could get one.

So I improvised. I cut the ends off of a pop can and then cut about a one inch wide strip out of the side. I took the remaining piece, spread a little oil on it, wrapped it up on a circle and slipped it inside the seal. Spread the end of this rolled up piece of aluminum so it would go over the crank and pushed the timing cover and the seal into position. Then I pulled the aluminum piece out. Easy as pie. Don't know if it will actually seal or not. Seals are kind of funny. Old, ugly seals can work fine. New seals with microscopic defects can leak like a sieve. The seal suffered quite a bit of abuse while we were fooling around trying to figure out how to get it in position, and the edge of that aluminum is pretty sharp. I could have nicked the seal while I was pulling the aluminum shim out.

Installing the crankshaft pulley took a little work. It is a press fit on the perfectly round end of the crank, there is no key. There is bolt that holds it on. If the bolt had been just an inch or so longer, we could have used it to push the pulley on, but no, can't make it easy. I was able to knock it on using a block of wood and a small sledge hammer. Once I got it most of the way on, the bolt was able to grip the threads and push it home. There is a tab on the bottom of the timing cover you use with a screwdriver and one of the pulley's spokes to keep the pulley from turning while you tighten the bolt.

Wiring Harness

When connecting the wiring harness to the three ignition coils on the front bank of cylinders, I noticed that there were four identical connectors. This sucks. There is also a connector on a sensor mounted on the intact plenum that uses this same connector. So which one is the odd one? From this photo, I can see that the connector with the brown wire on top goes to the intake plenum. The ones with the green wire on top go to the ignition coils.


Ole Phat Stu said...

"I've been to church two weeks in a row."

Explanation : Charles is repairing a Chrysler Sebring DOHC engine and needs all the help he can get ;-)

Lorie Graves said...

Hi Charles my name is Grady Graves. I am working on a 2.7 liter engine.I timed the cam shafts with the plated links over the timing marks and the primary chain the way you illustrated. We then rolled the engine several revaluations to make sure the engine was free. When we rolled the engine back to the point where the timing marks on the primary chain were back in position. The timing marks on the cam shafts didn't line back up with the plated links on the cam chains. We set them at the rite position when we installed them. Is this ok or do I need to reset them?

Charles Pergiel said...

Yes, it is confusing. You set up everything just so, it all looks good and then you crank the engine over and nothing lines up anymore. The problem is the chain has a mind of its own. The crank sprocket has, what, 2 dozen teeth? The chain has like 200, and I am pretty sure the number is not an even multiple of the crank teeth. If you set it right and the chain hasn't slipped, it is still right no matter what the marks say.

Anonymous said...

I had the same issue turn up when I turned the engine over but it lined back up after another turn of the crankshaft. It should always end up with the timing marks realigned. it may go two complete revolutions of it may go four. But it has to be an even multiple or the timing would not work.

Valerie Bourque said...

Ok...very important question here...are you saying you turned the crank shaft with the chain off? And as long as it is turned in even multiples it is lined back up appropriately to install the chain using the marks??? So, like for instance the crank was accidentally rotated a partial turn without the chain, if I rotate it the rest of that complete turn and one more (2 total turns with chain off) it will undo the accidental partial turn and my timing will be safe???? Please advise!!!

Chuck Pergiel said...

Valerie - NO, do not turn the crank with the chain off. Once you have the camshafts installed, some of the valves will be open and projecting into the combustion chamber. Turning the crank will cause the pistons to impact the valves and they will get bent, ruining all your hard work.
1. Install the heads.
2. Set crank to mark.
From this point on DO NOT TURN CRANK
3. Install camshafts.
4. Install chains.
5. Make sure ALL marks are lined up.
NOW you can turn the crank.