timing question 4.0 SOHC | Ford Explorer Forums - Serious Explorations

  • Register Today It's free!

timing question 4.0 SOHC


Well-Known Member
November 25, 2010
Reaction score
City, State
Prattville, Alabama
Year, Model & Trim Level
1997 XLT; 325,000 miles
My third chain tensioner has just went out so I replaced that. At the same time I thought that since this was the third time doing this the jack shaft chain may have stretched. So I replaced it also without locking down the cams. I did mark everything to make sure I put it together the same way I took it apart. I did get it started but ran like crap. Turned it off to check everything now it won't start. Here is my question if I remove only the main jack shaft bolt to replace the chain can the driver side cam rotate on its own?

Join the Elite Explorers for $20 each year.
Elite Explorer members see no advertisements, no banner ads, no double underlined links,.
Add an avatar, upload photo attachments, and more!

Yes, without using the special tools to hold the camshaft, they will move when you loosened the jack shaft bolt,

Well I took it all apart again and it did jump time. From what I can tell the passenger side chain is where it should be. On the drivers side it looks like it jumped one or two links. From what I can tell each of the cams have notches that are off center and these are used for the cam tool to lock into. Am I right to assume that the cam offset notches should be on the bottom?

I do have the crankshaft at TDC

If I remember correctly, yes the notches are on the bottom.

timing slots

The camshaft timing slot should be below the axis of the camshaft and parallel to the head surface that mates with the valve cover.

I doubt the chain jumped teeth on the sprocket. The camshaft probably just rotated from compressed valve spring pressure since there was nothing to keep it in position once the jackshaft sprocket retaining bolt was loosened.

Thanks for the pic 2000StreetRod and both of you confirming the cam position. Right now I am working on making some temporary fixtures to hold the cams in place so they don't rotate while I put the guide and tensioner on. The hard part will be to get the driver side cam in the correct position without changing the passenger cam position or moving off of TDC. Am I correct to assume that the driver side cam gear that drives the cam is not keyed? It is held in place once you tighten the jackshaft bolt.

not keyed

As I recall the only timing chain related components that are keyed are the crankshaft sprockets and the jackshaft sprocket that rotates the chain to the driver side camshaft sprocket. The design allows camshaft timing flexibility but is a pain to time according to factory specification.

Well I got it all put together and its running. But it is running rough. My question is where is the cam sensor located and does each side have its own?
I checked for spark and I have that and when pull the wire you can smell gas. So I know I have spark and fuel.

camshaft position sensor

The camshaft position sensor is located on the driver side (left) camshaft. There is only one (blue arrow).

When cylinder one piston is at TDC on the compression stroke the camshaft position sensor should be in the position shown and the right camshaft timing slot should be below the camshaft axis and parallel to the head surface that mates with the valve cover.

The engine will start and run (poorly) with the camshafts 180 degrees off (one slot above and the other slot below camshaft axes).

I worked on it this weekend and found a vacuum leak. Fixed that and it helped some also replaced one bad plug. It ran a bit smoother

Next pull valve covers

Well finally got the valve covers pulled off to make sure everything was right. I put the crank at TDC and checked the passenger (right side) cam and that matches what is shown in the picture. On the driver (left side) cam it is off just a hare, about 3 degrees. My question is will this small variation cause the rough running or should I be looking for something else?

3 degrees x 2

Since the crankshaft rotates twice as fast as the camshaft the 3 degrees represents 6 degrees of crankshaft. There's only one camshaft per bank so the timing between the intake and exhaust valves doesn't change but when they open relative to the crankshaft does. Also, if you didn't use the timing tool kit was the traction side of the chain taught? The spring in the hydraulic tensioner is not strong enough to keep the chain taught on the traction side. The actual timing can be observed by holding the crank from rotating while attempting to rotate the camshaft in the normal direction until the traction side of the chain is taught. It could show that there is more error or it could eliminate the error. Depending on the direction of the error the idle could be better than stock or worse. Some Mustang owners advance their camshaft timing 5 crankshaft degrees to improve the top end performance at the expense of idle.

Thanks for the explanation and would explain why it ran down the highway fine but did not idle worth a crap.

I did a compression check today and found that the middle cylinder had no compression. The other two cylinders had a compression of 115 psi average. So the cam being off is mute now as I have to pull the head. Hopefully its not a hole in the piston but just a bent valve or blown head. All I can say is FML.

Well I pulled the head off and all three pistons showed signs of the valves hitting them. But the middle one hit hard enough that it bent the valve. Funny thing was only the intake valves hit the exhaust valves showed no signs of hitting the piston.

So now the question is should I]
a) Do a valve job on the head
b) Buy a reman head
c) Replace the motor

Any input is appreciated.

Well I went ahead and had the head worked on and put it all back together. The Ex is running good now and hopefully better once the computer makes its adjustments. Thanks to everyone who helped me get it back on the road.