Where or how do I get the timing marks for my van? 1990 4.0 Aerostar Is there anything I should know before I put it all back together?

 

You don't have to take anything apart to check the timing marks. Clean the crankshaft pulley. Look at the crankshaft pulley and you will find a series of fine scribe lines with one central long one that should be marked TDC (Top Dead Center) and there should be a corresponding pointer directly above the pulley that also carries the CPS (crankshaft position sensor). Mark the longest one (TDC line) with white paint and a toothpick.

Remove the #1 sparkplug and insert a 3/16-1/4" wooden or plastic dowel rod until it contacts the piston. By turning the crankshaft pulley, you will be able to feel the dowel rod rise and fall (approx 2 inches) as the piston moves up and down. You want the piston positioned at the topmost portion of travel (TDC). Note: the piston moves into this position twice during the normal four stroke cycle. Once on the compression stroke, which is where you want to measure for TDC and once again at the end of the exhaust stroke and begining of the intake stroke. During the later, a valve is open and you will not "feel" the resistance that you will on the compression stroke. If you are unsure, have a helper work the wooden dowel while you rotate the crankshaft pulley in complete cycles several times until you get a feel for the difference in compression vs exhaust strokes. (The more sparkplugs you remove, the easier it is to turn the engine over.)Since the 4.0 lacks a distributor, there is no easy way to check for TDC.

It is essential you locate the piston exactly at TDC, a few degrees one way or the other will throw off your exam. Once you locate TDC, the longest scribe mark on the pulley and the pointer should match up. If they don't, your timing chain has slipped. Be sure you are not 180 degrees off, i.e. you are on the exhaust/intake stroke rather than the compression.

You can also do this with a timing light which produces a strobe light effect, "freezing" the crank pulley allowing you to see both the pulley scribe marks and the pointer while the engine is running. This sounds good in theory but is dificult on the 4.0 due to restricted access. You will notice on the CPS a short hollow tube. This is a plug in port for a remote sensor the dealership uses to test timing.

All the above said, throwing a timing chain is very rare on the 4.0 engine. This is the first such case I've seen addressed on this board or anywhere else. I would urge you to seek some local advice before tearing into the engine on the assumption it is the timing chain. Your inital post certainly sounds like a timing problem but it may be money well spent to rule that out. A badly worn timing chain or broken tensioner are harbingers of bigger problems to come.

Post back with your findings for future reference for others. Good luck!

 

[updated:LAST EDITED ON 03-May-02 AT 10:13 PM (EST)]Brought number one piston TDC on compression stroke, on a clock scale the pointer is at 12 and the harmonic balancer is at 3 o'clock about 90 degrees off according to the 0 to 10 degrees. Thats what I'm concerned about due to the fast spinning of the engine and the backfiring. It might even be a head gasket but with 300000 km on it I don't think it would hurt to change the timing chain. I never got to the timing chain yet due to the fact that I broke a bolt in the harmonic balancer. Once I put the new timing chain in is there marks on my new timing chain that will line up. That's what I'm looking for, I need the lineup marks so I can retime it. I like my van. I'll post again when I figure it out.

 

[updated:LAST EDITED ON 04-May-02 AT 08:43 AM (EST)]found partially burnt wire crank shaft position sensor it hooks up to the pointer would that be the problem its all one piece explain how it works i wont do nothing else until i know for sure is there a way i could test it or find a quick fix thanks

 

The worn wires were the problem. It got so bad all three wires shorted out. I'm not sure what they were rubbing against. If you have the same problem check this out first before ripping it all apart. It sucks. Thanks again for all your help.

 

Glad to hear the problem you found was a "simple" fix. Better than a tear down. The wires could have been damaged in the past from a broken serpentine belt.