And what are the symptoms and how do you correct it?

Thanks, Ced

 

when i was very young i had a 1967 mustang that was a constant battle to keep running. radiator hose split, i had no money, so i spliced in a section of PVC. after running a short time the PVC pipe melted, spewed out coolant, and not being in a conditon to notice the engine finally died.

like i said, very young, dumb, full of stupidity;

next morning i towed the car home, would not start; turned out timeing was like almost 180 degrees out!!!!!!!!!! reset timing and it ran fine for years.

at any rate, loose timing chains can cause timing jump, but somehow that night my timing jumped, and i to this day cant explain that.

 

A timing chain jumping would cause cam timing change, a real problem! Jumped timing could happen if the distributor hold-down bolt/clamp was loose.

 

loose timeing chain will cause problems no doubt;

never thought of a loose distributor clamp, but obviously it would do it;

when mine overheated to the extreme, none of those factors were obvious, but perhaps after the engine cooled the timeing chain stretched eased ????????????

 

Nope. If you have loose timing chain, it will be that way 'till you replace it.

 

Hmmm.. I wonder if it could be that the distributor isn't dropped in completely?

 

A motor can jump time for several reasons.....
The chain can stretch with mileage and with wear (esp. if you have heavy valve springs). Along with this the gears it runs on wear and get thinner. All this causes the chain to get loose which in extreme cases it will slip over a tooth or two or "jump time". Some of the timing gears have a plastic covering over the teeth so they will be quieter and sometimes this plastic will shell off and jump time. If you have these conditions hard acceleration can cause it to jump when just normal driving it may run a long time. A backfire can stress a chain and cause it too. The real problem comes in when if it does jump time and it does it more than a few teeth your pistons can strike a valve and bend them or break a piston. If you have one of the nylon covered gears and you find there are any teeth missing you had better drop the oil pan and clean out the debree. Otherwise, your oil pump will suck a piece of it up and lock the pump....had this happen once myself....motor will stop though so you likely wont smoke it, unless by some way your dist. is still able to turn in which case the motor might still run a while.

If you is wondering if yours is too loose you can tell by several methods. With dist cap off, slowly move crankshaft back and forth with a socket on the center crank bolt. If you can move crank more than a degree or two without the dist shaft moving you likely have worn and stretched parts. You can also see a loose chain with a timing light. At idle, ie. no engine load, your timing mark seems to float back and forth rather than be steady. You should also be able to see this with a vacuum gage. The needle will not be steady.
Hope this made scense.
Correct it with new chain and gear and quit hot roddin your vette.

 

Well a degree wheel can accurately show it but u can get eyeball close with just dist rotor.
Since i know when #1 is TDC (with TDC gauge in plug hole) the dist rotor should 10* before either #1 or #6 - where i set it with my timing light. I can verify which set of vlvs are closed (on cam base circle) by turning the p-rods and which vlvs are rocking (in overlap and p-rods tight). The cyl with vlvs closed should have the rotor pointing at it (trying to fire) while cyl in overlap should have rotor pointing 180* away. What i like to do is take a long straight edge like a yard stick and align it with the rotor pointer way out on the fender or where-ever and leave a tape marker to better judge angles - compare to the dist cap terminals (again marked with a long straight edge).

Now i can verify every cyl through the firing order (18436572) on the dampner at every 90* (turning CW facing mtr or CCW from drivers seat). My Streetdampner has timing marks at 0*, 90*, 180*, 270*. I'm not bragging just its easy to do with a piece of caulk and marking the dampner with 2 simple 90* lines X crossing the center.
Take notes and write down what the vlvs are doing and where the rotor is pointer every 90* crank turn. Now that rotor will turn only 45* for each 90* turn of crank. Notice the rotor turn only once for every 2 turns of crank.

Now say that dist slipped in just 1 tooth off. Well with 13 teeth on dist gear then 360*/13 = 'bout 28*/tooth. What i'm saying is that if ur only off by <30* its probly 1 tooth off. If 180* +/- 30* then dist installed 180* off.
And if ur notes show ur shut vlvs don't match ur rotor position for the entire firing order u have a timing chain/gear set problem.

This all sounds like a lot of work but really much easier than pulling the timing cover.

Hope this helps. cardo0

 

Good response
I have beat my brains out, trying to correct those problems.
Not trying to start a chevy/ford war, but i have only had problms with Ford blocks.

 

The symptoms are lousy gas milage and less performance.
Change the chain and sprockets.
Usually its slack in the chain but it can skip teeth too.

Taking the engine apart for a timing chain change is short of changing the cam only by taking off the valve covers and intake. Your almost there and is a good time to do this if your wanting to do it.

I'm pretty sure you can see the chain and sprockets through the fuel pump mount. Poke the chain for slack and check the teeth on the sprockets. Usually factory setup so the plastic teeth only have the metal core.