Every once and awhile the question gets raised if it's possible a 2.8 has jumped it's timing chain. There are a number of people on here that swear up and down that it is impossible, and they will argue with you to no end.

Well here's proof that it can and does happen.

With the timing chain and gears properly installed, the dots on both the cranskshaft and camshaft gears point up at 12 o'clock with number 1 cylinder at TDC - Top Dead Center. With number 4 cylinder at TDC, the dots point towards each other- crankshaft gear at 12 o'clock, and the camshaft gear at 6 o'clock.

In these pictures I set number 4 cylinder at TDC to get better view of the dots in refrence to one another. The timing chain has jumped 2 teeth.

The chain doesn't look quite 2 teeth out due to the amount of wear on the camshaft gear and chain as seen in this next picture.

Here is the amount of stretch due to the worn chain and gears.

In this picture you can see the chain hanging well off the back side of the crankshaft pulley.

Here is the inside of the timing cover, you can see the timing chain has never made any contact with the timing cover.

Hopefully this will clear up the common mis-conceptions and opinions that the 2.8L timing chain will not jump it's timing.

BTW, this is only the 2nd 2.8 that I've seen actually jump the timing chain in over 15 years of working on Fiero's daily, it doesn't seem to be a real common problem.

This car came into the shop with no power and no ability to rev over 3500 RPM, and a rough idle. Checking ignition timing showed it set at 31°. Compression was 150 psi at the lowest cylinder with the chain that way.

Maybe this is off topic but why the helll would they make it si both dots face up in stead of towarsd each other if the timing marks are in the inside? What happens if they are pointing toward each other? Will it cause a thump or misfire? Can this be corrected without opening the engine again?

Wow, that timing chain is REALLY loose! Get a Cloyes double-roller and be happy.

Yeah, here's what the timing chain in my '86 looked like:

The chain would jump if the crank was turned backwards for any reason, but it seemed to hold time when turned in the normal direction of rotation.

Even so, that was a LOT of slop:

Ed

quote Originally posted by goatnipples2002: Maybe this is off topic but why the helll would they make it si both dots face up in stead of towarsd each other if the timing marks are in the inside? What happens if they are pointing toward each other? Will it cause a thump or misfire? Can this be corrected without opening the engine again?

?

If you turn the crank 360 degrees, the cam mark will be up too. Turn the crank 720 degrees, the cam turns 360 degrees.

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It's always possible for timing chains to jump. I dont know why some insist it's impossible. I have a 87 Oldsmobile with a 3.8L V6 thats jumped time. It bent some valves when it did it too.

quote Originally posted by goatnipples2002: Maybe this is off topic but why the helll would they make it si both dots face up in stead of towarsd each other if the timing marks are in the inside? What happens if they are pointing toward each other? Will it cause a thump or misfire? Can this be corrected without opening the engine again?

quote Originally posted by elly2m8: With the timing chain and gears properly installed, the dots on both the cranskshaft and camshaft gears point up at 12 o'clock with number 1 cylinder at TDC - Top Dead Center. With number 4 cylinder at TDC, the dots point towards each other- crankshaft gear at 12 o'clock, and the camshaft gear at 6 o'clock.

As stated the only difference is #1 and #4 being at TDC, therefore, it makes no difference. It will not cause a miss fire. I build all my engines At #4 TDC, adjust the proper valves turn crank 360* (#1 TDC) and finish the valve adjustments. That way I know where to index my distributor without question. NO correction is necessary as both statements are true.

A stretching timing chain is not an unusual occurance. We've seen this on many different vehicles. A little stretch can be tolerated while excessive stretch will cause the chain to jump links. Best to inspect everything and replace gears and chain when this happens. Usually the timing chain really shows wear after 100,000 K miles but frequesncy of oil changes can influence things..

I was one of the doubters a couple of years ago, but something I had never considered was the fact that the chain becomes slack when the transmission turns the engine, rather than the engine turns the transmission, as for example in sharp deceleration without braking. This was a concept I had never considered, and I now,as a while ago, admit that it is possible for the chain to jumpa cog, or more, under these circumstances.I think the likelihood of this happening, would be sharp decelleration, from high to no throttle in a low gear.I am glad I learned something here, and am glad to admit, again, I was wrong.
https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20040710-2-043998.html

Nick

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fierofetish.PFF'S self-confessed Snowbird!!

Responsibility: the solution for our World's Dilemmas..

[This message has been edited by fierofetish (edited 08-30-2005).]

I'm a believer. It happened to me at around 135K.
It's waaay down on the troubleshooting list too.
And one way to get a new water pump.