3400 timing chain noise and slack, causes?

[kflo 93 gt]

For starters the engine is a late model year 03 3400 that came out of an 04 Grand Am. The engine has 38k miles on it, and I've only owned the engine for less than 3 weeks - during which time its sat on an engine stand catching cleanings, parts, and awaiting install.

Anyways, I went to install my crank scraper earlier this evening and it installed without a hitch. On the test rotations there was no noise from the engine what so ever. But, after I got the main cap bolts torqued back down to 37 ft lbs + 77 degrees, I turned the engine over and it was making noise from the timing cover. In the midst of getting pissed I figured it was the timing chain, so I pulled the cover and sure enough the timing chain now has some slight slack and it hops enough to make a fairly loud noise 2-3 times per revolution of the engine.

I'm pretty baffled and wondering what the consensus is here on what went wrong... It's a low mile engine, clean as a whistle inside, and I don't think that my installing of the scraper would give any ill effects like this. I've got a lot of years turning wrenches and what not so I don't think I noobed anything to death... Any input at all from anyone with any ideas is going to be super helpful because I'm feeling pretty upset right now.

[ForcedFirebird]

Is the tensioner on?

[kflo 93 gt]

Actually... is it a hydraulic tensioner? If so I'm a dumbass because I didn't have the oil pump or driveshaft installed at the time.

I'm going up to the garage now to see if that's the deal.

[kflo 93 gt]

The tensioning shoe was never off of the engine... I've looked at as much as I can without taking the heads off and it seems like a stretched chain or worn gears are the culprit. I've got a video of the noise watch the left side of the chain and you can see it hopping. It's a .MOV video which is quicktime, but most newer versions of media player will play it.

http://kflo.berettaspeed.com/3400swap/chainslack.mov

and here's a picture of the actual slack itself, never mind my shitty camera.


A new timing chain is $45 for a Cloyes, so I'd try that if it's the problem. The gears don't seem worn, and so far the only reply I've gotten on another forum was from loner the rmt corsica guy who said he didn't change gears, just the chain when he did his. Should I look into changing the gears as well, or would just the chain be the place to start?

[PCGUY112887]

http://autorepair.about.com/library/images/bl438lib.htm

Apparently up to 12mm is fine... seems like a lot but my 3500 chain looked very similar, a bit tighter than that I believe. It only had 10k miles.

[ForcedFirebird]

I bought some aftermarket (cheap) gearsets, they will work. I think the last set I bought was like $40 from Discount. This was for a stock engine, if you are building something nice....

the slack doesn't look bad, but who am i to know?

[kflo 93 gt]

Well, today I was messing with it some more and the chain jumped a tooth and set the cam and crank 1 tooth off of timing. So after that I ordered a new timing set from Cloyes. $105 for a chain and the 2 gears.

What is the timing procedure for setting the timing when it is off like this? Does the crank need to be at a certain point to be able to rotate the valvetrain back to where it needs to be? Or does one leave it at TDC on the crank and then set the cam into time?

I don't have any of my service manuals with me so sorry for the noobish questions.

[PCGUY112887]

I was told to take the dot on the crank sprocket, and the line on the cam sprocket, and line them up to point at eachother in the center.

[kflo 93 gt]

I put the new gears and chain on earlier, that was most definitely the problem. The engine is now silent again with the new chain and gears. I'll take a pic of the new stuff tomorrow to show slack differences if anyone cares.

[ForcedFirebird]

Pics are good.

[kflo 93 gt]

[ForcedFirebird]

Yeah buddy!

[kflo 93 gt]

Heck yeah, thanks for your help and suggestions too man. I really appreciate it.

[bszopi]

Not to rain on your parade, but I'd look at that chain in ~15k or so. I had a Cloyes setup on my 3100 when I replaced the cam. When I swapped in the 3400 ~20k later, I looked at the timing set. What I found was a chain that was looser after ~20k than the stock chain had been after ~85k. Needless to say, if I ever have to replace a chain again, I will be going with a set from the dealership.

[kflo 93 gt]

Thanks Brad, I'll keep that in mind for sure. The thing is, as often as I drive this car it will be 5 - 6 years before it sees 15k miles.