Pupkin

Hi,

I noticed that I can turn the crankshaft 4 degrees without the distributor is turning. Engine is a 3.1 LH0 from 1990.

I guess that the timing chain become longer than it should be. Am I right? What is your experience?

Thanks.

maroe624

Timing chain needs replacement no doubt. Dizzy is supposed to turn at the same time you turn the crankshaft. Timing chain is stretched big time.

Six_Shooter

iTrader: (2)

I wouldn't instantly condemn the timing chain based on just this...

Yes there is likely some stretch, because they all stretch very quickly but then slow on the stretching from what I've seen.

there's plenty of slop in the parts between the crank and the dizzy, which cann all add up to cause what seems like excessive slop, but may just be the addition of all of the tolerance between the crank and the dizzy. I've had new engines give me some slop when performing the same inspection.

NoEmissions84TA

iTrader: (1)

I would not consider 4 degrees as being excessive.

OrangeBird

iTrader: (1)

Both you and Six Shooter are right on the money , even a brand new chain is gonna have some small amount of slack , were it 100% tight the friction would cause excessive wear . To move the crank 4 degrees either direction before distributor movement is seen is pretty much an indicator that the chain isn't worn very much at all , considering how small 4 degrees of movement actually is , coupled with the fact that the camshaft to distributor drive gears will naturally have a fractional degree of clearance between them as well (the normal very slight "backlash" of any mated gear set) .

Maybe the thread's first respondent mistook just how small 4 degrees of crankshaft movement actually is , considering the factor of two sets of backlash in the picture (the timing set itself and the distributor drive gearset) ?

Pupkin

So I understand that you guess that this 4 degrees are the result of wear of the engine components (dizzy, chain, crank gear and cam sprocket).

Still I think that the slack comes only due to worn gears and a worn chain. I can hear a "click" in the engine front cover when I turn the crankshaft forward or backward what is telling me that this is a timing chain / crank or camshaft gear issue. After the click the dizzy starts to turn what would not be in this way when the gear of the dizzy would be worn.


My 3.1 engine is 100,000 miles old and many people know that there is a timing chain problem with this engine.


Look at the worn gear at 22:30:

OrangeBird

iTrader: (1)

Well , it sure sounds as if you've got yourself convinced , despite a few informed opinions to the contrary , so by all means tear into it . Either way , it'll be good practice in replacing the parts (whether they actually need replacement , or not) .

PS , I've been around the GM 60 degree V6 for quite some time now and have never once heard a word about these having any kinds of chronic "timing chain problem" as you suggest .....

Pupkin

Ok, you have experience with V6 engines.


Please let me know why there are metal flakes in the oil pan of my engine (oil filter is clean) and why the O2 sensor signal is switching like shown in the attached picture.

OrangeBird

iTrader: (1)

Hi pupkin ,

Those metal flakes look like bearings to me , how is the engine's oil pressure , especially at idle ? If I'm seeing the picture correctly the flakes look to have a bronzish/brownish kind of color and that is my basis for suspecting bearings , either crank or cam . As to your 02 values being all over the place like that my #1 suspicion is the sensor itself , have you replaced it and the fluctuation persists ? I don't think the flakes and the fluctuating reading are related . Tell me , are there running issues your trying to track down or are these things you've found while looking around that are or are not showing symptoms in the actual running of the engine ?

W.E.G.

An oscillating O2 sensor waveform at idle is normal.

Your wave pattern looks a bit raggedy. My first suspicion as to the cause of the raggedyness would be vacuum leak.

Pupkin

The engine's oil pressure is between 45 and 51 psi at idle.




I thought this too, but in the Service Manual which I own is mentioned that "Four steel-backed aluminum bearings are used, with the # 3 bearing being the end-thrust bearing."


This is why I gave up thinking the flakes are a bearing problem.




Yes, I replaced the sensor an this raggedy fluctuating is still there. I also replaced the fuel injectors. The new injectors are from Standard Motor Products.




The engine of my car has not a good idle at warm coolant temperatures. I checked for vacuum leaks but could not find any.



I asked another Firebird owner to record the o2 sensor signal of his 3.1 engine. You can see how his signal looks like in the attached picture.


Compare the MAP signal of his engine with my engine also. You'll see that the "waves" in the picture of my engine are a little bit higher an longer.

OrangeBird

iTrader: (1)

Hi pupkin ,

I know it said steel backed aluminum , but I still believe the aluminum may be alloyed with a bronze type material , my reason for believing this being that I know of no other surface in the engine that would cause brown flakes like that . The distributor drive gears are hard steel and the timing chain and gears have no bronze looking elements in them either .

I am somewhat in the know about the mechanical aspects of the engine itself (I've rebuilt at least 3 GM 60 degree V6 engines over the years , rings , bearings , the "works") , but I will freely admit to you that I have not ever really delved into the ECM as to things like your 02 readings , so I will not offer comments on something I'm not 100% familiar with . My ego will allow me to tell exactly what I know , and also to tell exactly what I don't know , instead of "playing expert" where my knowledge is somewhat lacking . I do know exactly how it works "on paper" and can describe the basic operational function , but the fine tuning aspects of what each out of spec set of readings means VS actual troubleshooting diagnosis is far better known by guys like Six Shooter , who know every aspect of what tuning indication means what , since guys like him have delved into each and every line of code the ECM lives (and dies ) by .

I do wish you the best of luck with it and I hope if you need any hard & fast answers ECM wise the folks in the know will jump in and help you out

Pupkin

Hi and thanks.

What about the lifters? Do they have components which consist of a bronze type material?

zs&tas

They do not.