4 degrees of "Play"

[6=8]

In checking into why my 87 GN is failing CA smog test, I used a Cam Sensor Adjustment tool to confirm my sensor is adjusted properly. This went as expected… Adjustment was OK, but I noticed something while cranking the engine by hand, and need to see if anyone has run into this.

When I turn the crankshaft by hand and then reverse the direction, I read 4 degrees of “Play” before I encounter serious resistance.

I assume this is timing chain “Slack”, aggravated possibly by a worn or missing chain tensioner.

From a SMOG TEST standpoint (I have an ongoing thread in the emissions area) I am blowing high HC's (Just enough to Fail). My ECM is seeing some of this, and pulling fuel out by lowering the BL to the lower limits at 15 and 25 MPH. This was why I was checking the Cam Sensor.

My question here is 4 degrees of play in the timing chain acceptable? I don’t think this is normal, and a see myself replacing the roller chain with a replacement steel + tensioner but wanted more opinions.

Especially any opinions regarding this amount of play affecting the Injector Timing enough to make it run rich!

So, could this 4 degree "Play" be affecting the injector timing enough to cause a rich condition?

Let me know what you think... Anyone else notice this much rotational play when cranking an engine (165K mi) over by hand?

 

[Ormand]

Don't think 4 degrees will affect injector timing enough to change emissions. If you have that many miles on a timing chain, it is most likely time to change, however. I'm not sure about the technique you used to measure slack, but still, more than likely the chain has stretched, and even a brand new chain has a little slack. The emissions would seem more likely to be from fueling or ignition issues, not related to the timing chain.

 

[6=8]

Thanks for the reply!

The method I used to measure the play was this:

Rotate the crank until Harmonic Balancer mark aligns with 0 degree mark.
Reverse rotation direction until "Serious" resistance is felt.
Read the timing mark again, which read 4 degrees.

 

[cruzn57]

Ca smog

what is your idle set at?
I believe you are allowed up to 1200, or 1500 rpm
run it up as much as the test will allow, (which ever it is)
the Hc and CO, will both clean up noticeably! NOX should reduce also,
its just a matter of being more efficient.
if you have an adj fuel pressure reg, drop the press from what ever you are running now, as much as 5 lbs, it will lean it up a bit,
but...... do not go too lean or you'll develop a lean miss fire, which will send all the numbers soaring!
good luck
cruzn57

 

[Nick Micale]

...................My question here is 4 degrees of play in the timing chain acceptable? I don’t think this is normal, and a see myself replacing the roller chain with a replacement steel + tensioner but wanted more opinions.
......................

This is normal, chain is not necessarily bad. The window on the cam sensor in NOT just off-on, it takes some rotation to put out the light.

 

[Blown&Injected]

Sounds like you are saying you have 2* +or -.

No big deal, my very young double roller chain had a fair amount of motion in it - a lot like a very old chain.

I have a .006 under chain on the engine right now, never run, and the degree wheel says about +or- about 1* but like I said - Never run at at -.006, it is TIGHT! I just installed it. I only degreed it because I'm doing a build journal with pics and the degree wheel with magnetic base dial indicators looks like such a special operation.

BTW, I found that my cam was at 110* on the intake center line set up straight up on the dots. It should be 112* and since I have a timing set that enables one to go + ot - 2, 4, 6, or 8*, I retarded the cam 2* and it came out to 112.25*, Very close.

Then I thought, these are such low RPM engines that I will never be short on top due to the cam so I probably should have just left it advanced a couple of degrees - it will loosen up anyway and it will help lower down - BFD!! each degree moves the power about 25 or 50 RPM's.

 

[6=8]

Thanks! I feel a bit better about it. Just kind of suprised me.

cruzn57: The test is on the "Emissions Dyno" at 15 and 25 MPH, and my idle test is not failing. Runing the idle up probably wont do much for the tests?

On a side note: I am seeing a fair amount of OIL on the intake side of the turbo (Seeing this with the MAF pipe removed.)

I'm going to look into this now. If i'm not mistakin, buring oil will show up as increased HC in the emissions test? I'll see what my Intercooler has in it tonight to see if this might be a bad turbo seal. I'm moving back to the Emissions board for this question!

Thanks for all the feedback guys!

 

[cruzn57]

Times Have Changed

when I lived in calif, I ran a smog inspection & repair shop,
I knew they were going to update the testing procedures, but never followed up.
retarding the timing always cleaned up the exhaust, (later burning caused more cyl heat, and less NOX)

let me know what you find out, who knows, someday we might have smog testing here!

Good luck
cruzn57