OK all you engine rebuild gurus, and especially Colonel Ken, I have a question.

Today I changed the thermostat and oil in my Atlas I-5 3.5 liter engine in my 2005 Chevy Colorado. When changing oil and filter I always start the engine, see that the pressure comes up on the gauge and then look at the filter to make sure it is not leaking. This time I was under the front of the Colorado and Laurie happened to be nearby. So I said to her "please start the engine and verify the oil pressure comes up. I remained on the floor looking up at the filter. When she started the engine, the crank pulley moved to the rear about a 1/4 inch during cranking and immediately returned forward on start up. I had her do this start / run / shut down sequence 4 or 5 more times and the pulley did the same thing every time. (1/4" back during cranking and return 1/4" forward while running.)

I then took a screwdriver and tried moving the pulley (and crank) by hand and it easily moves forward and backwards without the engine running. The pulley retaining bolt is tight to the crankshaft.

I have never seen this before.

I have no engine running, oil consumption, oil pressure, or oil leak complaints.

Is this something normal?

Ken,

That sounds as weird to me as to you. I'd check the end play specs and
overhaul procedures for that engine before getting too concerned. I just
called John Beaver, my engine builder friend, to ask him -- and caught him
in his deer stand whispering into the 'phone that disturbed him right as he
saw a nice buck.

​He'll call me later. If he's not too ticked off at me, he may be able to
help. :-)​

Ken H.


On Wed, Nov 26, 2014 at 12:27 AM, Ken Burton wrote:

> OK all you engine rebuild gurus, and especially Colonel Ken, I have a
> question.
>
> Today I changed the thermostat and oil in my Atlas I-5 3.5 liter engine in
> my 2005 Chevy Colorado. When changing oil and filter I always start the
> engine, see that the pressure comes up on the gauge and then look at the
> filter to make sure it is not leaking. This time I was under the front of
> the Colorado and Laurie happened to be nearby. So I said to her "please
> start the engine and verify the oil pressure comes up. I remained on the
> floor looking up at the filter. When she started the engine, the crank
> pulley moved to the rear about a 1/4 inch during cranking and immediately
> returned forward on start up. I had her do this start / run / shut down
> sequence 4 or 5 more times and the pulley did the same thing every time.
> (1/4" back during cranking and return 1/4" forward while running.)
>
> I then took a screwdriver and tried moving the pulley (and crank) by hand
> and it easily moves forward and backwards without the engine running. The
> pulley retaining bolt is tight to the crankshaft.
>
> I have never seen this before.
>
> I have no engine running, oil consumption, oil pressure, or oil leak
> complaints.
>
> Is this something normal?
>
> --
>
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I just realized that this pulley is part of the harmonic balancer. I checked the movement at the pulley face, but I never really looked at the bolt going through it as I moved the pulley backward and forward. I will go out again tomorrow and move it backwards and forward while looking at the bolt holding it to the crank.

I may luck out and find that this is a harmonic balancer problem. I just can not buy that the crank end play is that far off and I have no other symptoms. This is a really strange condition to me.

It is 1 AM and it is 23 degrees outside, so I'm going to bed and I'll look at it some more tomorrow.

Yes, It only has 111K on it and I intended to keep it for another 100K. My Blazer is at 240K. Laurie's Jimmy is at 140K.

My biggest problem at this point is nobody I know is experienced or knows anything about this engine line. I also do not understand what exactly would need to be done. I haven't checked but I think the pan could come off without pulling then engine. It is 2 wheel, rear wheel drive and not much is hanging under it to block it's removal. I also do not understand exactly where the bearing with the thrust surfaces we are discussing is located. On an airplane engine it is located up front and is part of the front main bearing. It is quite beefy because the propeller is pulling on the crank all the time. On an automotive engine there is no pulling on the crank. So I'm imagining it is a much smaller surface and probably is in the rear. I guess I'll have to learn more about it this winter. If it could be replaced with the engine in the vehicle, I might be willing to attempt it.

I guess right now I'll just continue driving it.

Maybe it will go another 100 K. without me doing anything.