Monday, April 17, 2006

Setting the timing on a 1991 Pontiac Sunbird

The question (from Mike):

I drive a 1991 Pontiac Sunbird with a 4-Cylinder, Overhead Cam, Throttle-Body-Injection engine. Something I've noticed in the past is that when the car is working, the Timing Belt Marks on my camshaft and crankshaft aren't aligned the way the manuals tell you they should be for proper timing (yet the car an for at last 15000 miles like that - hey I just bought it that way).

Recently I lost a Timing Belt Tensioner, which threw my timing all out of whack, and when I returned it to it's proper timing the way the manual suggests (by lining up the timing marks with the marks on the rear Timing Belt Covers), I find that the vehicle won't start; it just stutters and backfires.

My question is: how can I get my car back into timing if I can't use the timing marks for reference?

Yikes. An automotive question.
Huh.
Mike, I'm going to have to really research this. As Austin Powers would say, "it's not my bag, baby."

But I'll dig around and see what I can find for you!

UPDATE #2:
Okay, Mike. As I said, I'm not a car guy. And I never purported to KNOW the answers to everything, just FIND them.

So, here's what an expert says about your situation:

You have to make sure the you have TDC on the correct cylinder, or the timing will be WAY off. The timing maks must line up correctly, but also at the proper time, which is why they are called timing marks.

For instance, the TDC mark will line up when the #1 cylinder is at TDC, and also when the #3 cylinder is at TDC, but the valve timing will be completely different at those two times, becuase one cylinder will be at the of its compression stroke, and the other will be at the end of its exhaust stroke.


I really have no idea what any of that means.
But it sounds good to me!

Please let me know if this helps at all.
I'm still consulting my resources . . . I'll see if anyone else has anything to say.

4 Comments:

Anonymous Anonymous said...

This site rocks. I really hope the traffic here gets big enough to make it really interesting.

5:26 PM  
Anonymous Anonymous said...

That's exactly what I needed to hear.

All it means is that in your car, you have two spinning shafts that have to be perfectly aligned, but one shaft takes two rotations to complete it's cycle. and the other only takes one (which I didn't know). So even though my marks on these shafts are perfectly aligned, one of them is an entire 360 degree revolution off. If he's right (and I think he is), all I should need to do is spin the 2-cycle shaft an entire 360 degrees and I'll be perfectly in time again.

I'll let you know what happens!

12:48 PM  
Blogger Tom said...

Please let me know if it works.
This could be my first actual success!

2:07 PM  
Anonymous Anonymous said...

I plan on jumping into this project this weekend, so I'll let you know what happens.

Could you ask your expert, however, how many different positions my cylinders could be in when the timing marks are aligned? I believe it's just two: once when the #1 cylinder is at Top-Dead-Center, and once when the #3 cylinder is at top dead center.

I want to say that (as long as my timing marks are correct) that if my timing marks are properly lined lined up and I still have a timing problem, all I should need to do is either rotate my Crankshaft Sprocket (the small wheel, to use my previous analogy) 360 degrees and bring them back into alignment, or rotate my Camshaft Sprocket (the big wheel) 180 degrees, and all will be good in the world again.

Please bear in mind that the only thing I know about cars it what I've learned by being too cheap to see a mechanic :)

Thanks!

9:33 AM  

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