simple question

[drayrunner]

I am going to advance the cam in my 02 malibu 3100 using a offset key on the crankshaft. will somebody tell me if i'm right or wrong. turnig the cam against rotation using a bushing will advance the cam,so using a offset key on the crank i should rotate the crank with rotation right or wrong. If thats not correct can someone explain the correct way. thanks

 

[FoMoCoMoFo]

you want to move whatever is attached to the crank including the outer half of the key forward the direction of rotation while the crank and inner half of the key stay put. does that make any sense? I got the impression from your previous posts that maybe you had put a cam in this engine along with some other mods and that you thought the cam may have been installed retarded. talk of an offset key now causes me to question that. advancing the cam will raise the vacuum at idle even if its timing is right on now. consider giving us a little history of this project ?

 

[drayrunner]

The car in question is a 02 malibu 3100, my dd it runs okey but botton in power seams to be lacking and the vacuum reading is low especially during cruise, checked for vacuum leaks ,compression check leakdown check everything is good. talking to some knowledgable people that say its because the cam is retarded and i agree. so i'm going to try and advance it and see what happens and besides i probably got to much time on my hands. also i enjoy trying to inprove my cars in any way i can. thanks

 

[patprimmer]

Has it always had poor vacuum or has it happende after repairs or modifications, or is this the first time you measured it.

It may be your gauge is wrong.

Changes in an engine that was not intentionally changed must be due to accident or wear.

Most likely point of wear is valve train, especially cam lobe wear.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[franzh]

You did not indicate what the vacuum readings were, but it is not uncommon to see modern automobiles with a lower cruise reading than what was considered commonplace 15 years ago. Smaller engines tend to run at lower vacuum readings since they operate in a higher power level than a large engine. Also, an engine running with a lower vacuum reading is losing less power than a larger counterpart due to suction throttling losses.

For example, in a 3500 lb auto with a 3.0L engine, it MIGHT be running at highway speeds at 9"hg, where as the same vehicle with a 5.7L engine may be running at 16"hg. Guess which one will get better economy?

Cam lobe profile can certainly cause problems as patprimmer indicates, but to add my small and barely significant thoughts, once a camshaft wears to the point where valve lift is compromised enough to cause a loss in power, the valve followers should be rattling like a bucket of rocks, and it just gets worse, fast. Once the camshaft lobe hardened surface is cut through and the followers suffer the same wear rate, the resulting action more closely resembles a bench grinder than a precision engine.

Franz

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[IceStationZebra]

I don't see why you think a bushing in the cam can only advance it whereas an offset key can only retard it. Both of them can advance or retard depending on how they are installed. ISZ

 

[FoMoCoMoFo]

i dont see why you think anyone thinks that.

 

[patprimmer]

The OP could be read that way. He says he can advance with an offset key and retard with a bush. To presume he thought each could be used only one way seemed to stupid to contemplate.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[FoMoCoMoFo]

sorry ISZ mistook you for drayrunner

 

[IceStationZebra]

No prob. I try not to overestimate the experience of "backyard engineers." - ISZ

 

[patprimmer]

If he can't figure out that you simply turn the bush or key around to advance or retard the cam, then:-

1) He should not be here.
2) He should neither assemble nor adjust engine components.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Ataloss]

This has been touched on by a few people, but have you actually looked at a service manual for your car and determined that the vacuum is low? If it is, have you measured the cam timing to see if it's actually set incorrectly? Just going off of anecdotal advice from some knowledgeable people might fix your problem, but it might get you into a lot more trouble. Is your engine an interference design? If it is, how much can you change the cam timing before valves start hitting pistons.

This may be a little extreme, but have you put your car on a dyno to see if it's actually lacking bottom end power, or if you just feel it is? Lets face it, it's a 2002 Malibu; they weren't exactly known for tearing up the drag strip. It could just be that your car, even in perfect form, had poor performance compared to many other cars on the road.

Make sure your vacuum is actually low, and make sure your cam timing is actually retarded. You should make sure something is broken before you fix it.

Bob

 

[NickE]

I have to agree with ataloss here... Realistically if the valvetrain is still stock, and the rubber band (t-belt) was replaced properly there really should be no reason to modify the valve timing.

There may be proven performance benefits from altering the cam, and even retarding or advancing the timing as a whole. It just doesn't seem to me that the OP is going to figure out exactly where the original engineers compromised low rpm torque, if they even did.

When was the last tuneup? How old is the airfilter? There are a whole lot of other things that may be causing your trouble. (is the catalytic converter plugged? I had a VW that just died till 3000rpm, once we cleaned the cat it again could accelerate in 5th from 25mph.)


Nick
I love materials science!

 

[thruthefence]

Many years ago, when discussing troubleshooting techniques, an old moss-back Aircraft Mechanic told me, " Steve, when you are out in the panhandle, and you hear the sound of thundering hoofbeats, you dont think of Zebras or wildebeasts, you think of horses or cattle, and you plan your next step accordingly."

I think the engineering folks refer to this bit of folk wisdom as "Ockham's razor".