Can A Timing Belt Being Off By A Tooth Affect Compression?


doug2060
01-08-2009, 09:49 PM
1990 Geo Metro
1.0 3cyl.
Manual Trans
162,000 mile

CAN A TIMING BELT BEING OFF BY A TOOTH AFFECT COMPRESSION?

I just replaced a timing belt on this car and now the compression is around 125psi on all cylinders. 2 weeks ago it was around 175 each.

It's too cold to go out to mess with anymore tonight so i thought I would ask...

Rooy
01-08-2009, 10:21 PM
Yes it could.

doug2060
01-09-2009, 01:07 AM
The weird thing is that it doesn't seem to have much power loss. The compression just shows up much lower. 50psi per cylinder should be noticeable. Weird...:runaround:

leonbentz
01-09-2009, 01:32 AM
yea, it's a good thing that Metros are a non-interferance engine. Otherwise, you could bend a valve, by missing timing marks. Fortunately, they have a ten dollar belt and are quite forgiving:iceslolan Gotta love the Metro. You're only running 175 pounds per hole? Must be an XFI model, right? I believe the LSI's are supposed to run at 199 psi.

doug2060
01-09-2009, 03:13 AM
Non XFI, just old.

I'll check it out later. I'm pretty sure the belt was right but who knows? It was cold and I really just wanted to finish up and get inside. I did warm it up before testing compression. I checked it because the idle seemed different but not by much. I just wanted to find out if it was off if it would affect compression and 50 psi is a lot. If it is off it's by 1 tooth.

DOCTORBILL
01-09-2009, 11:48 AM
Could being off by one tooth ( 5 degrees ?) cause any of the valves to get burned ?

Wouldn't the valves be opening or closing before or after they should be?

DoctorBill

Woodie83
01-10-2009, 06:55 AM
Valves would be opening and closing either before or after when they "should be" and yes, that could lead to burned exhaust valves. "Should be" is not a firm number though, valve timing is a variable that can be moved around just like ignition timing to tune the engine and give it different driveability characteristics, the only difference is they decide at the factory and lock it down to a specific number. Advancing the valve timing will give you more horsepower and less torque, retarding it will give you more torque but it will run out of steam at high rpms. (possible I have that exactly backwards, but I think that's right) Problem is, one tooth is far too much to adjust it, it's about 20 degrees and 10 is as far as you'd ever want to go. There are adjustable sprockets available for this very purpose and the newer cars with the spoked cam sprocket already have two settings built in, one is marked "E" and the other "I". Can't remember which is which and what the effect is supposed to be, I've read it on TeamSwift.

Compression numbers when cranking the engine on the starter are not the same as they will be when the engine is running. Things are happening so fast that a cylinder can built up some compression even though theres a big leak. That's why cars with 100psi compression are hard as hell to start, but will run fairly well once started. That 50 pound difference is probably 20 when running.

leonbentz
01-10-2009, 01:08 PM
162,000 and your compression is that low? Wow. I pulled mine down at 207,000 and it had much better compression than that. I only tore it down because all the seals went tits up and the front tranny seal did too.:iceslolan

Rooy
01-10-2009, 01:11 PM
Advancing the valve timing will give you more horsepower and less torque, retarding it will give you more torque but it will run out of steam at high rpms. (possible I have that exactly backwards, but I think that's right) Problem is, one tooth is far too much to adjust it, it's about 20 degrees and 10 is as far as you'd ever want to go.

Yeah, you have it backwards. Advancing it will move the power band down, retarding it will shift it up.

+1 on the adjustable cam sprocket. One tooth is way too much.

doug2060
01-10-2009, 01:36 PM
175PSI is not that bad on a 19 year old 3cyl metro. 199 is what it is new and the minimum is 156. I've seen much worse!

leonbentz
01-10-2009, 01:58 PM
Yea, I can believe that. Most people who drive these things don't use good oil in them and they wear out quicker. At 205,000 I was running abouut 187psi and better. Someone must have taken care of it. Mine is a 1991 LSI :smokin:

doug2060
01-10-2009, 02:53 PM
You're lucky. I also have a 91 automatic. Before i put new rings and valves and all those goodies in it the compression was #1=148psi #2=128psi #3=157psi. Cylinder 3 would have been much lower but oil was coming into it steadily. It would foul a spark plug within 1000 miles. It's running great now though. I seem to be collecting these things now. LOL.

leonbentz
01-10-2009, 03:21 PM
Yea, mine is an automatic too, plus it has air, which works good. I love the little shit. I bought it with 178,000 on it and it was quite peppy for the size engine it has. When I pulled it down, the ring end gap was still .016 and the clyinder walls were taperless. So, when I rebuilt it, it really didn't make any improvements on it, but at least, I know what I have and I put a jdm tranny in it.

Did you get your car running better?:smokin:

doug2060
01-10-2009, 04:14 PM
I just got in there messing with it. I believe the belt may be stretched. No matter how many times I line it up, the notches just won't stay lined up exactly. I can line up the top but the bottom looks half a tooth off. I'm going to buy another belt later. The belt is less than a year old. Has anyone had this trouble. It's strange for a fairly new belt to stretch but even the alt/ps belts on these things have that problem.:runaround:

Rooy
01-10-2009, 06:44 PM
I'm not sure that a belt that has stretched would cause that. Has your head or block ever been shaved/decked? Or do you have a replacement head that could've been? That will change the relationship between the cam and crank and cause the timing marks not to line up exactly.

doug2060
01-10-2009, 07:04 PM
The head has been shaved in recent months but would the 1/2 notch be cause for concern. That's quite a bit of slack for a head thats probably only been shaved once.

Rooy
01-10-2009, 08:07 PM
The head has been shaved in recent months but would the 1/2 notch be cause for concern. That's quite a bit of slack for a head thats probably only been shaved once.


Is it really off half a tooth? Set the crank to exactly TDC (it's best to use a method to find true TDC rather than relying on the marks) and see where the cam mark is lining up. Shaving the head (moving the cam closer to the crank) will retard timing, which is not usually ideal. It of course depends on how much material was removed, which we don't know.

doug2060
01-10-2009, 11:54 PM
Wow, This really pisses me off. It truly does look like half a tooth. I guess I just have to deal with it. The car still runs fine but I'm trying to get the best I can out of a 20 year old Metro... Maybe the head has been shaved too much over the years...

leonbentz
01-11-2009, 01:17 AM
buying heads can sometimes be a pain. I bought a reman head that has no PC valve inlet. I'm still running it, but it's strange though. Different countries use different applications. My car doesn't even have an EGR either. It was built in Canada, so they are different. California cars are the real shits, because they have so much smog crap on them. As far as your timing deal though, I never seen anything like this.
Maybe you can check the height of yours, to another head to see if it has been shaved. You should be able to get an idea, without removing it.
How does the cam gear look? Check the keyway hole and make sure it's not oblonged. This can happen over time, if the bolt is not torqued properly. The hole for the pin in the cam pulley will get obrounded and shift the pulley around to make it a half a tooth off. It won't take much. If the hole is out of round by .030, then that can make it a 1/4" out to the edge where the teeth are.:smokin:

doug2060
01-11-2009, 02:27 AM
Now all you guys are going to be pissed at me. After screwing with this for a while I got my girlfriend to come look at it. She looked at it after I explained everything to her then she looked at me like I was stupid and went in the house. I thought she was mad because she hates it when I have her come out to help when I'm tinkering with the cars. She came back out and handed me my glasses (which I haven't wore in 2 years) and told me to look again. I'll be damned it was dead on. The good thing is that it had to have been off a tooth because the compression was back to normal. Sorry for wasting your time...:runaround:

I'm going blind...:sunglasse

leonbentz
01-11-2009, 02:36 AM
Hey it's okay. We are here to help. Don't worry, I'm going blind too.:smokin:

Rooy
01-11-2009, 03:35 PM
Ha...glad to hear everything's OK and the compression is back.

doug2060
01-11-2009, 03:41 PM
Thanks, I must be getting old. Once I had those glasses on everything was where it needed to be. The way those timing marks are kind of off center to the right must have been throwing my bad eye off.LOL... I think it's time for a Lasik consultation or I can just keep my glasses in the tool box...:banghead:

DOCTORBILL
01-11-2009, 05:08 PM
How old are you Doug2060 ?

I've always needed glasses, but within about a year my vision became strange - streetlights
had bulls eyes and flashes around them as did oncoming headlights.

Finally it got so bad that an eyeglasses doctor told me I had Cataracts.

So I had them removed and occular implants put in.

My God - I had no idea !

My lenses were Root Beer Colored and had fleckies embedded in them - AGE....

Anyway - with glasses, "I can see clearly now, the rain is gone...." (song)

You get so used to the slowly developing cataracts, that you don't realize how
crappy your vision is ! I didn't realize how WHITE white was until the 'Root Beer'
colored lenses of mine were removed.

They were so bad that now I need sunglasses all the time so much light is getting thru !

My point?
Have your "eye doctor" check your lenses in your eyes for embedded flecks of
stuff and for becoming dark yellow colored - if you are over 45 or so....and smoked (?)

http://www.allaboutvision.com/conditions/cataracts.htm
http://www.healthscout.com/ency/68/114/main.html
http://www.mayoclinic.com/health/cataracts/DS00050

DoctorBill

doug2060
01-12-2009, 12:34 AM
I'm only 28. I got my glasses when I was 19. I rarely use them but I guess it's time to go to the eye doctor. This is one more thing to add to the list of vision related issues in recent months. I think my vision problems may be related to all these strange gray hairs starting to show up on my head. WTF LOL...

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