Snapped my BS belt

[da_reeseboy]

Like the title says, I snapped my balance shaft belt yesterday. I guess I'm lucky tho since it didn't take the timing belt with it. However, when it happened i had a really bad backfire and noticable power loss along with an erratic idle, so I'm sure the timing jumped a tooth. I did a compression test tho and it looked good. I got 132 in all four cylinders, and when you equate for elevation (I'm at 5300ft.) that comes out to around 158 or so. Am I ok here or is there something else I need to check?

 

[1992awdlaser]

Did you actually check the timing?

 

[da_reeseboy]

I haven't yet but I will be before it is started again. The car is currently parked at work so I am waiting until the weekend before I dig into it really. I just snooped around yesterday after work before it started raining on me. Is there something else I need to check?

 

[r1991_4g63t]

check the timing before anything, even though the belt didnt break it could still bend valves if its a couple teeth off. i didnt think it was possible for that to happen til i pulled the head off one with a slipped belt.

 

[robbo185]

i snapped mine. Same symptoms and everything. I bent 8 valves and my timing had jumped 6 teeth

 

[da_reeseboy]

I'm assuming if I bent valves I would have bad compression. Am I wrong? Either way I'll be checking timing...

 

[da_reeseboy]

your altitude has nothing to do with cylinder pressure. either way 158 is pretty low

158 is low? On the Vfaq it states that a 1G 2.0 turbo is at 164 from the factory and that 121 is the service limit (linky). I thought I was well within the range there.

As far as altitude goes, I am going off of this article I found online - Pelican Technical Article: Time to Rebuild? - Part I
Quoted from that article about 3/4 down the page in the "Compression Tests" section -

Altitude and temperature also affect the compression readings. Manufacturer’s specifications are almost always given at a specific altitude (14.7 psi at sea level), and 59° Fahrenheit. Both temperature and barometric pressure change as you go up in altitude, so you will need to correct your measurements if you wish to compare it with a factory specification. The following chart provides conversion factors for correctly compensating for changes in altitude:


Compression Test Altitude Compensation Factors
Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773

A standard compression reading of about 150 psi at sea level in Los Angeles would measure significantly less in the surrounding mountains. For example, at an elevation of 6000 feet, the expected reading would be 150 psi X .8359 = 125 psi. The cylinders would be reading low if compared to sea level measurements, yet perfectly fine at this altitude.

Am I reading this wrong?

 

[da_reeseboy]

I just got to the timing belt... WOW!! its kinda off a little - about 4 teeth. Am I screwed anyway?

 

[da_reeseboy]

Is it possible to have good compression with bent valves? I guess that is what I am trying to get at here. Does anyone know?

 

[jking29]

Have you ever done a compression test on your motor before? If so, what was your compression before? 132 is pretty low, and you may have dinged some valves and they have just a slight bend.

 

[JusMX141]

Was this photo taken with the bottom timing marks lined up? If not it appears that your cam marks would align perfectly if the cams were simply rotated to center with both dowel pins facing up.




If it's any consolation, this is what we found when while performing a routine timing belt service to my buddy's 2G:

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The belt had been broken quite a long time....all of the cogs were stripped from the belt and laying in the bottom of the timing cover. There was no noticeable power loss- the car still ran a 12.55 @ 109 even with only one balance shaft turning. For all we know the belt was broken the whole time he owned the car!


The finished product:

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[da_reeseboy]

132 - ish is what its been since I bought thte car. no change there, just curious if I need to check anything else...I'm a paranoid person I'm told.

Jusmx141 - You are right, the crank was off by 2 teeth. (edit - as in, with the crank timing mark set 2 teeth off, everything else lined up)

I bought a new timing belt today since it got a little chewed up and just left the balance shaft belt off. Put it all back together and it started right up. Going off this thread (link) it seems I should be ok running without the balance shaft belt, tho it really doesn't seem to be recommended (only one guy actually had a big issue, but I personally don't see how the belt being absent caused the OTHER shaft to mark the block like it did in the pics). At any rate, I got the car home. I figure this is my hint to start saving for a full buildup .

Thanks to everyone for their quick responses!!

 

[1992awdlaser]

You really should put a balance shaft belt on the car.

Consensus is that it sucks.

It's cheap, dirty and doable much like the chubby girl at the end of the night, but it's bad for a number of reasons just like the chubby. I'll explain...

The front balance shaft is belt driven, the rear shaft is integrated into the oil pump. Removing the belt only makes things vibrate, this does and will loosen up bolts. Many of those bolts are important. You can feel if a balance shaft belt is broken just by sitting in a car at idle, you can really tell about 3000 rpm. Those who say it's not that bad aren't quite right if you ask me.

Removing the rear shaft and replacing it with the stubby shaft or a turned down shaft is preferred. You can do this with the engine in the car. This frees up three things: some hp, some oil pressure is gained and you'll no longer live in fear of having that rear bearing back there seize up. Odds are when it seizes, it'll take out a rod bearing and other important stuff too.

Leaving the front shaft in is where alot of people live though. After removing the rear shaft, cutting the balance belt is tempting, very easy and you won't fight the vibration issue as much. It's still bad though, even worse. Cutting that belt for the front shaft gains you only two things: frees up some more hp and even less fear of catastrophic engine damage. No oil pressure is gained here; this is where it gets important and is why you shouldn't do it.

That front balance shaft has two bearing surfaces on it. The front bearing surface, by the sprocket, has a groove all the way around it constantly losing oil pressure. This bearing surface always has lost some pressure though, it is designed to flow that way and is accounted for by the DSM Gods.

It's the rear bearing surface that's got chubby chick all over it. It has an oil groove that is only cast into half of the bearing surface. If the balance shaft is always sitting so that the groove is up on the oil galley, you're constantly losing oil pressure on that galley. Your oil system was not designed for that to happen like that. It was designed to spin X times crank rpm and this allowed for a set oil pressure and flow drop at that point. Now the bad news is that your crank thrust bearing is fed from that very same oil galley. Now the bad news is that your crank thrust bearing is fed from that very same oil galley. Now the bad news is that your crank thrust bearing is fed from that very same oil galley. So it's 50/50 on whether leaving your front balance shaft in is gonna cost you a crankshaft or not at some point. Do ya feel lucky? 50/50 is probably about the same as whether or not your friends catch you with the chubby. You'll remember a crank and that chubby for a long time, if you know what I mean.

Do it right.

 

[da_reeseboy]

Could I install a Balance Shaft Eliminator kit without removing the engine? I assumed I would have to remove the oil pump a distance of the shaft's length from the block, which wouldn't happen with the engine still in the car. If so, I'll buy the kit next Friday (payday) and get it done. In the mean time, the car can stay parked at the house... I don't want to damage anything. I don't really want to install another BS belt tho, since that one didn't even make 12,000 miles - I installed it and the timing belt new last summer when I did the water pump. I would say it snapping and not damaging the motor was lucky enough and don't want to push that luck again. I will search, but help is always appreciated .

 

[1992awdlaser]

I don't know if it can be done on a 2g with the engine in the car.

 

[da_reeseboy]

I just found this thread that has a decent description part way down on getting to the balance shafts on a 2g -Balance Shaft Removal Question. I'll have to do that as soon as possible I guess.

 

[da_reeseboy]

That front balance shaft has two bearing surfaces on it. The front bearing surface, by the sprocket, has a groove all the way around it constantly losing oil pressure. This bearing surface always has lost some pressure though, it is designed to flow that way and is accounted for by the DSM Gods.

It's the rear bearing surface that's got chubby chick all over it. It has an oil groove that is only cast into half of the bearing surface. If the balance shaft is always sitting so that the groove is up on the oil galley, you're constantly losing oil pressure on that galley. Your oil system was not designed for that to happen like that. It was designed to spin X times crank rpm and this allowed for a set oil pressure and flow drop at that point. Now the bad news is that your crank thrust bearing is fed from that very same oil galley.

From this pic, its the balance shaft thats attached to the oil pump that has a groove go only half way around, so the front shaft not spinning should not cause any problems.