Timing belt issue.

[Ivant]

Hi all. I have a 91 T/T gto. Recently I took the left side timing belt dust cover off to inspect the condition of the belt, and in doing so snagged it on the belt on the right side cam wheel causing the cam wheel to jump two notches forward on the belt. I know I should have been more careful, as I know the right side of the belt can be a little bit loose on the right side going down to the pully when the engine is cold. But it's done now and there's no good moaning about it. The motor still starts first pop, despite a tiny bit of missing. The missing goes away when warm and drives well, but runs a bit rough at idle. I don't want to live with it, and was wondering if I can get the cam wheel back a couple of notches without going through an entire timing belt replacement process, as the belt has only done 27 thousand ks.
Any ideas on the matter will be much appreciated.

[stealthee]

Only way to do it is to do it right.

[box]

Stick a pencil sized allen key between the timing gear and the belt and turn the engine slowly by hand, it should move the belt over a tooth. Never actually tried it on a 6G but it should work....it seems to work on everything else.

It shouldn't have jumped timing that easily IMO.

[Alex3000gt]

Hi all. I have a 91 T/T gto. Recently I took the left side timing belt dust cover off to inspect the condition of the belt, and in doing so snagged it on the belt on the right side cam wheel causing the cam wheel to jump two notches forward on the belt. I know I should have been more careful, as I know the right side of the belt can be a little bit loose on the right side going down to the pully when the engine is cold. But it's done now and there's no good moaning about it. The motor still starts first pop, despite a tiny bit of missing. The missing goes away when warm and drives well, but runs a bit rough at idle. I don't want to live with it, and was wondering if I can get the cam wheel back a couple of notches without going through an entire timing belt replacement process, as the belt has only done 27 thousand ks.
Any ideas on the matter will be much appreciated.

Sounds like the tensioner gave up the ghost and now you’ve got a loose timing belt. Imagine what might happen if all four cams jump timing while the engine is running?

Could be time for a new belt and tensioner. How old (years) are the ones on the motor?

[stealthee]

Sounds like the tensioner gave up the ghost and now you’ve got a loose timing belt. Imagine what might happen if all four cams jump timing while the engine is running?

Could be time for a new belt and tensioner. How old (years) are the ones on the motor?

The problem is the tensioner will "rest" after the vehicle sits. Many people have found the belt to have slack after the car has sat a bit and thought the worst. As soon as the engine cranks the tension is taken up. If you hit it while it is slack then you could potentially cause it to do what happened here.

[Ivant]

Stick a pencil sized allen key between the timing gear and the belt and turn the engine slowly by hand, it should move the belt over a tooth. Never actually tried it on a 6G but it should work....it seems to work on everything else.

It shouldn't have jumped timing that easily IMO.

I might give that a try, as it only needs to go back two teeth for the correct timing. I have found that when the engine is cold the timing belt on the right side going down to the water pump can be a bit slack. But after the engine starts it tightens up. I read somewhere on a gto site that, that can be normal.

[Ivant]

Sounds like the tensioner gave up the ghost and now you’ve got a loose timing belt. Imagine what might happen if all four cams jump timing while the engine is running?

Could be time for a new belt and tensioner. How old (years) are the ones on the motor?

The belt has only done 27 thousand ks. But it was replaced back in 2000. I was a bit worried about it and showed it to my mechanic, and he said it still looked brand new, and should be fine for ages yet. It's really just a weekend car these days and is garaged everyday of it's life. So not getting the heat from hot days on the rubbers etc in the car.

[Ivant]

The problem is the tensioner will "rest" after the vehicle sits. Many people have found the belt to have slack after the car has sat a bit and thought the worst. As soon as the engine cranks the tension is taken up. If you hit it while it is slack then you could potentially cause it to do what happened here.

I think you've hit the nail on the head with you're comments, and are bang on.

[Ivant]

Stick a pencil sized allen key between the timing gear and the belt and turn the engine slowly by hand, it should move the belt over a tooth. Never actually tried it on a 6G but it should work....it seems to work on everything else.

It shouldn't have jumped timing that easily IMO.
On re-reading your comments, it's not the belt that's moved, it's the right side cam gear, moved two teeth forward and needs to go two teeth back. So it's the cam that I'm going to try and move back until it's in it's proper place lined-up with timing mark on the block. The left side cam is properly lined-up, but the right one is two teeth out, and needs to go back.

[box]

On re-reading your comments, it's not the belt that's moved, it's the right side cam gear, moved two teeth forward and needs to go two teeth back. So it's the cam that I'm going to try and move back until it's in it's proper place lined-up with timing mark on the block. The left side cam is properly lined-up, but the right one is two teeth out, and needs to go back.

It should still work.

While you're at it, pull the bottom cover off and make sure the tensioner eccentric pulley has been set up properly, a lot of mechanics cock it up in a way that allows the belt to slacken too much.

[Ivant]

It should still work.

While you're at it, pull the bottom cover off and make sure the tensioner eccentric pulley has been set up properly, a lot of mechanics cock it up in a way that allows the belt to slacken too much.
I would do, but I think there's a bit more to do to get the bottom cover off. Don't all the accessories, PS, ALT, AC, crank pulley, have to come off first so you can get to the cover? Whereas it's only three small bolts to get the top ones off. Still it's something I may have to do at some stage. I'm a little bit weary of moving anything too much on this engine due to it being an interference engine. So I'm a little bit unsure of just how much I can move anything before damage can occur. Give me a non-interference engine any day. At least when you get the timing wrong on one of those, there's no damage to worry about.

[Alex3000gt]

The belt has only done 27 thousand ks. But it was replaced back in 2000. I was a bit worried about it and showed it to my mechanic, and he said it still looked brand new, and should be fine for ages yet. It's really just a weekend car these days and is garaged everyday of it's life. So not getting the heat from hot days on the rubbers etc in the car.

5 years or 60,000: Replace belt and tensioner. Your engine hit the former.

[Ivant]

5 years or 60,000: Replace belt and tensioner. Your engine hit the former.
That's actually another topic on it's own? Many people say a belt should only be replaced when it hits the required Ks. (We do Ks in NZ. I think it's Miles in the US) While others say it should go off time regardless of Ks. I think it's one of those arguments that will go on forever. I personally know some people who have never changed the belts on their cars, and in some cases are on their second time round on their mileage clocks. God only knows what state their belts are in?

[box]

I would do, but I think there's a bit more to do to get the bottom cover off. Don't all the accessories, PS, ALT, AC, crank pulley, have to come off first so you can get to the cover? Whereas it's only three small bolts to get the top ones off. Still it's something I may have to do at some stage. I'm a little bit weary of moving anything too much on this engine due to it being an interference engine. So I'm a little bit unsure of just how much I can move anything before damage can occur. Give me a non-interference engine any day. At least when you get the timing wrong on one of those, there's no damage to worry about.

Yep, it's a bit of work. Up to you though.

You've already had the engine running so there's no point worrying about damage at this point, just don't let it slip another tooth while you re-time it.

In the hundreds of timing belt jobs I've done, I've only seen one belt that was really cracked and ready to fall to bits due to age.....the rest generally look pretty good when they're removed and thrown in the bin. It always seems to be a pulley or water pump failure that causes the belt to shred.

I guess you could say the same about most preventative maintenance.

[stealthee]

Exactly, its not the belt that fails, its a component. Water pump, tensioner, pulley, etc fails and caused the belt the shred/jump.

[Ivant]

Yep, it's a bit of work. Up to you though.

You've already had the engine running so there's no point worrying about damage at this point, just don't let it slip another tooth while you re-time it.

In the hundreds of timing belt jobs I've done, I've only seen one belt that was really cracked and ready to fall to bits due to age.....the rest generally look pretty good when they're removed and thrown in the bin. It always seems to be a pulley or water pump failure that causes the belt to shred.

I guess you could say the same about most preventative maintenance.

Yes you're not wrong about the old belts still looking ok. I haven't changed as many as you have, and have never done one on a GTO. But I have done a lot of 1996 2.2L SOHC Subaru Legacy's. The wife's actually, and they always looked as good as the day I last fitted it. I was even in two minds about leaving it for another 50ks, but The manual said change it, so I did. In all truth I didn't really mind because it was so easy. Subaru's must be the easiest timing belts to do. Only the fan and fan belt and the crank pully to get off, and then the covers and hey presto your onto the belt. If only the GTO had that kind of access.

[box]

In all honesty, the GTO really isn't too bad to work on once you get into it....it's just a 90's Japanese car held together with nuts and bolts after all. Rip into it, you'll have that bottom cover off in 45 minutes.

I might be wrong, but I don't think the alternator has to come off to get the cover off. Neither do the power steering or A/C pumps. Just take the two belts and the crank pulley off. Maybe take the engine mount off so you can lower the front of the engine a touch.

Could be worse, you could be working on a Peugeot. Or a V6 Alfa Romeo.

[Ivant]

In all honesty, the GTO really isn't too bad to work on once you get into it....it's just a 90's Japanese car held together with nuts and bolts after all. Rip into it, you'll have that bottom cover off in 45 minutes.

I might be wrong, but I don't think the alternator has to come off to get the cover off. Neither do the power steering or A/C pumps. Just take the two belts and the crank pulley off. Maybe take the engine mount off so you can lower the front of the engine a touch.

Could be worse, you could be working on a Peugeot. Or a V6 Alfa Romeo.
Yes it's all the stuff in front that's the biggest hassle isn't it. I remember way back when I used to work on my old small block chev... so simple, and the best access, all the room in the world. A 9/16''and 5/8'' ring spanner, and a Philips screw driver was all I needed to pull the engine to bits.

[Ivant]

Just an update. Yesterday I decided to have a go fixing the issue. I started with a cold engine, as I find that is when everything is a bit loose. I used three tiny screwdrivers, about 3mm wide in place in-between the cam wheel and belt. Then using a socket and bar I slowly edged the cam wheel back the two teeth it needed to go to get the timing back aligned. After I cleared everything off it, I started the engine and it went great. All the minor missing was gone. I was well pleased. I will have a go at replacing the belt at some stage, with all the hours it requires to get it done, and have been watching some youtube videos on the subject. One thing that I don't understand is why the crank sprocket has to be turned back one tooth from the timing mark on the block before the belt is fitted and moved up to the tensioner pulley? I will have to investigate that a bit more. Wouldn't that put the timing out?
Anyway I just thought I would let you guys know how I got on.
Cheers

[box]

Well done.

I've always done it with the crank at TDC, but I don't lock the cams. Work anticlockwise, starting from the crank, keep the belt tight and cable tie the belt to the cam sprockets as you go. Once you get to the end, the timing will be right, the belt will be tight and any slack will be at the tensioner.

If the cams are locked (with bolts through the sprockets into the head or with plastic cam locks), you turn the crank back a tooth because you can't get the belt tight enough between the crank and cams to get the crank on the right tooth of the belt. Once you get the belt on this way, you turn the crank forwards to TDC and that takes up the slack between the crank and rear exhaust sprocket and puts the slack at the tensioner.

Two different ways to do it, same outcome. It's one of those jobs where three hands is useful.

[stealthee]

As mentioned you clock the crank back one tooth because when you take up the slack it will roll it forward that one tooth. If you don't put it back one tooth then you'll be doing it again because you'll be off that one tooth.

I had to do something similar recently when doing a head gasket job on a Toyota Tundra with a 3.4 V6. Every time I installed the belt I'd end up off two teeth. Nothing in the instructions said anything about rolling anything back, but when I watched the cam gear pull back as I set the tensioner I knew what was going to be necessary. I pulled the belt back off, clocked the cam gear forward two teeth and as I set the tensioner I watched it pull the cam gear right into time.

[Ivant]

Well done.

I've always done it with the crank at TDC, but I don't lock the cams. Work anticlockwise, starting from the crank, keep the belt tight and cable tie the belt to the cam sprockets as you go. Once you get to the end, the timing will be right, the belt will be tight and any slack will be at the tensioner.

If the cams are locked (with bolts through the sprockets into the head or with plastic cam locks), you turn the crank back a tooth because you can't get the belt tight enough between the crank and cams to get the crank on the right tooth of the belt. Once you get the belt on this way, you turn the crank forwards to TDC and that takes up the slack between the crank and rear exhaust sprocket and puts the slack at the tensioner.

Two different ways to do it, same outcome. It's one of those jobs where three hands is useful.

Oh well that explains it then. Thanks for that. I think the way you do it seems the better way, and the way I think I'll do it.

[Ivant]

As mentioned you clock the crank back one tooth because when you take up the slack it will roll it forward that one tooth. If you don't put it back one tooth then you'll be doing it again because you'll be off that one tooth.

I had to do something similar recently when doing a head gasket job on a Toyota Tundra with a 3.4 V6. Every time I installed the belt I'd end up off two teeth. Nothing in the instructions said anything about rolling anything back, but when I watched the cam gear pull back as I set the tensioner I knew what was going to be necessary. I pulled the belt back off, clocked the cam gear forward two teeth and as I set the tensioner I watched it pull the cam gear right into time.

I was going to do it the way box does it. But on second thoughts maybe I should just do it the way it's supposed to be done. I won't start it until it's all lined up anyway. Now I just have to figure out how I'm going to retorque the crank bolt, as I don't have access to garage air guns. I don't have any problems getting them off, as I use the old crank the engine over with a bar against the engine bay method. It works a treat. But unlike a Subaru the GTO doesn't have a hole in the side of the trans for retorquing the bolt. Well not that I know of anyway. So I suppose it's put it in gear with the handbrake on, and try to do it that way?

[stealthee]

I used to put it in gear then jam a heavy screwdriver in the front rotor vane so it jammed against the brake caliper bracket. Worked great for crank pulley and axle nuts.

[Ivant]

I used to put it in gear then jam a heavy screwdriver in the front rotor vane so it jammed against the brake caliper bracket. Worked great for crank pulley and axle nuts.
Good idea. I might try that way myself. Gets the caliper to take up some of the strain.