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timing belt jumping/skipping teeth question


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As you all know, the 05 LGT/OBXT engine (and all later MY I think) is an interference engine. This means that if the timing belt jumps and skips several teeth, the valves will most likely hit the pistons (or each other), which will result in bent valves.

 

The manual states that the timing belt can skip up to three teeth without any damage. More than that, and you may bend some valves.

 

Question: can the timing belt skip one teeth on say the driver side cam pulleys, and the engine still runs fine? How about two, or three? Or does the engine stop running as soon as one teeth is skipped?

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are you setting a new timing belt? if so I had some trouble setting it myself. the important thing to do is follow the manual for the order in which you turn the cams and the directions you turn them. there are some good videos out there. when it comes to making sure the teeth are on their perfectly you will need to apply tension to the belt from the outside with a screwdriver to simulate the tensioner being activated then check your marks for the timing belt cams/engine marks. It can be really frustrating so make sure you check out some videos on how to do it well. The dohc runs like shit if the timing is even a little bit off in my experience.
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I installed a timing belt before. And yeah, I encountered the frustration you described. I will have to install another timing belt this weekend on another subie.

 

But I was just curious to know if the engine can run if the belt skips just one tooth for instance.

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Yes it will run especially if it's an exhaust sprocket since the cam sensor is on the intake cam.

I find using heavy duty paper clip like these helps keep the belt in place ( clip the belt on the cam sprockets ) when fussing with the timing. The intake cam on the driver side is the ball buster........I usually set those driver side cams and have can assistant hold the intake cam by the center hex bolt under the cap on the sprocket.

image.thumb.jpg.dd9d01e62c0d1cf6b8de3e56f64f663a.jpg

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Yes it will run especially if it's an exhaust sprocket since the cam sensor is on the intake cam. .

 

That's interesting. I did not think about that. I would guess that roughness should be detected in the affected bank by the ecu, wouldn't you think?

 

Thanks for the tip about the paper clip.

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are you setting a new timing belt? if so I had some trouble setting it myself. the important thing to do is follow the manual for the order in which you turn the cams and the directions you turn them. there are some good videos out there. when it comes to making sure the teeth are on their perfectly you will need to apply tension to the belt from the outside with a screwdriver to simulate the tensioner being activated then check your marks for the timing belt cams/engine marks. It can be really frustrating so make sure you check out some videos on how to do it well. The dohc runs like shit if the timing is even a little bit off in my experience.
What he said.. it looks fine before you pull the tensioner pin but if it's too much slack and then it's taken up it will cause the driver's side head to be off..

 

that's the huge pita part.

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Just make sure the timing marks on the pulleys line up don't worry about any marks on the belt.

 

Make sure you have enough clearance on the guides.

 

If the drivers side spring free just reverse the rotation of that cam back to where the marks line up. It's only going to spring a small amount.

 

Remember only #1 piston is at TDC, #3 is at BDC, 2 & 4 drivers side are at mid travel.

 

That is correct right, GTTuner ?

 

I know in one of the timing belt threads we talked about it once.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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Just make sure the timing marks on the pulleys line up don't worry about any marks on the belt.

 

Make sure you have enough clearance on the guides.

 

If the drivers side spring free just reverse the rotation of that cam back to where the marks line up. It's only going to spring a small amount.

 

Remember only #1 piston is at TDC, #3 is at BDC, 2 & 4 drivers side are at mid travel.

 

That is correct right, GTTuner ?

 

I know in one of the timing belt threads we talked about it once.

 

When the crankshaft sprocket is at it's "TDC" mark for aligning the timing belt all of the pistons are half way down. It's really not TDC.

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Yes mine spun once too, that's when I came up with the ford wrench and the C clamp to hold the gear.

 

http://i185.photobucket.com/albums/x40/92Si/Picture074.jpg

 

That was like 6 years ago.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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I'll be using a small vice grip to hold 2 and 4 cams in place just as I did last time. Just have to be careful not to put too much pressure as the pulleys can break.

 

Just so u know what happened to us. Went camping 2 hrs away from home during labor day weekend. While driving on dirt roads, loud pop from exhaust and engine died. Tried to crank a few times and did not want to start. Further checking showed 2 and 4 were about three teeth off. Timing belt apparently jumped due to a guide rubbing on the belt.I used lots engine braking so it may have contributed to the issue. Had to find a way to break down camp and tow the car and go home. It sucked especially with a little one..

I hope valves are OK as this engine has been running great.

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Thanks, I thought you'd had seen that years back. That's what I'm known for at work. When Engineers have a problem they come ask me what do I have that could work. I've been told I have devious mind... :)

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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  • 8 months later...
are you setting a new timing belt? if so I had some trouble setting it myself. the important thing to do is follow the manual for the order in which you turn the cams and the directions you turn them. there are some good videos out there. when it comes to making sure the teeth are on their perfectly you will need to apply tension to the belt from the outside with a screwdriver to simulate the tensioner being activated then check your marks for the timing belt cams/engine marks. It can be really frustrating so make sure you check out some videos on how to do it well. The dohc runs like shit if the timing is even a little bit off in my experience.

What he said I had problems with this until you see what happens when you pull that pin so I rotate the cams more then what it should be so when the pin is pulled it rotates to the correct marks

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