Quick question about rear exh cam

[Eclipsed]

I'm resetting the timing on my car due to the shop I paid to change the timing belt screwing it up (asked them when I picked the car up if they set the timing and the answer was "nah man the cam's didnt even move", which is utter BS but whatever)

anyhow my question is this, i know you have to retard the rear exh cam one half tooth when you TDC the engine. When the cams are locked in place (using the 5mm punches) does that include the one half tooth retard?

 

[ftuhy]

When I did my '96 2 years ago, the 1/2 tooth was for intitial installation of the belt with the tension adjusting pulley released. Once the final belt tightening proceeedure was done and the engine rotated two or four turns (CLOCKWISE Only), all 4 cam timing marks all lined up exactly with the crank at TDC.

 

[Daedalus]

I'm resetting the timing on my car due to the shop I paid to change the timing belt screwing it up (asked them when I picked the car up if they set the timing and the answer was "nah man the cam's didnt even move", which is utter BS but whatever)

anyhow my question is this, i know you have to retard the rear exh cam one half tooth when you TDC the engine. When the cams are locked in place (using the 5mm punches) does that include the one half tooth retard?

1) Are you certain the timing is screwed up? How do you know?

2) You need to *advance* the rear exhaust cam 1/2 tooth, not retard it.

3) The 5mm punches do not locate the cams perfectly; that is what the marks on the cam pulleys are fore. The punches just get you close and allow for some adjustment.

 

[Eclipsed]

1) Are you certain the timing is screwed up? How do you know?

2) You need to *advance* the rear exhaust cam 1/2 tooth, not retard it.

3) The 5mm punches do not locate the cams perfectly; that is what the marks on the cam pulleys are fore. The punches just get you close and allow for some adjustment.

i'm positive the timing is jacked, you can hear it in the exhaust and its idled around 200-500 since the day I picked it up.

And yes advance, not retard, sorry about that. The only real problem I'm having right now is sighting in the rear cams to the marks, very hard to see them but a mirror did the trick.

 

[pgilliam1]

Just make sure you don't try and advance the belt (by hand turning the crank) with the tensioner loose. If you do this it will cause the belt to skip 2 teeth on that rear cam gear. I did that (the manual states not to do this in a side note that I didn't read) and got the same results you're having now. That would be my bet as to what they did to yours. Make sure after you align the belt to hand turn the crank (if you have the sparkplugs out it should turn smoothly) about 4 times and check all the gear and crank marks. These valves bend easily so no pressure should be felt when turning the crank by hand. Good Luck!

 

[Eclipsed]

Just make sure you don't try and advance the belt (by hand turning the crank) with the tensioner loose. If you do this it will cause the belt to skip 2 teeth on that rear cam gear. I did that (the manual states not to do this in a side note that I didn't read) and got the same results you're having now. That would be my bet as to what they did to yours. Make sure after you align the belt to hand turn the crank (if you have the sparkplugs out it should turn smoothly) about 4 times and check all the gear and crank marks. These valves bend easily so no pressure should be felt when turning the crank by hand. Good Luck!

all plugs are out, got the cam's locked in place and the crank at tdc right now. Working on getting the belt back on then on to final adjustment, adjustment bolt is loosened at the moment.

 

[nis350]

i'm positive the timing is jacked, you can hear it in the exhaust and its idled around 200-500 since the day I picked it up.

And yes advance, not retard, sorry about that. The only real problem I'm having right now is sighting in the rear cams to the marks, very hard to see them but a mirror did the trick.

Just curious how the exhaust sounded? Did it lose any power or idle really rough?

I see that you have the engine open up now... How many tooth was it off?

Just asking for future reference. Thx..:smile:

 

[pgilliam1]

Just curious how the exhaust sounded? Did it lose any power or idle really rough?

I see that you have the engine open up now... How many tooth was it off?

Just asking for future reference. Thx..:smile:

Mine was off 2 teeth only on the rear exhaust cam gear. It sounded like it was idleing on 3 cylinders and was running very rough. I shut it off promptly but I'm sure the loss of power would have been substantial.

 

[Eclipsed]

Mine was off 2 teeth only on the rear exhaust cam gear. It sounded like it was idleing on 3 cylinders and was running very rough. I shut it off promptly but I'm sure the loss of power would have been substantial.

idle would jump from 200-1000 rpm, acceleration was very rough, exhaust was sputtering all the time. when I pulled the belt off the rear head cams were completely out of wack, almost pointing opposite directions

 

[nis350]

Mine was off 2 teeth only on the rear exhaust cam gear. It sounded like it was idleing on 3 cylinders and was running very rough. I shut it off promptly but I'm sure the loss of power would have been substantial.

So this is quite different than many posts I read about the rear exhaust cam being off just one tooth (or retarded one booth) because the install didn't advance half of a tooth to get belt on and then retard it back during installation.

Would I be able to verify the timing marks if I were to remove both valve covers? Would the marks on all four cams be lined up with the top of the cylinder heads the same way?

I also read that you have to turn the crank (clockwise ONLY) a number of complete rotations in order for the timing marks to be all lined up....

Thx...:wink:

 

[Daedalus]

Would I be able to verify the timing marks if I were to remove both valve covers? Would the marks on all four cams be lined up with the top of the cylinder heads the same way?

I also read that you have to turn the crank (clockwise ONLY) a number of complete rotations in order for the timing marks to be all lined up....

The marks will eventually re-align themselves, except of course the rear exhaust mark will be off slightly. You need to be at TDC on the compression stroke on the #1 cylinder. It takes 2 revolutions of the crank to complete all 4 cycles, so at most you'll have to turn it 2 revs to get the marks lined up. That said, a quick vacuum test will tell you if you have anything to be concerned with.

when I pulled the belt off the rear head cams were completely out of wack, almost pointing opposite directions

This was when the front head marks were lined up? Seems like you would have bent some valves if one or both rear cams were mis-timed by 180 degrees.

 

[pgilliam1]

Would I be able to verify the timing marks if I were to remove both valve covers? Would the marks on all four cams be lined up with the top of the cylinder heads the same way?

Yes. If you remove the valve covers the cam gears are exsposed enough to reveal the timing marks on them (the rear cam gear marks are hard to see - but they're there). When you have the #1 (on the front intake cam gear) aligned with the mark on the exhaust cam gear you are at #1TDC. At this point the marks on the rear cam gears should line up and the white mark on the crank pulley should line up with the marker on the timing cover. At this point your timing is properly set. And - YES - only turn the engine clockwise. Happy Motoring!

 

[nis350]

From the above two posts, one said the timing mark of the rear exhaust cam should be slightly off (advance?) and the other said it should line up...

Just for clarification on the timing mark of the rear exhaust cam...

Should it line up with the timing mark on the rear intake cam as well as the timing belt cover or advanced half of a tooth which would put it slightly lower than the timing cover and the timing mark on the rear intake cam.

I realized that the rear exhaust cam should be advanced (clockwise) half of a tooth during timing belt install and not sure how it should be after everything is done.

 

[Daedalus]

From the above two posts, one said the timing mark of the rear exhaust cam should be slightly off (advance?) and the other said it should line up...

Just for clarification on the timing mark of the rear exhaust cam...

Should it line up with the timing mark on the rear intake cam as well as the timing belt cover or advanced half of a tooth which would put it slightly lower than the timing cover and the timing mark on the rear intake cam.

I realized that the rear exhaust cam should be advanced (clockwise) half of a tooth during timing belt install and not sure how it should be after everything is done.

Sorry I stand corrected. They should line up. Looks like we've had this discussion before.

 

[ftuhy]

One last point that I'll add from experience doing my '96 and helping someone with a '91: With the punches locking the cams in place, the belt has to be pulled very tight between the crank pulley and the front exhaust cam. I put reference marks on the old and new belts per Gary Kentosh's write-up, and when I pulled the belt "reasonably tight" to that first cam, I found I was one tooth off. So, I lifted the belt slightly and gave it one last hard tug to "shorten" the belt one more tooth between the crank and the cam pulley. The reference marks then lined up perfectly (note that I'm talking reference marks made by me per the Kentosh write-up, not the timing marks on the cams and crank - which are fixed in place by the punches).

So, its possible to have the belt section one tooth "too long" between the crank and the first cam, and still have all the timing marks line up. I'm not sure what would happen if the belt was installed that way. But my unfounded suspicion is it could jump one tooth at high RPMs and then have all 4 cams off by one tooth ( or worse? ) with respect to the crank.

 

[RYU]

Old thread I'd like to bump. Is there a way to check cam timing without removing the valve covers and engine still in the car? I'm running into another troubleshooting abyss on a fueling problem and I want to rule out a cam gear being off by a tooth or two.

Will a leakdown test be able to diagnose this? Assuming a perfect TDC vacuum measurement of course.

 

[Honcho]

Old thread I'd like to bump. Is there a way to check cam timing without removing the valve covers and engine still in the car? I'm running into another troubleshooting abyss on a fueling problem and I want to rule out a cam gear being off by a tooth or two.

Will a leakdown test be able to diagnose this? Assuming a perfect TDC vacuum measurement of course.

The only way I know of to check cam timing without pulling the cover is to put a vacuum gauge on the manifold and watch the needle- if the needle is "dancing" (as LarryB says), you are off. The needle should be steady.

Another method is to snake an inspection light through the oil fill hole and look for the timing marks on the rear sides of the cam wheels. They should line up with the head edge. You can check the front bank this way but not the rears...

 

[RYU]

The only way I know of to check cam timing without pulling the cover is to put a vacuum gauge on the manifold and watch the needle- if the needle is "dancing" (as LarryB says), you are off. The needle should be steady.

Another method is to snake an inspection light through the oil fill hole and look for the timing marks on the rear sides of the cam wheels. They should line up with the head edge. You can check the front bank this way but not the rears...

Would the MAP sensor pickup that fluctuation? When you say manifold you mean the intake manifold, right?

 

[Honcho]

Would the MAP sensor pickup that fluctuation? When you say manifold you mean the intake manifold, right?

Yes, the intake manifold. The MAP sensor may not have the response time to show the fluctuation. The way LarryB told me to do it was use an analog gauge and watch the needle.

 

[RYU]

Yes, the intake manifold. The MAP sensor may not have the response time to show the fluctuation. The way LarryB told me to do it was use an analog gauge and watch the needle.

That's very interesting. I wish I had some kind of high frame rate video to refer to. (HINT HINT!) haha

I'm sure even a perfectly timed stock motor has some minor fluctuation? I'm also on ITBs so I wonder how this will impact the vacuum reading thru the balance bar.

 

[ralph cerbone]

I have an old post from 2008 you will have to search after I did tb , vacuum gauge picture , 21 " of vac. at idle , dead nuts steady . This is exactly how you know you have it timed correctly , I replaced it again in 2020 same picture .

 

[docjohn]

One last point that I'll add from experience doing my '96 and helping someone with a '91: With the punches locking the cams in place, the belt has to be pulled very tight between the crank pulley and the front exhaust cam. I put reference marks on the old and new belts per Gary Kentosh's write-up, and when I pulled the belt "reasonably tight" to that first cam, I found I was one tooth off. So, I lifted the belt slightly and gave it one last hard tug to "shorten" the belt one more tooth between the crank and the cam pulley. The reference marks then lined up perfectly (note that I'm talking reference marks made by me per the Kentosh write-up, not the timing marks on the cams and crank - which are fixed in place by the punches).

So, its possible to have the belt section one tooth "too long" between the crank and the first cam, and still have all the timing marks line up. I'm not sure what would happen if the belt was installed that way. But my unfounded suspicion is it could jump one tooth at high RPMs and then have all 4 cams off by one tooth ( or worse? ) with respect to the crank.

Gone but not forgotten...

 

[RYU]

I have an old post from 2008 you will have to search after I did tb , vacuum gauge picture , 21 " of vac. at idle , dead nuts steady . This is exactly how you know you have it timed correctly , I replaced it again in 2020 same picture .

21" - got it and thank you!