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2G Timing belt flop

Tigerinstincts

Proven Member
198
20
Mar 1, 2015
Sacramento, California
Wondering if it's normal for the timing belt to resonate at certain rpms and vibrate/flop around?

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New timing belt was recently installed along with all new OEM tensioner, tensioner pulley, idler, and balance shaft pulley. Belt tension has been gone over multiple times and re-adjusted to compensate for timing belt vibration/flop. Belt tension is within spec but a tad on the looser side (grenade pin inserts into the first hole on the body of the tensioner, into the hole of the push rod, but does not slide into the second hole on the body of the tensioner). Balance shafts are installed on the car.

I've never bothered to actually look at the timing belt while manually pulling on the throttle body butterfly valve when the car is running, but my coworker pointed out the timing belt bouncing around to me.
 

Mello

15+ Year Contributor
1,457
603
Jul 4, 2003
Albuquerque, New_Mexico
Grenade pin should go all the way through all holes after rotating & letting sit to settle. If the pin doesn't go through the timing belt tension is not correct.
 

Tigerinstincts

Proven Member
198
20
Mar 1, 2015
Sacramento, California
Grenade pin should go all the way through all holes after rotating & letting sit to settle. If the pin doesn't go through the timing belt tension is not correct.
Tension should be set between .150" and .177" and mine is just over .168". I measured with a dial caliper and used the drill bit method just to double check. A 5/32" drill bit will fit with minor play but a 11/64" drill bit will not fit.
If you actually do the grenade pin passing through all the holes method, you'll find you're just over the minimum tolerance (I measured this to be max .155").

Either way, I've set belt tension with the grenade pin method initially, ran the car, was told the belt flopped around, re-adjusted belt tensioner again, found the belt still flopped some, then finally settled on a looser measurement and the flopping doesn't look as violent as it used to. However I'm still concerned...

+1 what Mello said. See if the tensioner arm has play. The bushing inside could be worn.
All timing components are brand new and this is actually my 2nd tensioner because I thought the first one from JNZ was causing this.
 
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AWD-Tony

Supporting Member
6,666
3,543
Sep 11, 2017
Cincinnati, Ohio
All timing components are brand new and this is actually my 2nd tensioner because I thought the first one from JNZ was causing this.
You have a 7 bolt? And tensioner pulley is being rotated counterclockwise?
 

Tigerinstincts

Proven Member
198
20
Mar 1, 2015
Sacramento, California
When you install the grenade pin, is the back hole lower? If so, I’d tighten the tension.
Yes, but it's not so low that the space between the body of the tensioner and the tensioner arm are out of spec. The holes visually look like they line up but the grenade pin just won't pass through the last hole

I initially set the timing belt tension using the grenade pin method and always have done it this way. It's just that when my coworker pointed out the excessive vibrating/flopping of the timing belt, I couldn't get it to settle down to the point you are seeing in the video without actually staying on the looser side of the tolerance spec.

And the belt only vibrates like that at certain rpms. I've taken it up to 5.5k rpms and it's not as noticeable, but there's other rpms where it looks...possessed.
 

Mello

15+ Year Contributor
1,457
603
Jul 4, 2003
Albuquerque, New_Mexico
Sorry but I still feel your T-Belt is not tensioned correctly. I follow this step from the FSM engine overhaul section 11B when tensioning the timing belt. These instruction specifically state the grenade pin should move freely and when finished the Dim A protrusion should be between .150" to .177".
As you stated your pin does not move freely (doesn't even go through all holes in the tensioner) and your .168" is not valid.
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pauleyman

DSM Wiseman
8,187
2,758
Nov 19, 2011
oklahoma city, Oklahoma
Did you check tension after you rotated the engine by hand? It's important because you can't have any slack on the non tension side. If there is slack the tension will not be correct.
 

Tigerinstincts

Proven Member
198
20
Mar 1, 2015
Sacramento, California
Sorry but I still feel your T-Belt is not tensioned correctly. I follow this step from the FSM engine overhaul section 11B when tensioning the timing belt. These instruction specifically state the grenade pin should move freely and when finished the Dim A protrusion should be between .150" to .177".
As you stated your pin does not move freely (doesn't even go through all holes in the tensioner) and your .168" is not valid.
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Weird. This is the first time I've seen these steps. I have Alldata and I don't remember it ever saying anything like this. Looks like I'll re-adjust the belt again

Did you check tension after you rotated the engine by hand? It's important because you can't have any slack on the non tension side. If there is slack the tension will not be correct.

I didn't make it a priority to check that but visually, it looked fine. All my marks lined up after 15 min and running the car multiple times now, and I thought that was the reason for rotating the crank 1/4 of turn counter-clockwise, then rotate it clockwise back to where all the timing marks lined up again. This step is supposed to move any and all slack to the tensioner side.

I see aftermarket cam sprockets, what else is not stock? Cams, Springs? Who's belt?
Do you have a build thread or vehicle profile?

Fidanza cam gears (degreed), FP2s, Evo 9 springs and retainers, with a Gates belt. I'll have to double check that I updated my profile.
 
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pauleyman

DSM Wiseman
8,187
2,758
Nov 19, 2011
oklahoma city, Oklahoma
I didn't make it a priority to check that but visually, it looked fine. All my marks lined up after 15 min and running the car multiple times now, and I thought that was the reason for rotating the crank 1/4 of turn counter-clockwise, then rotate it clockwise back to where all the timing marks lined up again. This step is supposed to move any and all slack to the tensioner side.
Yes that works fine also.
 

waltah

Proven Member
369
154
Mar 2, 2011
fairfield, Virginia
Wondering if it's normal for the timing belt to resonate at certain rpms and vibrate/flop around?
It's certainly normal for a system with this structure -- it is basically a string under tension and supported at the ends (exhaust sprocket and tensioner pulley -- to want to do it. Without damping to absorb vibrational energy it will vibrate as you are seeing at some speeds. Higher tension will move those speeds up as will a greater timing belt 'spring constant' -- increase of tension required to get a given amount of elongation. More damping -- energy absorbed by the belt as it is stretched -- will tend to make the amplitude of the vibration lessen or even disappear.

About the only abnormal condition that would contribute to this other than of out-of-spec tensionng would be something loose so that bending of metal contributes. A loose idler pulley bolt, perhaps a worn bearing would be possibilities. Air in the oil supply to the tensioner would certainly do it -- how is that bled, anyway? Foam in the oil pan caused by too high oil level or ???

Different manufacturer's belts will be different -- In theory none of them should allow enough of this to cause trouble. But who knows?
 

Tigerinstincts

Proven Member
198
20
Mar 1, 2015
Sacramento, California
It's certainly normal for a system with this structure -- it is basically a string under tension and supported at the ends (exhaust sprocket and tensioner pulley -- to want to do it. Without damping to absorb vibrational energy it will vibrate as you are seeing at some speeds. Higher tension will move those speeds up as will a greater timing belt 'spring constant' -- increase of tension required to get a given amount of elongation. More damping -- energy absorbed by the belt as it is stretched -- will tend to make the amplitude of the vibration lessen or even disappear.

About the only abnormal condition that would contribute to this other than of out-of-spec tensionng would be something loose so that bending of metal contributes. A loose idler pulley bolt, perhaps a worn bearing would be possibilities. Air in the oil supply to the tensioner would certainly do it -- how is that bled, anyway? Foam in the oil pan caused by too high oil level or ???
I'll most likely tear the timing section down sometime next week. Inspect everything, make sure my balance shafts are correctly phased, re-verify my timing tensioner is set correctly, etc.

If I find the timing belt is still resonating/vibrating/flopping, whatever you wanna call it, around after I re-check everything, I'll have to assume something mechanical is off.

I'll report back sometime next week or weekend.
 

motomattx

Proven Member
3,720
1,466
Dec 9, 2010
wampum, Pennsylvania
I wouldn't be overly concerned about it, all belts have a certain amount of deflection under use, you dont normally see the timing belt on a car when its running or you would have seen this before. As far as setting the tension on the timing belt, its not actually that critical, the auto tensioner/dampener unit has what around a half inch of throw? that thing can take up more slack than the belt will ever see in its life time before it breaks, in any case after setting the initial tension using the pin, the belt will stretch and settle in, this will make the piston shaft in the tensioner/dampener unit protrude to take up that slack and therefore you wont be able to re-insert that pin anyway, this is all normal operating conditions for these parts guys, nothing to go anal retentive about, again the install instructions are for INITIAL install on new parts to get things in spec to start out with, they WILL move over time, you wont always be able to insert that pin back into the dampener body for the life of the belt and tensioner/dampener assembly, if you could then there would be no reason to have a hydraulic tensioner unit at all, we would just use a solid piece of metal and set it up and manually reset it from time to time, you guys are treating these auto tensioners as though they are manual tensioners, let them do their job, set them and forget them.

It's certainly normal for a system with this structure -- it is basically a string under tension and supported at the ends (exhaust sprocket and tensioner pulley -- to want to do it. Without damping to absorb vibrational energy it will vibrate as you are seeing at some speeds. Higher tension will move those speeds up as will a greater timing belt 'spring constant' -- increase of tension required to get a given amount of elongation. More damping -- energy absorbed by the belt as it is stretched -- will tend to make the amplitude of the vibration lessen or even disappear.

About the only abnormal condition that would contribute to this other than of out-of-spec tensionng would be something loose so that bending of metal contributes. A loose idler pulley bolt, perhaps a worn bearing would be possibilities. Air in the oil supply to the tensioner would certainly do it -- how is that bled, anyway? Foam in the oil pan caused by too high oil level or ???

Different manufacturer's belts will be different -- In theory none of them should allow enough of this to cause trouble. But who knows?
There is no engine oil in the auto tensioner/dampener in the 4g63, it has permanently sealed oil inside of it, it does not get bled or replaced by anything, if it leaks it gets removed and tossed, oil fired tensioners are usually used on cars with timing CHAINS on them such as the Chevrolet Cobalt or the Toyota Tacoma pickup trucks, both with chains not belts.
 

Tigerinstincts

Proven Member
198
20
Mar 1, 2015
Sacramento, California
I wouldn't be overly concerned about it, all belts have a certain amount of deflection under use, you dont normally see the timing belt on a car when its running or you would have seen this before. As far as setting the tension on the timing belt, its not actually that critical, the auto tensioner/dampener unit has what around a half inch of throw? that thing can take up more slack than the belt will ever see in its life time before it breaks, in any case after setting the initial tension using the pin, the belt will stretch and settle in, this will make the piston shaft in the tensioner/dampener unit protrude to take up that slack and therefore you wont be able to re-insert that pin anyway, this is all normal operating conditions for these parts guys, nothing to go anal retentive about, again the install instructions are for INITIAL install on new parts to get things in spec to start out with, they WILL move over time, you wont always be able to insert that pin back into the dampener body for the life of the belt and tensioner/dampener assembly, if you could then there would be no reason to have a hydraulic tensioner unit at all, we would just use a solid piece of metal and set it up and manually reset it from time to time, you guys are treating these auto tensioners as though they are manual tensioners, let them do their job, set them and forget them.
Thanks for the reassurance and I do agree with you on all points, but I do wish I took a video before I readjusted the belt. There was much more vibration/flopping of the belt than shown in the video I posted. So much so that I thought if I put the timing covers on, it would physically slap it.

I wouldn't be posting here if I didn't think it was an issue. My understanding was there's only supposed to be minimal-to-no amount of deflection in the belt while the engine is running. I've definitely reduced it by staying on the looser side of the tensioning specs. I'll probably remove my stationary rev limiter and see what the belt does at +5.5k rpms.

Thank you guys for all your help btw
 

Tigerinstincts

Proven Member
198
20
Mar 1, 2015
Sacramento, California
Wanted to report back because I'm pretty sure I figured out what was causing my timing belt to violently flop around.

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My exhaust Fidanza cam gear looks to be out-of-round and physically wobbling as the engine rotates. I didn't take a video of this area but when the timing belt teeth and the gear teeth initially mesh/make contact, the Fidanza gear oscillates the belt from an off-centered position causing the belt to not only flop/vibrate, but actually walk on the exhaust gear slightly. It is completely straightened out by the time the belt reaches the intake gear and looks centered as it travels down the idler pulley. Very strange find and disappointed I didn't see this earlier.
 
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