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Discussion Starter #1
So I am in the middle of replacing the timing belt (02' 2.0L), and in the process I've run across these four supposed Torque To Yield (TTY) bolts on the engine mount. What I can't find out, though, is if the three bolts that hold the lower part of the mount to the engine block are also TTY bolts. I don't want to find out later and then have to drop the motor again to replace them...or worse have them shear off!

So I took a trip to the local VW dealer to see if I could get some answers. They were not able to tell me for certain if the bolts were replaced or not during timing belt changes...but then told me they don't even carry the bolts in stock! That suggests that they likely never replace these bolts at all.

Since it looks like I can't even get my hands on these bolts in the near term, I have two options: 1) replace w/original bolts or 2) locate conventional grade 10.9 bolts. In either case, it's probably wise to drop the torque/angle specs and rely on some standard torque values for particular size/grade fasteners?
 

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VW dealers are notorious for not replacing motor mount bolts which results in a lot of engines dropping on the ground and scraping the pavement. They are then more than willing to monetarily rape you for the resulting repairs.

The three bracket to block bolts are not TTY, but it is a good idea to replace them. Most "good" timing belt kits include them.





The 4 motor mount bolts ARE TTY and MUST be replaced with new and torqued properly with no weight being placed on them.
The large ones are torqued to 74 lb. /ft and the smaller ones are torqued to 30 lb. /ft PLUS 1/4 turn.

 

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Discussion Starter #4 (Edited)
Thanks for the info on the mount to block bolts. Do you have the torque specs on those bolts by chance?

I'm not in any way knocking the importance of replacing TTY bolts, but I just did several searches online and and on this site only found a two instances of a vehicle having the engine mount fail. The NTHSA website does not a single "defect" as being related to the tranaxle mounts.

I'm simply puzzled as to how 1000's of independent shops and dealers can replace timing belts left and right and there aren't more instances of these bolts failing. Based on the sheer numbers of these cars sold (over 1million worldwide since 1998) I would expect to find hundreds of cases of damaged oil pans/skid plates.

NOTE: Oddly enough, I just read that ECS recommends replacing the three bolts that aren't supposed to be stretch bolts, saying it's recommended per VW. I'd like to see where they are getting their info from.....
 

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Engine Mount, right side

Mount to body bolt (front and rear (2) same size) 30 ft.-lbs. plus 90 degrees

Mount to body bracket (the smallest bolts (2)) 18 ft.-lbs.

Mount to engine bracket bolts 44 ft.-lbs. plus 90 degrees

Engine Mount bracket to cylinder block 33 ft.-lbs. (I like to clean them good and put on some sealant type Loctite)

This info is from Bentley, which is the official VW repair/service manual. It appears to me that only the mount to body and mount to engine bracket are stretch bolts.
 

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...The three bracket to block bolts are not TTY, but it is a good idea to replace them. Most "good" timing belt kits include them...The 4 motor mount bolts ARE TTY and MUST be replaced with new and torqued properly with no weight being placed on them.
The large ones are torqued to 74 lb. /ft and the smaller ones are torqued to 30 lb. /ft PLUS 1/4 turn...
Looking through Bentley and I found different info depending on if it was a diesel, 2.0L, 1.8T or not (VR6)--I have a Jetta/Golf book too.

The "large bolts" as you describe them are the mount to engine bracket bolt--my Bentley says 44 ft.-lbs. + 90 degrees. The plus 90 degrees indicates they are stretch bolts. In that you torque them to the specified number, give them a moment to "set", then make the 1/4 turn. This is what is indicated in my book for the 2.0L and the TDI (and the VR6), however, the 1.8T indicated the 74 ft.-lbs. number you state with no additional 1/4 turn which to me indicates they are not a stretch bolt...?

Anyway, my Bentley says your 74 number only for the 1.8T--the OP has a 2.0L, so I think you got this one wrong?
 

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Looking through Bentley and I found different info depending on if it was a diesel, 2.0L, 1.8T or not (VR6)--I have a Jetta/Golf book too.

The "large bolts" as you describe them are the mount to engine bracket bolt--my Bentley says 44 ft.-lbs. + 90 degrees. The plus 90 degrees indicates they are stretch bolts. In that you torque them to the specified number, give them a moment to "set", then make the 1/4 turn. This is what is indicated in my book for the 2.0L and the TDI (and the VR6), however, the 1.8T indicated the 74 ft.-lbs. number you state with no additional 1/4 turn which to me indicates they are not a stretch bolt...?

Anyway, my Bentley says your 74 number only for the 1.8T--the OP has a 2.0L, so I think you got this one wrong?
The 44 ft-lbs plus 90 degrees for the larger bolts is an outdated spec which was resulting in failure of the threads in the aluminum mounts. It has been revised to 74 ft-lbs with no additional turn for all 4 cylinder MKIV cars, I'm not sure what the VR6 cars use.

It is still a TTY bolt and needs to be replaced regardless of whether it has the +90 portion of the spec or not. There are non-TTY bolts which have a torque setting +90 degrees and there are TTY bolts which don't have the +90 degree spec.

Clear as mud? ;)
 

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Thanks for the info on the mount to block bolts. Do you have the torque specs on those bolts by chance?

I'm not in any way knocking the importance of replacing TTY bolts, but I just did several searches online and and on this site only found a two instances of a vehicle having the engine mount fail. The NTHSA website does not a single "defect" as being related to the tranaxle mounts.

I'm simply puzzled as to how 1000's of independent shops and dealers can replace timing belts left and right and there aren't more instances of these bolts failing. Based on the sheer numbers of these cars sold (over 1million worldwide since 1998) I would expect to find hundreds of cases of damaged oil pans/skid plates.

NOTE: Oddly enough, I just read that ECS recommends replacing the three bolts that aren't supposed to be stretch bolts, saying it's recommended per VW. I'd like to see where they are getting their info from.....
NHTSA likely gets very little data pertaining to this. There is no problem as long as the bolts are replaced. Trust me, there are more than a handful of engines that have dropped and been damaged by not replacing the bolts. Just as there have been hundreds of TDI's tooefed by dealers and independent shops who treat them like any other gasser belt and skip using the proper tools and using the proper procedure. But that is a whole different story for a different engine section.

Its a few bucks for new bolts...why risk it?
 

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Discussion Starter #10
The 44 ft-lbs plus 90 degrees for the larger bolts is an outdated spec which was resulting in failure of the threads in the aluminum mounts. It has been revised to 74 ft-lbs with no additional turn for all 4 cylinder MKIV cars, I'm not sure what the VR6 cars use.

It is still a TTY bolt and needs to be replaced regardless of whether it has the +90 portion of the spec or not. There are non-TTY bolts which have a torque setting +90 degrees and there are TTY bolts which don't have the +90 degree spec.

Clear as mud? ;)
It makes some sense, so...yes. I did some more homework, and when I realized that there was no firm convention that all TTY bolts will have a two or more part tightening sequence (and likewise that non TTY bolts will only have a single torque value), all bets are off. If it says to replace the bolt in the book, then you should replace the bolt.

In their use of TTY fastners, the mfgr. probably shaved a few kg off the curb weight, a few $$ in manufacturing, but added to the overall maintainence costs through the use of consumable fasteners. Most importantly, they also cost me some sleep :)

Thanks for the torque specs, wawalker. I wish I had bought that service manual before, but we were planning to have a shop do the work until I got some quotes to do the work.
 

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TTY bolts for the motor mounts are not used to save VW money or keep the bolts tight. They are meant to break away in a collision so the engine drops and goes under the passenger compartment. There is no reason to yield a bolt to keep it tight. That can be done before reaching yield. In fact, when metal yields the stress drops, or at least stops increasing with greater strain. So TTY is just a way to weaken the bolt enough so it breaks in an accident.
 

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TTY bolts for the motor mounts are not used to save VW money or keep the bolts tight. They are meant to break away in a collision so the engine drops and goes under the passenger compartment. There is no reason to yield a bolt to keep it tight. That can be done before reaching yield. In fact, when metal yields the stress drops, or at least stops increasing with greater strain. So TTY is just a way to weaken the bolt enough so it breaks in an accident.
I very much doubt that this is the reason. A non TTY bolt will shear just as easily as a TTY bolt. There are numerous other TTY bolts that VW uses all over these cars; head bolts, rod bolts, main cap bolts, flywheel bolts, timing belt idler bolt (TDI), subframe bolts and others that I am forgetting.

They are used to keep the bolt tight. Simple as that.
 

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There are other good reasons for TTY bolts. Yielding the head bolts maintains a more constant clamping force as the head gasket compresses. This means the bolts don't have to be re-torqued after some break-in period. And any bolt where it is critical to achieve a certain clamping is a spot fot a TTY. As mentioned previously, after yielding the stress plateaus, independent of thread friction. For motor mount bolts, if tightness were the issue, why wouldn't the mount to engine bolts be TTY? Yielding the bolt does bring it closer to breaking, so less energy input will shear them in a crash.
 

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Funny story, My engine mount bolts were on so tight that with my wrench and a breaker bar the wrench broke before the damn screw came lose.


Seriously, the entire ratcheting mechanism exploded out of the wrench.
 

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Mount to body bolt (2 bolts same size) - 30 ft-lbs. plus 90 degrees.

Mount to body bracket (smallest bolts (2)) - 18 ft-lbs.

Mount to engine bracket bolts (2 bolts) - 44 ft.-lbs. plus 90 degrees (UPDATED) Now it is 74 ft-lbs.

Engine Mount bracket to engine block (3 Bolts) - 33 ft.-lbs.

** If anyone has any other updates, please feel free to repost **
** When installing the engine bracket, I found it was easier to remove the bolts, wiggle into place, then insert the largest bolt closes to the front of the engine. Then pivot the entire bracket from the back, upwards. Insert both bolts and then line it up. Super easy this way. ** Thanks for those that contributed before me. Very helpful discussions.
 
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