Timing belt tensioner bolt broke while driving

[Kestas]

It doesn't always take a massive shear force to snap. It could have seen lower loads that sometimes result in high cycle fatigue. But this could only happen if there was movement in the assembly. Properly fastened, the bolt acts as a clamp and the assembly should not see movement.

We can conjecture all we want. I can give a long list of maybes. Only a proper forensic analysis would tell us what happened.

 

[Hokiefyd]

Originally Posted By: Kestas
Properly fastened, the bolt acts as a clamp and the assembly should not see movement.


Great point. Sort of like how the weight of the vehicle is not carried by the wheel studs or even by the hub's center bore. The lug nuts (or wheel bolts) clamp the wheel to the face of the hub, and THAT is what carries the weight of the vehicle.

In this case, properly torqued, the bolt shouldn't have seen much shear force, if any at all. There could have been a defect in the bolt from new, which was exposed by the initial torquing of the fastener. Once the defect was stressed, it could have lost torque against the tensioner, and allowed it to then move around on the bolt, further fatiguing the bolt until failure.

 

[Nate1979]

Whatever the cause it is a known issue with many reports of it happening, both with aftermarket and OEM components over many years.

 

[zzyzzx]

Originally Posted By: Vikas
Even assuming improper installation, I just do not see how that particular bolt could be subjected to lateral shear forces.


Bolt was made of Chineseium.

 

[sxg6]

Before I said I'm not convinced the bolt broke, but after looking into it a little bit, this is a little more common than I thought. The thread below has some good pictures of a couple tensioner bolts, and broken bolt pictures.

http://www.subaruforester.org/vbulletin/...392/index2.html

Another person in that thread had a similar failure. He said his friend is a metallurgist, who said this about his broken bolt:
"You have a clear indication (red circle) of high-cycle fatigue at the circle. That was the start of the break. The bolt was bending at that point, and did so for a fairly short time, until 3/4's of its usable surface was compromised. It then did a final fracture. This was not a torsional break, but rather a simple bend (like both ends of a see-saw being pushed down). I see good case hardening all the way around the bolt (That is the silver "skin" on the edge of the break). It started in the base of the threads, where it would fail if put in overload. I see some scarring on the thread faces leading to this failure start region. It might have come from the damage after it broke, but it lends credence to something being put into the threads (filings in the surface) or it was not tightenend in all the way and this was the first point it stuck out. This looks like an overload caused by a pressure point or some repeating out-of-balance. It broke pretty quickly too, so whatever the event was it was traumatic and repeating. The only thing I don't know is if the material was adequate in the first place (used weaker metal). That would take some other analysis tools. But my first indication is the bolt was not the issue."

 

[Hokiefyd]

Originally Posted By: sxg6
"But my first indication is the bolt was not the issue."


If it happens to OEM and aftermarket parts, then it does seem more like a design issue than a material one.

 

[coachditka]

Originally Posted By: Hokiefyd
Originally Posted By: sxg6
"But my first indication is the bolt was not the issue."


If it happens to OEM and aftermarket parts, then it does seem more like a design issue than a material one.


Maybe, but it's not exactly like there are dozens of companies producing these parts. OEM and quality AM often use the same suppliers, just a different stamp.

 

[sxg6]

Also interesting that gates suggests loctite on the tensioner bolt in subaru's. In the subaruforester.org link I posted above, some people talked about the bolt possibly backing out a little, putting more stress on the bolt.

https://www.gates.com/~/media/files/gates/automotive/resources/tech-tips-and-tsbs/subaru_loctite.pdf

I didn't see anything in the legacy factory service manual about using loctite or anything else on the tensioner bolt. Maybe the oem bolt comes with some loctite already on it?

 

[kschachn]

Originally Posted By: sxg6
Also interesting that gates suggests loctite on the tensioner bolt in subaru's. In the subaruforester.org link I posted above, some people talked about the bolt possibly backing out a little, putting more stress on the bolt.

https://www.gates.com/~/media/files/gates/automotive/resources/tech-tips-and-tsbs/subaru_loctite.pdf

I didn't see anything in the legacy factory service manual about using loctite or anything else on the tensioner bolt. Maybe the oem bolt comes with some loctite already on it?


FWIW a new Toyota tensioner has thread locker on the bolts, and the FSM states to reapply it if you remove and replace the old one. So that makes some sense to me.

 

[nthach]

Originally Posted By: coachditka
Originally Posted By: Nate1979
It's recommended to not get the Gates WP for Subies.



I've heard. If I was going to do it again, I'd get the OEM or Asin.

Aisin doesn't make the OEM water pump on Subarus - but they do rebox the OEM Yamada pump. Yamada is a Honda and FHI supplier. Subaru also used Hitachi/Unisia/Paraut water pumps thanks to their Nissan ownership in the 1970s-1990s.

 

[Bottom_Feeder]

Originally Posted By: kschachn
... and the difference in appearance between the Aisin water pump and the Gates one was like night and day.

I had the opposite experience with the Gates kit pump for my Subaru. I posted it a few years ago, being hesitant to install the Gates pump, and was talked into buying an Aisin one. Strictly from an appearance standpoint (which is obviously purely subjective), the Gates pump actually looked a lot better than the Aisin one. The quality of the aluminum casting looked better as did the impeller design. The two coolant passages on the Aisin pump looked smaller and rougher. I returned the Aisin pump and used the Chinese Gates one and didn't have an issue for 18k miles until an unrelated rod bearing problem brought the fun to an end.

 

[coachditka]

Originally Posted By: Bottom_Feeder
Originally Posted By: kschachn
... and the difference in appearance between the Aisin water pump and the Gates one was like night and day.

I had the opposite experience with the Gates kit pump for my Subaru. I posted it a few years ago, being hesitant to install the Gates pump, and was talked into buying an Aisin one. Strictly from an appearance standpoint (which is obviously purely subjective), the Gates pump actually looked a lot better than the Aisin one. The quality of the aluminum casting looked better as did the impeller design. The two coolant passages on the Aisin pump looked smaller and rougher. I returned the Aisin pump and used the Chinese Gates one and didn't have an issue for 18k miles until an unrelated rod bearing problem brought the fun to an end.



Interesting. I know that they are made in China, but most things are these day. That does not mean less quality, it just means that's where it's made.

The Gates WP comes with a lifetime warranty, which is why I got it over the OEM pump originally. Like I said before, the shop said they have installed Gates WP for decades with no problems, so that was also a factor.

 

[coachditka]

Well, shop called and the engine is toast. No compression at all.

I'm going to do an engine swap, but need to figure out the best place to source an engine.

Any suggestions?

2008 Legacy 2.5 NA SOHC auto transmission, federal emissions

 

[Trav]

It wont have any compression with bent valves but that doesn't make the engine toast, the heads on these are very easy to do.

 

[rslifkin]

It's worth at least pulling the heads to see how bad the damage is. If the pistons are in ok shape and none of the valves snapped the heads off when they bent, it should be very fixable.

 

[nthach]

Originally Posted By: coachditka
Well, shop called and the engine is toast. No compression at all.

I'm going to do an engine swap, but need to figure out the best place to source an engine.

Any suggestions?

2008 Legacy 2.5 NA SOHC auto transmission, federal emissions


Many of those "used" Japanese engines will be in decent to poor shape. Call around to a few importers. Make sure it has good compression.

Provided the pistons didn't get perforated by the valves, I'd do a valve job, new head gaskets with the updated OEM design or Fel-Pro, reseal the engine and replace the oil separator baffle. Subaru's engines aren't too bad to work on - out of the car.

If $ is no object, swap in a EJ257 WRX motor

 

[coachditka]

Well, I'm having it moved to a Subaru performance shop that can deal with the engine. My shop is great for most things, but they agreed that it would be best to have the car moved to an engine or performance shop. The shop is going to help me with the Gates claim.


I did call one engine shop and they quoted me 3200 for a rebuilt swap with a 3/36 warranty which is not too bad.

But I think I trust this Subie performance shop. The shop that tuned my Titan and installed the headers referred me to them because they also used to work on Subaru but now send that work to this shop.

Wish me luck...

 

[coachditka]

Well, Subaru performance shop wanted over 6k to rebuild the engine. No thanks.

I contacted the largest engine shop in Houston that has been around for 85 years with a good rep.

They quoted me 3100 for a long block install with a 3/100k warranty on the engine.

That seems to be the best choice and I hope to have my car back soon.

 

[Vikas]

how of that Gates is going to be covering?

 

[Merkava_4]

Gates is gonna pay for that engine I hope !!