Sube timing belt tensioners are crap?

[Todd H.]

Apparently the timing belt tensioners from subaru are 100% hydraulic,
and are quite prone to issues, not coming up to tension quickly
enough, and generally being unreliable. I know mine is about to have
the 6th Subaru timing belt tensioner put in in its 110k mile lifetime
because a brand new one put in about 10,000 miles ago turns out to be
defective. Apparently it's the root cause of my periodic missing on
acceleration problem I've had ever since that preventive maintenance.

Lack of tension on the initial startup after the job is likely to
blame for the belt jumping a tooth, damaging the belt, and
intermittently allow the timing off just enough to be an intermittent
pain in both my and my tech's ass.

Apparently, as the story further unfolds, not only is there a TSB on
the issue (which was followed to the letter on the actual replacement
of the belt), but upon the re-replacement of the belt, and manually
turning the engine 10 times (vs the prescribed 3) this thing still
hadn't come up to tension. As the story further unfolds, we learned
that aftermarket tensioners apparently include a spring as a backup to
the hydraulic tensioning, and once it's pumped up to tension it wont'
recede the way a Subaru tensioner would. Subaru relies only on the
hydraulic action to tension, and has no backup.

So yet again (in addition to the stories of aftermarket head gaskets
being superior to OEM sube), we have a story suggesting strongly that
aftermarket parts makers have done what you'd expect expensive OEM
parts to have done -- fix design flaws.

Anyone with experience have data points confirming or denying this?



Best Regards,

 

[AS]

I have replaced belts in one 2.2lt and in two 2.5lt engines. So far I
only needed to replace one of the tensioners because it was leaking.
The wife's car has about 95k miles on it and the timing belt and
tensioner will be replaced for the first time at around 100K as
suggested in the manual.

During installation, it is important to compress the tensioner very
slowly, using the weight of the car and the jack or a hydraulic press,
block it with a suitable pin, adjust its position as to "pretension"
the belt, tighten it in position and only then, releasing the pin. To
help the tensioner, what i do is to turn the crankshaft and camshafts
with a wrench as to make sure that the slack in the belt is towards the
idler with the tensioner. Never had a problem this way and never turned
the engine 3 times.

As far as the missing during acceleration, I would suspect the ignition
system, including coil pack, HT wires, spark plugs, crankshaft pos
sensor, etc. Are u using Bosch plugs?

The only problem I had with the first engine I did, was trying to get
the crankschaft pulley bolt tight to specs. This problem cost me a new
balancer, new timing sprocket, new bolt, and a new key. Grrr, Subaru's
minimal bearing surface between the crankshaft and balancer, grrrr!!

Good luck Todd!!

 

[Todd H.]

As far as the missing during acceleration, I would suspect the
ignition system, including coil pack, HT wires, spark plugs,
crankshaft pos sensor, etc. Are u using Bosch plugs?

Plug wires and plugs (NGK) were brand new with the original timing
belt change at 95k that started this drama. These new wires and plugs
were among the first things defected out and replaced again, and the
probelm remained. Coil pack tested okay at the time, but it is still
something on my list of stuff to suspect.

Crankshaft and cam pos sensors got replaced on the next round of
debugging this problem. Still no fix. Next up was the common
wiring harness between them.

The missing, it appears by all accounts now, is because of one timing
belt tooth being flattened thanks to the defective (yet brand new)
Subaru OEM tensioner. We hadn't looked at the timing belt until now
because the trouble codes were sending us on a wild goose chase with
cam sensor codes, crank pos sensor codes. Most likely neither of
these sensors were bad it seems.

The only problem I had with the first engine I did, was trying to get
the crankschaft pulley bolt tight to specs. This problem cost me a
new balancer, new timing sprocket, new bolt, and a new key. Grrr,
Subaru's minimal bearing surface between the crankshaft and balancer,
grrrr!!

Good luck Todd!!

I'm feeling good now that the smoking gun of the flattened tooth on
the new belt was found, and the defective tensioner has been ferreted
out. Time will tell, though--I should have the car back on Monday
depending on when the new tensioner gets in.

Thanks for the good wishes--we need em with this damned car lately.


Best Regards,