Sube timing belt tensioners are crap?

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, -- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA
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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. wrote:

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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.

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, -- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA
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