IceShark

As many know my car has been self destructing since I washed the engine bay.

Latest item is the timing belt tensioner. Since I had to take so much off the front to get to the thermostat, I thought I may as well check out the timing and balance shaft belts, too. Good thing I did because they were so loose I'm sort of surprised I didn't skip a tooth or two and lunch the valves.

As I loosened the pivot nut the thing didn't take hardely any effort to unscrew. I thought this is strange. Then I tried to snug it up and the bolt started to either turn a bit and pull out the stud or just spin the whole works. So the thread where ever that stud is supposed to anchor is stripped. Must have been the Porsche mechanic when I had belt replaced 5 or 6 years ago.

So what to do now. It looks like there is a pilot alignment bushing pressed into the back of the tensioner plate or maybe that is the block, I can't see too well without taking off all the belts, rollers etc. The tensioner pivots on this bushing and the 8mm stud and nut which go inside the bushing are there to clamp this point down but really keep the tensioner from walking out, I guess. Sure the clamping pressure will keep the tensioner from moving some but that duty is really carried most by the other adjustment bolt, which is fine.

I don't really want to tear apart the front of the motor so am thinking a helicoil or something on that order. As this bushing has a 5/16th" / 8mm ID I could get a 1/4" helicoil insert into the threaded portion and then tap in a 1/4" ID x 5/16" OD bushing inside. But I have probably screwed those threads up so bad that a 1/4" coil won't hang on. And if I stay with a 5/16" / 8mm stud then I need to ream out that pressed in bushing to tap a 3/8" thread and that bushing looks to be only about 11 mm OD which doesn't leave much wall thickness left. Like about 0.75mm.

And does anyone know how tight that bushing is pressed in? If I could pull that out without too much trouble then I could go with the 5/16" helicoil, pound the bushing back in and be done.

HELP!

pete944

The stud you're talking about is part of the tensioner assembly itself. it's not threaded into the block. I wouldn't try to rig it. It would be best to buy a new spring tensioner unit. I think they're around $200.

IceShark

OK, Thanks. Does anyone have a diagram or description on how the tensioner assembly bolts up to the block? I guess if I pull off the tensioner roller plate I'll see what remains.

pete944

There are 3 nuts in a sort of triangle pattern. You have to remove the crank pulleys to get at the bottom one.

Matt Sheppard

Well, I drilled and tapped an '86 block to attach an '87 on tensioner. I wouldnt try it while in the car, but . . . you go!

Perry 951 has done this too and has some info on his web site. At least that's where I got the idea.

If the adjustment bolt on the '87 and later tensioner loosens, the spring should keep at least some tension on the assembly. The yellow circles represent where holes need to be drilled and tapped.

83na944

Do you think that washing the engine caused the thermostat and belt tensionor to fail. Maybe it is just coincidence.

IceShark

Of course not. I have no idea how the thermostat went south and the belt tensioner was busted 6 years ago by Lynch Porsche in Chicago. I just found it now.

I'm just noting how a engine bay wash job is leading to a never ending list of discoveries and headaches. And problems to fix.

craig001

If you decide to try to fix it rather then replace I would recommend a Time-cert over the helicoil. Just my $.02.

Also, Dan - I may be contacting you about trying to figure out how to adapt the wiring kit to a 911.

Charlie

I put the tensioner on mine with the engine in the car. I had an angle drill. My main concern was drilling the holes straight into the block, and not at an angle. I had the belts off and it took less than 1 hour to put the tensioner on.

IceShark

Well, I got the tensioner out of the car and inspected. Only had to remove the balance shaft belt and loosen the timing belt and slip it off the cam sprocket to find and remove the 3 bolts holding it to the block. Wasn't too hard and I didn't have to take the crank pulleys off so no chasing down a flywheel lock.

An interesting discovery was the tensioner adjustment bolt hole had a helicoil in it!

I tried to get that pivot bushing out but no dice without taking the chance of ruining it. So off to the machine shop tomorrow to get them to pull it out, then I'll helicoil it and put things back together. Craig, I don't know if a Time-cert will work here as they have that shoulder you need to counter bore. Well that shoulder is going to be half way down the hole after the bushing. Starting to look like the battle is almost won.

pete944

You're lucky, on mine there was no way to get it out without removing the pulleys.

Yabo

sorry for the trouble... but you successfully scared me away from cleaning my engine bay! old engines suck to work on huh!

83na944

Well, I guess the best way to look at it is that those things needed to be repaired anyway.

Since I've started doing maintenance and repair, I've found a couple of things that were patched together. With the labor rates the dealers charge, looks like they would have replaced the tensionor they broke at their cost.

IceShark

Of course. It had to be done sooner than later and I'm glad I didn't lunch my valves out. Would have been pretty easy as far as I can tell if you were at high RPMs for awhile. At least the dumb Porsche F%CK didn't miss the timing. Everything was on mark. But I'm really pissed off that he helicoiled the easy lock thread and left the pivot thread alone to fend for itself, knowing it was lunched also. Guess it would have cut down on his repair rate having to farm it out to a machine shop. These guys are like HMOs that have the first thought as to how to make the cost less. Who cares if that is the correct direction or not.

Anyway, someone like John D. or whoever is taking over the forum should put this discussion and the prior one in an archive. I'm sure I'm not the only one that has this problem. My 88 951S has only 42000 miles. Owned it since 90 or 91. Maybe a retension before I got it but nothing else since Lynch had their hands on it to replace belts 6 years ago.

Be carefull, boyz.

Matt Sheppard

People pay these guys $70 an hour to do this stuff. . .


In reality, you are the only one who cares enough to back up when something isn't right. I have a lot of respect for some peoples knowledge, but the majority of the "I've-been-working-on-Porsches-for-X-decades" types think their knowledge is what your car lives or dies by. Your fortunate you found this out in time and thanks for the heas-up.