KY928

This week Greg Schickel and I tore down my shark because of a coolant leak coming from the water pump area. Turns out the tensioner bolt had backed out, and coolant was flowing from the loose shoulder bolt and throwing the tensioner arm out of alignment. The belt was hanging half off the pulleys and cam gears, and about 1/4" more narrow than a new belt. It accually rubbed a groove in the back side of the tensioner arm. I bought a new belt, shoulder bolt and bushings for the arm. When Greg torqued the shoulder bolt in, he said it just didn't feel right the way it seated. We looked at the set up, checked out parts pictures, and think we discovered a washer that's not supposed to be there. It's between the head of the bolt and the bushing shoulder on the arm. The shoulder of the bushing was worn off, by the washer it looks like. Can any one confirm that this washer isn't supposed to be there? We're thinking that this washer is the reason for this failure 15k after T/B replacement. We don't see the washer in any drawing, but it was there when we removed everything. We're thinking this washer caused the bolt from seating right, and possibly caused some binding in the bushings, and some how causing the bolt to work out. Any comments would be appreciated.

Bill Ball

You're probably right about that washer causing the problem. I know you are correct that it is not supposed to be there. There is one on the other side of the arm spacing the idler. Good catch before this created a bigger problem.

Mako 928

Just did a timing belt along W/ head gasket on MY 85'. As I remember there is a large washer between the tensioner arm and upper idler roller.
Bolt, nylon bushings, tensioner arm, large washer,idler roller.

derporsche928

Yep, the shoulder bolt has a shoulder length that allows for the tensioner arm to pivot, and the washer up front caused the tensioner arm to be pinched tight rather than allowing it to pivot..... Hence the worn to nothing shoulder on the back bushing, and then the subsequent loosening of the bolt.....
Just goes to show, how it came apart isn't necessarily how it goes back together..... We were fortunate to catch this, and it all points to keeping the utmost attention to detail when you're working on these cars.....
Another thing I was amazed by is that these things must have some really bad TB issues before a belt goes, because I'm in awe that this one didn't fail..... It was tracking badly, rubbing the crooked tensioner arm,... along with the crank damper.... It's width was worn down by 3/16", ... (That's what all the trash was at the bottom of the cover......) ...... and it was running at a tension of 3.2, and was soaked with antifreeze........ Wow.....!
(The 87's and newer I've done, have a longer post on the water pump which comes to just past flush of the tensioner arm assembly, and it has a bracket, washer, and 6mm phillip's head screw to button it up.....)
I'd guess the dealer mechanic decided a washer would be nice in front of the shoulder bolt head..... Simple mistake, as nearly all bolts have some type of washer under them, but this was apparently done without thinking of is effect in this application......

Peace-Out,

mark kibort

i seemed to remember a drawing that showed a washer, a very thin one, used in that position to take up a little slack that the tensioner arm would/could have.Im thinkingit was the reason for a "walking forward" timing belt on an older 928 i had. it was just a little bit of movement that allowed the arm to point down and let the belt run forward a bit. like i said, there was a drawing that showed a thin washer there, but certainly not a thick one. it could effect the ability of the arm to move as was said.

Mk

derporsche928

Just got it buttoned up, and all looks good now... FYI, the shoulder bolt with the (thick) washer had the tensioner bound up... After the tensioner adjuster was backed-off, the tensioner arm couldn't be moved....
The dimension of the shoulder on the shoulder bolt was .015" longer than the tensioner arm with bushings is wide...... Pivoted nicely without being sloppy without the aforementioned washer.......
Also now have a functioning tensioner light,...... The dealer had just grounded the wire that was supposed to go to it and left the tensioner wiring all undone.....
After we buttoned it up, and confirmed no leaks, good TB tracking, etc, we checked the auto - thrust bearing issue, and found .0075" crank movement....(just within spec) and took care of the preload problem here...... Also, did away with the air pump, and fixed or made better a lot of other small things too.... Tomorrow we'll shake it down and double check everything....
We found a lot that had been done wrong, but we enjoyed making it right.....

john gill

Love your avatar , where was this taken please , funny how all crashing 911s are shown backwards .

Bill Ball

Actually, that is well within the spec. Endplay limit is 0.4mm or 0.016". I have not found a car that is below 0.007". My car is 0.008"

KY928

Mark, looking at the drawing, it looks like a thin washer, but I'm pretty sure it's the shoulder of the bushing, even assembled, it looks like a thin washer.

KY928

Sorry, Don't know what race this pic. was taken. It was in a e-mail attachment I received from some one in our local Porsche Club.