Timing belt tracking problem

[Hkp7]

84s 928 US. Have had this problem since I got the car. The timing belt slips off the tensioner roller and what keeps it from falling off is it dragging against the tensioner arm. I later had a reputable shop install a new belt and water pump. I rebuilt the tensioner. The tensioner pully was replaced with a new one, the plastic hinge bushings and shoulder bolt are new. Belt still tracks away from engine off pully about a quarter inch. I am not sure where to turn so I am asking for help here.
Here is what I found, the tensioner arm listed for my car is 928 105 540 05 the arm I have comes up as a number for an 82 model although 2-84 is stamped on the arm itself. The idler roller part number is F-220097. and the idler roller on the water pump looks like one for a 87-95 and I am curious if it is the wrong one installed from the last 26 years or not. I included pictures of the belt falling off, the idler on the pump, the tensioner arm with part number on it and the idler roller that I believe is the one I need which is part number 928 105 571 00.

[Hkp7]

Some new updates for my post. I found after installing new shoulder bolt it bent and I am guessing it could be due to either my overtightening or the fact that the washer it mates with has smash marks on it which makes it sit funny as you can see in picture. Still curious if either tensioner arm is wrong or idler pully is wrong causing tensioner arm to be off track pulled by belt which is in turn bending arm bolt.

[Mrmerlin]

in the last picture the washer on the left looks like it is too big ID

you will need a new pivot bolt and a washer to fit it

[Mrmerlin]

washer PN
928 105 572 00

Pivot bolt PN
928 105 574 03

need to find out the engine code for your engine?? as there are 2 different tensioner arms,

[Hkp7]

Thanks for the post, I was thinking the same thing about that washer because it just didnt make sense why the hole was so much larger than 12. I looked around for the washer and found a picture of one which looked very similar to mine. It may have been just a generic picture as well. Maybe who ever did the timing belt in the past lost the washer and used one from a hardware store, I dont know.
I am wondering about those engine codes, once I get them how do I use the code to figure out what part I need. Is that number what you see to the right of the listing for the part on the dealer list of parts? Also is there another way of retrieving the code other than calling the dealer? They gave me the engine code once but I didnt write it down. Thanks, Bill.

[Hkp7]

One other thing, what do you think about that idler pully, the one in the bottom pic is one that is listed for an 84 and the one on the car "looks" like on from a later model. Thinking maybe the spacing of that roller is different than what my car should have. Maybe it could be placing the arm to close toward the engine.
Thanks, Bill.

[Mrmerlin]

the engine code is on the top front of the engine block.
its just under the top radiator hose about 1 in. forward of the top hose clamp and under the hose it will be M28/ _ _
Once you know this then you can figure out if you have the right tensioner arm.
The idler bearing should not change where the arm sits but lets work on the arm first

[Landseer]

Can you post a picture also of the front of the engine showing the cam gears?

[Mrmerlin]

this is a picture of my 86.5
The engine code will be just to the left of the lower rad hose outlet where the thermostat housing is, and its on the block .
This picture also shows the oil pump removed to replace the O ring and radial seal

[Hkp7]

Here are the pics of the cam gears as well as a few others. Engine code is M28/20 81E07072. I plan to replace the belt during all these parts removals and decided to go with the one from the dealer just to eliminate any question. I have another question about that as well, I have read that it is significant to which way the writing on the belt faces. I am having trouble believing this but is it true?

[Mrmerlin]

please remove both rad hoses and the thinner hose that goes to the coolant bottle also remove the 2 10MM bolts that hold the top rad shroud on, your working too hard

[Hkp7]

Ordered a new washer and a tension tool today, I have another non bent pivot bolt and dealer said tensioner arm is for my vehicle engine code. We will see by Friday. Decided not to change belt yet, will try these new parts first.

[Hkp7]

Washer still on order, decided to have machinist at work make me one out of stainless steel with the proper ID hole being 12mm. Installed washer, shoulder bolt and timing belt, belt tracks a lot better but not perfect. It does not rub against tensioner arm anymore but still hangs off idler slightly. The shoulder bolt I put back in had a very slight bend and may be causing this. I thought that ID of the washer hole seemed wrong and thanks to Mrmerlin for pointing it out. Also I thank Mason from 928 worldwide for helping me as well. Here are some pictures of everything. I plan to have the machinist at work to make me a new shoulder bolt to complete the job. I would also like to add, if anyone wants a shoulder bolt made of stainless as well as the washer email me at Hkp7@live.com. I plan to sell them at a reasonable price to make this job easier for the next person.

[chesireIsugaree]

nice work Bill

[JK McDonald]

Hkp7 – It seems like you located the initial timing belt tracking problem when you found the bent shoulder bolt with the incorrect ID washer assembly. Just for discussion sake – Perhaps someone could offer the nominal expected clearance between the timing belt and the arched portion of the tensioning arm.

Once this clearance is established, you may be within spec’s as you are. If you feel that a few additional mm is required, the simplest (and least expensive) solution would be to relocate the tensioning arm slightly farther out away from the engine block by using a thicker stainless 12mm ID washer and a longer threaded portion on the shoulder bolt. Just add a notation in your maintenance log to progressively check the status of your updated parts.

Michael

[Hkp7]

Well, I went one step further, used a non bent shoulder bolt and a thicker washer and it is tracking perfectly. I got my Kemph? tool in the mail today, set the timing marks, set the tensioin, rotated the engine about 6 times and all seems well. I still think the tensioner arm is incorrect for this vehicle, that is why I used a thicker washer. With the old washer, the plunger from the tensioner was at an angle even after it seemed to be tracking better. With the new washer, the belt is completly centered on the idler and the plunger runs straight into the tensioner arms socket. Now its time to clean everything up for re-assembly. I guess draining the coolant first could have helped. Thanks everyone, glad its done, Bill.

[Hkp7]

Here are some pics.

[Mrmerlin]

you still need to install a new belt

[Hkp7]

I plan to, I am waiting for another porsche parts buying payday because I need a flywheel lock tool, to get the harmonic balancer off, the belt itself and Im waiting for a new/used timing belt cover that (I broke being impatient) Mason has sent me. I dont plan to drive the car as it sits I just want to run the engine to get back to my high idle problem I have been having. Pinched off the line going to my auxillary air regulator and Idle drops to normal. And on that note, I just dont understand, I got a used auxillary air regulator because the book said it should read 40-75 ohms and the one I had reads .01 and the new/used one reads the same. Ordered another and it reads .01 also. Maybe they are all bad or the book is wrong or I am wrong. Who knows.

[JK McDonald]

Hkp7 - Glad your timing belt alignment issue worked out. Your high idle problem sounds like you may have an unwanted air source in parallel with your Auxiliary Air Valve (AAV). When you pinch off the hose connected to either side of the AAV and your idle drops back to normal (800-900 RPM), your engine is probably pulling in air from a split rubber hose. Sometimes you can locate an unwanted air source by alternately spraying a little carburetor cleaner along the intake runners, rubber boots, brake booster, etc…. to make the rpm jump enough to find your problem. Don't forget to verify that your idle adjustment screw is not set too far out. On the 84 model, it is a large flat head screw pointing up towards you at an angle - located just under the front end of your intake spider.

A reading of .01 ohms read across the two leads of the heating coil inside the AAV is a virtual short. But if you find the same reading on several AAV perhaps your ohmmeter is no longer accurate. I am a bit rough on meters so I usually keep one of the cheap-0 Harbor Freight digital multi-meters on hand. With a good set of batteries installed in these meters, they are actually pretty accurate on all Volt/Ohm scales. On sale they can occasionally be found for < $10 with the regular price around $12.00 – 13.00

UPDATE - The heating element wrapped around the bimetallic flex bar in the AAV is designed to generate a very specific amount of heat vs flex/movement vs time to allow extra air just long enough to properly warm up the 928 aluminum V8 engine. Although many of the fuel injection system components engineered by Robert Bosch look similar externally they are each precisely calibrated per vehicle application.

Perhaps someone would have a spare 928 AAV laying around rather than you trying to rewind and duplicate the heating element. To help in future troubleshooting - An excellent manual on Bosch Fuel Injection / Engine Management from Bentley Publishers is ISBN 8376-0300-5. I think it was about $25 with shipping.


Good Luck,
Michael