3.6 timing chain failure

[Deanh]

So, my 964 hasn't given me the most pleasant welcome in to P car ownership, but I am not deterred at all. I'm a mechanic by trade so the needed repairs will be done by me. I have rebuilt engines before, but never a flat six, so ill need all the help I can get from the community.

I bought the car (90 964 c4) knowing the engine needed pulling due to a toasted clutch, but before I could even get one day of driving in, what seems to be the pass side cam sprocket bolt backed out causing the timing belt to jump, then get stuck in the intermediate shaft gear enough to pop a hole in the case right where the drivers side timing chain housing bolts up. I now have the engine out of the car, haven't been able to break it down yet, but using a using a small camera, we are able to see that the outermost timing gear is now trashed and can actually be moved up and down a small bit. In all of the pics I see, the 3.6 intermediate shaft has the gears held on by c clips, but I'm not sure.

Background on the engine before failure. Had a full rebuild done at 50k (183k on the chassis now) by Porsche. No knocks or serious leaks, no smoke, no warning of the impending doom i experienced. Now for my questions.

Is the 3.6 intermediate shaft specific to that engine?

Can the seperate gears on the shaft be replaced?

Do the case studs need to be replaced?

Are the stock head studs ok to use in a stock application? (plan on a serous forged rebuild for a turbo setup in the coming years)

Do I need to buy the timing chains with or with out the master link?

How can I test my chain tensioners to make sure their working properly

The small black timing gear behind the main timing sprocket serves what purpose?

Thats all I have for now. Any help is appreciated. Will have pics of the damaged case asap.

[Flat6pac]

I'm not going to answer all but will tell you
The intermediate shaft as a unit can be replaced completely with another by looking at the number stamped on the left side of the case by the crank pulley. Either a 0 or a 1
The big gear on the shaft will be marked with matching number
All intermediate shafts are the same through 964 from the 70's on

Case studs should be dilivars and replaced unless they are the full threaded 10mm dilivars known as 993 dilivars. If you are replacing with steel variant I recommend the Supertec studs with the fine threads on the outside for better torque control. I am not associated with them but prefer the product.

Buy chains without master link
Bruce

[bigel]

Bruce,

Your response is extremely informative and interesting, as usual.

I'm interested to know why the " full threaded 10mm dilivars" are considered a viable option. Do they not fail at the same rate as the others?

Thanks in advance,

Steve

[Flat6pac]

Generally, they are considered the bullet proof option. At $45 each I wouldn't expect failure. The style are used in the water cooled head GT3 and turbo but are slightly longer.
Over the years I would install dilivars over the broken ones in sets of 12 and never had to go back into the engines for failure. Remember, most lasted 20 years or more from the factory as we see c2 with all 24 holding 20 years or more.
Bruce

[Deanh]

Thank you Bruce. I've taken a look at some of your threads well before I made this post, and im thankful to have someone as knowledgeable as yourself answer. I just need to fine the time to get the engine broken down so I can take a list of what I need. A guy named Dennis here makes a nice vid of 3.6 assembly which ill be ordering, and I have the book by Adrian Streather, is there any other "must have" literature I need to help? Question, are the vw engine stand adapters exactly the same as ones used for our engines? I see them advertised as the same I just needed to know, as I know may vw guys that I can grab from.

[Flat6pac]

The vw stands are made for 150# but will bolt up. My stands are generic style and I bolt up to the engine with the half moon mount. I remove the bell housing studs an install with 10mm half shaft bolts to attach the engine cases. I see pictures of supports with room for the flywheel but I usually am splitting the case so I don't need to have clutch and flywheel remain attached.
Bruce

[brp914]

The small black gear behind the main sprocket - a small cylindrical piece straddles the 2 gears. The position of the piece is used in setting cam timing. The threaded tip of a spark plug will thread into this piece and may be a good way to prevent losing this piece until you're putting things back together. Although, you may throw away the plug thinking why am I keeping this lousy old plug?

[KTL]

Porsche has expermented with various installations of the dilavar studs. The turbos have always come with all 24 studs being dilavar. The cars after the turbo used steel upper and dilivar lower. Broken dilivars have been quite prevalent in that mix. The 964 came with all dilivar. Then the 993 non turbo had all steel.

The dilivar has been used in various forms- first uncoated & then coated partial thread, coated full thread. The full thread is the latest and greatest and were introduced with the 993 twin turbo.

The sprockets on the intermediate shaft appear to be held in place by external c-clips. However they're basically pressed on. You need to heat up the sprockets and pull them off with a gear puller. Typically like Bruce said you're best bet is to buy a complete used intermediate shaft assembly.

Yep brp914 is spot-on. The small piece behind the cam sprocket is an indexing hub that does two things. 1) it allows the sprocket to be connected/pinned to the camshaft. W/out the indexing hub the sprocket would just spin freely on the cam snout. 2) it allows precise timing of the cam. All those holes in the sprocket are not for lightness/cool factor. They're to allow alignment of the indexing hub and cam sprocket to occur. When you time the cam, you'll find that only one of those holes will allow the indexing pin to be inserted and lock the cam to the sprocket. Pull the pin, rotate cam or crank to change cam timing, reinsert pin into the next available hole with holes that line up.

[Deanh]

Thanks for all the info guys. Engine stand ordered and the pfixit dvd on the way also. Hope to have it all dissassembled next week, order parts, and have it back together two weeks later, but you know how that goes.