I think I have a big problem..

mazdaverx7 · 08-12-2014, 04:34 PM

As many of you have read, I have been repairing an 86 that I bought with bent valves. Turns out that all 8 valves were bent. In taking it apart, I found no obvious signs of failure in either belt or any of the tensioners. The belts were all tensioned properly but the timing belt had somehow jumped time and cause catastrophic results. Once I put the freshly rebuilt head on, I decided to take a look at replacing the seals in the cam box. Going through the procedure for disassembly, I found this:

It appears as if the cam sprocket shifted on the cam itself and allowed the timing to become misaligned, thus causing valve and piston contact. I'm not sure at this point what I will have to replace. Maybe just the cam sprocket and woodruff key..maybe the entire camshaft. I'm having issues getting the woodruff key out and removing the sprocket. Any thoughts on this damage?

emoore924 · 08-12-2014, 06:08 PM

Quote:

Any thoughts on this damage?

Something caused that to stop really fast. You need to find the cause.

Slam · 08-12-2014, 06:08 PM

Ouch! Pics like that really hurt. Good news is used cams, cam towers, cam sprockets are cheap and plentiful. I'd get a complete good used cam tower with lifters, cam and sprocket right here on Pelican.

Or if you want the no-risk option, talk to George at 944Ecology.

Arizona_928 · 08-12-2014, 06:50 PM

Lol would have been a shame to rebuild the head and not noticed that. Get a 87 88 cam for a more agressive grind

Jfrahm · 08-12-2014, 07:03 PM

Check the cam journals for spalling. Maybe it was run out of oil and the cam seized.

porschetub · porschetub's Garage

Quote:

Originally Posted by Jfrahm

Check the cam journals for spalling. Maybe it was run out of oil and the cam seized.

Looks like a lock-up...but,takes a lot to roll that key,unless it wasn't tightened properly to start with and just flogged out.

mazdaverx7 · 08-13-2014, 10:21 AM

The engine spun freely and cranked over fine.However, the cheesehead bolt that retains the nut and cam gear was finger tight. I took everyone's advice and got a new one on order fearing it may be extremely tight and may strip the hear and that its a stretch bolt, etc. I put the cheesehead bit in and tapped it lightly with a hammer per the Clark's Garage instructions, attached my ratchet and there was no resistance. At first I thought that the bolt was broken. It threaded right out and I placed it on the work bench. Right then and there I knew something was not right.

Lapkritis · Lapkritis's Garage

A loose bolt can cause things to chatter and dance resulting in damage.

This type of failure is common on high rev, heavy spring engines on the VW side of the house. They've gone with a solution that includes a specific ARP fastener and a patented nickel and diamond coated friction shim to simply help hold the cam gear to the cam. These are manufactured by ESK in Kempten, Germany (ESK- Advanced Technical Ceramics); they're not cheap but they are proven technology. I imagine they could cut a 944 shim to work just as well.

DannoXYZ · 08-14-2014, 04:39 PM

Quote:

I put the cheesehead bit in and tapped it lightly with a hammer per the Clark's Garage instructions, attached my ratchet and there was no resistance. At first I thought that the bolt was broken. It threaded right out and I placed it on the work bench. Right then and there I knew something was not right.

With a properly tightened bolt, you don't have to worry about loose cam. This is only the 2nd time I've ever seen this issue. Probably caused by a previous mechanic who didn't use the proper tool to hold the cam steady while tightening the bolt.

When installing the bolt, I prefer to add a little blue Loctite to the threads. Then when the bolt has been snugged down to correct torque, I smack it lightly with an impact-screwdriver to add a tiny bit more. Then on removal, I give it a little harder smack with the impact-screwdriver in the loosening direction.