Audi DOHC 20 Valve Timing Belt Damage

We regularly see the twenty valve DOHC VW and AUDI cylinder heads and have a good idea what damage can be expected when a timing belt lets go.
Normally we find bent inlet and exhaust valves with some valve guides distorted as their valves were bent together with a few indented or cracked hydraulic lifters. Source: Norman Wilson down in Melb. 03 9527 1010 usually has the parts.
But our local dealer alerted us to another problem that will be difficult for our staff to find during inspection. The camshafts are connected by a loop chain where one shaft drives the other. When trying to get a recent head to work properly, after such a crash of valves and our recon work, the mechanic established that one of these sprockets had slipped around on its camshaft. With the cam timing out it was some time before the mechanic located the problem. No complaint back onto us but we now add the following wording to invoices for heads with this camshaft design:
“INDUSTRY REPORTS THAT A CAM SPROCKET MAY MOVE DURING A SEVERE¬† VALVE CRASH.¬† WE HAVE NO METHOD OF INSPECTING CAM SPROCKET TIMING: CAUTION.”

Please add:
Whilst a valve crash does not always damage their valve guides, it is common to damage the lifters from the crush between a bent valve and the corresponding camshaft lobe. Make sure your inspection looks CLOSELY at the top of the lifter for indentation and fine cracking.
Also, when a valve head comes off, usually several, we have seen a top ring grabbed in the piston. We always recommend that the pistons get pulled out.
Oh, and we had an incident that was heading for a blew with our client after we reco’d one head from an engine that had blown a piston. Audi TT turbo.
It hit lock up when the mechanic tried to turn it over. I was able to establish that when the piston blew, the crankcase pressure expelled several cup fulls of sump oil up into the intake manifold. This was sucked in at start up and the engine hit a hydraulic lock up.

Regards
Hedley James
Ph 03 9372 3111
www.engineaction.com