Cam Gear Failure

elise111 · Posted: Mon Aug 24, 2009 9:34 pm Post subject: Cam Gear Failure

The engine in my single cab surprised me the other day after exiting the freeway...

Image may have been reduced in size. Click image to view fullscreen.

This is a VW Mexico longblock from 1998 with 18k real miles on it. Completely stock. No surprises inside the case other than the worn off teeth. My guess is that the cam gear pitch radius was incorrect- perhaps too tight to cause teeth to break off. The only stamped in mark on the back side of the gear is what looks like a -6, it is hard to tell because half of the number is missing. Could it really be a -0.06mm cam?

Anyone seen this before?

Ian · Posted: Mon Aug 24, 2009 10:15 pm Post subject:

That is very strange. Usually a gear that is binding will wear evenly. It appears something else might have gotten stuck in the gear. Also, I believe the 2BR stamping indicates the cam gear casting is of Brazilian origin.

I would start over checking the crank for any cracks and the case for any excessive wear and be sure to set the cam gear lash correctly.
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BarryL · Posted: Tue Aug 25, 2009 6:46 am Post subject:

I thought the rumor was they stopped making + and - which is absurd. It would have taken a long time to grind enough to skip a tooth if it was backlash but you're thinking binding so maybe. What a bummer.

iamdonquixote · Posted: Tue Aug 25, 2009 7:42 am Post subject:

what did the engine sound like ?

elise111 · Posted: Tue Aug 25, 2009 10:03 am Post subject:

Hard to say- sounded fine at speed, idle was noisier that I would expect- may have been the gear drive giving warning signals.

SkooobaSteve · Posted: Tue Aug 25, 2009 11:15 am Post subject:

We had a mexi long block come to us no miles on it barely engine would turn over, but no valve movement. Think it was the same thing, or the geawr fell off.
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Andrew · Posted: Tue Aug 25, 2009 11:47 am Post subject:

What'd the brass gear on the crank that drives the cam gear look like? It is much more likely to have teeth shear off like that than the steel cam gear... Confused

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elise111 · Posted: Tue Aug 25, 2009 12:59 pm Post subject:

Do you mean the brass gear drives the distributor ? That one looks looks like new. The crank has a steel gear for driving the cam gear and looks good, although I wouldn't reuse it in this situation. The cam gear in the picture is aluminum.

Andrew · Posted: Tue Aug 25, 2009 2:04 pm Post subject:

elise111 · Posted: Sat Aug 29, 2009 12:07 am Post subject:

Looks like I may have found the root cause for the cam gear failure. I measured the root of the teeth and the tops of the remaining teeth. I found up to 0.010in run out. I think the gear was not machined properly. Mexican long blocks appear to have a mix of Mexican and Brazilian parts.

I picked up a copy of the Muir book (a fun read and good complement to the Bentley book) and learned that factory cams could range from -7 to +7, so my -6 cam makes sense.


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