<VV> Re: cam break in

[djtcz@comcast.net]

-------------- Original message -------------- 

> From: "Geoffrey A. Johnson" 
> Subject: Re: Shredded Cam Lobe 
>Not sure if I did get it 
> "Run in" correctly after the rebuild. I was still under the impression I 
> needed to run non-detergent service SA oil in there (GAG). 
Weak oil >>may<< enhance piston ring break-in on some cylinder wall finishes, but the cam and lifters need all the help they can get.  I always use Assembly lube, and check for interference in the valve train. Even stock parts sometimes have "issues."  Sometimes I gently polish untreated lifter feet with dull 800 grit paper backed by soft rubber.
Most hot rod cam manufacturers used to provide a tube of black sticky cam lube to coat the lobes and lifter feet at assembly.  I'm sure they did not do that just because they got 2 boxes of them for Christmas.  GM's Super EOS used to have a good reputation as assembly lube.
As I recall the Crane 292H cam I put in my car 100 years ago did not require :
- long slot rockers (checked with a paper clip)
-  notches in the pistons (checked with clay)
- valve guide shortening to provide retainer/seal clearance (paper clip)
- precise spring shimming to avoid coil bind (feeler age and eyeball)
- offset keys to fine tune the cam timing.  (degree wheel and dial indicator)
But I checked all those things. 
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Stock part nightmare - 
About 20 years ago I bought a Pushrod engined 100,000 mile Volvo wagon, complete with an inch of yellow maintenance records proudly provided by the doctor's wife.  A selling "feature" was just a few 1000 miles before they had the cam replaced and head redone by their favorite independent foreign car repair shop in an upscale New England town.  I chased the noisy valve adjustment for a few months, and then checked the valve lifts.  One had VERY low lift, and several were clearly deficient.  The autopsy revealed several serious problems that almost certainly had been installed during that "professional" repair.  The one that I was satisfied killed the cam was that the shop (probably actually their machine shop of choice) threw in their standard valve spring shims  (standard rebuild procedure), but without checking to see if they would go to "coil bind" at full lift. By my actual measurement that stock Fuel Injection Volvo had enough lift so the un-shimmed springs were near coil bind.  When running, the cam would compress the shimmed valve springs to the point they became  solid slugs of steel, causing wicked high loads on the already struggling valve-to-lifter interface.  Once the surfaces scuff, there is no return, and wear progresses rapidly.