Timing Chain Cover and TDC marks

The original timing chain cover was crunched but I kept it as a reference for the timing mark positions. I'm glad that I did as I found out that somewhere around 1980, the timing reference mark for TDC was changed from the 2:00 position to the 12:00 position and some SBC didn't even have a TDC timing mark on the timing chain cover! Of course this was after I picked up two at the wreckers which didn't match the original sitting in my garage. Back to the wreckers and couldn't find a decent one at 2:00 position which I needed that didn't require complete dismantling of the front end of the car. I did find one but I couldn't pull the vibration damper off cause the crank turned so easy. I gave up cause it was -15 below and I could use one of the two I had already.

I purchased timing tape for the outside of the harmonic balancer so that I can accurately time the engine at idle and with full vacuum/mechanical advance. The timing tape will be clear painted on as the doublesided tape is not reliable enough to keep it on. The timing tape also helps solve the problem of the missing timing plate on the timing chain cover. All I have to do is make a pointer so that it marks where TDC is.

timing tape

Timing tape on balancer (needs to be clear painted on) and TDC pointer mark yet to be made

I used the bent up timing cover as a reference and cardboard as a template. After a little fiddling and testing I came up with a nice little pointer that is referenced off of 2 timing cover mounting bolts. I figure that it is accurate within 2 degrees of TDC. I like to use a vacuum gauge for setting my idle timing so as long as it is close then I'll be happy. How do you determine TDC? Here's a webpage on a unique method.

pointer

The timing pointer blinded by the flash but the general shape is outlined

I have been collecting old car magazines and came across a great article (1984 Chevy Camaro - Car Craft series) on SBC timing markers. Chevy has 3 over the counter bolt on tags that you can purchase:

  • Part #3991435 - Used on 69-78 Vettes, 69-76 std 350, 68-71 1st design 307, 77-79 305 Monza
  • Part #3991436 - Special hi performance (8 inch balancer) 69 Z/28, 69-78 LT-1 & L-82, all 69-74 performance engines, 71-76 400 small blocks.
  • Part #3997780 - 71-73 2nd design 307, 76 262 cid V8

The 3991435 and 3997780 differ by approximately 2 deg. Bolt on tags were used after 1968 and until 1977 when the went back to welded on tags. To add confusion to the mess, there is an 8 degree difference between bolt on tags and the welded on ones. The harmonic balancer are different with an 8 degree offset too.

Here's a list of Chevy timing covers and part #s:

  • Part #361925 - 67-68 Z/28, 350 Camaro, 64-68 Special hi performance 327
  • Part #361926 - All 62-67 timing covers, it had dual tabs, you knocked off the one you didn't need!
  • Part #361927 - 68 standard 327 only
  • Part #462845 - 267, 305, 350 77-82 with late style tag

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Copyright May 2011 Eugene Blanchard