KJL

I have always thought that the indexing marks on the cam and crank gear are suppose to be together, crank at 12 o'clock and cam at 6 at TDC. I recently read a detailed installation article the said the both index marks should be a 12 oclock. Are there some engine applications where this is done? My engine is a "72" L48.

Thank you.

paso

Your L48 when at TDC would both be at 12 o'clock. Most engine buiders align the two marks one above each other 12 and six like you said but it is not TDC For #1

1979toy

Yep. Align the marks at 12 on the crank and 6 on the cam. You are now 360 crank degrees from being at top dead center on the compression stroke.

Tom454

The answer to your question is "yes". Some engines are assembled using the 12/12 configuration.
But your SBC should be 12/6 as posted.

We GM folks tend to be a bit "ethnocentric" when it comes to engine building... we judge the whole world by how a SBC is assembled because that is what most of us know best.

Check out the cylinder numbering scheme for Ford V8 v Chevy V8.

Tom

john's '81 mouse

This was discussed at length some time ago. For proper camshaft to crankshaft timing, it really doesn't matter. You can do either 12/12 or 12 crankshaft / 6 camshaft and your camshaft will be properly timed to your crankshaft. For most of us, it's easier to see that the two are lined up properly when using the 12/6 method. (Two crankshaft rotations to to one camshaft rotation.)

Tom454

John is correct... technicaly it won't matter. But... there are some applications (non- Chevy) that do come with specific instructions to use 12/12. So, don't be confused by it.

Dino_'72

If your cam and crank marks are both at 12 o'clock your engine will be ready to fire cylinder #1, at 12 and 6 o'clock you will have cylinder #6 in firing position.

I remember the first time I did a cam swap. I aligned the timing mark at 0 degrees firing on #1. When I eventually pulled the timing chain cover off, I noticed that the gears were 12\12. I thought something was was screwed up. I was expecting 12\6.

The article probably suggested 12\12 method so they would not have to explain why it is not firing on #1. Personally I would install the cam, as others have suggested, using the gears in the 12 and 6 o'clock position. Then after you set up the rockers you can get it firing on #1 to get ready to drop the distributor.

Dino.