Timing Chain marks on BBC - Chevelle Tech
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post #1 of 23 (permalink) Old Dec 24th, 04, 2:47 AM Thread Starter
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I recently got my shortblock back from the shop. I had a Cloyes true roller chain installed.
When I got it, the top gear (cam) was set with the mark at 6 o'clock, which is normal. But, the bottom was set with the mark at what looks like 9 o'clock and there was a mark that looks like the key hole (rectanglar) facing the twelve o'clock position.
I thought I took a picture. But, for some reason it didn't turn out and I've already installed the timing cover.

Ron
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post #2 of 23 (permalink) Old Dec 24th, 04, 12:15 PM
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It sounds like they installed the cam timing 4 degrees retarded. You might double-check with them for an explanation why. Some cams are ground with 4 degrees of advance and maybe they didn't want that for your combo, or maybe degreeing it required it to be retarded to get the intake centerline correct.

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post #3 of 23 (permalink) Old Dec 24th, 04, 12:31 PM Thread Starter
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Yeah, I remember something about that when I was reading the box.
I don't think they're in today and I discovered it after they were closed yesterday. Looks like I'll have to wait until Monday to ask.
My friend had mentioned it looked off when we picked up the engine. But, i never thought anything of it. He didn't notice the little key mark though (it was still in plastic). Since it's lined up with that mark, I figured it was some sort of an offset.

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post #4 of 23 (permalink) Old Dec 24th, 04, 12:36 PM Thread Starter
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Here's a picture I found

My crank is set the same as the picture (you can see the rectangular mark at 12 o'clock). But, my cam is lined up with the dot at 6 o'clock.

Ron
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post #5 of 23 (permalink) Old Dec 24th, 04, 3:30 PM
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The rectangle/square will yield the cam 2 degress(cam)/4 degress (crank retarded). Typically the only time you would consider this (cam retarded) is for too short duration with high compression. You better double check on this. Unless the cam you have is real small, you will want to run the cam straight up ( "0" on crank gear) or with additional advance. Depending on the cam make and duration, you would be best with the cam ICL of 104 - 106 degrees.
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post #6 of 23 (permalink) Old Dec 24th, 04, 6:53 PM Thread Starter
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My engine is definitely not high compression. It's likely about 8.75:1. The duration is 280, which I believe is pretty typical.

Ron
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post #7 of 23 (permalink) Old Dec 24th, 04, 7:03 PM Thread Starter
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Only thing is, wouldn't that mean that 1 and 6 were not at TDC though?
Looking at this pic, you can see #6 is at the top

They are only .100 dome pistons. They took almost nothing off of the deck (the serial numbers are still mostly in tact). The crank and Rods are stock.

Is it possible they just put the crank gear on that way and the crank is still aligned?

Ron
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post #8 of 23 (permalink) Old Dec 25th, 04, 12:41 AM
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You are going to want pull the crank gear off and reinstall it so that the crank keyway is pointing to about the 2 o'clock position and have the cam crank gear mark ( "o" for straight up , ^ for advanced). The mark on the cam sprocket should point down [6 o'clock position] when #1 cylinder is ready to fire. Both #1 & 6 will be a TDC at the same time. Personally I would set the cam at 106ICL, either straight up or advanced, whatever it takes.
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post #9 of 23 (permalink) Old Dec 25th, 04, 12:52 AM
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Quote:
Originally posted by GRN69CHV:
You are going to want pull the crank gear off and reinstall it so that the crank keyway is pointing to about the 2 o'clock position and have the cam crank gear mark ( "o" for straight up , ^ for advanced). The mark on the cam sprocket should point down [6 o'clock position] when #1 cylinder is ready to fire. Both #1 & 6 will be a TDC at the same time. Personally I would set the cam at 106ICL, either straight up or advanced, whatever it takes.
=
Just being my picky self but #6 is on compression not #1 when the cam mark is down
And your piston will be at TDC regardless of which mark you use as you put the triangle, round or square mark straight up towards the cam depending on which mark you use at the keyway
In other words, you would use the rounded keyway slot on the crank key for the round mark on the outside of the gear.

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post #10 of 23 (permalink) Old Dec 25th, 04, 9:32 AM
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A short lesson - never discuss (well - hardly ever) anything after consuming an entire bottle of dark red wine at dinner - by yourself.

That said, Ron, check your #1 piston, it should be at TDC with the cam mark pointing down. You are probably going to want to pull them crank
gear and reinstall it. Also, what cam did you install?

One other thing to consider. If the block was not decked much, you can run the GM .022 head gasket and pick up fair amount of compression. You can check this fairly simple. If you have access to a dial gauge great, if not, place a metal straightedge over the piston flat area at TDC and measure with a feeler gauge. As long as you have .014 or more you can use the .022 gaskets. Using these picks up about .3 to .4 CR. Get them from any Chevy dealer for about $20.00.
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post #11 of 23 (permalink) Old Dec 25th, 04, 9:43 AM Thread Starter
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Quote:
Originally posted by Wolfplace:
you would use the rounded keyway slot on the crank key for the round mark on the outside of the gear.
Oh, so, each of the three marks matches up with which keyway you choose? So, they must've used the tall rectangular keyway?

This guy sounds like he had a pretty bad problem with these marks:
http://www.hotrodders.com/t42146.html

Ron
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post #12 of 23 (permalink) Old Dec 25th, 04, 9:51 AM Thread Starter
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Quote:
Originally posted by GRN69CHV:
check your #1 piston, it should be at TDC with the cam mark pointing down. You are probably going to want to pull them crank
gear and reinstall it. Also, what cam did you install?
Yeah, that's the way it looked when I got it. That mark was right at 6 and you can see the position of the pistons (1 and 6 at TDC).

Here's my cam. They (Dougans) picked it and installed it.
http://store.summitracing.com/defaul...t=CCA-11-208-3

I'll have to call them Monday and find out exactly what they did. I already installed the timing cover. But, it looks like I may have to pull it off.

Quote:
Originally posted by GRN69CHV:

One other thing to consider. If the block was not decked much, you can run the GM .022 head gasket and pick up fair amount of compression. You can check this fairly simple. If you have access to a dial gauge great, if not, place a metal straightedge over the piston flat area at TDC and measure with a feeler gauge. As long as you have .014 or more you can use the .022 gaskets. Using these picks up about .3 to .4 CR. Get them from any Chevy dealer for about $20.00.
Heads are already on. The guy I got the engine from said that I would gain little from decking the block more or using smaller gaskets in terms of compression and HP. He said that the possible benefits of a thicker gasket would outweigh the benefits of the thinner one.
Anyway, I just went with the standard blue core Felpro gasket.

Ron
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post #13 of 23 (permalink) Old Dec 25th, 04, 5:48 PM
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well those kinda people who say such things about decking or thinner gaskets or either lazy (dont want to do the work) or dont pay attention to the details that make the horspower one is looking for........and or is old and still dont understand the importance of the small details.......

and i tell ya, a .4 makes a difference in a motor specially when your dealing with one that is short for the cam that is being used.....that 230/230 cam needs some help in the comp. department.

and whats the benifit? of thicker gasket.....gm used them on stock cars for a lot of years ......so there is no durability problem.........and i used them all the time for cheap compression gain.......
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post #14 of 23 (permalink) Old Dec 26th, 04, 9:36 AM Thread Starter
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I think he just didn't want to do the work, since my engine had already been there a few months and I think they like doing pure race stuff more.

As far as the gaskets, he had nothing to gain telling me to go with standard gaskets. So, I went that route. If it proves to be a problem, I can always change them later. (I am assuming I might notice a slight hesitation or somethign at lower RPMs?)

I was looking though and my numbers for my cam and compression are pretty similar to a 454 HO.

Anyway, back to the original topic, I'll call them tomorrow and see what they did with my timing (if they can remember).

Ron
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post #15 of 23 (permalink) Old Dec 27th, 04, 3:52 PM Thread Starter
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Okay, just got off of the phone. I'm still pretty new to the intricacies of camshafts and timing. But, I think he said it was degreed to 105. The camshaft has a lobe separation of 110. So, does that mean it's advanced 5 degrees or retarded?
He said it was set to zero and then degreed accordingly from there, based on my camshaft and the rest of my combo. So, that's why the marks aren't lined up. He has all of the information on my build in his records. So, it was done the way they think is correct and I haven't touched it. SO, I'll trust them, since they've been doing this for like 30 years and I have about 1 month of experience!

Ron
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