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Old 08-24-2005, 10:06 PM
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305ci Timing Gear Marks Do Not Line Up

I'm replacing the camshaft, timing set and lifters on my '76 Chevy C10.
It has a transplanted '78 305 cubic inch V-8 from a Caprice.

I set the engine to TDC and removed the timing cover. The dowel pin on the camshaft was a nine o'clock at it should be (actually a little before nine o'clock, which I chalked up to the fact that the timing chain was pretty stretched). The old timing gears did not have ANY TIMNG MARKS (checked both sides). Not sure how unusual it is not to have timing marks on the gears...

The NEW gears have timing marks.

The Haynes manual sez the timing marks should be at 6 and 12, but the cam gear mark is at 12 o'clock, and the crank gear is at 11 o'clock. The Woodruff keys are at about 1 o'clock. WHAT GIVES???

If you know this is not right, please respond before noon tomorrow. Otherwise, I'll assume it's OK and slap the timing cover on tomorrow.

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Old 08-25-2005, 06:46 AM
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I would check the Top dead center again, the number 1 piston, which is the 1st cylinder on the drivers side, when it`s at top dead center, the crank mark should be at 12 o`clock, and the keyway should be at 2 0`clock.
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Old 08-25-2005, 11:43 PM
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Setting TDC AFTER replacing cam and timing set???

[DoubleVision: I would check the Top dead center again, the number 1 piston, which is the 1st cylinder on the drivers side, when it`s at top dead center, the crank mark should be at 12 o`clock, and the keyway should be at 2 0`clock.]

The Haynes manual says to position the motor to TDC (for piston #1, on the compression stroke, of course), you turn the crankshaft until the line on the vibration damper is directly opposite the zero mark on the timing plate AND the distributor rotor is pointing to the number one spark plug terminal on the distributor cap.

...That's what I did before I took any parts off the motor (which ran fine before I started the work -- started it just to make sure)...

When I took the timing cover off, the arrow on the cam gear was at 11 o'clock, and the Woodruff key on the crank was at 1 o'clock.

How would I go about re-checking the motor is at TDC now (with the distributor out)???

To get the timing marks on the crank gear and cam gear to line up now, I'd have to remove the timing set, and how do you find TDC and get the cam and distributor positioned correctly without the timing set on?

Is there a way to use the lifter positions to determine which cylinder is currently at TDC? The tops of the (new) lifters for cylinder number one are currently just above the block (about 1/16 inch).

I could really use detailed steps for aligning the parts from anyone who regularly assembles engines from scratch, please!

Thanks!!!
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Old 08-26-2005, 07:37 AM
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Put the engine on tdc. Use the balancer and timing chain cover to get it there. Yes, 1:00 on the crank keyway sounds right.

The cam pin should be at 3:00. It sounds like you need to spin the engine over one more time. FYI, the cam spins at 1/2 the crank speed. So one more rotation should move the cam pin from the 9:00 to the 3:00 position.

So, put the old chain back on, spin the engine one rev. And use the balancer and timing chain cover mark to get back to tdc (it doesn't need to be super precision tdc, just close).

Then install remove the old chain and install the new one. The crank gear mark should be at 12:00 and the cam gear mark at 6:00.

Or just leave the engine position were it is and install the cam and crank gear mark at 12:00.

Or just leave the engine position were it is and remove all the rockers and spin the cam into the right position (3:00 pin), then install cam and rockers.

A lot of ways to skin a cat. good luck.
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Old 08-26-2005, 12:19 PM
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Timing mark on gear does not match crank!!!


So, I rotate the camshaft 180 deg. to get the timing mark on the cam gear to point at 6 o'clock, and turn the crank until the timing mark on the crank gear points at 12 o'clock? Then I install the distributor so that the rotor points to cylinder number one's terminal (and pointing to front of engine), and that's it???

Once I change the crank and camshaft positions, the distributor will not go back in the same position that it was in when I removed it. How do I figure out how to position it -- all the information is based on making index marks before removing it and putting it back in the same place!

I don't see how this motor ran before with the cam 180-off and the crank somewhere between 10 and 15 degrees before zero!!! GROAN...
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Old 08-26-2005, 01:05 PM
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There is no such thing as a cam 180 degrees off on in a 4 stroke engine.
If you just rotation the cam 180 degree and left the crank at tdc, it would just change the compression stroke to the power stroke and the power stroke to the compression stroke. The engine block wouldn't know the difference. However, the distributor shaft would need to be spun 180 to follow the cam position.

BUT, you just can't rotate the cam without rotating the crank because the valves could hit the pistons. It depends on the cam lift and piston design but it is never a good idea to do that. That is why the rockers should be removed first before rotation the cam. But removing rockers leads to a lot of work

BUT, if your cam pin is in the 9:00 position (180 off as you call it) then the easiest way would be to install the new timing chain with BOTH the cam and crank marks at 12:00. Then spin the crank one rotation and then the crank gear mark should be back at 12:00 and the cam mark should be at 6:00 (in the proper position). If the marks don't line up after spinning the engine, then you may need to move the chain over one tooth. And like I wrote earlier, use the mark on the balancer and the timing chain cover mark to find tdc. You don't need to put the balancer all the way on.

Yes, then drop in the distributor as your normally do, tdc on the crank and the rotor pointer towards number 1. If it back fires up the carb it that position then pull up the distributor and spin the shaft 180 and drop it back down.

That is it.

Don't worry about where the distributor was before you took it out.

FYI, the keyway on the crank is not in the 12:00 position at tdc. 1:00 is right. The mark on the crank timing chain gear is at 12:00 at tdc

You know about the oil pump and distributor shaft alignment right?
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Old 08-27-2005, 04:07 PM
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Lifter Positions for Number One Cylinder at TDC

My brother suggested that I compare what the Haynes manual (for Chevrolet and GMC pick-ups 1967 through 1987) says to another source like a tune-up book. Haynes says it's all the same for all small block GM motors, but he says there might be some motors that don't have the same specs.

Is there a web site that describes the full combustion cycle of a small block V-8 (including what state valves should be at each point in the cycle)???

My brother sez the cam should be positioned at the point half way between cylinder number one's intake valve closing and it's exhaust valve opening. When I do this, it puts the camshaft exactly 180 degrees from where it was before I removed the old timing set (the dowel pin on the camshaft is now at 3 o'clock position instead of at 9 o'clock where it was originally). IOW, the cam was between exhaust valve closing and intake valve opening.

With the vibration dampener at the 0 degree mark on the timing cover, the timing mark on the crank gear is at 10:30 instead of 12 o'clock. This is where it would have been when I pulled the old gears IF the crank gear had not been reversed. The marks on the new gears match those on the old gears -- they were not facing each other when I started -- cam gear mark was at 1 o'clock (not 6) and crank gear (would have been) at 11 o'clock (not 12).

The Haynes manual sez to position the cam so the dowel pin is at 9 o'clock, then to rotate it if necessary to line up the timing marks.
Q1: Why does it say to put it at 9 o'clock, which seems to be exactly one half turn OFF from where everyone says it should be?
Q2: Why did my motor run fine when my cam was between exhaust valve closing and intake valve opening with the crank set to 0 degrees and distributor pointing to #1 terminal?
Q3: Why shouldn't I just assemble the parts the way the old ones were, since the motor ran thay way? TO PUT IT ANOTHER WAY... Why should I believe that changing the positioning will work?
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Old 08-29-2005, 07:45 AM
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I think you and your brother are making this way too hard.

Installing a timing chain is not rocket science. Line up the marks, install the chain, and put the front of the engine back on. That is it.

If the crank gear mark is not at 12:00 at the timing chain tdc, then there is something wrong with the timing marks on the balancer or timing chain cover. Chevy did make different chain covers and balancers that would put the timing make on the left or right side of the engine. You could have a mismatch. I would go with the timing chain gear marks.

What kind of chain set are you using? Does it have different positions on the crank gear (muiltple keyways).

When the cam pin is in the 9:00 position then the cam gear mark should be at the 12:00 position.

When the cam pin is in the 3:00 position then the cam gear mark should be at the 6:00 position.
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Old 08-30-2005, 01:10 AM
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Not Rocket Science

You're right about it not being rocket science, but it sure helps to understand the process is for a complete cycle.

I guess I did not have it at TDC to begin with. Piston #1 was at top of stroke, but the camshaft was 180 degrees off (not between intake open/close and exhaust open/close). Not sure if I screwed up identifying which terminal on distributor was #1, or what. Anyways...

I attached the new cam gear in the same position as the old one,
then rotated the engine until the timing marks on both gears faced each other
and verified that the lifters for cylinder #1 were both in the down position and that the intake lifter had just closed.
Then I slowly turned the crankshaft in 90 degree intervals and verified that the lifters for the appropriate cylinder in the firing order moved at the correct place in the sequence (intake opens, then closes, piston reaches top of stroke, exhaust valve opens, then closes).

I did this a couple of times just to make sure, then returned it to the starting position (timing marks on gears facing each other).

I think you're right about the timing cover and/or vibration dampener being mismatched, tho I don't know how (dampener had "350" painted on it, but I thought this part was the same for all the small-blocks of this vintage).
I'm going to paint a mark on the dampener that aligns with the zero mark on the timing cover when the timing gears are aligned (the new gears have marks in the same place as the old gears).

I just got the intake manifold back on. Will probably be ready to crank it in 2 days and see if I got it right. Thanks!
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Old 08-30-2005, 06:22 AM
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Doc here,

If I understand this thread correctly... ( and it's way too early for me to be astute..) You are having difficulty lining up the gears Dot To Dot (6 & 12 O'clock) at # 1 TDC??

Go back to your Haynes...6 & 12 ( Dot to Dot ) SHOULD be # 6 TDC...not #1...

Crank at 12 O'clock and Cam at 12 O'clock... SHOULD be TDC #1...and if I read your very first post right you were ONLY 1 tooth off to start with when you thought it was way wrong...

That is after wading through all the data here...and I understand what you are trying to do...although I could have mis~understood!

Doc
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