SBC timing gears

I installed a set of timing gears on my SBC, I set the dots according to the instructions. As i turn the motor over on the compression stroke the dots No longer line up.. Is this normal?

 

When the crank gear comes back around (full revolution) they should line up.
edit: actually "cam" gear, oops

 

The camshaft rotates twice for every crank revolution so they will only line up for every full revolution of the crankshaft which every two for the camshaft.

 

As said, keep rotating.

 

So will there be another compression stroke at 1 before the marks match? Or will they match at each compression stroke?

 

"Every" time the dot on the "cam" comes around they should match up.

 

Actually, no, I think they'll match up only when the cam gear mark comes around. (It's the larger gear.)

 

One time the camshaft mark will be straight down when the crankshaft mark is straight up, the next time the crankshaft mark is straight up, the camshaft mark will also be straight up.

 

I'm so confused!

Play with it, watch what happens....it's interesting

 

Sorry, my bad! I meant cam gear. You know, the big one.

 

When you install the gears and chain as instructed crank dot at 12.00 oclock and cam gear at six o clock that is correct,but you assume that it is top dead center,well actually at top dead center exhaust. Always has been that way except many think it is top dead center compression,"nope taint so" its at tdc.exhaust.where it should be.

Tig

 

Nope cam runs at 1/2 speed of crank

Tig.

 

With a comment like that I just have to keep my mouth shut. I have an answer but that there is a watch and learn moment.

 

Dots on both sprockets should be at 12 o'clock when number one cylinder is on tdc at the top of the compression stroke.

Number 6 will be on TDC at the top of compression stroke when the crank sprocket is at 12 o'clock and the cam sprocket is at 6 o'clock.
Larry T

 

Larry T let the cat out of the bag

 

So when the dots point to each other, that is when the rotor should be pointing at the number one nipple/electrode inside the distributor cap-right?

 

when the dots line up on a sbchevy the engine is at tdc for #6

 

Shit-I think that means I'm 180 out!

 

Now that's funny!

 

What Larry T said. When the dots are together it's actually at TDC compression stroke for #6. when both are at 12 o'clock it's at TDC for #1. NO idea who the idio....ahhhh......individual was at Chevy in 1954 that made it come out like that.

 

When dots are at each other the rotor points at #6,because 6 is at tdc. compression.

Tig.

 

When the 2 dots are aligned, crank gear dot at 12-oclock and cam gear dot at 6-oclock this is actually the Overlap Stroke. The firing or compression stroke will pair the dots with the crank gear dot at 12-oclock and the cam gear at 12-oclock >>>>.

 

He got that backwards as the Cam rotates once to every two revolutions of the crank but yes they should line up after each complete two rotation cycle of the crank.

 

I thought the 4 strokes on a 4 stroke engine were intake, compression, power, and exhaust.
Larry T

 

Some guy named Otto developed this and I guess it's race engine phrasing. It'seven been called the Scavenge Stroke and even named the 5th cycle. Isky's book talks of this also. Don't mean to be confusing just trying to state where the dots should be for placement of the distributor >>>>.

 

Not a problem, I just need to keep things as simple as possible for me to understand. (G)
Larry T

 

It was designed for the crankshaft gear and the camshaft gear dots to be straight up. When they are both on top, #1 is at top dead center between compression and firing strokes. Many people like to have the camshaft dot at the 6 o'clock [down] position because it is easier to see. I was taught to have both marks aligned at their 12 o'clock positions. Some builders use the 6 o'clock position and measure the valve lift to check the cam angle.

 

This is what I did. Installed the timing gear's dots matching up and facing each other. Then I cranked it over by hand untill my thumb over the #1 plug hole feels the compressed air and leaks/rushes by when I let go. I stick a straw in to see where the piston is and it is all the way up-with both valves closed.
Then I looked at the timing mark and see it is at O.
Sound alright?

 

Yep, that should be number 1.

The discussion is kinda of interesting, because it's not very often that you stab the distributor by looking at the dots on the timing gears. I never pull the distributor when a timing chain has jumped a tooth, just line the dots up with the new chain and gear and you're good to go. If I'm dropping the distributor in a fresh built engine on the stand, I usually run the valves, going through the firing order and after I finish 2 roll the engine another 1/4 turn and it's on the mark for number 1.

It could be a good time to discuss where number one is on the cap. It's different on a point style distributor and an HEI. I always set them up the way they came from the factory, sure makes trouble shooting easier later on.

Should look something like this (number 1 TDC) on Chevys with points, number one is on the "passenger side" of the points adjusting window. As a side note, if the early distributors (that don't have the full groove around the distributor shaft) aren't indexed right, the lifters don't oil on one side.
Larry T

 

Holy cow! Now there is an engine I'd pay to see run! A cam spinning at 6000 plus rpms at cruise speed.