The motor is a mid 70's 350. If you have the heads off and you were to put the timing chain and sprockets on would it matter if the marks were lined up between the sprockets? It seems like it wouldnt matter, but I'm not sure. Alrite now berate the FNG. Thanks.
No, can you say your 120% sure that the cam and crank didn't move when you had the chain off? I would say no. But are you that sure? Your best bet is to put it back in time. That way you are 150% sure. It's tooooo easy to get it in time just do that I would say. By the way (just so you know, you can't get it 180* out like you can the distbutor) line up the marks and bolt it up.
Thank you for your response. Yes assembly to run. Can you tell me why it matters though? If the sprockets are symetrical and not balanced and the heads and lifters are out...I understand why you need to line them up on an interference motor.
On a pushrod engine, the timing chain marks, set the cam timing in relation to the crank. So yes! they matter whether the heads are on or not.
They need to line up so that the operation of the valves is timed with the movement of the pistons. Intake valves need to begin opening approximately when the corresponding piston begins to move down the bore, etc. Otherwise the engine will not run. FYI, on an interference motor, the reason they are "lined up" is the same reason they are on any motor, the choreography of valve and piston movement needs to be timed, or you've just got a lump of parts that might look good, but it won't run. Go here for an animation, and explanation of each of the four strokes. It might help you understand why they need to be "lined up". http://www.animatedengines.com/otto.shtml
The pistons and the valves have to be in time, just like anything else in a engine. Please don't take this the wrong way, I promise I'm not being a dick, promise!, but go to howstuffworks.com or something and look up V-8 or internal combustion and watch how it all has to move correctly.
One more reply saying...YES!! Line up the marks!! Even one tooth off can lead to a poorly rnning engine...if it runs at all. This is SO basic that I cannot even explain it. If the marks don't line up now, be VERY careful turning the engine over. Turning the crank can easily bend valves. Turn VERY SLOWLY. If (when) you feel anything...STOP!! Turn the cam a little one way or the other. Try the crank again. It'll take some time and a LOT of caution. But, get the cam and crank to line up, pop on the sprockets/chain assembly and you are good to go. Believe me, when I was a kid (a LONG time ago) I bent more than one engine's valves.
The mark (dot on the tooth) that you have at 9 o'clock should be at 6 o'clock and the matching mark on the crank gear should be at 12 o'clock and they should line up with each other. As Lippy said, do yourself a favor and buy a manual or one of the how to rebuild your small block Chevrolet books at the book store. It is a well spent 20 bucks and I used one as a teaching aid when I was teaching High School Auto Mechanics. This is the book I was thinking about and you should be able to find it at almost any Borders, Barnes & Nobel, Hastings or a lot of parts houses. http://www.amazon.com/How-Rebuild-Your-Small-Block-Chevy/dp/1557880298/ref=pd_sim_b_6
if you drew a line between the cam center and the crank center you will want the dimple on the cam gear and the dimple on the crank gear to fall on that line ( thus as on a clock with hands 6:00 cam 12:00 crank) OK?
All of the above are right. But if you put in one of those three way deals, make sure you install it per the instructions.
One other thing to bring to everyones attention is the roller chain setups that use 3 or 5 timing positions used to "dial in" the cam. Be absolutely sure the triangle on the crank sprocket lines up with the triangle on the cam sprocket (if that is what you've determined your engine wants), or the square with the square, the circle with the circle, etc., etc.. Tell you why. A friend built up a hot 355 street engine, did a nice job of it, but in an absent minded moment lined up the triangle with the circle. It would not start. I am amazed that he got away without bending any valves. He will not make that mistake again. BTW, it did run very nicely, once the triangles were properly "clocked". Another friend built a serious sbc racing engine with a gear drive reverse rotation Isky roller tappet cam, and in one of those "moments" installed it two teeth retarded. It started and ran, but blew the engine in the pits! New aluminum heads, pistons, valves, etc. turned into junk. Expensive mistake. Heed Lippys advice. Get onto a learning curve ASAP! "Concealing ignorance is harder than acquiring knowledge" Don Garlits
What did you tear it apart to do anyway? Get you a manuel,or one of your mechanically inclined buddies to help you time it right,you mess up alot more taking a stab at something instead of just getting it done right.GOOD LUCK,many a good engines CHEVYS,FORDS,MOPARS turned into scrap iron because of wrong timing setup.!!!
While I realize that I am losing my patience as I get older, I sometimes have to ask the obvious question. The right answers are included in most of the above replies. Follow their instructions, DO IT!!..... LINE UP THE DIMPLES, THE POCK MARKS, THE DIMPLES...WHATEVER YOU CALL THEM. YOU KNOW, HE DAMNED MARKS!! PUT THE BOTTOM DOT (CRANKSHAFT) ON TOP. THE TWO ON THE CAM GEAR GO ON EITHER SIDE OF THE BOTTOM MARK!! ARRGGHH!! Maybe you should take up another hobby if you get through all the above advice and still don't get it. (there, now I feel better.....damned kids...smiling)
Look i get it. I knew they were supposed to be lined up. But for some reason figured that if the cam could spin freely while i was installing the chain that it would not be as crucial. Like the lifters would land on the lobes where they were supposed to anyway. I guess i was wrong and i can admit that. I did not just tear into a running engine. I pieced it together from a bunch of junk and am preparing to stab it into a car. I really dont care your personal opinion about my skills or "your" hobby. Thank you EVERYONE for your replies.
Are you being serious here? "for some reason figured that if the cam could spin freely while i was installing the chain that it would not be as crucial. Like the lifters would land on the lobes where they were supposed to anyway" WOW I am not sure YOU should be assembling anything on this engine. Valve timing is one of the simplist to "get" when building an engine, and far more can go wrong without a good understanding of the internal combustion engine. Get a manual and read it, understand it before you put a bunch of time and $$$ in this small block and end up using it as a boat anchor!!!
ATTENTION: CreepyCreeperson When you ask a question, fair enough. When you get the answer, if you don't understand, ask for clarification. But, when you posted the photo with the question, "Does this line up", that was the final dumb question. Stevie Wonder and Ray Charles would know that they were NOT "lined up"!! Don't take it personal, but be prepared to be flamed when asking for help and then and doing or saying something stupid. Keep trying, you may just get it.
Ya, well actually I had the crank sprocket on backwards and for some reason thought that the dowel pin on the cam sprocket was the indicator while the notch on the crank sprocket was the other indicator. Once I flipped the crank sprocket around I could see that there actually was a dot on it. Its lined up now. Keep the flames coming... on a positive note maybe now when some other moron wants to know why they have to be lined up they can use the search function and read this. Haha.
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