QuestionQUESTION: The normal timing marks are dots. There aren't any dots on the gears I have. All I see is a letter c on the crank gear and a groove on the cam gear. Are these the marks I'm looking for? Is there any other way to verify the correct timing before I go too far in assembling the engine?
ANSWER: You can always verify the correct valve timing on any engine by looking up the degrees before or after top dead center at which the #1 exhaust or intake valve should begin to open. I can't give you those specs without knowing which year 235 you have, and whether the engine is from a Corvette or a normal passenger car (the valve timing changed many times during the 235 production run). If you post a follow up question to me with that information, I'll give you the specs for this.
Ignition timing also is different for different years of 235, and also whether the engine is a hydraulic lifter version or solid lifter. All 235s are timed off the flywheel markings and ball.
You can also verify correct valve timing by noting the following:
the cam gear and the crank gear should have dots near the teeth of the gears. If you position the gears so that the keyway on the crank gear is vertical, its dot should be at the tooth that is 4th in the CCW direction from the tooth that is lined up with the keyway. The dot on the cam gear should be at the valley between the two teeth of the cam gear that straddle the dot on the crank gear - at which point the cam gear keyway will be at 45 degrees in the CW direction from vertical. To double check the setting, use a straight edge and verify that a single straight line will bisect both gear centers exactly and also pass through both dots.
If you cannot see the dots, it is possible the gears are on the shafts backwards.
If there are no dots on the gears, perhaps the gears are not the right parts.
I hope I've answered the question you were asking; if not, post a follow up and I'll try again.
Dick
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QUESTION: Thanks Dick the engine is a 1956 truck with solid lifters.I'm overhauling the engine and when we took it apart we didn't think to look to see if there were mark on the cam gear before we took it apart.The way you told me to find the mark on the crank gear is where the c is that ones found.I just need to find where it is supposed to be on the cam gear.The engine was running when it was taken out and we didn't change the timing gears so I'm assuming that it is correct. Thanks again for all the help.
AnswerOK< I understand. The timing gears must be aftermarket gears - but I still can't understand why they would have omitted the timing dots on the gears. Did you look at the back side of the cam gear? Maybe the machine shop pressed the cam gear on backwards.
Anyway, here are the specs for a 56 engine. My books only cover cars, so we'll have to hope that yours is the same as a car engine, but I'm about 95% certain that it is.
For a 56 engine, the intake valve should just start to open 10 1/2 degrees BTC (Before Top Dead Center on the compression stroke), the exhaust valve should just start to open 49 degrees before bottom dead center.
Since there is no easy way to measure these positions without a degree wheel, what you will have to do is note the exact TDC position by stopping the piston at the exact top of its stroke, and then estimate the degrees by putting degree marks on the crank pulley spaced so that you can estimate degrees by sighting against a reference mark on the block that you put there at TDC. You should also mark Bottom dead center on the pulley, then divide up the distance between those two marks on the pulley as precisely as you can into degree marks for 90 degrees, then every 45 degrees and so forth until you will be able to tell where the crank is after the head is on. Then you can note where the crank is when the valves start to move.
I don't know if degree wheels are still available for this old an engine, but you could contact a vendor such as Summitt Racing Products to see if they have one - that would help you quite a bit. Otherwise, you are not going to be able to do this very precisely, I'm afraid.
If this were my engine, I think I'd spring for two new gears, frankly! The cam gear is pressed on, so you'd have to have a press or get a machine shop to press the old one off and the new one on for you. While you are going that far, you should consider having the cam reground, or buying a replacement camshaft too!
I'm still puzzled about the lack of timing marks on your cam gear - I've never run into that problem before!
Dick
