Is a 273 an interference engine???

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65Val

65Val

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Hi gang. A rookie question, probably. I'm assembling my '67 273 using stock 2 bbl pistons, "302" casting heads and a fairly mild cam. I have #1 piston at TDC. I have temporarily installed the drivers head, and camshaft (260*/.430 lift/46* overlap), as well as intake lifter, pushrod and rocker for cylinder #1. Now if I rotate just the camshaft, I can't go all the way around as the intake valve hits the piston. The heads or the block have not been milled. Should this be happening?

Thanks guys! (I'm probably just dealing with some brain-fade on this)
 
If you had the timing chain/gears hooked up to both cam and crank, the number one piston would be going down as the intake valve is opening up, therefore, you wouldn't be hitting the piston with the valve.
 
What you are doing defies all logic. There is never a reason to rotate the cam with any piston "up."

To answer your question, "yes" all small blocks are "interferance" engines

On an engine with high compression pistons/ milled heads and a high lift cam, it is IMPORTANT to realize that the closest clearance between the valves and piston DOES NOT OCCUR at TDC. That's why it is so important to actually check. That cam you have does not fit that category
 
chuck perry said:
I might be wrong but don't the 273 pistons come out .020? With the 302. Head
wouldn't that cause a issue?
Click to expand...


I think so on the 4bbl motors but what about the 2bbls motors??

Can you turn the rotating assembly all the way around with the head attached?? Might be a good indicator if the piston is going to smack the head. Depends on the gasket thickness though too.
 
All small block Chrysler v8 engines are interference. This means that the valve occupies the same area inside of the cylinder as the piston does at a different time.

If you have the engine assembled and you can't rotate the engine without sparkplugs, STOP.

Take your rocker arm shafts off to back the valves out completely and check your cam against TDC on the crank. You likely have it in at 180 degrees if it's on the mark.

It doesn't take much to look at a cam and figure out if you are on 0 or 180 installed on the gear. At true top dead center, or 0 degrees on the crank, the valve cycle should be coming up for the exhaust, which means the exhaust lobe on the cam for the #1 cylinder should be just before (just counterclockwise) of the lifter, for correct TDC and you should see the mark on the gear to match the one on the crank (check it with a straight edge!), to make sure it's not a tooth off. One tooth off can bend a valve on a 360. Two may do it on a 318 or 273.
Which one is the exhaust lobe or intake lobe? just look at it's position against the rest of the valvetrain and the intake or exhaust port it's above, to determine which valve it opens.
 
Thanks all. I can rotate the engine with the timing chain on,. so I'm OK. I just wasn't sure a 273 was an interference engine or not.
 
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