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454 timing chain replacement

Looks are sometimes very decieving. Just imagine that size of the intake valve which is open while the piston is traveling downward in the bore, now imagine that same valve being in its full open position while the piston is coming upward since the timing chain is no longer keeping things in sync, Guess what happens now. Whammo, bent valves.
 
You do realize that if the valve lift is not very much over stock, then the piston and valve will never occupy the same space, thus there are interference and non-interference engines.
 
Being an automotive machinist i realize what you are thinking but there is more to it than that. It has a lot to do with the design of the head and the position of the valves in the head in relation to the cylinder bore and design of piston being used.
 
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I understand very well what makes an engine an interference engine. Is it not true that the valves are in a location on a SBC and BBC that would require much valve lift and/or domed pistons to become an interference engine? I hope someone else chimes in with more experience with this so the original poster doesn't think he needs new valves and heads now because his timing chain broke.
 
BlueBlazer62 said:
I understand very well what makes an engine an interference engine. Is it not true that the valves are in a location on a SBC and BBC that would require much valve lift and/or domed pistons to become an interference engine? I hope someone else chimes in with more experience with this so the original poster doesn't think he needs new valves and heads now because his timing chain broke.
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Ok, lets back up a minute. I never told him he will definately have bent valves. I said he will not know until he has replaced the timing chain and then does a compression check. Just because an engine is an interference engine does not mean that the valves will bend everytime. Maybe there was some miscommunication here somewhere. I have seen timing chains break on SBC's before and never bent valves and i have also seen then bend valves. It mainly depends on how fast the engine RPM's were when the chain broke and where the valve train came to rest when it broke and also if someone kept trying to start it before they realized what happened.
 
Well lets see if you can agree on this info. What size cam lift can the stock 454 springs handle. I am looking at a cam with .475/.500 lift and need to know if I would need to upgrade springs or just get some new stockers? As far as the valves go I am not too worried about it as I said the heads need a rebuild anyway I just hadn't planned on doing it yet so no big deal I'll just get them rebuilt. I was already having compression issues due to burnt valves. No biggie!
 
Every head is a little different. The springs themselves can handle .500" lift without trouble but it all depends on if your heads use rotators on the exhaust springs or not. I would highly recommend to use the springs that are matched for the cam in question.
 
Well it is actually a cam from summit and they dont have springs so I have looked at buying some for similar grinds from Crane, Comp etc. just haven't had time to call Summit to get their recomendation. I would really hate to spend $100+ on springs and retainers if the stokers can handle the new cam. Stock springs are like $2-3 each. What are rotators and how do I identify if I have them or not? If not then the stock style springs should handle the .500 lift and be just fine? I don't intend to do any high reving on this engine or anything like that, just daily driving and occaissional towing.
 
The rotators are located under the valve spring against the head. These are designed to help make the exhaust valves rotate as well as open and close but when using an aftermarket cam with larger specs than stock and requiring slightly higher spring pressures they are known to fail. Comp cams makes an eliminator shim for this purpose and i believe they are .300" thick and simply just take place of the rotator.
 
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