I need a quick answer to this one. Got a family member with a genuine honest to goodness '70 LT-1 350 that he installed in an O/T mid 70's nova many moons ago. It seems to have lunched a timing chain. Before he tears into it, we need to know if the LT-1 is an interfearance engine... Does he just need to replace the chain and gears,,,, or will he find a bunch of bent valves? Thanks guys.
I'm not sure but i got a nice set of 71 350 LT-1 heads that i might come off of.3 angle valve job new springs and retainers,and umbrella seals only ran for about 100 miles.
Appreciate the offer Slickster. He's good on parts, just needs to know if it's a bandaid fix, or if major surgery is required.
Definitely an interference fit. I don't know if SBC's are, but I have done regular low compression 350's with bent valves after a timing chain failure. At very least do a compression or leakdown test after changing the timing chain. My experience is that it depends on when the chain went. If it was running, it probably has bent valves. If it jumped time when cranking, you may get lucky. Paul '56 Nomad
best answer i can give is i've seen them with bent valves and without bent valves. it seems like if they where at lower rpms it less likely then at freeway speeds.
What he told me was that, since the weather was nice today, he decided to take it around the block. Been in the garage since a couple weeks before X-mas. Fired right up, warmed it for about 2 minutes, backed out of the garage onto the street, put it in first, and about 30 feet later it died. Barely 2000 rpm, and he was not getting on it. I know the majority of SBC's are not interfearance, but a handfull are... I'm afraid with the 'LT's big cam and pistons, he may have won the bad luck lottery.
A simple compression test should be enough to tell if the valves are bent. I've never broken a timing chain in an SBC that had a cam bigger than a stock smogger - gear drives don't break very often. Tim D.
pushrods will generally fail in a stock lt1.i've seen bent valves,,,i've seen bent pushrods...and then there's the pushrods that the ends peen closed...compression test is first place to start..if any cylinders come up questionable, check pushrods..if they are good and is questionable on test, probable bent vavle...remember they can bend and also screw up the guides and stick...2,000 rpm's??not straining???maybe...maybe not....if stainless valves, look at other components..it standard, oooopppsssssss also check spring pressure and height ...and then there's the dreaded "whats up with the lifters"....
I think most of them would be interferance. I've only torn down about 40 SBC's, but seems like most of them have flattops with a little valve relief, and any valve that's open much at all would kiss the piston at TDC.
if it was a "true " lt1...it would have a little dome on the piston....350 hp or a little more in the vette.....big valves as well..... brandon
Some engines have enough piston to valve clearance that you can literally stop the valvetrain in any position, and allow the crank to spin without pistons hitting valves. Those are non-interference. With an interference engine the valves have to be synched with the pistons or they'll hit. And the valvetrain is generally weaker than the piston, so it suffers the damage when they interfere with each other. Non-interference engines are more prevalent in the modern era when the engine is designed around a rubber timing belt. Timing chains are 2x-4x as durable as a belt.
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