1981 Corvette - Interference or Non-Interference

[V8Adam]

Hey everybody,
I just had a quick question regarding the engine in the 1981 Corvette. Is it interference or non-interference? I am guessing it is non-interference but wanted to check.

 

[Oneball]

I’d have thought pretty much all SBC will be interference due to the valve angle. If you look at a lot of the stock pistons there’s a valve cut out

 

[V8Adam]

The reason I am asking is because I am considering how important it is to get the timing chain replaced. I understand that the 81 Corvette has a nylon timing gear and that is what concerns me.

 

[Oneball]

They wouldn’t put valve cut outs in the pistons if they weren’t needed.

Either way its probably quicker to replace the timing gear than the wait for the RAC. It’s not a particularly hard job on SBC.

 

[Roscobbc]

I’d have thought pretty much all SBC will be interference due to the valve angle. If you look at a lot of the stock pistons there’s a valve cut out

The piston 'cut-outs' are not exactly deep, certainly on a stock engine with stock valve lift. Allowing for manufacturers safety margins it would be interesting to get confirmation of 'interference'.

 

[Stingray]

A thread here that's worth a look, including reference to the nylon component,

Are sbc's non-interference engines? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Are sbc's non-interference engines? Engine & Drivetrain

67-72chevytrucks.com

 

[V8Adam]

A thread here that's worth a look, including reference to the nylon component,

Are sbc's non-interference engines? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Are sbc's non-interference engines? Engine & Drivetrain

67-72chevytrucks.com

Thanks very much! That's really useful and made the decision that I will be getting the timing gear and chain replaced!

 

[Oneball]

The piston 'cut-outs' are not exactly deep, certainly on a stock engine with stock valve lift. Allowing for manufacturers safety margins it would be interesting to get confirmation of 'interference'.

The cut outs are for clearance with the timing working correctly, if something goes bang then a valve at full lift and piston at TDC will bring them closer together than they would otherwise be in correctly functioning engine.

On an engine like an A Series where the valve is perpendicular to the piston crown you’ve got the whole depth of the combustion chamber before the valve hits a flat top piston. With an inclined valve like the SBC that’s much reduced.