This video covers how easy it is to calculate piston-to-cylinder wall clearance. It's too easy. This is important because too loose of a gap and the rings won't seal properly. Too tight and the. Piston to valve clearance Piston to valve clearance is determined by cam lift, lobe separation, duration, valve margin, head design, and aftermarket milling of cylinder head. Minimum recommended clearance for intake & exhaust valve would be 0.100' deep and.050' radially. Check by using clay or follow cam manufacturers.
Click to expand.I would not try to slice hairs with piston to valve clearance with a 383. I've bent several intake valves and actually busted a head with these issues and a 383 with flat tops. Hydraulic cams make matters worse. What ever the tappet pre-load is is how much the tappet will pump up and how much valve lift will increase if the springs are floated. I'll almost bet you have.515' lift at the valve with adjustable rockers; could be wrong but doubt it.
I'd almost bet you've got some retainer to guide issues if your using unmodified iron heads. Tight lobe separation angles and advancing the cam will decrease piston to valve clearance on the intake side. I would not try to slice hairs with piston to valve clearance with a 383. I've bent several intake valves and actually busted a head with these issues and a 383 with flat tops.
Hydraulic cams make matters worse. What ever the tappet pre-load is is how much the tappet will pump up and how much valve lift will increase if the springs are floated. I'll almost bet you have.515' lift at the valve with adjustable rockers; could be wrong but doubt it.
![Piston to valve clearance calculator online Piston to valve clearance calculator online](http://www.vdubn.com/sandrailing/engine/vlv_clr1.jpg)
I'd almost bet you've got some retainer to guide issues if your using unmodified iron heads. Tight lobe separation angles and advancing the cam will decrease piston to valve clearance on the intake side.
If I understand the question correctly, there is no clearance. If a valve is open when the piston goes to TDC it will hit.
Diesels (all of them, I think) are 'interference' engines due to the amount of compression they require. Most gasoline motors can use a dished piston which will make room for the valves.This is why it is so important to make sure the timing belt is changed on time. A broken belt with the engine running will cause the piston to hit at least one valve. If the engine is spinning fast enough you could hit all of them.
The worst case scenario is valvs breaking, falling into the combustion chamber and causing broken rods and cracking the crankcase. I think the question was misunderstood. I know what he's talking about.The engine is indeed an interference engine, but interference only occurs if the cam and crank timing is 'out of sync', i.e. If the belt breaks. Under normal conditions when everything is timed properly, there HAS to be clearance between piston and valves.
The cam profile and the recesses in the top of the pistons results in clearance during normal operation.I don't know how much clearance there is. I do know that the camshaft has 'negative overlap'.
The exhaust valve closes before TDC and the intake valve opens after TDC, which is an indication that there ain't much clearance to be had.I don't know how much is available but I can suggest how to check it, and it ain't easy.Method 1: Position engine at TDC #1, remove camshaft (ideal time to do this is during a timing belt job, because it's all gotta come off!), remove the valve lifters. Install a dial indicator pointing at the end of the valve stem, and compress the valve spring by some suitable means until you feel it touch the piston, and read the dial indicator. It might be possible/easier to do it with the lifter in place if you collapse the lifter completely because then you have more area to work with.Method 2, if you have the engine apart: cylinder head has to be off. Using suitable tools, measure the depth of the pockets in the pistons with the cylinder at TDC, add the compressed thickness of the head gasket, subtract the distance that the valves project above the surface of the head.These two methods only tell you how much 'static' clearance is available. The next method tells you how much 'running' clearance is available, including the cam profile allowance.Method 3: Remove cylinder head and clean everything up. Place Silly Putty or something similar on the edge of each valve pocket.
Re-install the head, camshaft, belt, and time the camshaft. Rotate the engine two complete revolutions by hand. Take it all apart again, and measure the thickness of the Silly Putty impression that was made by the valve.The latter method is used when building engines with non-stock pistons/heads/valves and really hot camshafts, to make sure you have the valve recesses in the pistons deep enough. Good post, thank you.There is some safety margin that can be exploited to our advance. Few cam manufacturers are out there doing this, and their cams run just fine in otherwise standard engine (i.e. Valve recesses are not modified on pistons).Many moons ago I managed to find a neat little Excel program that will show piston distance to top of block at any given time BTDC or ATDC.
![Piston Piston](/uploads/1/2/5/3/125383225/326597330.jpg)
User just had to puch in how many degrees BTDC/ATDC piston is, and hey presto, the program tells you the distance.Coupling this with cam lobe ramps, one can map out interference margins throughout the engine cycle.At this point your method No1 looks most attractive, as it is my daily driven car, I'm not too keen on pulling the cyl head off.Let's see if someone has this bit of info I'm after.