As a winter project I’m porting and polishing the heads on my 302 ford. This engine has about 6000miles since rebuild, it’s a 302 roller HO with stock e7 heads. All of the intake valves were black and the exhaust valves were all grey except for this one. What’s causing this and what’s the fix?
Can't see clearly but sure looks like it's leaking. Remove the spring and valve and inspect valve and seat. Probably needs seat and valve touched up o'r maybe new valve. With that low mileage I'd suspect it was not properly seated when new.
Assuming conversion to carburetor, what cam/ignition timing do you have? What does the top of the piston look like?
That’s consistent with my thinking, Doesn’t look like the valve was lapped on properly, the other valves still show a nice clean ring where they were seating.
Stock HO cam, timing at 14°, duraspark ignition. first two photos are #7 with the questionable valve and the next two are #6 for comparison fyi the plugs have about 500miles on them because I cracked one changing a header gasket.
It was probably leaking based on your photos. As a quick check I turn the head with the ports up and fill them with solvent like mineral spirits. A leaky valve will show leaking solvent into the combustion chamber. A good serviceable valve will show none or minimal seepage after time. FYI I do my own valve jobs and use a valve seat runout gauge to insure seat concentricity. I have found it beneficial to grind 1/2 degree interference angle into the valve/seat. Then I use fine lapping compound to lap the valve in and check the contact pattern for correct seat width, seat placement, and final spring installation heights. Often times when shops recondition the valve guides they do not necessarily check seat concentricity / runout. That's where the trouble begins.
I use this to check my valve jobs. I will take a mallet and strike the valve stems to bounce the valve against the seat and use diesel fuel to check.
Blown up it has me asking questions. Like what cause that? So is that an intake or exhaust? Looks intake? And just because I over think this stuff, if this was a EFI engine converted to carb, has it still got the OG cam in it?
That circle in the intake valve is from the valve spring compressor, it is just a mark in the carbon on the valve. yes, it still has the fuel injection cam, I don’t think the cam is an issue as it runs well and none of the other valves have this discolouration.
Shot in the dark- if running the HO cam, using the HO firing order? It appears though a leaking valve.
It's either leaking or running a tad lean. As in that side of the valve has been a lot hotter than the rest of the valve.
What colors are you (everyone ?) expecting in a gas burning engine ? What's wrong with you people...you want green or orange valves ? With the exception of the intake valve looking like it's got a carbon buildup on it (running a bit rich), BOTH of the valves are "colored" fairly nicely !!! In a good running engine, the exhaust valve runs much hotter than the intake valve, plus all of the gas has...been burned. The ignition timing also has some effect on the valve color. Again, a cream to off-white exhaust valve color is a GOOD...thing ! The intake valve will always, be darker, mostly a very dark grey to black. The fuel is unburnt, the valve runs much cooler, so the fuel byproducts are not...burned away, hence the darker color. As far as the burnt valve... Yeah, what some have said. 1 - A loose valve stem to guide clearance. 2 - A mis-machined guide, to the valve was off center of the seat. 3 - Opposite from above, the valve seat was mis-machined off center of the valve guide (more likely than #2). 4 - A piece of garbage (carbon deposit) broke loose from the chamber or piston top, and got stuck on the valve or seat, for enough time to over heat that portion of the valve. Once the burning starts, there's no stopping it. This type thing could have started MANY...miles ago, and took that amount of time to show its ugly head...so to speak. It looks to me like...just one of those things that can happen in a daily driver, gasoline burning engine..! Mike
It is possible the rocker arm is preloading that valve and holding it off the seat . push rod too long? Valve stem too long? When you assemble it, do a leak down test to make sure there are no leaks with and without rockers installed.
I’m not sure it’s possible for the valve to be held open, it’s a stock valve with stock rocker and pushrod on the stock hydraulic roller cam, but I’ll definitely check the pushrod and valve length and straightness. I’ll certainly do a leak down test on all cylinders after lapping the valves, thanks for the suggestion
After only 6000 miles,,,,it was probably not sealing correctly to start with . Always double check the valve seal after a valve job . If they are not sealing at the start,,,,,hot gases are already burning the surface ring and they won’t last long . I always assemble my own ,,just to be sure . And like one guy said,,,,,,whack the valve stem top with a hammer,,,,,that will help the seal as well . Just a few love taps is all it needs,,,,,,before fire up of course. After it’s burnt,,,it’s too late . Don’t assume that the valves are sealing perfectly from a machine shop valve job . 30 years ago a friend of mine purchased a brand new set of aluminum heads from Reyer Morrison,,,,,BBC ,,,,,,complete assemblies,,,,,new valves and all . Just so happened he put them on his bench and put fluid into the ports . They leaked on almost every valve ,,,,,,a few you could see light through . After a complete valve grinding,,,they were perfect . I’m not bashing Reyer Morrison,,,,,,,I’m just saying that if a professional race shop can do that,,,,,,then a regular machine shop could have a slight leaker as well . Tommy
If you don’t have a concentricity gauge which most people have clean up the valve and seat and try lapping it in. Go easy on the compound and don’t lap to long. If it’s out you will see a pattern on one side of the seat and not the other. But before you start the guid clearance needs to be checked. I’ve seen poor workmanship cause guide work to get real wide after low mileage. And it may be carbon but that valve seems to have a step worn in it. Maybe just the pic though.
Also, try checking the "collapsed tappet gap" by levering the rocker arm back against the pushrod until all the oil gets squeezed out of the lifter cavity. Gently and slowly - don't buckle a pushrod. (They make a tool for that.) There should be clearance such that the rocker arm when installed did not use up all the lifter plunger travel. Generally about .075" of travel should be extant. If there is no clearance the valve will hang open and overheat.
Cool. Wasn't sure but assumed it to be, yet there they were in the holes like you just flipped the head off and over to take a pic. So the valve pictured was which? As far as my cam inquiry, nothing to do with the valve, just general interest. But assuming the exhaust valve, I'd have been curious what a compression test reading would have shown. Maybe even a vacuum reading.
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