valve stuck!!

[propit21]

heres the background

The last race we had on the motor 383 worlds 220 heads we lost a power steering belt so we just cruise around the whole race, didn't even turn that many RPM's. During our weekly maintiance we notice that the nmber 5 exhuast valve was stuck open a little and would not come up. When we looked further into it we found that the header gasket was blown out a little around the number 3 and 5. So we took the motor out and sent to our engine guys that been helping us with our engines, and very trustworthy engine builder locally. So we are thinking bent valve for sure, but when he took the head off and took the spring off the valve and tap the valve it fell right out, he checked it and it wasn't bent and it moved freely up and down the giudes. The number 5 intake was the same stuck but fell out with a tap of a hammer and then again no binds moves freely. Heads and valves taken to the machine shop heads were mag guides were check and came out just fine. Heads our just fine no problem, no visable marks or any think on the valve stems. Springs are good.

Question has this ever happened to anyone before or anything like this. This is a gas motor 383 with worlds 220 motowns. Valves are straight and true, heads and guides are just fine... Any suggestion, comments, or anything that can help we are stumped.

[usafracer]

Stick the valves in an oven at 250 and measure them. I have had some that will expand more than others.

[propit21]

is there any vavle brands that are better then others as far as expanding with heat? Whats the min clearance that there should be?

[Dirt Racer]

If the heads have ever had the guides replaced, it could be defective guides. Had a batch that would get hot and grab the valve, then cool off and seem fine. It took a while to find this out, replaced them and everything was fine. Ignition timing could cause excessive heat in the exhaust port, if the timing is retarded to much. Some builders choose not to run seals on the exhaust valves to reduce the chance of sticking the valve.

[50j]

If the heads have ever had the guides replaced, it could be defective guides. Had a batch that would get hot and grab the valve, then cool off and seem fine. It took a while to find this out, replaced them and everything was fine. Ignition timing could cause excessive heat in the exhaust port, if the timing is retarded to much. Some builders choose not to run seals on the exhaust valves to reduce the chance of sticking the valve.

I had that happen a few years ago.

[propit21]

heads are used we have a quite a few races on them but were updated with new springs about 4 races ago.

[Milford Motorsports]

Is it possible the spring seats are not square with the valve guide?

[propit21]

it happened again found it tonight. it the number 5 exh valve only this time. Try to get it loose myself with no luck. We have about 4 races with this not happening and now it did it again. What should we do? new guides, valves, heads, looking for suggestions please help. Timming is at 34 degree advance and car runs around 180 to 200 in temp.

[perfconn]

Cast iron heads with stainless valves will stick the exhaust valves if you get the engine too hot

[diggindirt]

If you have access to a dyno, check the EGT and Feul Curve. I had this happen and had to adjust the jets and fuel curve to keep the EGT temps down. My car ran 180 all night long, but the EGT's were running 1300*. Changed the FC and jets, still runs 180-200, but EGT's are down in the 900* range and no more stuck valves.

[propit21]

thanks guys, motor never been on a dyno but it might be time to look into it. Yeah motor never shoots out water or gets hot at all. but i guess the exh temp could be higher then normal and we don't know that. We place a temp gun on each exh tube at the flange and haven't seen any kind of crazy numbers. Perfconn what valves do you recommneds for these heads? Thanks for the help guys this is just getting really pain taking.

[perfconn]

If the rules say stainless then I use Ferrea.Titanium I use Del West

[dynoman14]

Obviously whatever you are doing is not working.

Have you ever measured guides for valve to guide clearance? Do you have any professional engine building tools like calipers and dial bore gauges to the .0001". I am betting not or you would not be having these problems.

If you plan on doing this yourself you should seek the help of a professional and plan on spending a couple hundred dollars on the mics required to measure valve stems and guide bores.

You really need a professional cylinder head person to check out your heads as you are real lucky you have not dropped a valve.

With my parts in stocker heads I use .00075"-.00125" on the intake & .001"-.0015" on exhaust. With a Serdi it is pretty easy to ream or hone and run these numbers. With hand held grinders or a drill I might add .0005" clearance because unless you are highly skilled or have some great fixturing you will never get round & internally straight guides.

If you run a good quality cast iron guide, I might run .00025" tighter.

I am sure there are a ton of folks out there with other numbers than what I use but that is with Manley or PEP stainless stuff that costs $5-$10 a valve. You can pay more but don't know you'll be getting any better unless you go with Ferrea Steels.

I also run metal clad viton stem seals on intake and exhaust on all of my heads from stockers all the way up to SB-2 850HP engines. Seals keep the stems clean and lubed way better than no seal at all. Your guides should also be chamfered on the top and bottom to allow oil to get to the stems, not too many people do this because it takes extra time to put a top and bottom finish on 16 guides that is 32 more machining operations but it is worth it. The is a couple other small machining operations to keep valves extra free in the honing process but we'll leave that discussion for professional head folks.

From what I read running offshore and import valvetrain stuff right out of the box is causing a lot of problems.