FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Rory428 on November 28, 2021, 08:40:20 PM
-
Last month, I found my 428 idling a bit rough, I did a compression test, and found number 8 cylinder very low, only 40 psi, compared to 185-195 for the other 7. Today I pulled the heads, and poured so solvent down all the ports, sure enough, on number 8, the solvent came pouring out of the exhaust valve. Removed that valve, and found the valve guide extremely sloppy, .150" of movement.I was talking to my machinist buddy, who has built dozens of FE engines over the years, including doing the machine work on several of my 428s, and he told me that over the past year or 2, the machine shop that he was 1/2 owner of, has stopped doing work on FE heads, he said that they have had several cases where they had similar valve guide issues, with valve stems galling and tearing up the guides. He said that they have only had this issue with factory FE heads, and has not been able to determine a cause. Just wondering if any other FE builders has been experiencing similar problems.
-
I've seen it twice, but it's been on new, aluminum heads. One was a set of CNC ported Edelbrocks and the other was a set of CNC ported Pond heads. Guides wore plum out, even with the geometry being correct.
I think the surface finish on the valve stems has a lot to do with it.
-
Just wondering if original Ford valves or after market ones?
-
Were the guides Brass or Cast Iron?
-
On my CJ heads that ate the guide, they were iron guides with OE (1969) Ford valves. The valve stem had noticeable pitting, almost looked like rust pits, about 1/2 way up the stem, that were not there when I assembled the heads. The valve seat in the head is also somewhat "sunk", which would explain where the valve lash went. These heads do not have hardened seats, and before I took it apart, I had assumed the maybe the unleaded pump gas was causing a problem, but with that much slop in the guide, I imagine the valve just didnt get to seat very well.
-
Rory....The heads I had on my 427 were a worked set of GT 390's with CJ valves (i believe you bought the valves)..In 17,000 miles the unleaded fuel had destroyed the exhaust seats.Car still ran fine..Found the problem when the heads were torn down..Dont remember how the guides were.I scrapped the heads and have gone aluminum..
-
Seems I have noticed a trend toward closer stem to guide clearance of late. Could this, in combination with modern valve seals be a contributing factor?
-
Do you mean with the tighter clearance and the seal giving less oil?
-
Do you have restricters in the heads
-
My thoughts are the valve stem was too dry. Stem got extremely hot and transferred metal to the guide and wearing the guide. Since the valve head was also overheated it could not take any heat away from the seat.
The seat then melted away on the surface and effectively sunk.
"Back in the day" we ran Teflon seals but allways lightly scored the exhaust seals with a jewelers file. Race motors got no seal on exhaust valve.
-
That is why I ask about restricted i also think like you its not getting the oil it needs i would check the rocker arm shaft for wear also,
-
The whole point of seals is to keep oil off the stems. You don't want oil running down the stems. The exhaust side is under positive pressure anyway. The only way oil would go down the stem is when the engine is not running or idling or maybe under hard de-accelerating. I tend to think bad metallurgy on the valve or too tight in the guide? IDK.
-
Do you mean with the tighter clearance and the seal giving less oil?
Yes
-
My CJ heads do have restrictors in the feed passage, like all my FEs have had for decades. This 428 has 40 psi of oil pressure at hot idle, and when I primed the oil pump, even with the restrictors in place, and cold oil, there was enough oil running out of the rocker arms within 30 seconds of building oil pressure, that it would have ran over the valve cover rails if I continued priming, so there was plenty of oil getting up top. The heads do have positive oil seals pressed onto the guide, but rubber rather than Teflon , and these are not new guides, I had used these same heads on my Fairmonts 428 previously. Plus it is only this one valve and guide that has issues. I am mainly wondering where or how the pits on the valve stem occured, they were not there when I installed the valves. Curious if maybe something with modern gas possibly is involved?
-
What do they make to add to the gas to take the place of lead the old tractor guys add something to save the seats
-
What do they make to add to the gas to take the place of lead the old tractor guys add something to save the seats
Older gasoline tractor engines generally don't make a lot of heat even when working so they are pretty easy on valve seats. The valve seat erosion is the result of a phenomenon called microwelding. At high metals temperatures, very tiny bits of cast iron head seat material attach to the valve. It's molecular, but it has the same affect as death by 1,000 cuts. Some engines by design, like flatheads, make so little combustion heat they have very generous octane requirements and can run on a variety of fuels without consequence.
-
I have had a couple occasions where we experienced guide issues on iron heads. Might not apply to the original question, but worth noting.
First is that I have seen some valves that had obvious issues with the stem plating. Most valves will use a flash chrome plate on the stems for wear resistance. Chrome is really hard and can be pretty abrasive if it's not glass smooth. I've see a few where there was almost a gritty or bumpy finish. I've run a bit of 600 wet or dry & WD40 on those with the valve in a drill to smooth them out. At one time somebody sold a little grinding fixture to put a cross hatch on stems for high end race stuff.
I ran into an issue where we were sticking exhaust valves on the dyno during power runs. Often the valve would release once the engine cooled down. Using full bronze replacement guides. Ended up fixing it by opening up clearances a little and cutting back the portion of the guide that extends into the port a good bit. I think the bronze and iron had different expansion rates and the guide would tighten up on power runs as exhaust temperatures increased. I'm sure that the guide would have worn prematurely in a less aggressive environment as it "dragged" when hot rather than fully sticking.
Lesson is that surfaces need to be smooth and straight, and we don't need guide clearances to be super tight "just because we can".
-
I've run a bit of 600 wet or dry & WD40 on those with the valve in a drill to smooth them out. At one time somebody sold a little grinding fixture to put a cross hatch on stems for high end race stuff.
When deemed necessary I will chuck the valve in the lathe, spin it fast and apply an appropriate grit W/D paper with cutting oil with a floating flat back-up 'shoe' to polish the stems. :)
Scott.