Valve Recession in 700 miles?!
Valve Recession in 700 miles?!
(OP)
I have a '52 Ford pickup with a flathead V8 engine, rebuilt last winter. I put about 500 miles on it around town to break it in, with occasional runs up to 55 mph (2300 RPM). It ran great. So I took it on a 3500-mile cross-country trip to meet up with some fellow enthusiasts.
My route took me across the panhandle of TX/OK while ambient temps were up to 95 deg F. No problems, cruising along at 55, 2300 RPM, a self-imposed limit. But by the time I got to Missouri, it would regularly die when I came to a stop for gas or whatever. It would restart but not easily. It got worse and worse.
I figured it for a fuel problem, because a brief cooldown would help, so I did some things to reduce heat on the fuel lines, to no avail. It has an electric fuel pump with regulator, both appeared to function perfectly. Disassembled the carb (in the parking lot of an Arby's), clean as a whistle.
Checked the timing, no problem there. The engine has been updated with an MSD distributor that is essentially a GM HEI style, with separate mechanical and vacuum advance, both of which can be (and were) tailored to this application.
The engine ran at normal temperatures the whole way, with only brief excursions a half-a-needle width upwards on long or steep hills, even in 95 deg weather (engine ran at the same temperatures whether it was 95 or 75 outside).
I barely made it home, and first thing I did was run a compression test. Only 1 or 2 cylinders had anywhere near expected pressure (90-100 psi at my altitude). One was only 50. So out it came, pulled the heads off. All of the exhaust valve seats had receded, enough that there was no clearance between the lifter and valve when cold -- clearly once hot, the valves were being held off the seat. Clearance is spec'd at .017" - .019" cold, so the valves sunk that much. This model engine does not have hardened valve seats, instead it has valve rotators.
The machine shop examined the engine and found that the margins on the seats had gone completely away, and the valves had sunk. The valves' surfaces were in great shape, no deformation.
So here's my question. Which of these (or another?) could have caused this in such a short time, under relatively modest loads?
1. The machinist believes there was too much ignition advance, due to the vacuum advance. The vacuum advance is limited to 8 degrees, and is run off the manifold vacuum. He believes at cruising speeds, that would provide too much advance. There was never any pinging at any time, even on long grades or hills in hot weather. Flatheads generally run hot if there is not enough advance, I am not familiar with problems with too much.
2. The stock road draft tube crankcase ventilation system has been changed to a PCV setup, using a PCV valve from an engine of comparable displacement (a Buick 3.8L). I've had that system on the engine for 7 yrs, but admittedly never for extended highway use. The thought is that the PCV addition requires additional fuel be added in the carb to compensate, and that there wasn't enough added. I went one jet size up to account for it when I added PCV. Plugs were gorgeous, light tan, throughout the trip.
3. For this kind of operation on unleaded gasohol (E-10), hardened seats are needed for durability.
4. The shop did a poor job on the valves during the rebuild; inadequate margins, poor stone quality/rough seats, leaving a surface that wasn't durable.
I would appreciate your thoughts! I have no pre-conceived notions, all four ideas make some sense to me, but to do this much damage in this short of a time is shocking.
My route took me across the panhandle of TX/OK while ambient temps were up to 95 deg F. No problems, cruising along at 55, 2300 RPM, a self-imposed limit. But by the time I got to Missouri, it would regularly die when I came to a stop for gas or whatever. It would restart but not easily. It got worse and worse.
I figured it for a fuel problem, because a brief cooldown would help, so I did some things to reduce heat on the fuel lines, to no avail. It has an electric fuel pump with regulator, both appeared to function perfectly. Disassembled the carb (in the parking lot of an Arby's), clean as a whistle.
Checked the timing, no problem there. The engine has been updated with an MSD distributor that is essentially a GM HEI style, with separate mechanical and vacuum advance, both of which can be (and were) tailored to this application.
The engine ran at normal temperatures the whole way, with only brief excursions a half-a-needle width upwards on long or steep hills, even in 95 deg weather (engine ran at the same temperatures whether it was 95 or 75 outside).
I barely made it home, and first thing I did was run a compression test. Only 1 or 2 cylinders had anywhere near expected pressure (90-100 psi at my altitude). One was only 50. So out it came, pulled the heads off. All of the exhaust valve seats had receded, enough that there was no clearance between the lifter and valve when cold -- clearly once hot, the valves were being held off the seat. Clearance is spec'd at .017" - .019" cold, so the valves sunk that much. This model engine does not have hardened valve seats, instead it has valve rotators.
The machine shop examined the engine and found that the margins on the seats had gone completely away, and the valves had sunk. The valves' surfaces were in great shape, no deformation.
So here's my question. Which of these (or another?) could have caused this in such a short time, under relatively modest loads?
1. The machinist believes there was too much ignition advance, due to the vacuum advance. The vacuum advance is limited to 8 degrees, and is run off the manifold vacuum. He believes at cruising speeds, that would provide too much advance. There was never any pinging at any time, even on long grades or hills in hot weather. Flatheads generally run hot if there is not enough advance, I am not familiar with problems with too much.
2. The stock road draft tube crankcase ventilation system has been changed to a PCV setup, using a PCV valve from an engine of comparable displacement (a Buick 3.8L). I've had that system on the engine for 7 yrs, but admittedly never for extended highway use. The thought is that the PCV addition requires additional fuel be added in the carb to compensate, and that there wasn't enough added. I went one jet size up to account for it when I added PCV. Plugs were gorgeous, light tan, throughout the trip.
3. For this kind of operation on unleaded gasohol (E-10), hardened seats are needed for durability.
4. The shop did a poor job on the valves during the rebuild; inadequate margins, poor stone quality/rough seats, leaving a surface that wasn't durable.
I would appreciate your thoughts! I have no pre-conceived notions, all four ideas make some sense to me, but to do this much damage in this short of a time is shocking.





RE: Valve Recession in 700 miles?!
Mike Halloran
Pembroke Pines, FL, USA
RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
or equivalent. If you'd rather use lead booster in the gasoline read the MSDS first, they tend to be a bit nasty.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Valve Recession in 700 miles?!
Are any of the lead substitutes "real"? Most appear to be just oil.
I should point out that I have never heard of anyone with the same style engine (without hardened seats), in similar old Ford cars and trucks, having this kind of problem. Literally dozens are driven coast-to-coast every year, some at much higher speeds/RPMs.
RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
In recent >decades<, engines have been built with either hardened inserts or locally hardened areas in heads that don't have inserts, specifically to deal with that problem.
Even if that engine model didn't have hardened seats when it was new, it needs them >now< to deal with today's fuel, or you need to feed it a semblance of yesteryear's leaded fuel.
I'm surprised that your machinist didn't just go ahead and install hardened seats while he was doing the block, or at least bring up the subject.
Mike Halloran
Pembroke Pines, FL, USA
RE: Valve Recession in 700 miles?!
Are none of the other factors considerations, or maybe just aggravating circumstances? I'm especially curious about the "too much advance" theory, many people are running the same ignition profile I am and apparently with very good results.
RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
My own very limited personal experience says it takes ~3500 miles of gentle driving to break in a newly rebuilt engine, so starting a long trip at 500 miles might have been contributory. Certainly the unleaded gas was.
Running E10 in a carb jetted for E0 might have made it run ever so slightly lean, but you did report good plug colors, so it couldn't have been _that_ lean.
I suspect that reports of good life of soft seats on unleaded were based on occasional trips around the block, not around the country.
Mike Halloran
Pembroke Pines, FL, USA
RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
The break-in was only 500 miles, but 20 hours. I could feel it noticeably loosen up. It only used 1/2 quart on the trip, despite these problems.
Actually the machine shop re-did the valve job for the cost of some new guides that it needed. We discussed putting in hardened seats; I opted to forego them for the time being but obviously I will have to re-think that. The engine is about halfway apart, it will be easier now than later...
Clive, that's interesting, that does seem to substantiate my situation, although an OHV has substantially higher seat pressures.
Thanks for your valuable input!
RE: Valve Recession in 700 miles?!
WE USE TO GET A LEAD REPLACEMENT FUEL [LRP] UNTIL RECENTLY, THIS SEEMED TO WORK ON THE OLDIES NOW NOT AVAILABLE . TO FIX PROPERLY INSERTS I,M AFRAID BUT CANNOT COMMENT ON THE VALVES, CONSIDERING THEIR AGE WHAT MATERIAL WOULD THEY HAVE BEEN MADE FROM?? MOST EUROPEAN MADE CARS AFTER 1973 HAVE SUITABLE INSERTS FOR UNLEADED GAS.
GOLFPIN RSA
RE: Valve Recession in 700 miles?!
A former SCCA GT1 champ who did a lot of his own quite successful race engine assembly rebuilt the (unhardened valve seat) 6 cylinder engine in his trusty Ford van, and kindly installed valve rotators at the time as an upgrade.
Within about a year the seats had recessed deeply, to the point the head had to be done over.
my theory - Seat recession , unlike valve burning, is a much more progressive wear thing, when the valve welds itself to the seat a little bit, and the tiny weld is torn the next time the valve opens (like picking a scab). TEL formed a layer of junk on the valve/seat, keeping the welding from happening. A layer of carbon or other combustion by products can protect the seats a little bit too. In the old days rotating the valve to break and crush excessive deposits improved valve seating and life (to prevent valve burning by a jet of hot exhaust leaking past), and made cooling more uniform. But continually rotating a valve on a dry, unprotected-by-lead seat jams weld pickup damage on the vavle into undamaged or at least unmatched portions of the seat preventing good sealing and cooling
I think some old TRW literature said valve springs with dampers sometimes improved valve life over 50% by reducing valve "chattering" (which I picture would reduce the "scab picks" per valve closing.)
The SAE paper describing Chevy's development of the 348 engine includes some info about valve closing loads (if not actual unseating motion) without dampers at 4500 rpm. Image attached.
RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
So, were the rotators first installed during last winter's rebuild?
regards,
Dan T
RE: Valve Recession in 700 miles?!
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RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
RE: Valve Recession in 700 miles?!
all those things can contribute to more valve seat wear - the pcv may lead to deposit build-up on stems, seats and valves, that buildup may lead to higher valve seat temperatures and thus faster recession. also the fuel has changed - no lead and some alcohol added. that may lead to a somewhat hotter operating temperature and some proneness to corrosion - another two factors that may contribute to valve recession. a third factor is the ignition timing. due to the other fuel used, a different ignition timing might be required - to early timing will lead to higher temperatures, not necessarily accompanied with (audible) pinking.
there are thus variations changes that may well have changed the operating conditions, all calling for more durable valve seat material. and yes, hardened seats would most likely have prevented it all....
whether the seats were decently hardened is no longer measurable due to the wear i suppose - you better make sure next time you get properly hardened seats installed.
RE: Valve Recession in 700 miles?!
@Romke, the original seats were never hardened -- plain cast iron. The rotators plus loads of lead in the fuel was an acceptable solution. My engine's last rebuild was in '74, so there was plenty of operation with leaded fuel after that work, there may have been enough residual lead on the seats to protect them, especially given its very light use until the current rebuild.
The seat inserts used from '40 until mid-'50 are readily available, high quality, and can be installed by machining the block. I'm taking the engine in shortly for just that purpose.