Grandson Ben has been driving the Celery Wagon, our B20-powered 66 220. He has
somewhat of a lead foot.
This is my 6-bolt engine in an 8-bolt block, IPD street perf cam, FI exhaust
manifold, 240 ignition. The innards were removed from a 6-bolt block a little
over 10 years ago in Panama and put in the only block I could find there.
It promptly blew a seal ring on the oil pump-to-block oil line so it had pretty
low oil pressure for about 4 years but apparently no serious damage. I fixed
that problem in 1999. A couple months ago Ben mentioned that the engine
was running rough, so we checked the spark plug wires and found no change
pulling #3. (This surprised me some because on all the ones I have had, over
80% of the problems showed up on #2, but anyway) So he put in new plugs and
it was fine for a few weeks. Then it got bad again, and a new plug didn't help.
I told him to check for missing aircleaner bolts (140 box on HIF6 carbs) but
they were all there. So yesterday we checked the valve lash. The vast majority
had less than normal clearance and one had negative clearance (would not close
completely) on #3 cylinder. We adjusted them back to the manual-recommendation
of 0.020" and the problem subsided. But in my experience, valve clearances
usually INCREASE. I wonder what's going on here. Is the spectre of valve seat
recession finally rearing its head? I've run a lot of them pretty hard over
the years and never seen it before. Any other possible answers? The locknuts
were all good and tight, so they didn't just self-adjust and they WERE OK the
last time they were adjusted.

Sowadda you guys think??
--
George Downs Bartlesville, Heart of the USA!

Gday George. I have been running 100mm of ATF to 30litres of fuel in my rebuilt b20e for 2years now with no sign of seat recession. ATF has high zinc content and is the base of most upper cyl lubricants on the market. It certainly looks like seat degradation, you can insert or try other head with ATF. I rev mine hard and am pleased so far with result. Regards Jack.

Hola Jorge. Mi rojo 121 sufre de algo parecido. Por ahora (y hasta que pueda encontrar una factoria confiable para poner asientos de valvula nuevos), el uso de Marvel Mystery Oil (vaya nombre para extraño) en la gasolina y aceite me ha "suavizado" al motor. Aunque esta es una solucion muy latina, de repente ayuda.

On english:

Hi George, My rojo 121 has the same maladie. By now (and up to the time I will find some factory here with experience on valve seat insertion), I use Marvel Mystery Oil (weird name!) on gasoline and oil, due it my engine "soften" (the roughness). My temporary solution are very latina, but could be help.

Con aprecio

Joaquin

Después de traducir algunas docenas esquemas para sermones en Español(la lengua celestial) para ayudar pastores en otro país, no pude resistir la oportunidad
de traducir más. ¿Qué te parece "Aceite Misterioso «la Maravilla»"?
¿Mejor?
Allí me llaman «el Tío».
--
George Downs Bartlesville, Heart of the USA!

No esta nada mal (esta muy bien), y si asumimos que "Marvel" no es un nombre propio, entonces otras posibles acepciones pueden ser:

- Maravilloso Aceite Misterioso
- Misterioso Aceite Maravilloso
- Misterioso y Maravilloso Aceite

De hecho, en español esa frase es un juego de palabras - no me extrañaria que tambien lo fuera en ingles.

(english-reader pals: we are jogging about the translation of the phrase "Marvel Mistery Oil" to spanish - too many options for one english phrase).

Joaquin

¡No hay nada peor que un gringo aburrido!

Hablando de eso, yo estaba traduciendo un canto de Salmo 139, vv23-24
en español y me pegaba en "pensamientos". ¿Sabes una palabra más corta
para "thoughts"?
--
George Downs Bartlesville, Heart of the USA!

No hay (en la linea de "thinking"). En http://www.cristomania.com/acordes/cantos03/salmo139.pdf encontre una version en español del salmo 129, tal vez ayude.

That is exactly what valve seat recession acts like. The F head I used to have on my PV did the exact same thing. I had to keep setting the valves (about ever 1500 miles or so) to prevent them from tightening up and leaking (which will quickly lead to a burnt valve!). When I took it off and replaced it with me R-sport head (thanks be to eBay!) all 4 exhaust valves were recessed into the head.

Good(ish) news is, however, that an F head has a LOT of metal around the exhaust ports. I've heard that they restricted the port for some sort of emissions reasons. There is little chance of the valve wearing past the seat and popping loose or ding anything catastrophic. So you can keep on loosening those adjusters until you are ready to put a new head on - you don't need to park it and yank the head off ASAP. Just don't let them get tight and burn - then you will have to fix it right away.
--
I'm JohnMc, and I approved this message.

You can check for recession without removing the head by taking off the rockers and laying a straight-edge across all the valve stem tops.

If some are 'taller' than others, you will need to have your head repaired and hardened seats installed.

My B20 has over 118,000 miles since it's last overhaul in 1991 and so far no valve recession problems (keep your fingers crossed!)

Good luck!

Steve