Well I didn't want to believe that the rough idle I've been trying to solve was due to an valve adjustment because I adjusted the valves 1600 miles (1608 to be exact) ago.....

BTW: there's only 17616 miles on the engine and car

The intakes were fine, .001 tighter (one was .000) than the last adjustment which could just be I was on the tight side last time, and this time I was on the looser side of spec.

The exhausts however have changed.....

The best exhaust valve was .005 tighter, the average was .008 tighter, and the worst valve (#6) was .012 tighter than last time. #6 is incidentally the valve that was quite a bit tight last time too.

The adjusters are nice and snug and I can't see how they would change adjustment, so it seems that my exhaust valves are actually receding (especially #6).


1. So how lose can I safely have the exhaust lash? (sort of let it wear thru, but I want to make sure I'm on the takeup-ramp of the cam lobe)

2. Found references to CD2 lead substitute, will it help or slow the recession down?

BTW2: found a reference on the internet of a car having a valve recession rate of 1.5mm / 12000km (think it was a MG), which is equivalent to .0118"/1500miles which is right in line with my #6 valve.


BTW3: idle is good again..

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Sounds like you need to adjust valves fairly frequently and think about a big valve head....

Lead substitute= bad

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Yeah....Im the one who destroyed this rare, vintage automobile.....

The valves may be getting too much heat as in the motor is running lean, I'd check the plugs and if they are white I would jet up until I got a tan insulator.

Valve recession is basically terminal. I experienced recession with the same symptoms - diminishing exhaust valve lash. At this point, the seats on the affected valves have sunk into the head and in all likelihood will not provide a good seal for long. Have you done a compression check? #1 exhaust seat on my head showed a very small area of blowby. Yet, the this cylinder showed 110 compression. The telltale sign was the lash. The question is: what is the underlying cause for this? In my case, I ran the engine a little too lean with too much spark.

Mitch

Not lean, if anything slightly rich.

Haven't recently checked the compression, but when I did about 5000 miles ago all of them were within 5PSI. (don't remember the number though)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Take it apart and have the valves machined. I did this on my truck and have liked the improvement.

If you have ever seen a burnt valve, it looks a lot like a rotary file. This rough surface grinds slowly at the valve seat. I bet on such a low mileage motor, that the #6 exhaust valve stayed open for a long time and got rust due to moisture, this will cause similiar decay as burnt valves.

A vacuum leak or blown vacuum acessoryon attached to #6 vacuum tree will create a lean condition and cause burnt valves as well.

I think I paid a couple bucks a valve to have them all refaced and then lapped them in with some compound. You may find that only a few of the valves need machined if you are doing just a spot fix. The valves that look really white are burnt. That should slow the progression down a good bit. This is a good bit of work, but low buck fix.

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1980 Aspen 225 super six

There's nothing on the #6 runner.

Valve adjustment did the trick for smoothing the idle.

When I got the car (was grandparents) it had 12200 miles on it, and had not moved for 11 years. So the #6 exhaust valve could have been open.

I did find a reference that the more valve rotation there is, the more valve recession you can get, so #6 maybe rotating more too.

It seemed fine until 16000 miles (the first time I noticed the #6 valve being tight).
From that, I'd quess the valve recession started after 14000 miles as that's when I finally got rid of the old bias-ply tires, and started driving on the highway, rather than putting around locally. Any residual lead wore away, then it started receding.

I'm not in a position to tear the head off at the moment, thus the lead substitute. Just want to slow it down until I can tear the head off.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Drive the car just like it is and see how long it goes before another five thousandth grows in the lash. My bet is the motor will normalize to a pattern that you can live with hopefully until you can get a set of hard seats.