I called a machinist about a possible rebuild of my 1974 engine, and he said some things I question. I'm curious what you all think.
1. My valve seats probably have been deformed by the valves slamming into them, so he would probably need to add hardened seats.
2. He would replace the valves with stainless to be compatible with unleaded fuel.
3. After rebuild I would need to use oil without the modern zinc phosphorus additives. I could have misunderstood him, but that's what I wrote down.

Not surprisingly, he also said he mainly deals with high-performance V8 engines.

1) It's not from the valves slamming into them, it's running lean and causing the metal to be like taffy... that being said if your head is a true '74 then it had hardened seats and would not have this problem unless the previous owner really rolled down the highway with a manifold leak....
Now that being said, if he regrinds the seats for new valves, or because you are adding OS valves, the seat hardening isn't that deep and he may wipe it out on the regrind, so you may need to go to new seats (I do on my exhausts just to be safe, and if a high compression engine I do both for insurance while I play with the carb....)

2) Most valves now are stainless of one variety or another, you don't have to have it to be compatible with unleaded, but that's what you will get on most replacement and OS valves.

3) Per our oil threads here, using standard API rated oil is not going to make a lick of difference on a solid lifter cam in our engines, you won't need to use a ZDDP additive... but it won't hurt to use Rotella if you did, and depending on your cam manufacturer, they may require a certain oil and additive for them to uphold the warranty on the stick... Your machinist may also require you to use a specific oil/weight ad break in additive to uphold his warranty (since I assemble and check the machinists work myself, I prefer to use mobil 10W30 with comp cams break in lube (my local parts store just calls it "the secret sauce"...LOL).

I agree almost entirely with DusterIdiot.

From my experience, if you use stainless valves (like the SI oversize valves), then you do not need hardened seats. Stock valves on stock seats (exhaust side) tend to recede with unleaded gas. That said, if you have a good machinist, then adding the hardened seats will not hurt you (except if you want to heavily port out your head - doesn't sound like it from your msg). I use stainless in all my engines and as DI said it can be hard to find valves that are not stainless these days.

Oil type is not so important. Keep it full and change it every 3-6000 miles and you will be fine.

Lou

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Home of Slant6-powered fun machines

There is no actual distinction between stock valves and stainless valves, so I don't agree with Dart270's idea that using stainless valves prevents seat recession; it doesn't. Stock exhaust valves were 21-2N austenitic stainless steel, right from the start of production in 1960. They got upgraded to harder 21-4N stainless for heavy-duty engines, and for standard engines with secondary air injection (California starting '72), and eventually all Slant-6 engines got the 21-4N exhaust valves. Starting in '73, all Slant-6 exhaust seats were induction-hardened at the factory to prevent valve seat recession with unleaded gasoline. This induction-hardening worked well, but it hardens the seat area to a depth of about 0.030". So on a pre-1973 head, or on a '73-up head that will get a valve grind, it is smart to have hard seat inserts put in -- and for the small cost it adds to the head work, I would call it foolhardy not to do so. All that said, even a pre-'72 Slant-6—with its small, well-cooled exhaust valves—does not experience valve seat recession anywhere near as rapidly or as severely as many other engines of that timeframe. An engine in good running condition doesn't warrant a teardown to put in hard seats, but that's not the question at hand here. The head's going to be apart...put in the hard seats.

There is nothing such as "the modern zinc phosphorus additives". A zinc-phosphorus compound (ZDDP) is present in most engine oils as an antiwear additive, and has been for many years. It is not new or modern, and its use has been declining with the rise of newer, higher-performance antiwear additives.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks everybody. So it sounds like even if he isn't that familiar with the slant in particular, he knows what he's talking about in general. It's kind of hard to imagine a machinist staying in business long otherwise, but you never know.

I told him I was interested in drivability more than anything else. In the end, he recommended to just keep driving it for now.

Sounds like a trustworthy person to use in the future, given that he advised you to not use his services! Often the best thing is to just keep driving your car and make adjustments to tune it.

Lou

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Home of Slant6-powered fun machines

Somewhere on this forum I learned that there are 'small' seats that should be used the slant head....................

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