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Like Chuck said, the valves will recede in the head. In fact on some engines I've had the valves needing adjustment every 5000 miles or so just to keep it RUNNING. The reason is, the valve recedes into the head, reducing the valve lash, and eventually the valve will start to stay open and the engine will misfire. It's an interesting chain of events.

As far as your braking problem, it could be the hoses as you've mentioned, but it could also very well be the vacuum brake booster. While the car is running, can you pull 'up' on the brake pedal and notice the front brakes are now released? I've been seeing a lot of this lately...these cars aren't getting any younger.

Bob
 

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One thing worth noting though, AV gas can sometimes be a pain to purchase. In CT for example, you can only buy it if you have a pilot's license, and it is dispensed INTO an aircraft. But in neighboring MA, my friend used to buy it all the time for his race car, and they put it into 5 gallon cans. I believe it cost him about $2 a gallon, compared to $4.25 for leaded race fuel. AV gas burns REAL slow, so slow in fact that it reduced his coolant temps at racing speeds by almost 20 degrees!

Bob
 

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The 1.8 engine used in the Chevy Luv and Isuzu (made by Isuzu) is an entirely different engine. It has an aluminum head, and MUST have steel seats!

The 1.9 Opel can use seats from J-Loy or any other aftermarket valve seat company...it can be looked up by size. The press-fit of the steel seats in an Opel cast iron head is different from that of the steel seats in the Isuzu aluminum head, so don't even reference the Isuzu head at all here.

Bob
 

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It depends on the usage. One engine I built years ago, one of my first personal big-valve heads, did NOT have hardened seats. Since it was driven hard, and had a performance cam and appropriately stiffer valve springs, I saw some fairly severe wear. In two years the exhaust seats were pounded out to roughly 150% their original width. So my three-angle valve job turned into one wide single angle valve job.

Now, if you drive your Opel 3000 miles per year, mostly to 'cruise', then this would not be a big concern. You will lose power as the seats recede, that is for sure. Also, valve adjustments will be frequent, the clearances will get smaller rather than larger. I simply won't build a head without hardened seats any longer, it is not worth the 'savings'.

Bob
 

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It depends whether it's a 10-bolt or 12-bolt head. The 12-bolt has the normal ten 12mm head bolts, plus two extra 8 mm socket-head cap screws that thread into the front of the timing cover to help reduce oil leaks. You can *just* see them under the front edges of the valve cover. If you have them, you have a head with hardened exhaust seats. NOTE: the seats in the head are simply induction-hardened, not inserts added later.

Bob
 

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Better in the sense they resist wear with unleaded fuel...yes.

But worse in the sense the heads crack like crazy. There was already a flaw in Opel's design. The heads have two exhaust ports side-by-side. They happen to be the best flowing exhaust ports in the head. And the intake ports happen to be deficient. So, there is a lot of overscavenging going on, and those center ports tend to run 200-250 degrees hotter EGT's than the other exhaust ports (proven on a dyno, we see 1400-1500 degree temps from these ports on a regular basis!)

To make matters even worse, there's NO WATER between those exhaust ports, nor even an intake port between with a cool intake air/fuel charge to help even-out the temps. Every other exhaust port is surrounded by water on one side and an intake port on the other. Oh, and when they changed the casting design sometime in 1972 to the 12-bolt style, they also changed the cast iron too. It's more brittle. The exhaust seats are VERY brittle. So it's a recipe for disaster. I'd guess that 80-90% of the late 1972-1975 heads cracked.

I prefer 1971-mid 1972 heads. They have 4 cam bearings still, unhardened seats (I add the hardened seats), and thicker ports with a more ductile material.

Bob
 

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Even better than that: When I port a 1.9 head, I concentrate of balancing the flow between exhaust ports, and increasing intake flow. Then I design a cam with split lift/overlap. I always run more intake lift and duration on a restricted intake engine (i.e., running with a single carb). So, not only does this drop exhaust temps, it increases power, and improves BSFC. The engine uses less fuel to make more power. It's a beautiful thing.

Bob
 
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