Opel GT Forum banner

1 - 6 of 6 Posts

·
Opeler
Joined
·
11 Posts
Discussion Starter · #1 ·
Leaded vs unleaded gas

Does anyone out there know if the 1970 1.9 GT engine had hardened valve seats?? I understand that they are needed to prevent valve "beat in" which results when using unleaded gas in an engine originally designed for leaded gas. Thanks.
 

·
1000 Post Club
Joined
·
4,116 Posts
I spoke with a machine shop a week ago, which specializes in older engines. They said the new formulations of gasoline do not require hardended seats. It should not eat valves as the gasoline from the '80's did. Just my .02
 

·
Banned
Joined
·
3,842 Posts
As far as I know there were no GT 1.9 motors that had hardened seats. I have had at least one of every year and not one has had them. I don't know about the 74 and 75 mantas it is possible but not likely.
 

·
Super Moderator
Joined
·
1,802 Posts
hmm...

As a very general rule, the newer heads with the "extra" 2 head bolts in the timing cover all had hardened valve seats. (Easily identified by only 2 bolts holding the thermostat housing to the head.) This is not to say they had a seat of some hard material machined in, which is what you have to do to the older heads, but instead the material of the head itself was hardened by a process known as induction hardening. While this did have the desired effect of greatly reducing the ammount of valve and head wear with unleaded gas, it unfortunatly also made the head more brittle, and more likely to crack and fail. Usually a single trip into the temperature ranges >220 will destroy these heads.
 

·
Super Moderator
Joined
·
5,883 Posts
Stephen is correct in that none of the Opel CIH engines imported into North America had hardened valve seat inserts, as in distinct separate inserts that are pressed into place. But beginning in 1971, Opel advertised their engines as being suitable for using no-lead gas. Of course, it wasn't a complete truism, since valve recession still occurred. In 1973 (I believe), Opel started using a process to "flame harden" the valve seat (or was it actually induction harden? Whatever, similar processes). But from what I have read, that process, along with different head metallurgy, created a valve seat that is prone to cracking. This might be repairable with pressed-in seat inserts, if the crack is not to deep or long. Otherwise the head is a total loss.

Do you need to install hardened inserts to run unleaded gas? There has been lots of discussion on this point. My opinion, for what it is worth, is that an engine that is run lightly (and put to bed dry) will operate satisfactorily on unleaded gas without either lead substitute or inserts. But if you plan on a high mileage, high output engine, plan on installing hardened inserts at the first valve job. But don't do a valve job just because you want to use unleaded gas without lead substitute. Wait until you actually need a valve job.

JM2CW
 

·
Opeler
Joined
·
11 Posts
Discussion Starter · #6 ·
Thanks guys for your opinions. I think I will take your advice and run the engine until it needs a valve job. It has 70,000 miles on it so it should go another 30,000 without any trouble.
 
1 - 6 of 6 Posts
Top