[johnbran]

GT-Leaded or Unleaded??

Hi,
I have a few questions for the GT gods in here. I have an all origional '70 GT with the 1.9L and 4 speed. My first question is regarding what type of fuel to run. I keep getting conflicting theories on whether or not it is safe to run unleaded gas with stock valve seats. I know that the older vehicles did not have hardened seats and eventually the unleaded gas would burn them out, but depending on who I ask, some say that they have run unleaded in their stock GT's for years with no damage to the seats, while others say it is the worst thing you could do to the little motors. Does anyone out there have a clear cut answer on this. I'd really hate to tear down such a good running motor just to replace the seats, but if it is going to burn them out anyway, then it may have to been done regardless. Any insight into this would be greatly appreciated.
Also, I had a question regarding the front brakes on the GT. I installed new pads and cleaned the cups and bores on the calipers, but when I use the brakes, the front brakes seem to want to stick and keep pressure on the rotors for a very long time and really never do seem to fully release the rotors causing the front wheels to have a lot of drag. I read on one of the posts about the front flexible lines collapsing on the inside and I was curious as to whether this sounds like something that could be causing my sticking brakes. Again, any information about this would be greatly appreciated. I apologize for this being such a lengthy post, but I wanted to pass along as much info as possible. Hopefully one of you seasoned GT veterans out there can shed some light on these problems.

Thanks in advance,
John

 

[chuckspeed]

On the lead question:

Two components come into play. The short answer? Replace the seats.

The long answer? Well...

When we burned lead as an antiknock compound, the compound would precipitate (drop out) on the exhaust seat. To prevent a build-up from causing exhaust valve failure, manufacturers bega to design in valve rotation to literally 'grind' the deposits down.

This works really well forleaded fuels, but in the absence of them, the valve literally 'grinds' itself into the seat - a phenomenon known as valve recession. Hardened seats eliminate this.

The reason some folks have not had trouble with their motors is the lead from many years of use bonds to the exhaust seat and forms a 'cushion' which saves the seat - temporarily. The 'cushion' is only good for about 15-20K miles - there's no guarantee how long it will last, but it 'fools' some folks into thinking there's no need for hard seats.

 

[RallyBob]

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

 

[Kristi]

Doh!

Ok, once again cluless girl learns something new... so the consensus is do NOT put unleaded gas in a GT? If thats the case where on Gods green earth do you find leaded? I can't think of one gas station I've been to in past years that sells anything other then unleaded.... (yikes)

 

[oldopelguy]

Valves

Actually the consensus is to put in hardened valve seats, which requires the removal of the head. As a stop-gap measure, I have been using lead "substitute" on both my truck ('63 Dodge max wedge heads) and my Kadett. Does it work? I don't know, but you can actually tell a difference in the pinging of the motor if I don't, so I can justify it.

There are different types of lead substitute, but the one I use comes "concentrated" and the bottle is supposed to treat something like 300 gallons for the bottle. Basically it is cheaper, so it wins, but I really don't know the differences.

 

[saxybiker]

I would have to agree with Oldopelguy. I've beenrunning a lead additive from CD-2 ever since I got into Opel GTs 13 years ago and I've never had a problem with valve recession. In Vickie's 69 GT she even runs 93+ octane gas. In my 72 GT it doesn't seem that the octane rating is an issue, but it does get the CD-2 additive at each fill-up.

 

[chuckspeed]

I've used CD-2 as a lead substitute in several motors over the years with no ill effects. I've not used it for long periods, so I can't comment on the long haul. A substitute is better than nothing, tho...Run the substitute until you start to have problems (if any) and then do the permanent fix.

That's how I ran Maggie the Opel until #2 rod bearing spun. After that, she got hard seats alla way 'round.

One other thought - this came from the engine guys @ McLaren a few years back...

Supposedly AV gas still has a sizeable amount of lead in it. When McLaren was developing the GNX, they had trouble with burned exhaust valves. As a stopgap 'till everything was all sorted out, they got a five-gallon can of AV blue (i think) and ran it thru the motor. Enough lead plated out on the seats to last the equivalent of 30K miles wikth no ill effect.

Just a thought,

Chuck.

 

[Kristi]

Ok, so I'll bite.. what's AV gas?

 

[chuckspeed]

AV gas = aviation fuel. It's formualted to an entirely different standard than pump fuel, and available in much higher octane ratings than we get o the street.

The high octane ratings are not needed for normal (less than 10:1) compression ratios, but the lead content is relatively high - even compared to the old 'ethyl' days.

I'm a fan of automotive history, BTW - It's how I know a little about a buncha stuff. That -- and workng in the center of the automotive universe provides an interesting perspective. Biggest internal combustion motor I've been near was a 3000 HP V-16 turbodiesel in Heavy Engine Test at Detroit Diesel. Bigger than a GT, that motor was - made BIIG noises!

 

[RallyBob]

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

 

[Kristi]

Ok so here's my dilemma: I was told to have the seats replaced expect to drop about 1k at the mechanic's... ouch. So how long can I use the additive before I have to installed hardened seats? Oh and I just got an email from my seller who said "Oh I never heard of that...I just put in premium unleaded and never had any problems." He had the car for two years...

 

[Maddyn]

100LL (100 low lead) which is actually a misnomer because it has a lot of lead in it is you standard aviation fuel. it's a great fuel, I've never run it for extended periods of time in a vehical, but it does have a bit more get up and go. The only real downside to it is the fact that it costs about $3.00 a gallon, and you can only get it at an airport. Some airports might sell you some if you showed up with a can, but they most likely won't pump it directly into your car.

My Uncle goes down to the local airport and buys it by the 55 gallon drum for his airplane he keeps at home, so I "borrow" a little bit every now and then to see how it runs in different vehicals

 

[chuckspeed]

Kristy-

Like the plate.

Run the additive until you need the seats; then drop the $$. it may be a 1000 miles; it may be 30K miles. Remember, the mech is in it to make $$, so you will always NEED it.

You'll know it's time when:

It starts to run rough; and

it's traced to low compression inna cylinder.

#3 seems to be the lean one; I'd expect that to drop first.

 

[70GT]

Hardened valve seats?

Just wondering if the Isuzu or chevy Luv 1.9/1.8 had them and if they would work on the Opel.

 

[RallyBob]

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

 

[70GT]

Sorry, What made me think of it was someone put a 1.9 Isuzu head on eBay. I thought it looked the same but see the difrence now though.

 

[George]

Did any of the gts have hardened valve seats from the factory?The reason I ask is because the owners handbook that came with my 1972 gt says to use unleaded fuel.

 

[kwilford]

Hardened Valve Seats

Bob should really answer this question. But I will take a whack at it.

My '71 Owners Manual says that low-lead or unleaded gas is actually recommended, but that regular leaded gas may also be used . I bought it in 1978 with 58,000 miles on it. I used leaded gas for at least 2 years after that. It probably had 80,000 miles by then, and a pretty good coating of lead oxide, or whatever compound that forms and deposits on the valve and seat that protects them from undue recession. I then switched over to unleaded gas, and racked up another 20,000 miles in the next three years, without causing any significant damage to the valves or seats. And from what I have read, it did NOT have flame or induction-hardened seats, which came in late '72 or '73 (Bob???). Now, did the early models have more severe valve recession when using unleaded gas? Probably, at least on a statistical basis. Do you HAVE to install hardened seats to use unleaded gas? Not likely for the kind of use that most of our Opels experience.

From what I have gathered from a number of articles I have read, the use of unleaded gas in virtually any vintage engine will NOT cause severe premature valve or seat damage, so long as the car is driven moderately, and especially for the duration that most vintage cars are driven. If you expect to use your Opel as a high-mileage, daily driver, then by all means have Tribaloy or Stellite or some other wear resistant seat insert installed on your next valve job. But don't waste your money and get it done before you need to.

IMHO.

 

[George]

I've been running unleded gas in my gt from the time leaded was not around anymore and never had any trouble yet.I was woundering if I should use a lead additive or just not worry about the valves till something goes wrong.I think you answered that for me.thanks

 

[RallyBob]

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