# 68 gto ho valve job--hardened seats?



## khinton (Jun 22, 2008)

Have a 68 gto 400 stock engine with 27,000 actual miles. Am pulling the motor to replace a leaky main seal. Did a compression test found one cylinder at 175 one at 180 one at 190 and two at 195 and three at 200. I assume I should pull the heads and do a valve job. Is that correct? If so should I have hardened valve seats installed? Any suggestions would be appreaciated by those of you who have experience with these details. Thanks, Ken


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## 68greengoat (Sep 15, 2005)

Absolutely, hardened seals are a must with todays fuel. Burning any oil? Sounds like you may have ring blow by too given your numbers. They're all over the board. MAy not be a bad idea to hone out your cylinders and install new rings. And if you're going to do that, you might as well replace bearings too. I'm sure you'll get other ideas too.


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## Rukee (Feb 8, 2007)

Squirt some oil in the 175 cyl and see if the compression comes up to the 190-200 range. If it does, that would indicate rings are worn. If it stays the same, one would think it's valves causing the compression loss.
And I don't think there is a machine shop around that would NOT install the hardened seats.


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## geeteeohguy (Feb 2, 2008)

Do what Rukee says. With 27k original miles, my bet is that the cylinders, rings, pistons, bearings are FINE. They are also original, un-messed with, made-in-America parts. Leave well enough alone, and determine the cause of the "weak" cylinder. The 25psi difference between high and low cyls on your engine is ok. If it were mine, I'd drive it and keep tabs on it. If it drops to 150 or less, THEN I'd worry about it. These cars are only original once....Good luck. I'm betting it's slight valve wear. These engines like to eat exhaust valves with unleaded fuel....


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## Too Many Projects (Nov 15, 2008)

I've heard mixed opinions on this. A number of people with older heads did NOT have hardened seats installed because they only drive the car a few thousand miles a year and not for extended periods on a freeway which pounds out the seats. 
The low compression you are seeing could be from non-use. The rings may be stuck and not sealing well on the low cylinder. Run some Seafoam down the carb while it's running and a can in the gas tank to see if it improves. Like geeteeohguy, I would be very hesitant to pull that engine apart until a firm diagnosis determines the need. 

We have a few machine shops here that will just do a valve grind at the owners request without insisting on installing the seats. I have a pair of vintage 67 Camaro 350 heads that I will be getting "freshened only" in the near future.


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## Rukee (Feb 8, 2007)

The seats don't get 'pounded', they burn from the extra heat of the unleaded fuel. Unless your running a lead additive 100% of the time, I'd have the seats installed.
And my car had one cyl with 150lbs compression and it ended up being a broken pistion between the first and second ring grooves.


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## Too Many Projects (Nov 15, 2008)

The machinist that I talked to about this explained that the valve is harder than the seat and it will pound the seat down over time and dish it out. Lead in the old gas was a cushion to prevent that. He's one of the people who said that if the engine wasn't going to be run at mid-rpm for an extended period of time, the hardened seats weren't an absolute must. Using the lead substitute will help deter any problems for some time too. 
If you plan to use the car on trips or racing, then the seats are a must. For the little time and distance I drive my cars, he said the heads would last 10+ years and the cost of the seats was unwarranted.


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## khinton (Jun 22, 2008)

What is Seafoam? Never heard of it.


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## Too Many Projects (Nov 15, 2008)

Sea Foam

I use it for stabilizing the gas in my seasonal vehicles while in storage.


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## 68greengoat (Sep 15, 2005)

You can use seafoam in any gas or diesel engine. Not only does it stabilize, it also cleans internal parts when added to your gas especially carbs. I've used it in cars, trucks, lawn mowers, string trimmers, pressure washer, tractor, chainsaw, snowmobile etc. periodically to keep the fuel system clean. You can also add some to your engine oil too, to clean up sticky lifters etc... I go thru many cans a year. It's a very good product.


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## Rukee (Feb 8, 2007)

Too Many Projects said:


> The machinist that I talked to about this explained that the valve is harder than the seat and it will pound the seat down over time and dish it out. Lead in the old gas was a cushion to prevent that. He's one of the people who said that if the engine wasn't going to be run at mid-rpm for an extended period of time, the hardened seats weren't an absolute must. Using the lead substitute will help deter any problems for some time too.
> If you plan to use the car on trips or racing, then the seats are a must. For the little time and distance I drive my cars, he said the heads would last 10+ years and the cost of the seats was unwarranted.


Why take the chance?? What happens if you want to drive to a car show an hour away?? Like your never going to drive more then 2 minutes on the highway at anytime or what??
I just don't understand why you would NOT want to have the seats installed and limit your car`s ability.


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## khinton (Jun 22, 2008)

Having Hardened seat installed and the entire head rebuilt --- had some worn guides also--thanks for all the advice!


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