Hardened Valve Seats, Exhaust Only???

[ericwevans]

So I was talking to a machine shop about installing hardened seats in a set of iron heads and there was a suggestion of exhaust only.  This idea intrigued me as my last set of heads was very thin between the seats and there was a small void where the iron had broke away in one cylinder after the seats were installed. 

So what are the group's thoughts on only putting a hard seat in the exhaust?  In my experience the exhaust is where you see the recession, so it makes some sense.

[CaptCobrajet]

No requirement for intake seats unless they are sunk badly.  The heat is what kills the exhaust.  It is good to just use a little bigger valve to get s fresh seat on the intake, and put seat rings in the exhaust only.  I would not go past 1.600 exhaust  on a 4.00 inch bore.  The 1.660 is fine at 4.050.  I'm doing a 2.15/1.600 for a 4" bore now.

[ericwevans]

Cool, I was thinking of using Cobra Jet valves, so I was worried about doing both, I think exhaust only is the way to.  :-)

[Barry_R]

I tend to agree with Blair's comments.  I will add that I prefer not to install seats in an FE head unless/until it's truly needed.  A lot of the factory heads can be brought back to a serviceable point with slightly larger valves.  It's a risk versus reward deal.

There is not a lot of room between the seat and trouble on many of these, and once you hit water its often not very easy or cost effective to fix them unless the heads are special - like a CJ or MR casting.  Most of these vehicle have become "toys" rather than daily transportation, so its less common to be concerned about needing a fresh valve job after 50,000 or 60,000 miles.

[ericwevans]

Yeah, mine sees about 10,000 miles a year which is why I'm concerned about it.  My last set of heads had the exhaust valve hammered in there pretty good.

[Gregwill16]

Thanks for sharing Barry because my shop says the exact same for FE heads and had me wondering. He said there isn't much meat in there and with limited use, it isn't worth it.

[tomsfe64]

Would lead substitute help with non hardened seats?

[machoneman]

Sure but even that may not make much if any of a difference. Valve seat recession in a cruiser, weekend warrior, occasionally raced engine that is lightly loaded for 98% of its life will do just fine w/o hardened seats. The lead substitute can/may help just don't overdo it as this stuff can foul spark plugs among other things.

Think of a daily-in-use, heavily loaded truck pulling loads up steep grades where long spans of time really heat-up the exhaust system and you'll find a prime candidate for hardened seats. Occasionally driven FE's? Not so much......

[ericwevans]

Going to have to think on that now as having no hardened seats at all was not the answers I was expecting.     I guess if I keep up on refreshing the engine yearly as planned I can just monitor and add seats when the time comes.  The heads I pulled off earlier this year were shockingly recessed, as in valve heads below combustion chamber recessed, so I thought there was no question that you'd want them on the exhaust side, but y'all have me rethinking that now.  No hard seats means a little extra green (albiet very little, but every little bit counts) in my pocket too.   

[Barry_R]

At 10,000 miles per year you should probably go for the seats if its gonna be a few years between freshens.  At 2 or 3 thousand per year it would take forever before a problem came up. Towing a boat or road racing - put the seats in.  Saturday night for ice cream - don't worry as much.

[Joe-JDC]

Another consideration is the valve springs used, and the seat pressure needed to control valve float.  I would consider hardened seats for the exhaust valves if you have a camshaft that requires anything over 110-120# seat pressure.  Not a must, but certainly a consideration in my opinion.  Joe-JDC

[ericwevans]

I will be seeing the strip with it, but I daily drive it as well.  Going to have a mechanical roller cam in it, pretty mild lift though around .580 .  Planned springs look like 377 lbs open.

[ericwevans]

And 155 lbs closed.

[Barry_R]

Probably not enough spring for a solid roller unless its a beehive or conical deal with a light retainer.  And solid roller, street use daily, lotsa miles - put the seats in there.  The heads have a lot working against them...

[ericwevans]

Yeah, it's a beehive.