You couldda zero decked that block and it would have never known it.
Hardened valve seats - do they really matter?
- Thread starter Princess Valiant
- Start date
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It came out to a measured 8.4:1 CR... Exactly textbook. I was hoping for more.
But it's together and running now, not coming back apart for the machine shop to have another shot at it. They took off what I told them to.
I hate to think what the actual CR was on that engine with all original parts as originally built.... I got it in pieces so couldn't measure. It was lacking the pistons and rods. I lucked out on finding a set of NOS rods for it for a too good of price to pass on from one of the "big racer guys" at the /6 site.
I do still have the original drool tube 74 head that hasn't been touched from new except for pulling it off of the engine. Never taken apart or machined.
But it's together and running now, not coming back apart for the machine shop to have another shot at it. They took off what I told them to.
I hate to think what the actual CR was on that engine with all original parts as originally built.... I got it in pieces so couldn't measure. It was lacking the pistons and rods. I lucked out on finding a set of NOS rods for it for a too good of price to pass on from one of the "big racer guys" at the /6 site.
I do still have the original drool tube 74 head that hasn't been touched from new except for pulling it off of the engine. Never taken apart or machined.
Probably 7.2 lol
I purchased a set of Slanty main studs off of a Member here, He has a set of the 1.70"/1.44" stainless EngineBuilder valves, & a set of 340HP springs that I passed on. Most aftermarket stainless valves come with stems that are .001-.002" under stock stem sizes, so if the guides have any wear of note they'll need lined or replaced, but I'm not sure about the EB ones. More importantly, replacing the stock valves w/quality stainless ones greatly reduces the need for hardened seats.
When I had my head done I told them that I wanted anything done/fixed that they saw fit to do.... Including guides if needed. They didn't do anything to the guides except for cutting them down on top to make sure my keepers didn't make contact considering that I put a little bigger than stock cam back in....
That machine shop sounds like they can't get the guides on center. All the MOPAR valve jobs, I've done the seats were pretty concentric. I used to have a guy grind my valves and seats, who blamed Amoco gas for his valve jobs not lasting. My cousin Kelly's dad had a shop in the same small town. One day Kelly told me Marvin's valve grinder was shot. When I looked incredulous, he said to just lap the valves on one of Marvin's valve jobs. Wow! It looked like saw teeth on the valve face. Kelly did my valve jobs from then on, till I got my own valve grinder. I still lap a couple valves to check seal and position on the valve face. As to the original question, I prefer stainless exhaust valves to hardened seats. I feel it keeps the centers better than trying to keep the guide, seat, and now the hard seat on the same center.
Well, that I know of they didn't do any guide work on any of the heads I have sent them, though I tell them every time to go ahead and do so if there's ever a question about them being good or not. So far they've all come back "good" on the guides. They did have to open up the ones on my EQ heads that I took them that were sticking brand new out of the box.... Heads That ruined my last 360 mag rebuild because valves kissed pistons and had to come out again with a whole 6 miles on the job. Those heads are now on another engine with so far 60k miles since they went thru that machine shop
I don't know why I didn't think about this earlier in the thread, I actually forgot I had this head til last nite
And the timing of it having become available couldn't have been worse but I bought it anyway since, well, I haven't come up with anything comparable since, either.
The day after I picked up the head I have on my engine as described earlier in the thread from the machine shop, I saw a /6 head come up for sale on CL a couple of hours away.
and the price was too good to pass up. Asking price was much less $$ than I have in the head im currently running.
A freshly machined peanut head, still in the machine shop shrink wrap, done 30+ years ago and put on a shelf.
All new guides seats, valves, everything //for not much more than junkyard core head price. And it still sits waiting for my next motor.
The relevant part to this thread and that head is this: the guy used to run 2 fishing charter boats on lake Michigan each powered by twin /6s.
He sold the boats and retired some years ago, but had gone to the junkyard and got a couple of heads off of "whatever" with a /6, to have as ready spares. Claims the unleaded gas ate up his valve seats. Boat's down, no money coming in.
He had it down to a couple of hours for a head swap, he said he did them so often. So he always had at least 1 done up ready to go.
And he always had "the works" done to them each time he sent one thru the machine shop no matter what they did or didn't need. And dust? Like snowblowers, most outboards I worked on had no air filtering. Out on the water, no dust/dirt cuz the water "held it down". So though I can see a bad air filter playing a part of eating the seats and burning valves but there's gotta be more to it than that. Granted this was a special application that's basically N/A to many of us. But when these boats ran they ran at a steady rpm most of the time.
And the timing of it having become available couldn't have been worse but I bought it anyway since, well, I haven't come up with anything comparable since, either.
The day after I picked up the head I have on my engine as described earlier in the thread from the machine shop, I saw a /6 head come up for sale on CL a couple of hours away.
and the price was too good to pass up. Asking price was much less $$ than I have in the head im currently running.
A freshly machined peanut head, still in the machine shop shrink wrap, done 30+ years ago and put on a shelf.
All new guides seats, valves, everything //for not much more than junkyard core head price. And it still sits waiting for my next motor.
The relevant part to this thread and that head is this: the guy used to run 2 fishing charter boats on lake Michigan each powered by twin /6s.
He sold the boats and retired some years ago, but had gone to the junkyard and got a couple of heads off of "whatever" with a /6, to have as ready spares. Claims the unleaded gas ate up his valve seats. Boat's down, no money coming in.
He had it down to a couple of hours for a head swap, he said he did them so often. So he always had at least 1 done up ready to go.
And he always had "the works" done to them each time he sent one thru the machine shop no matter what they did or didn't need. And dust? Like snowblowers, most outboards I worked on had no air filtering. Out on the water, no dust/dirt cuz the water "held it down". So though I can see a bad air filter playing a part of eating the seats and burning valves but there's gotta be more to it than that. Granted this was a special application that's basically N/A to many of us. But when these boats ran they ran at a steady rpm most of the time.
Dave999
Well-Known Member
potentially run at max torque for hours and hours, great potential for oil longevity provided you have good rings and a filter. i.e no short runs spend most if its running life at optimum temperature, any in-block condensation driven off pretty smartly every use, Being on or close to the water you'd have to expect some humidity and dampness when the sun went down
but with little or no on off the throttle the variation of what pases through the inlet and exhaust would not match the variation seen in street driving...
the longer the valve is on the seat the more heat it can shed to the head and coolant
4000 rpm for 4 hours gives no variation is seat time, exhaust valves probably glowing but Not being cooled enough by intake charge.
no accelerator pump action gives no variation in burn no variation in unburnt fuel going out the exhaust.
i'm guessing in an ideal world you would swap to a cam suited to marine use
if a marine use cam is anything like an LPG cam then it would have specific lobe shape to deal with the valve and seat impact (in both senses of the word) caused by the change in use
quick open and gentle landing is I think what an LPG cam has (LPG burns hot has no additives and can cause seat recession)
i know nothing about marine engines but i would suspect any issues he had could be tamed by a cam and springs for the job, that focused on max torque at mid range rpm.
make best use of the fuel you have and not be wringing the neck of a motor that has to get you home without the use of an SOS flare and your radio.
or as mentioned earlier stainless valves into an iron-head seat, different materials that don't like to stick together when they slam together ...less micro welding so less seat recession
you can friction weld two pieces of the same bar together easier than two pieces of different material
spin speed or pressure or both need to change to be effective in both cases and id suggest greater friction is probably necessary in the second case ferrous metals and those used in alloying ferrous metals
Iron based standard valve head and nodular iron seat, work or induction hardened, need chemicals in play, to stop them doing it. tetra ethyl lead or some modern alternative.
standard valves seat recession problem
ferrea stainless (5000 6000 series) less chance of a seat recession problem
spend the money you saved on the seat inserts on the valves and use em in the next 3 engines
Dave
but with little or no on off the throttle the variation of what pases through the inlet and exhaust would not match the variation seen in street driving...
the longer the valve is on the seat the more heat it can shed to the head and coolant
4000 rpm for 4 hours gives no variation is seat time, exhaust valves probably glowing but Not being cooled enough by intake charge.
no accelerator pump action gives no variation in burn no variation in unburnt fuel going out the exhaust.
i'm guessing in an ideal world you would swap to a cam suited to marine use
if a marine use cam is anything like an LPG cam then it would have specific lobe shape to deal with the valve and seat impact (in both senses of the word) caused by the change in use
quick open and gentle landing is I think what an LPG cam has (LPG burns hot has no additives and can cause seat recession)
i know nothing about marine engines but i would suspect any issues he had could be tamed by a cam and springs for the job, that focused on max torque at mid range rpm.
make best use of the fuel you have and not be wringing the neck of a motor that has to get you home without the use of an SOS flare and your radio.
or as mentioned earlier stainless valves into an iron-head seat, different materials that don't like to stick together when they slam together ...less micro welding so less seat recession
you can friction weld two pieces of the same bar together easier than two pieces of different material
spin speed or pressure or both need to change to be effective in both cases and id suggest greater friction is probably necessary in the second case ferrous metals and those used in alloying ferrous metals
Iron based standard valve head and nodular iron seat, work or induction hardened, need chemicals in play, to stop them doing it. tetra ethyl lead or some modern alternative.
standard valves seat recession problem
ferrea stainless (5000 6000 series) less chance of a seat recession problem
spend the money you saved on the seat inserts on the valves and use em in the next 3 engines
Dave
slantsixdan
=..=
People don't realize this because it isn't so. The mechanism behind valve seat recession is well understood, and it's nothing to do with a lack of air filtration (which will do a job on the rings long before it has any effect on the valves).
Seat recession happens because above a critical temperature, the exhaust valve, when it closes, micro-welds to the unhardened cast iron seat if the valve/seat junction is not buffered by residue from the likes of a lead, manganese, or phosphorus compound. The next time the valve opens, the micro-welds are broken; they pull apart like taffy, leaving a rough surface. The valve keeps opening and closing, and—remember, valves rotate—that rough surface works as an abrasive, grinding up (grinding down) the seat. See page 2 of the 1964 Chrysler paper attached to this post, and also see here (and the subsequent page), and here. And here's confirmation from Chrysler's many-decade chief engine engineer, Bill Weertman, on page 164 of his book, "Chrysler Engines 1922-1998":
So, blah-blah-blah. How much does this really matter, practically? On a stockish Slant-6, not a whole lot; the exhaust valves are small and well cooled, so in ordinary service they seldom reach the critical temperature required for the badness to happen. Seat recession just isn't high on the list of failure modes. And that generalizes to a lot of other engines, too; see the other PDF attached to this post.
Nobody reasonable would say "You can only get unleaded now, so you have to tear down your motor and put in hard seats or else you're DOOOOOOOOOOMED!". But adding hard exhaust valve seat inserts adds only a little to the cost of an ordinary head rebuild, and the rest of a Slant-6 is notoriously durable, so putting in hard seats can reasonably be seen as cheap insurance protecting the investment of money-time-effort in the project, so from that standpoint it's wise to do.
Since we're on the topic, the Slant-6, like the rest of the engines in the stable, was built with stainless steel exhaust valves right from the start. The standard-duty engines used 21-2N alloy; heavy-duty truck 225s used 21-4N, which is a bit harder; 32 versus 28 as you can see by comparing the data sheets for 21-2N and 21-4N. The heaviest-duty Slant-6s, the 225-3 motors put in the biggest and heaviest-duty trucks and buses, had positive exhaust valve rotators, which extend valve life on leaded gasoline, sharply reduce valve life with unleaded gasoline and unhardened seats, and are probably not beneficial with unleaded gas and hard seats.
(And all that said: yes, good air filtration is important to engine life, so use real air filters—don't fall for the likes of K&N's fraudulent claims)
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