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Am I pushing my engine too hard? |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4741 |
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Posted: Sep/10/2016 at 1:19am |
Totally stock 1977 232 with a 1bbl carburetor in a Hornet sedan. When I rebuilt it at 119,000 miles I did not install new valve seats, valves, or guides. They all appeared to be in pretty good shape, so I lightly touched up the seats on the grinder, refaced my valves with good margin left, and simply cleaned the guides. This is cutting corners from my normal valve job procedure that involves hardened exhaust seats, Stellite exhaust valves, and new steel guides. I have put 15,000 miles on it since, most of them over the interstate highways of the southwest. I maintain 75-80 MPH whenever possible within the power limits of the engine. At normal cruising I am around 1/3-2/3 throttle to maintain that speed, sometimes up to 3/4 if there is a headwind. Rarely do I have to floor it to maintain that speed, but I sometimes do on particularly bad hills. I'm not too concerned about running so long at such wide throttle opening because people tell me it's a small carburetor and can't fully feed that engine anyway. Typical ambient temperature in these conditions is 80-100 degrees, so I have the A/C running. My engine temperature gauge usually reads 200-220. I do not drive like grandma going to church. I keep up with average interstate traffic. Fast-forward only 15,000 miles and my engine has already burned a valve, #1 exhaust valve to be specific. Compression is only down to 125 PSI from the 145 it was when I rebuilt it, so it's still running great, but I know that valve will only get worse. I suspect the other valves are not far behind, because all cylinders are showing slightly weaker numbers than they were 15,000 miles ago. Since this 232 has virtually the same head, valves, and seats as a Jeep 4.0L yet it only produces 1/2 the power, I feel like this 232 should be able to take anything I throw at it. After all, I make the same power at full throttle as a 4.0L does at only half throttle and we have the same valves, right? Shouldn't this engine be able to take my driving style? I've driven a 4.0L's past 150,000 miles without blowing them up.... So my questions is: did my cutting corners on the valve work kill my engine, or did my driving style kill my engine? I'm used to V8's and 4.0L's that have enough excess power to handle sustained interstate speed without high stress, but this is my first carbureted I6, and I am unsure of what it can or cannot handle. Perhaps you can help me? Edited by FSJunkie - Sep/10/2016 at 1:28am |
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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1970390amx
AMC Addicted Joined: Jul/11/2008 Location: colorado Status: Offline Points: 3311 |
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Have you done a leak down test or are you just guessing?
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1970 390 4speed Bittersweet shadow mask AMX
1970 Amx missing most everything, or in a box |
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scott
AMC Addicted Joined: Jul/10/2007 Location: Wildwood Pa. Status: Offline Points: 3498 |
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It's possible to know too much about your engine. Having a compression test just gives you something to worry about. Just
drive your car. Stop worrying about it. It's a tough little engine and
can take it.
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purple72Gremlin
AMC Addicted Charter Member Joined: Jul/01/2007 Location: Illinois Status: Offline Points: 16591 |
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leakdown will tell.
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tyrodtom
AMC Addicted Joined: Sep/14/2007 Location: Virginia Status: Offline Points: 6199 |
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When you did the head, did you check the valve spring pressures open and closed ?
Old springs ? New springs ? Any idea of the rpm you're turning at 80 MPH ? Even with new springs you're not necessarily safe. A lot of the new oem replacement springs are China sourced and fall far short of oem standards I have come to find out on my own. Then a springs can have good seat pressure when you test it on head assembly, but fall short at 200-220 degrees. Any spring loses tension as it heats . You might have burned a valve because you didn't install hardened valve seats, or you may be floating a valve, or valves, which doesn't take long to destroy valve sealing also. |
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66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
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uncljohn
AMC Addicted Joined: Jan/03/2013 Location: Peoria AZ Status: Offline Points: 5394 |
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Edited by uncljohn - Sep/10/2016 at 10:09am |
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70 390 5spd Donohue
74 Hornet In restoration 76 Hornet, 5.7L Mercury Marine Power 80 Fuel Injected I6 Spirit 74 232 I-6, 4bbl, 270HL Isky Cam |
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4741 |
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Yes I know it has a problem because I did a routine compression test and found cylinder #1 to be down 20 PSI from the normal 145 this engine used to be. A follow-up leak down test revealed 40% leakage on that cylinder; it used to be 20%. While doing the leak down test I put my hand over the tailpipe and felt quite a bit of pressure, so I know the air is leaking out the exhaust valve on #1 cylinder. No other cylinder did that, they all had only minor normal leakage past the rings. At 80 MPH I'm only a 2900 RPM, so that's no problem. It takes quite a bit of throttle to go that speed, but RPM is no issue. I have a slightly higher lift cam than stock (stock duration and overlap, but .030" more lift), so I installed slightly stiffer valve springs to match, just in case. There was no coil bind. What I meant by the seats were "touched up" is that they were sealing fine before I rebuilt it, though a few exhaust seats were starting to pound out too wide. They only required minor grinding to make them right again. I figured I could lightly grind the seat face without breaking through the thin factory surface hardening and then simply hit the seat with narrowing stones to center the seating area on the valve face. I lapped every valve to check the seating position on the valve face, and I recall the exhaust valve seating area being a little wider than I'd like, but not bad. But like I said, all my other engines automatically received hardened exhaust seats, Stellite exhaust valves, and spiral groove steel guides when they were rebuilt, and I have never burned a valve in them. Looking back now, I wonder if I broke through the factory surface hardening on the exhaust seats and have been driving the last 15,000 miles on plain cast iron seats....without any lead in the gas. I've burned the seats out of engines before by doing that because I didn't know they didn't have hardened seats. I need hardened seats for the speeds I drive continuously. Keep in mind this engine holds my record for the number of miles traveled in one day. I went 980 miles in 15 hours, stopping only for gas, food, and bathrooms. I've taken it up over 100 MPH on several occasions and have outrun rednecks in their lifted trucks who thought it would be funny to cut me off. Point is: this isn't a show car or a grocery getter. I drive this thing. Edited by FSJunkie - Sep/10/2016 at 12:12pm |
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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amc67rogue
AMC Addicted Joined: Nov/05/2008 Location: Phx. AZ. Status: Offline Points: 1578 |
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77 232 would have had induction hardened seats. 4.0 valves are larger.
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Keith Coggins 67Rogue X code
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FSJunkie
AMC Addicted Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4741 |
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1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
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amc67rogue
AMC Addicted Joined: Nov/05/2008 Location: Phx. AZ. Status: Offline Points: 1578 |
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You have 134 thou. mile on the OEM guides. When they get sloppy enough the valves starts loosing there ability to seal. 304s had the same size valves.
Edited by amc67rogue - Sep/10/2016 at 12:30pm |
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Keith Coggins 67Rogue X code
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