TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > AMC 6 Cylinder Engine Repair and Modifications
  New Posts New Posts RSS Feed - Am I pushing my engine too hard?
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

Am I pushing my engine too hard?

 Post Reply Post Reply Page  123 4>
Author
Message
FSJunkie View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/09/2011
Location: Flagstaff, AZ
Status: Offline
Points: 4741
Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Topic: Am I pushing my engine too hard?
    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
1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
Back to Top
1970390amx View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jul/11/2008
Location: colorado
Status: Offline
Points: 3311
Post Options Post Options   Thanks (0) Thanks(0)   Quote 1970390amx Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 2:13am
Have you done a leak down test or are you just guessing?
1970 390 4speed Bittersweet shadow mask AMX
1970 Amx missing most everything, or in a box
Back to Top
scott View Drop Down
AMC Addicted
AMC Addicted


Joined: Jul/10/2007
Location: Wildwood Pa.
Status: Offline
Points: 3498
Post Options Post Options   Thanks (0) Thanks(0)   Quote scott Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 6:42am
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. Wink
Back to Top
purple72Gremlin View Drop Down
AMC Addicted
AMC Addicted
Avatar
Charter Member

Joined: Jul/01/2007
Location: Illinois
Status: Offline
Points: 16591
Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 6:48am
leakdown will tell. 
Back to Top
tyrodtom View Drop Down
AMC Addicted
AMC Addicted


Joined: Sep/14/2007
Location: Virginia
Status: Offline
Points: 6199
Post Options Post Options   Thanks (0) Thanks(0)   Quote tyrodtom Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 9:33am
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.


66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
Back to Top
uncljohn View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/03/2013
Location: Peoria AZ
Status: Offline
Points: 5394
Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 10:02am
Originally posted by FSJunkie FSJunkie wrote:


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

It would seem to me that a wet/dry compression test would tell you whether the valves have a problem or not.
And what do you mean lightly touched up he seats on the grinder.
As far as replacing the seats, valves and guilds if they did not need it I never have and have driven hundreds of thousands of miles after words.
What I did not see you say was lapping the valves in with a simple valve grinding tool, a stick with a rubber suction cup on the end of it and some valve grinding compound which is all I have ever done and never had a problem.
That is generally and easy thing to do.
As to your driving habits, what has that got to do with anything?

As to hardened seats I have yet to feel the need to install them and also have yet to have a problem not installing them.

The final step in a valve job and some times the only step actually needed is to lap the valves on to the seat with valve grinding compound. If you did not do that AND you actually have a valve seat problem, that is probably the reason why.











Edited by uncljohn - Sep/10/2016 at 10:09am
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
Back to Top
FSJunkie View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/09/2011
Location: Flagstaff, AZ
Status: Offline
Points: 4741
Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 12:03pm
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
1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
Back to Top
amc67rogue View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Nov/05/2008
Location: Phx. AZ.
Status: Offline
Points: 1578
Post Options Post Options   Thanks (0) Thanks(0)   Quote amc67rogue Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 12:10pm
77 232 would have had induction hardened seats. 4.0 valves are larger.
Keith Coggins 67Rogue X code
Back to Top
FSJunkie View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Jan/09/2011
Location: Flagstaff, AZ
Status: Offline
Points: 4741
Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 12:14pm
Originally posted by amc67rogue amc67rogue wrote:

77 232 would have had induction hardened seats. 4.0 valves are larger.
yeah, but how much can you grind the seats down before you break through the thin induction hardening and are riding on plain cast iron? My original seats were starting to pound out and I ground them down a bit to recondition them, but if I broke through that hardening it would be problematic.
1955 Packard
1966 Marlin
1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
Back to Top
amc67rogue View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Nov/05/2008
Location: Phx. AZ.
Status: Offline
Points: 1578
Post Options Post Options   Thanks (0) Thanks(0)   Quote amc67rogue Quote  Post ReplyReply Direct Link To This Post Posted: Sep/10/2016 at 12:27pm
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
Keith Coggins 67Rogue X code
Back to Top
 Post Reply Post Reply Page  123 4>
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.125 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or