TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > AMC 6 Cylinder Engine Repair and Modifications
  New Posts New Posts RSS Feed - 258/4.0 head swap
  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.

258/4.0 head swap

 Post Reply Post Reply Page  <123>
Author
Message
1977 Hornet guy View Drop Down
AMC Fan
AMC Fan
Avatar

Joined: Jul/21/2013
Location: Wichita Fall
Status: Offline
Points: 18
Post Options Post Options   Thanks (0) Thanks(0)   Quote 1977 Hornet guy Quote  Post ReplyReply Direct Link To This Post Posted: Jul/27/2013 at 5:02pm
Newbee needs help so I replaced 258 head with junkyard 7120 head after valve job and decked .010 now started and ran for a few seconds roughly now I can't get restarted replaced intake with offy open plenum intake 4v new header dizzy dist. Stock 258 cam Holley 1950 600cfm will only pop and spit gas back out carb sounds 180 out but tryed that just made worse any ideas????😁
Back to Top
firefly View Drop Down
AMC Nut
AMC Nut
Avatar

Joined: Dec/23/2008
Location: wi.
Status: Offline
Points: 355
Post Options Post Options   Thanks (0) Thanks(0)   Quote firefly Quote  Post ReplyReply Direct Link To This Post Posted: Jul/27/2013 at 5:31pm
600cfm...still too much carb. Make sure the rotor is under the no. 1 distributor wire. maybe 1 tooth off? Did you check the timing when you spun the motor? That will tell you a lot.
Back to Top
1977 Hornet guy View Drop Down
AMC Fan
AMC Fan
Avatar

Joined: Jul/21/2013
Location: Wichita Fall
Status: Offline
Points: 18
Post Options Post Options   Thanks (0) Thanks(0)   Quote 1977 Hornet guy Quote  Post ReplyReply Direct Link To This Post Posted: Jul/27/2013 at 5:33pm
Ok will double check thanks!!
Back to Top
EagleFreek View Drop Down
AMC Addicted
AMC Addicted


Joined: Oct/11/2008
Location: Fayetteville,TN
Status: Offline
Points: 828
Post Options Post Options   Thanks (0) Thanks(0)   Quote EagleFreek Quote  Post ReplyReply Direct Link To This Post Posted: Jul/27/2013 at 10:40pm
Did you check lifter preload? Do a compression test. If it comes back low on a couple cylinders, check for bent pushrods. 
1986 AMC Eagle Wagon 4.2L/4.0L head, AW4,NP242, Chrysler 8.25" rear. SOLD
1981 AMC Eagle Wagon-As Seen On TV Lost in Transmission

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: Jul/28/2013 at 12:53am
I think if you have not already done that, checking for bent push rods might be a good idea before you go any further.
It seems to me that there is a possibility that by changing the cylinder head that actually affects how long the push rod actually wants to be. Not to mention the possibility that the the rocker arm ratio might be different than that used on the 258 which might cause the valve itself to move further than it was designed to move.  Thus either running into coil bind or a piston.  Neither of which is a good idea.  So fi there is bent push rods you need to know why and take care of the why before you go much further and cause damage that becomes exponentially more destructive and expensive to deal with.
I have not done this modification for a variety of reasons.  One being I really have not found myself in the position of needing it.
And needing to know these things before I did this change over so as to not have to solve them after-the-fact.


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
1977 Hornet guy View Drop Down
AMC Fan
AMC Fan
Avatar

Joined: Jul/21/2013
Location: Wichita Fall
Status: Offline
Points: 18
Post Options Post Options   Thanks (0) Thanks(0)   Quote 1977 Hornet guy Quote  Post ReplyReply Direct Link To This Post Posted: Jul/28/2013 at 10:31am
That could very well be will take valve cover off and crank her over should of done already just wasn't thinking and didn't want oil all over new paint.. Haha probably need to pull rockers off and check push rods also!! Thanks you guys are great since my godfather and dad are gone no one to give me another view on matter Thanks again!!!!
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: Jul/28/2013 at 3:40pm
Originally posted by 1977 Hornet guy 1977 Hornet guy wrote:

That could very well be will take valve cover off and crank her over should of done already just wasn't thinking and didn't want oil all over new paint.. Haha probably need to pull rockers off and check push rods also!! Thanks you guys are great since my godfather and dad are gone no one to give me another view on matter Thanks again!!!!

I got to thinking about this question this morning and realized I really don't know the answer nor have I had the reason to know it.  But I pride myself in remembering some where I ran across a reason to know things obscure so did some research:

Jeep Push Rod Lengths

Length Part Number Engine Year

9.639 PR-437 4.0L 1987-96

9.728 PR-399 4.2L 1989-90

9.700 PR-353 4.2L 1983-88

9.622 PR-333 4.2L 1977-80

9.594 PR-301 4.2L 1972-76 Stamped Rocker

9.656 PR-332 4.2L 1971-74 Cast Rocker

Custom Length Push Rods

9.500 PR-310 Used with the aluminum head on decked engines.

9.547 PR-327 Used with the aluminum head on stock engines.

9.560 PR-310A

9.668 PR-303

And low and behold I ran across his information.
Now I am not sure what the PR-XXX part number is unless it might be a Hesco part number. 
I have bent push rods on both my 1980 258 and the engine I have in my Spirit which started out as a 1975 engine from a Pacer.  That is also  the one that I rebuilt and decked the block on to get 9:1 compression which I guess only tells me that there were different deck heights made during the 70 and 80's and I bent them due to leaving the car sit with todays gasoline in it causing a valve guide to get sticky thus freezing the valve and turning the push rod into the letter Z.
Also as AMC hydraulic valves are non-adjustable thus depending on the tolerance of the lifter to automatically compensate for difference rather than needing adjustments.
The point being I guess, is I have had to replace push rods in both engines and have done so after purchasing a handful of them from my autoparts store and using them in either engine with out a problem.
I am not really sure how much of a difference you really have to worry about. Apparently I have not worried about push rod length and have not had a problem.
I kinda think looking for a bent push rod is a good idea. If you find one or so, you need to find out why and if the reason is that you installed that particular 4.0 head you will have to figure out what length push rod you need.
But there seems to be a maximum difference of .134 inches between the longest push rod and the shortest ones.
The early 70's engine would be the lowest compression with the middle 80's engine having the highest compression.
Not sure what difference that would make in anything related to push rod length nor do I remember what I had to say to buy the ones I have.  But like I say, I have used them in my modified 1975 engine and my 1980 engine with out a problem
But you have some kind of a problem and it needs to be identified as to what and why.  I guess not wanting to do something because it was just painted is about as silly a reason I can think of, but it is one I have used in the past and will probably end up being used again in the future. I just hope you find something to make it worth while to have done so.


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
1977 Hornet guy View Drop Down
AMC Fan
AMC Fan
Avatar

Joined: Jul/21/2013
Location: Wichita Fall
Status: Offline
Points: 18
Post Options Post Options   Thanks (0) Thanks(0)   Quote 1977 Hornet guy Quote  Post ReplyReply Direct Link To This Post Posted: Jul/28/2013 at 4:21pm
Wow that's a great help so if I pull them out should be able to roll them on the work bench to tell if they are bent right? I see the rockers moving up and down when I crank I know the 258 ones I put in are shorter was playing it safe in using them maybe I need to go to the 4.0 ones? Mine is 1977 258 block with a 1995 4.0 head #7120 I just thought you allways matched up push rods with cam but I can see that it is totally posiable that the 4.0 head may be taller thus needing longer pushrods..
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: Jul/28/2013 at 5:05pm
Rolling the push rods across a kitchen table should be more than adequate to indicate you have a bent push rod.
I think I would inspect them for being bent just in case before I would worry about IF they are bent.
The AMC cylinder head design is very flexible as to be tolerant to a lot of different variations, even the one where you Frankenstein things together by incorporating a 4.0 head on a 258 engine.
Their depending on the hydraulic lifter tolerances to adequately deal with not needing to make an adjustment if pretty tolerant of a fairly large change in components.
What ever is going on ended up with the following problem:

Newbee needs help so I replaced 258 head with junkyard 7120 head after valve job and decked .010 now started and ran for a few seconds roughly now I can't get restarted replaced intake with offy open plenum intake 4v new header dizzy dist. Stock 258 cam Holley 1950 600cfm will only pop and spit gas back out carb sounds 180 out but tryed that just made worse any ideas????

And I personally think that if you have a bent push rod as a direct result of anything you did you are going to have a major mechanical problem and it should be obvious.
If nothing is bent and the rockers and valves are moving sort of correctly you have something else going on.

While the carburetor is in all reality too big for the motor, it should run.  At least better than you are describing things. I ran a 650 CFM AFB on a MOPAR 225  for a while. It ran richer than a cob and laid down a cloud of black smoke from being too rich, but it ran.
your engine is not running.
Now a holly has a Power Valve as part of it's function and if it is damaged, a Holly can run like that.  Hollys are not very tolerant to being miss-applied and as a 600 is in fact too big for your engine it is possible that if it has a power valve problem it could run the way you are describing. You need to know that for sure.
So if you can verify that you do not have a bent push rod indicating a valve problem. And that all he valves look like they are moving correctly, that distributor is indeed pointing at the right cylinder and has the right firing order on it, and the power valve either is or is not damaged on the carburetor it should fire better than your description says it does.
I mean!!!
if I can pull a Mercury Marine Motor out of a boat, carry it from Florida to Arizona in my van, pull all the Marine stuff off of it and install car stuff on it, purchase a made in China Air gap no-name intake on it with a 1971 Chrysler Carter thermo-quad carburetor on it and a 1969 Camero distributor and a new cam shaft, put into my Hornet and wire it up and all and have it start!!!!!
You ought to be able to put an all AMC Frankenstein motor together and get it to start too don't you think?
I think you should!

But you also need to know that your timing is more or less correct and the basics are on the edge of being correct.


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
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: Jul/28/2013 at 5:27pm
There's possibilities of causes for your problems other than pushrods, though that does sound the most likely.
When you changed distributors, what gear did you use on the new distributor?
When you pulled the dist. to see if it was 180 out, did you get a good look at the dist. gear ?
Check firing order ? 1-5-3-6-2-4 , clockwise rotation.

Is the intake you mounted made for a 4.0 head ? Or did you modify a intake made for a 233-258 to fit on a 4.0 head ?

66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
Back to Top
 Post Reply Post Reply Page  <123>
  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 0.094 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