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291c Heads |
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GREM
AMC Apprentice Joined: Feb/12/2011 Location: Colorado Status: Offline Points: 46 |
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Posted: Feb/28/2011 at 8:39pm |
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I bought a set of 1970 291c heads. They have about 70,000 miles on them. I have a 1969 390 Gen II motor from an AMX with stock logs & intake manifold. I would like to install these heads, & add either a Performer or Air Gap manifold, & a set of dogleg headers to help things flow a little better. Couple questions...
It's my understanding that I will need the (4) step up dowels & the 70-72 head gaskets to install. What about the head bolts...weren't they smaller on the 68/69 blocks but I don't know what size holes the 291c heads have as I haven't picked them up yet. Are they the same & if not what am I going to have to do to make these heads fit? Any help would be appreciated. |
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SC397
AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5428 |
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The 68-69 390 blocks have 7/16" head bolts. The "91C" heads have the through holes for 1/2" head bolts. To bolt the 91C heads to the '68-'69 390 block requires the step dowels. The step dowels help locate the gaskets but more importantly, they locate the heads. There are a few sources for the step dowels so, they are not hard to find.
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GREM
AMC Apprentice Joined: Feb/12/2011 Location: Colorado Status: Offline Points: 46 |
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Wow...that was fast! Thanks... So nothing needs to be done to the block itself right?
Next question...They need to be cleaned up so does anything need to be done to be able to use today's unleaded gasses as far as a rebuild. What's recommended?
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SC397
AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5428 |
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"Wow...that was fast! Thanks... So nothing needs to be done to the block itself right?" Right, nothing needs to be done except you should use the step dowels.
"Next question...They need to be cleaned up so does anything need to be done to be able to use today's unleaded gasses as far as a rebuild. What's recommended?" This one will get some commentary. AMC heads did have a higher Nickel content in their castings than most other passenger car heads of the era. However, AMC did harden the seats in about '74 when the unleaded gas came in. Personally, I have ran a lot of real street miles (thousands)on the the older heads with out the hardened seats with no ill effect. It is your call and your pocket book. If the seats are worn and need replaced anyway, I would put the hardened seats in. If not, I wouldn't. |
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69 ambassador 390
Supporter of TheAMCForum Joined: Nov/22/2009 Location: Peoria, AZ Status: Offline Points: 3539 |
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Ditto. !00,000 miles on the current set of non hardened seats. No issues. I am now pulling them for use on my 84 wagoneer. I will not be doing a valve job but just a clean and paint. The new 291s I am installing just came back from the shop and only needed a touch up on the seats. I have seen more recession problems on later heads and they may have lowered the nickel content when they went to induction hardened seats. I Think those problems were caused by the machine shop hogging out the hardened areas. If putting larger valves in I would add the exhaust seats but if not you should have no problems providing you don't overheat the enging.
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Steve Brown
Algonac, Mi. 69 Ambassador sst 390 84 Grand Wagoneer 69 Cougar XR7 65 Fairlaine 500XL 79 F-350 Super Camper Special |
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GREM
AMC Apprentice Joined: Feb/12/2011 Location: Colorado Status: Offline Points: 46 |
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Thanks...kinda the response I was hoping for. I have a new four core sitting here so hopefully cooling won't be a problem.
I'm leaning towards a Performer intake manifold #2131 & a set of Hedman headers # 98316. Am I on the right path for a good combo with a 2.25 exhaust system?
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jeremy0711
AMC Addicted Joined: Dec/12/2008 Location: Southern IN Status: Offline Points: 1547 |
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Your best bet would be to ask your machine shop if your heads need them. I had three sets and they all shown some sign of wear with sucken seats and all. Mine also had worn out guides too. They ran great though. I guess there is a tolerance of what some allow. Your question would fall into the line of asking them if you valves were and good or not. The heads on my car are a 22,000 mile 993 heads that needed 660 bucks of work somehow. Recon was the reman company. Had the same issue with a set of 289 heads too. Could I have driven them? Yeah, but it wasn't right.
are any of your valves sucken? Pop off a few springs and see if you have any side to side play in a valve when not fully seated. |
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amx39068
Supporter of TheAMCForum Joined: Feb/21/2008 Location: Arizona Status: Offline Points: 11576 |
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A local guy here in Phoenix and on the forum makes the step dowels if you can't find them elsewhere. His price is very reasonable and a little less than you will find elsewhere. If you use the 291C heads and a performer or airgap, be sure to get the earlier one and drill new center bolt holes in either the heads or the intake. The later intakes are wider than the early intake and should be milled to fit right or you can just use the earlier intake and redrill the center bolt holes for the intake. |
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Dan Curtis-Owner and CEO AZ AMC Restorations; Facebook: https://www.facebook.com/amcmusclecars/ & Curtis Real Estate Development
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69 ambassador 390
Supporter of TheAMCForum Joined: Nov/22/2009 Location: Peoria, AZ Status: Offline Points: 3539 |
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Also, you will always find a little wobble in the exhaust stems as they are not a constant diameter. They are tapered toward the valve end about a thou. because they expand from the heat. The intakes are not tapered and should have very little side play. The exhaust would have a little just off the seat. Pull the exhaust way out from the seat to get past the taper to check those. Edited by 69 ambassador 390 - Feb/28/2011 at 11:14pm |
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Steve Brown
Algonac, Mi. 69 Ambassador sst 390 84 Grand Wagoneer 69 Cougar XR7 65 Fairlaine 500XL 79 F-350 Super Camper Special |
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jeremy0711
AMC Addicted Joined: Dec/12/2008 Location: Southern IN Status: Offline Points: 1547 |
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My 289 heads had all undersized valves, wrong guides installed, I personally called and verified if they install hardened seats and was told, "Yes", I was also suppose to have flat top pistons which I didn't get. I sold the car and got the engine back for free after hitting a cherokee head on at 80 mph and totaled the car out. The car was wrapped around the engine so I paid for it really. My AMC heads which I thought just needed an inspection and clean up... My machine shop called me up and laughed cause I already told him the story on the 289 heads from Recon. 4 bad valves, guides completely worn out, and seats needed to be hardened( I was expecting that from them). 22,000 miles?..with a laugh is what he kept saying.... They were still in business through local parts stores....not for sure but oreilys and advance did two years ago. autozone which is who I bought the engine through dropped them a long time ago. |
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