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291c Heads

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69 ambassador 390 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/22/2011 at 5:42pm
They are the same.  Only the exhaust gaskets are different.
Steve Brown

Algonac, Mi.

69 Ambassador sst 390

84 Grand Wagoneer

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Post Options Post Options   Thanks (0) Thanks(0)   Quote FuzzFace2 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/22/2011 at 7:26pm

I was throwing together a motor from parts I had trying to make a AMC event, 2 weeks and no money, and the gaskets that came off where mangled so could not use them. I did want to check valve/piston as I did not want to take the word of a Summit tech it would fit and find out he was wrong!

Because I did not add to the push rod with the headgasket on I must have more room between valve & piston Wink
Dave ----
TSM = Technical Service Manual

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70 Javelin SST 390/4sp (360/5sp now)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/22/2011 at 8:32pm
Originally posted by GREM GREM wrote:

The old head gaskets coming off are the square port ones. Will they work?
Those are exhaust manifold gaskets.  Head gaskets are the ones between the block and the head and are the same for 390s and 401s
Dan Curtis, AZ AMC Collector Quality Restorations & Parts - amcmusclecars.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/22/2011 at 8:42pm
Oh! Man.  I forgot to tell him to remove the clay before he bolts the head back on.Wink
Steve Brown

Algonac, Mi.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SC397 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/22/2011 at 9:01pm
Don't worry, that chit will bun out of there eventually. No problem!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/22/2011 at 9:54pm
But what if it turns to ceramic and glazes the cylinders?
Steve Brown

Algonac, Mi.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GREM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/23/2011 at 3:07am
Originally posted by SC397 SC397 wrote:

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.

All in good funCheers!...The step up dowels from Keith Coggins arrived yesterday & look to be very nice. Tapered & everything. So if I'm reading this right there should be no problem using my 1968 390 AMX square port head gaskets with the 7/16" bolts providing I don't put the step up dowels in first?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote amc67rogue Quote  Post ReplyReply Direct Link To This Post Posted: Mar/23/2011 at 12:31pm
If you're old gaskets are aftermarket the dowel pin holes should have 4 little tabs in them. If you push the gaskets down on the larger dowel they'll bend out of the way.
Keith Coggins 67Rogue X code
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/23/2011 at 9:21pm
no such thing as early and later 390 head gaskets.  One size fits all unless you go custom to be exactly equal to your bore.
Dan Curtis, AZ AMC Collector Quality Restorations & Parts - amcmusclecars.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GREM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/27/2011 at 9:25pm
I stopped into the machine shop on Fri to see how things were progressing. Even tho the consensus is the stock seats would work fine I decided to go ahead & spend the extra money on hardened seats & SS valves. I don't have much confidence in the quality of fuel getting any better. The machinist ensured me that the new valves are identical in length to the one's in the square port heads so I won't be doing the clay test (great info tho!). He is installing the shallow seats. I've heard that because of the shift in some of the castings from the factory the deeper seats in the forward cylinder may have an issue. The valves were on backorder, but arrived on Wed so the heads should be done the end of next week. The roller rockers & adjustable studs, & gaskets have arrived.

The motor should be out of the car in about two or three weeks & on an engine stand for a few more; so I'll have the option of doing the mockup on the heads & the pushrod measurement out of the car. I have the 7/16" ARP head bolts as well... So if I'm reading this right I can remove the old heads & use the existing head gaskets (squished) for mockup. Before placing new heads on block I'll replace one of the valve springs with a weaker one (I don't have one yet but I'm working on it). Super glue a spare lifter so it won't compress. Bolt on new heads using the 70+ torque specs and adjust the roller rockers so they are centered.

Now for the questions...

- I'm assuming at this point the backlash on the adjustable pushrod should be 0?
- Once one valve is done is it safe to order all the pushrods this length or do I need to go thru this whole      procedure for each valve?  

Thanks once again

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