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291c Heads

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amx39068 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/14/2011 at 4:11pm
unless the base circle on the 71 and later cam was different than the 70 cam the pushrod length should be the same from 70 up until bridged heads. Even so and unless he is using a stock cam, stock rocker studs and stock rockers, the pushrod length needs to be specific to the combination of after market parts he will be using.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GREM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/14/2011 at 9:02pm
Originally posted by 69 ambassador 390 69 ambassador 390 wrote:

Mock an intake and exhaust rocker up with special light checking springs and adjustable push rod.  Summit has these cheap.  you will then know your length.

I know someone that has an adjustable push rod but could you elaborate on the light checking springs?

Thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeremy0711 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/14/2011 at 10:30pm
about 20-25 bucks if you have to buy it new.
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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/14/2011 at 11:35pm
You replace the heavy valve spring with the very light(maybe 10 pounds) checking spring so the lifter does not collapse and you get a good reading.  Summit and Northern sell them.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GREM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2011 at 11:44pm
Originally posted by 69 ambassador 390 69 ambassador 390 wrote:

Mock an intake and exhaust rocker up with special light checking springs and adjustable push rod.  Summit has these cheap.  you will then know your length.

I think I have a grip on how this works & it makes sense but I have some questions. When you say mock up the rockers I'm assuming you are meaning bolting up the heads to the block & bolting them down with proper torque with the head gaskets in place? If so, how do I replace the spring without the valve's falling into the combustion chamber?

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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/21/2011 at 8:55am
Two ways to do it.  You should be checking the piston to valve clearences anyways so just mount the springs before the head goes on.  Put non-hardenning modeling clay in t thin pancake over the valve releifs on the piston head you are working with.  Now bolt the head on with a used head gasket of the same compressed thickness as the one you will be running.  Now run your checks with a checking lifter that is made out of a new lifter superglued on the inside so it can't compress.  Also turn the engine over twice to let the valves smash the clay.  After removing the head you would then cut the clay with a razor blade and read the thickness at the thinnest part.  This is your piston to valve clearence.  The reason for the used gasket is so you don't ruin a new one.  The other way to do it is with an overhead valve compressor and an air hold fitting in the spark plug hole.  You apply air to the cyilnder at TDC and remove the spring.  The reason for TDC and not BTC is that if the valve does drop it will stay where you can get it.  Make sure you are really at TDC or the motor will turn to BDC when you hit it with air.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FuzzFace2 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2011 at 1:24pm
Could this be checked with out the gasket and add that to the reading of the clay? If not how far off would it be?That is what I did and figured if the valve clears with out a gasket that it will with one. I found springs that worked from the local hardware store, it was a time issue thing.
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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/21/2011 at 5:51pm
Yeah, you could do the clay without the gasket and add the compressed thickness of the gasket but you would have to do the same with the pushrod also.  I would at least put some paper bag type paper between the head and block so you don't hurt the sealing surfaces.   If you are changing heads why don't you just use the used gasket that comes off?  If the heads are staying on then you can assume there is valve room and skip that though I do like to check.  If it is close and you get float you could eat a motor.  If you have already been ragging on the engine your probably O.K..  I personnally don't like probably when working with my money.  The hardware store spings should be just fine.  I use a couple of sailboat block standup springs myself.  Not designed for it but been using them for years.

Edited by 69 ambassador 390 - Mar/21/2011 at 5:57pm
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84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special



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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2011 at 6:24pm
You can also use a cleaned up old head gasket for measurement if it didn'tget all bunged up when you pulled the head.  It will already be compressed and fully capable of protecting the surfaces. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GREM Quote  Post ReplyReply Direct Link To This Post Posted: Mar/22/2011 at 4:24pm
The old head gaskets coming off are the square port ones. Will they work?
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