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GT40(P) head swap |
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cperry11 
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Joined: April-17-2020 Location: Central Florida Status: Offline Points: 11 |
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 Topic: GT40(P) head swapPosted: November-22-2020 at 5:15pm |
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Hey guys, so question for the off season project, i pulled the valve covers and discovered the engine e has miss matched heads. so i want to remedy this, and a cheap thing i know do as a Ford guy is to pull some heads from a junkyard, probably some GT40P heads from an explorer. my question is to anyone who has done this before possibly.
the engine is a '77, so the heads have stud mount rockers, and the newer GT40P heads have bolt in rockers. to anyone who has swapped these newer heads on these older motors, what is your input. thank you.
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1977 American Skier
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Gary S
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Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: November-22-2020 at 9:23pm |
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If your pulling them yourself just grab the rockers and associated parts that are on the donor. Drill out the head bolt holes to match the 351's and add brass core plugs. You'll need different size sparkplugs,someone here will know the size (Ken perhaps
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11118 |
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Posted: November-23-2020 at 7:12am |
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I'm kinda figuring your Boat probably has a 302 in it. (77 CC American Skier)
Putting 302 heads on a 302 will be pretty straightforward. You won't have to get the head bolt holes drilled out, but it would be a good idea to replace the steel plugs Gary mentions with brass. Like he said also get the heads with the rockers, springs etc all intact and it will be easier. The pushrods may or may not be the same length, but you should check your valve lash/ lifter preload just to be safe when everything is bolted together. The pedestal mount rockers just get tightened down and aren't really adjustable so shims could be needed for getting the right preload depending on whether you get any machine work done on the junkyard heads. For spark plugs a good choice would be Autolite 764 or 104 or an equivalent from your favorite spark plug outfit because the old ones won't thread into your heads Do some reading on SBF head gaskets and how to make sure they're oriented right when installing them. Now silly question time Is the boat running good in spite of the head numbers mismatch? What are the head numbers? They could be basically the same head with no real differences. Are you gonna just throw on some 20 plus year old junkyard heads or get them refurbished at a machine shop?. If just throwing them on, you probably have a good chance of ending up with hi mileage heads with plenty of wear and tear that may give you some running issues......or maybe you'll get lucky and have no problems |
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cperry11
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Joined: April-17-2020 Location: Central Florida Status: Offline Points: 11 |
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Posted: November-23-2020 at 8:58am |
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yes its a 302, and i thought i might be able to just grab the heads dressed, just wasn't sure since they weren't adjustable on the late models, so thank you for all that info. i am fairly savy with many of these things, i was actually a mechanic and have built engines before, but it usually like for like or an upgrade engineered for that application haha, so this in my first venture where things were expected to be different.
didn't know i would need different plugs, hadn't thought about it actually, i was so fixated on the valve train, so thanks for that heads up the boat runs pretty good, she runs hot after a pull or two, main reason for opening her up, when i got her the raw water pumps was gone, so I'm assuming rubber chunks throughout her. and also she was tricky to get running right, tuning the carb by vacuum gauge, i never could get the needle steady enough, it was always bouncing a bit more than i like, which to me now could mean different flow rates causing different pulses in the intake runners. i don't know their true casting numbers yet i haven't pulled the heads of, will try to do that today, i only get to work during nap time for the girls haha.but the casting markings through the head and under the valve cover are different, maybe they are the same head but from different years or something, will see when i get them off and can see the bottom casting. i am mostly going to just swap them unless they need machine work, after pulling i was planning to clean them, check them for warpage or damage and wear, then replace the valve stem seals, possible lap the valves and seats to freshen them up a hair. which brings me to my text question of would the factory valvsprings be adequate for the boat, the P heads have a reputation of possible valve float above around 5200rpm, but the boat never revs close to that 4k at absolute most. my only fear of aftermarket springs is increased wear on the oldscholl flat tappet cam, and not knowing what the cam specs were for these boats to properly spec the spring if i did go aftermarket. thank you guys a bunch for the input, and sorry for typos and such two young kids and a cat climbing all over me and the keyboard haha.
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1977 American Skier
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11118 |
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Posted: November-23-2020 at 12:23pm |
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Yer spelink and tipoes are no problem. Better than some people who don't have cats and kids climbing all over the keyboard
The stock gt40P springs and the rest of the valvetrain will be fine with the stock cam if they're all in good shape. it isn't a whole lot different than a stock auto or truck cam. It sounds like you won't have any problem doing the swap.
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cperry11
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Joined: April-17-2020 Location: Central Florida Status: Offline Points: 11 |
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Posted: November-23-2020 at 4:09pm |
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Awesome to hear, thank you for the input, this is one of the better forums I've been on.
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1977 American Skier
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Gary S
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Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: November-23-2020 at 4:54pm |
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FYI there are shim kits available to adjust your lifter preload in case it's needed rather than than having to measure and get custom length pushrods. You most likely not need them but it is an option if you do.
https://www.summitracing.com/parts/fms-m-6529-b302?seid=srese1&gclid=CjwKCAiA2O39BRBjEiwApB2IkmRXJbWMbND4Ht3_yDfGTvcxOYw691kP5YCHZCc-trjPXj3SZLr_kBoCtWgQAvD_BwE
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