GT40P question |
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joshjanae
Groupie Joined: October-11-2015 Location: Arizona Status: Offline Points: 87 |
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Posted: June-04-2017 at 2:34pm |
From what I have read here on this forum the only thing that needs to be done to install a set of gt40p heads on a 351W is to drill the bolt hols to 1/2". I am installing a set of gt40p heads on my 83 sn2001 this week and the one question I haven't been able to find an answer to is;
Do you recommend drilling the head bolts out yourself or is this something that needs to be done at a machine shop or mechanic? Thanks for the help? |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Josh,
I don't see a problem drilling them yourself since they are not a precision locator of the head position. I do recommend a drill press and sharpening the drill bit for cast iron. |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Here's a picture. Basically the cutting edge is ground to a 0 degree rake. "dulled" See the flat on the cutting edge in the K picture.
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joshjanae
Groupie Joined: October-11-2015 Location: Arizona Status: Offline Points: 87 |
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Great, thanks for the response. I'm really hoping to get this done in the next few days. I have a 6 day canoe trip planned with a youth group and the boat is suppose to accompany for safety...and fun.
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KENO
Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 10688 |
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Hi Josh
the first time I did this I had a short conversation with myself It went like this Me #1 I wonder what size drill bit I should use for this ? All over the internet people seem to say 1/2 inch Other smarter me Why don't you measure the hole in the original 351 head? Me #1 Why didn't I think of that? Other smarter me That's a good question, just go do it Me #1 OK I did it, the hole is 17/32 inch Other smarter me Are you sure? Me #1 Yep a 17/32 drill bit fits perfectly in the bolt hole Other smarter me Good job So take it from both versions of me, you'll need a 17/32 inch bit. I figure Ford knew what they were doing when they made the heads and that's the hole size they made. And like Pete said use a drill press. People have done it with a hand drill but the chances of drilling at an angle are a lot higher. If you drill at too much of an angle, you end up with a hole into the water jacket, then you have water in the oil. The casting isn't very thick where you're drilling. Me #1 might know this from experience in case you're wondering Also you'll need some new spark plugs. A good Autolite number is 764 or 104. They're functionally the same plug but the 764's are half threaded and the 104's are full threads. If you look in the plug hole when you get the heads you'll see why either will work Or you could cross reference to your favorite brand. One Ken O or the other Oh and by the way, me #1 ain't so smart and I just used a good 17/32 bit with no modifications , went slow with the press and it was no problem |
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joshjanae
Groupie Joined: October-11-2015 Location: Arizona Status: Offline Points: 87 |
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Thanks Ken. I was having the same conversation with myself. I plan on drilling tomorrow, with a drill press. I'm going to pick up some good drill bits from fastenall, apparently size 17/32.
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Duane in Indy
Platinum Member Joined: October-26-2015 Location: Indiana Status: Offline Points: 1578 |
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The slower the drill press the better. 150 RPM or less is good. No coolant, just drill it dry.
Cast iron tends to glaze with oil. If the press is too fast then you can use straight water to cool the bit. Little tip: cut a small piece of cardboard and lay it over the existing hole. Crowd the drill bit gently into the cardboard. The cardboard tends to center the drill bit over the hole. Drill thru the cardboard. Obviously you need a new piece for every hole. It keeps the drill from grabbing and walking around till it finds center. (.531 and 17/32 all the same when you are searching for the bit) |
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Keep it as original as YOU want it
1978 Mustang (modified) |
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MrMcD
Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3598 |
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Great advice already given above to do this job correctly. I have only done one set but I don't think I had a 1/2 hour tied up from start to finish. Not that big a deal if you follow the advice given to stay out of trouble. I've never heard of the cardboard trick. Nice.
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96SNEFI
Senior Member Joined: March-23-2009 Location: Canada Status: Offline Points: 138 |
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Well I'll tack on to this thread so as not to make another one. Who knows...maybe this could become the GT40P reference thread. I searched and found just a few threads and this seemed to be a good candidate to add to.
So say one has stumbled across a pair of used heads somewhere somehow. What can one do in that moment to decide if they're worthwhile to take? Can one reasonably see warpage? Can one reasonably see cracks? Can one reasonably see burnt valves, weak springs, bad seals? Anything else to reasonably look for? What might be the going rate on used heads? Would one need to take them to a shop after deciding to take them and spend more money on real examinations and/or re-doing rockers/springs/seals/valves anyway? |
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