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Some Punk Kid
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786 Posts
Discussion Starter #1
While adjusting the rockers when I was looking for TDC I noticed the dome of the piston was what seems like very close, which leads me to my question. Will any plug clear it or should I be looking for a plug with a specific reach and thread length. First engine build with dome pistons so I am not sure of myself on this. Thank You for any replies regarding my question.
 

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Some Punk Kid
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786 Posts
Discussion Starter #3
Engine 1970 Impala 2 bolt 300 horse block
stock crank and con rods
Pistons-Speed Pro
Bore (in): 4.040 in.
Bore (mm): 102.616mm
Piston Material: Forged aluminum
Piston Style: Dome
Compression Distance (in): 1.560 in.
Dome Height (in): 0.213 in.
Piston Head Volume (cc): -10.60cc
Valve Reliefs: Two

Heads are used GM stockers. The engine shop says they are either 72cc or 76cc. I believe they are 76cc. If you want casting numbers I can get them. I just asked for heads they had around the shop nothing special. They put in new valves and the comp cam springs I bought. The guy I bought the engine from had camel back heads on the engine. But I am not sure if 70 impalas still had camel back heads. Any way I did not buy them as i want to hang accessories.
 

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Race it, Don't rice it!
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7,734 Posts
You kinda have to know the what head yuo got. My best guess say's you won't have problems with those big chambers. You should check anyway.

The head will usauly dictate what plug you'll need. It's probably a 14mm, 3/4 reach.
 

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Some Punk Kid
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786 Posts
Discussion Starter #5
Alright, thanks for the advice. Ill go out and buy some cheap cold or medium heat 3/4 reach plugs and see what happens when I spin by hand and when I fire it up for the first time.
 

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Some Punk Kid
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786 Posts
Discussion Starter #6
They are 3998993 hencho's. mortec says they are goodwrench crate motor heads. 75cc chambers. Havent got the 3/4 plugs yet as I need to readjust my rockers with a new technique. The engine manual says to use the twist pushrod method instead of the up and down jingle method when adjusting rockers. My cousin says using the twist method could bind up the lifter internal spring. He says I should check them and see if I had them too tight as If I started engine like that i could screw up the tappets.
 

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Registered
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17,612 Posts
"My cousin says using the twist method could bind up the lifter internal spring."

Having been there, done that, I agree with your cousin.
 

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Race it, Don't rice it!
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7,734 Posts
Try the AR 133 for that head in a short style or a R45TS ACdelco for the long ones.


It's very hard to tell when the lifter spring is being pushed down. Take extreme care and pay close attention. Wiggling up or down with a very light touch is best.
 

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Some Punk Kid
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786 Posts
Discussion Starter #9
I re-did the rockers. Majority of them were too tight on the lifters. Problem with them spinning method is the lifter will spin with rod as you tighten it down until spring is smashed all the way down. I cannot believe this is the method adopted by the author/publisher of the small block chevy book(HPbooks). The jiggle up and down method was by far smoother and it allowed for proper gap between rocker and stem when you push down on the rod side of rocker.

P.S.-Johnsongrass1 can you take a peak back at my other thread again. 2 bolt RPm and power. Its a couple pages back already. I am really lookin for a lot of opinions on this motor.
 
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