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Old 05-04-2021, 05:05 AM   #1
tannerg1223
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Default Mysterious misfire episode 2- BURNT VALVES!!!

Thanks to the folks who helped me thus far in my journey into figuring out this damned misfire my truck has. Through various tests and many parts interchanged, I believe that I have finally figured out my issue. I have reason to believe that my cylinder 2 misfire is due to a burnt out exhaust valve. Being the person that I am however, I got ahold of 2 custom 240sx heads that need a bit of love.

Today I took it upon myself to disassemble both of the heads to find that one is warped and cracked- no biggie. I still have a spare. So after hours of compressing springs with my crappy Harbor freight tool, I finally managed to tear open the unscathed head only to find out that every single one of the intake valves has been sharpened to the point of surgical precision. Can anyone tell me what my best course of action would be? I’m new to the performance side of things and I plan on porting the cylinder head myself. What should I do to address the valve issue?? I just want this problem fixed so I can turbo my poor hardbody

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Old 05-04-2021, 05:16 AM   #2
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Here are some before and after side profiles of the intake valves. Before and after when I hit them with the drill press and the scotchbrite pads LOL
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Old 05-04-2021, 09:35 AM   #3
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Install new valves and valve guides. Have the head polished first, not ported, to specs. You may need to provide the specs from the factory service manual.

Messing with the valves if you haven't done this much before is really tricky. And you are talking about adding speed gear afterward. Also tricky.

Not impossible, but I hope you have some experience here.
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Old 05-04-2021, 11:26 AM   #4
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https://www.headsonly.com/
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Old 05-04-2021, 05:40 PM   #5
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That's allot of wear on those valves. How are the seats? How are the guides?
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Old 05-04-2021, 08:01 PM   #6
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are the bowls replaceable on these heads? if not probably a junk head.
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Old 05-04-2021, 11:06 PM   #7
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Quote:
Originally Posted by XoXSciFiGuy View Post
Install new valves and valve guides. Have the head polished first, not ported, to specs. You may need to provide the specs from the factory service manual.

Messing with the valves if you haven't done this much before is really tricky. And you are talking about adding speed gear afterward. Also tricky.

Not impossible, but I hope you have some experience here.
Iíve rebuilt many 4 stroke small engines but now want to move on to cars. I definitely am nowhere near a professional, but I do have some wrench time under my belt. I plan on running my truck (for now) at around 7psi, but want to port the heads to get rid of the factory cast lines and increase airflow. Took my cylinder head to a local machine shop that Iím well aquatinted with and he told me it shouldnít be an issue- I had another set of valves laying around that he thinks are usable and he will be lapping them to the cylinder head. Also, he is going to resurface it for me and check all the tolerances. Ted (the expert) has built many a drag car in his lifetime and is well versed in turbo builds as well. He is on board and told me he will set me up straight!
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Old 05-05-2021, 01:53 AM   #8
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Quote:
Originally Posted by tannerg1223 View Post
<<snip>>

.... Ted (the expert) has built many a drag car in his lifetime and is well versed in turbo builds as well. He is on board and told me he will set me up straight!
Well, I look forward to seeing where this goes. Keep us posted! Like your PICs... keep um comin'.
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What he is saying it the aerodynamics of a D21 is a brick in the wind.
Probably at least as bad as a Jeep so worse than a cow.
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