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Help W/ 420A bent valves

Posted by screwlegg, Jan 27, 2018

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  1. screwlegg

    screwlegg Proven Member

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    Joined Jan 27, 2018
    Sebring, Florida
    Hello yall, so I got a 420A that's been sitting for at least a year due to the timing belt slipping also this will be my first time messing with internal engine components so bare with me if I don't know everything . I'm pretty sure the valves are done because I put the timing belt back at what I believe is spot on and still not starting with new spark plugs and I checked the fuel pressure so I'm sure its compression.

    Tomorrow I'm going to do a compression test on it to figure out for sure cause it's dark out already.I guess my first question is does it matter if I have all the spark plugs out while I'm doing the comp test or do I just take one out and screw the spark plugs back in when I'm done w/ that cylinder and my car wont start so to do the comp test so how will I get the vehicle to operating temp or will that not matter as much . The second question, is everything pretty much just taking bolts off to get to the valves other then the valve compressor to get the keepers and taking bolts off in order so I don't warp the engine or is their anything I need to know specifically while getting to the head. Please get back to me I'd greatly appreciate it, I will follow up on this post to let everyone know how things are going
     

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  2. silvreclips

    silvreclips Proven Member

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    Joined Jul 19, 2005
    Greenville, South Carolina
    Take out all of the plugs when you do the test. It will let the motor spin easier. The test is normally done at operating temp, but if it doesn't start then you have to do a cold test. The numbers will be lower but your really just looking to see if it has compression and if the cylinders are equal. You should plan on doing a leak down test if you find low or no compression. That will tell you if the valves are bent
     
  3. techboy

    techboy Proven Member

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    Joined Feb 3, 2018
    Lehigh Valley, Pennsylvania
    My suggestion would be to you if it's your first time messing with internal engine components - the head is not the place to start. Take the head off and take it to a machine shop that can diagnose it and get it fixed right - otherwise you'll be chasing your tail.

    If the timing crashed you most likely have bent valves. I had a timing belt break on a 420A break on me at idle a LONG time ago and it bent 12 out of the 16 valves.
     
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  4. KYLE JORGENSEN

    KYLE JORGENSEN Probationary Member

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    Joined Sep 22, 2018
    SPOKANE VALLEY, Washington
    get new set of intake and exhaust valves, time right and make sure belt is tight and there should be no issues if the timing is on I have rebuilt 3 or 4 heads on my 420a it is not that difficult the amount of money charged in labor will be in the 1000 and valves are only 130 for set of 16 since belt is broken your already at a good point to rip the head off and do the work your self now if there are Knicks where the valves bent and hit the seats they will have to be re-grinded down to fit the new valves and seat properly you can do this by hand or take to a machinist I personally did it myself just so I know how to do it.check piston tops for gouges good indicator you also bent a valve
     
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  5. arrowhead

    arrowhead Proven Member

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    Joined Apr 19, 2011
    miami, Florida
    So you started backwards, a compression test will be futile at that stage, I would try to find some help to take your head out, by your post your knowledge is very limited, you will probably do more damage than what you already have if procedure is not done properly.
    About your compression test, plugs out, engine at normal temp, (not possible now), disable either ignition or fuel, and press gas pedal fully.
    At your level get a MACHINE SHOP to do your head, just replacing valves does not make a valve job.
    Skip the leak down test at this time, it will not tell anything different from what you already know.
     
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  6. 19gsx91

    19gsx91 Proven Member

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    fwiw I've got a 420a head sitting here I'd send out for pretty cheap if you just wanted to slap a new head on. sometimes that's a better alternative because trips to the machine shop can add up fast
     
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