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Technical SBC Knock and Power Loss

Discussion in 'The Hokey Ass Message Board' started by BowtieGoofy, Oct 12, 2020.

  1. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    I mentioned it before, but will do so in another way now.

    Say I get ready to go for a drive. Notice my tire is worn down. Put my spare on. Now my car looks higher/ lower that it did before and pulls to one side or the other.


    Do I rebuild the suspension?

    If it didn’t knock before the change in parts, it has to be something you did that causes it to knock/vibrate.

    last thing I would look at is the bottom end
     
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  2. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 6,079

    scrap metal 48
    Member

    Like reinstall the distributor and have it retarded or advanced to much.....
     
  3. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,212

    Elcohaulic

    I would be more inclined to think it would be being its new..
     
  4. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    I pulled the pan for my own piece of mind. No metal shavings in it (thank God), so I got it back together. Gonna start it up and have my buddy eyeballl the lifters to see if anything looks suspicious.

    I checked the distributor just in case. Tje rotor on top dead center points at the terminal on the cap just after the access door, which is where put my #1 wire. Image.jpeg Image%20(1).jpeg Image%20(2).jpeg Image%20(3).jpeg

    Sent from my SM-G970U using The H.A.M.B. mobile app
     
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  5. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,600

    Johnny Gee
    Member
    from Downey, Ca

    I asked earlier on in this thread, "what balancer is on the engine now?"
     
    scrap metal 48 likes this.
  6. Late valve or ignition timing
    Not sure what’s going on here.

    but usually if all was good, then ya fiddled with something and now it runs like crap, generally it’s what you last fiddled with.

    Double check your spark plug wires that they are in the correct spot.
    I had a 4.3 with 2 wires crossed, idled perfect but under and type of load knocked and backfired like the engine was toast.
     
  7. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    I can see it on the cap, 1-8-4-3...etc Looks like # 1 is routed to the correct side of the engine, so is #8...where/why does the 3rd plug wire go to an odd bank?
     
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  8. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    Its got the original pressed on 283 balancer. It doesn't seem to be loose, and even running, there's no evidence of wobble at all. I'm going to pull the distributor tomorrow and reset it to see if I'm maybe a tooth off and can come up with the right position.
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  9. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    Look up...check plug wire routing...

    SBC is 1-8-4-3-6-5-7-2

    I see 1 and 8 correct, I see next wire going to the wrong side of the engine. Just looking at your cap in hand, normally facing he window, 1 is on the right of the window, the 8 to the left. The rotor turns clockwise, so fires 1, then 8, then...
     
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  10. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,600

    Johnny Gee
    Member
    from Downey, Ca

    While out look to see if bushing that limit's mechanical advance is still there. The reason I asked what balancer is because late model ones are keyed differently and throws off timing mark.
     
  11. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    #1 is actually where my thumb is in that photo. This is why I think I may have made an error when i dropped in my distributor. It ran rough as a cob before I moved the wires over to those positions. I pulled the cap and saw that the rotor on TDC was pointing so far over and adjusted the wire positions accordingly.
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  12. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    Johnny, are you referring to late model distributors? I got a brand new one a year ago. Are you saying that could that have changed my timing mark? That may account for some of my issue. The more I read and the more I see in my motor, I think I may have a detonation issue and thats a result of timing.
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  13. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    He’s referring to the mark for TDC on the balancer, there are 3 different ones for SBCs as I recall. The bushing in the distributor he.is talking about limits mechanical advance in the distributor. Ie if the distributor has 22 degrees of advance, and the bushing(s) we’re missing, it could add another 10-12? Degrees of advance
     
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  14. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    The bushings in the distributor are not something im familiar with. Most likely because my dad never was comfortable with electrical, so never taught me anything beyond points and wire position. I don't even know what to look for.

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  15. Last thing worked on, first thing checked. One of the Golden Rules at work.


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  16. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,600

    Johnny Gee
    Member
    from Downey, Ca

    What Budget36 said.

    This bushing.
    upload_2020-10-14_11-11-25.jpeg
     
  17. greybeard360
    Joined: Feb 28, 2008
    Posts: 2,074

    greybeard360
    Member

    You never said but did you verify you had the firing order correct?
    Another thing that can cause some of this is a head gasket blown between cylinders. Have you done the compression test yet?

    You ask for advice and doing BASIC diagnosis(vacuum, timing, compression) can tell a lot about what is going on. Pulling the oil pan isn't one of them.

    Go back to the basics and report in. If you don't know how to do them, ask a friend that does or take it to a mechanic. This is high school stuff. I hate to sound harsh, but if you can't do the basics, you don't need a hot rod.
     
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  18. Dick Stevens
    Joined: Aug 7, 2012
    Posts: 3,710

    Dick Stevens
    Member

    It sure looks like the plug wires are not right, on a SBC the firing order is 1,8,4,3,6,5,7,2 and the distributor rotates clockwise! Get the plug wires in the correct order before you do anything else!
     
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  19. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    I have checked and double checked (and again) my plug wire order. I'm happy to do it again because when something is off, im happy to redo it all.

    Greybeard - I had compression tested this last year and all cylinders tested comparatively, so im not really afraid of a blown head gasket. Although it still is possible even though I've not run it much since. I dropped the pan because I had a bad leak and needed to replace the pan gasket, so I wanted to make sure I checked what I could while it was out. I'll be tuning it today and running with the valve covers off to check for sticky valves and bad springs. Im just confused why TDC ends up on the terminal after the window on the distributor cap I stead of before.
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  20. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,212

    Elcohaulic

    This bushing was designed to help older GM cars blow holes in the pistons so they end up in the junk yard sooner..
    When GM made the mistake of firing Herb Adams all there dirty little secrets started coming out..
    Herb was fired for intentionally not putting the intended defects into the frame and chassis molds. He thought the GM exects would be happy that the new cars handled so well and they would sell a lot more... But turns out they didn't want the Malibu, F-85, etc.. riding and handling as good as the Coupe Deville... I was told this by a very well respected suspension engineer/designer who specializes in GM A body suspensions.. I remember driving my brothers new 74 GTO 400 4 speed. Wow did that car handle and so did my cousins new 74 Malibu. It had this crazy looking bar across the bottom of the rear end, I never saw one of those before.. I started out with bia plys, three on the tree, manual steering and brakes. Hmm remember when we were all so happy being able to do 80-90. Actually those GTOs and Hemi Cudas ruined the hot rod scene..



    [​IMG]
     
    Last edited: Oct 14, 2020
  21. Dick Stevens
    Joined: Aug 7, 2012
    Posts: 3,710

    Dick Stevens
    Member

    That comes from where the rotor was pointing when you installed the distributor and that doesn't really matter, just that you have the firing order right and that you have it timed right.
     
  22. Johnny Gee
    Joined: Dec 3, 2009
    Posts: 12,600

    Johnny Gee
    Member
    from Downey, Ca

    And if no bushing matter's get even worse. While I never destroyed the engine in my off topic Chevelle I did chase a dull knock for nearly a year then I just let the car set. One day I pulled distributor out of the Chevelle and put it in another car. BAM!!! the other car knocked as well. Two plus two equal...
     
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  23. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    Ok, so new question. Having that single plane manifold creates other tuning challenges on such a small bore motor. One of my dads old hot rod buddies said that it would be necessary to advance timing far more than normal to get it to run right. If that's the case, how far? 10-12 BTDC is normal and anything more is off the tab. Really makes me question my ability to time it correctly.

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  24. Elcohaulic
    Joined: Dec 27, 2017
    Posts: 2,212

    Elcohaulic

    That little piece of plastic makes a world of difference.. I never knew about it until one day I had two distributors side by side at the junk yard and noticed one had the bushing and one didn't. The one that had it was demolished, the one that didn't had a blown motor. It was a Olds 98 455, 1970 too, high compression, 90 octane, nice big air conditioning compressor, 5000 pounds of luxury car and 55 degrees of mechanical timing will do it..
     
  25. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    99% of the guys working on engines cannot accurately set the timing on an engine without a timing light. You can get it close with the vacuum gauge though.

    I've pulled the distributor back out and moved the rotor and brought the engine back up on compression on #1 and realigned the rotor with #1 on the cap time and time again to avoid rotating the wires in the cap. That is something I just flat won't do and hate following behind someone who did.

    Flexplate or loose torque converter bolts. They usually knock/rattle at an idle with no load and quiet down with a load. Just dropping it in gear with the tires off the ground and no load against the driveline would not be under load if the tires were able to turn.

    I'd still run the compression test; Take all 8 plugs out and prop the throttle and choke wide open and let each cylinder hit 5 times on the gauge and record your readings. Along with decent pressure you are looking for even pressure across the cylinders or within 10 to 15 lbs high to low. The closer the reading is to each other the better.

    Never upon never change more than one thing at a time when you are trying to trouble shoot and it is best to just take it to someone with more knowledge to have it checked rather than just trying this and trying that.
     
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  26. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    When you put things back together, run the GM intake. Keep an eye out for an Edelbrock performer. Good intakes and used in the 50-100 Range
     
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  27. Jmountainjr
    Joined: Dec 29, 2006
    Posts: 1,672

    Jmountainjr
    ALLIANCE MEMBER

    I would verify TDC #1 compressio stroke with a piston stop and confirm that the damper timing mark is showing TDC on the pointer. They have to be in sync. You can install the distributor anyway you want and make any cap position #1 as long that's the position that is going to fire #1 on your damper pointer and the plug wires are installed in the correct order after the #1 position. Any SBC should start and run with 8 to 10 degrees initial advance assuming a correctly functioning distributor.
     
    Last edited: Oct 14, 2020
  28. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    Ok, as everyone said, go back to the beginning. This discussion earlier about the distributor made me question everything about mine. I pulled it and noticed that the points were not even working right(or not at all really). I could not adjust them where I needed them and the spring was HEAVY. I think my dad got the wrong points set and I didn't even think about it. I replaced them and then noticed that I had dropped the distributor in the wrong position to begin with at TDC. I reset TDC(verified 4 times) and re-dropped the distributor in the correct position. She now runs rough and has a pronounced valve clatter, so it seems lash is off.

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  29. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    You're getting there, does your balancer have a mark on it? If so, put a timing light on it at verify timing. Then keep it at idle and set the valves, start at # 1, when it stops clattering, go 3/4 a turn more...continue, if one isn't clattering, back it off till it does, and repeat the process.

    Some say 1/4 turn, etc. GM set's them up on the engine line at zero lash +1 turn, I assume I always went a tad past zero when stopping the clatter, tis why I go 3/4.
     
  30. BowtieGoofy
    Joined: Feb 13, 2019
    Posts: 74

    BowtieGoofy

    I tried to set a towel off to the side and made a mess...lol. I'll have to get some junk valve covers and cut the center out so I don't repaint my engine bay in 10w-30.
    Sent from my SM-G970U using The H.A.M.B. mobile app
     
    Budget36 likes this.

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