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#1 |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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First motor start, terrible knocking
Fired up the motor today for the first time to hear a horrendous, fast-paced knocking. We quickly shut her down and pulled off valve covers, but didn't see anything obvious.
Engine was partially rebuilt. I pulled the heads off for a valve job but didn't touch the cam or pistons. This sound did not exist prior to tear down. I'll be pulling the pan tomorrow but was wondering if anyone knew immediately what may be producing this knocking? https://youtu.be/VAxGZIOPXL0
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1972 C/20 LWB, 350/350 |
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#2 |
Senior Member
![]() Join Date: Dec 2013
Location: Gods country East,Tn
Posts: 8,545
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Re: First motor start, terrible knocking
Did you soak / fill the lifters before you installed them ?
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![]() 1967 Factory short bed - Old school '71 - 350 / 4bolt / 487 heads / Edelbrock C3BX Muncie M-22 4 speed / Hurst Comp plus Factory 12 bolt posi 3.73 / 255-70-15 Smoothed firewall / Factory cowl induction Power disc brakes / power steering / 3.5-5" drop |
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#3 |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
I did soak the lifters for a couple hours before installing. Then the motor sat for a couple months before firing up.
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1972 C/20 LWB, 350/350 |
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#4 |
Registered User
![]() Join Date: Sep 2015
Location: Charleston, WV
Posts: 228
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Re: First motor start, terrible knocking
Total shot in the dark, but you might check as a last resort that the fly wheel is tight. I built a flathead once and the bolts on the flywheel were just a little too long and bottomed out. Could be the flywheel needs tightening.
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Steve My Build Thread: http://67-72chevytrucks.com/vboard/s...=morning+glory 1971 C10 Inline 6 250 700R4 "Marlene" 1934 Chevrolet Master Sedan 350 700R4 "Iris" 1941 Ford 1/2 Ton 5.0 H.O Roller C-4 "Rose" 2019 Honda Ridgeline |
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#5 |
Senior Member
![]() Join Date: Jan 2001
Location: Orem, Utah
Posts: 7,915
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Re: First motor start, terrible knocking
Are you missing any nuts? A nut bouncing around on too of a piston sounds just like that. (Ask me how I know.)
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#6 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: First motor start, terrible knocking
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#7 |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
Is there a way to check this without pulling the motor? The valve job was done at a pretty reputable machine shop but I'll be calling them immediately if this is the case.
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1972 C/20 LWB, 350/350 |
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#8 | |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,622
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Re: First motor start, terrible knocking
Quote:
Whatever amount of turn you last put on the rocker nuts, just back them off half that amount. If you did one turn, back them off 1/2 turn. That way the lifters are still quiet. Or it might be just as easy to re run them. |
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#9 |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
We aren't missing any that I know of and were extremely careful to avoid this when putting everything back together. I would be really surprised if this was the culprit but it's worth looking into.
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1972 C/20 LWB, 350/350 |
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#10 |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
I actually never removed the flywheel but I'll check today to see if it's loose.
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1972 C/20 LWB, 350/350 |
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#11 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: First motor start, terrible knocking
Did you pull the distributor and prime the oil system before firing?
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#12 |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
I turned the motor over a few times while working on electrical before priming the oil system and firing the motor up for more than a few seconds. Is it possible I damaged something doing this?
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1972 C/20 LWB, 350/350 |
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#13 | |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: First motor start, terrible knocking
Quote:
Have you drained any of the oil to look for "glitter" (metal shavings). With everything you've described, I'm wondering if you have a bent rod or valve.
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#14 | |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
Quote:
When I tore down the engine, I found a single bent push rod and replaced it. I wonder if I should have just replaced all the push rods.
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1972 C/20 LWB, 350/350 |
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#15 |
All about them K’s
![]() Join Date: Jun 2014
Location: Land of Entrapment
Posts: 6,393
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Re: First motor start, terrible knocking
Any chance the valves are adjusted wrong?
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Tyler '57 3100 http://67-72chevytrucks.com/vboard/s...d.php?t=813888 '72 K20 Cheyenne: 5” lift, 35’s, front dana 60 blah blah blah… http://67-72chevytrucks.com/vboard/s...d.php?t=662879 ‘69 K10 SWB: 4” lift 33”s… in a million pieces http://67-72chevytrucks.com/vboard/s...d.php?t=805206 '98 Silverado LT K2500HD ECLB Vortec 454/4l80E: 6" lift 315/75/16's |
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#16 |
Registered User
Join Date: Sep 2016
Location: Vancouver BC
Posts: 784
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Re: First motor start, terrible knocking
If you disconnect the coil wire, then crank the engine, does it sound normal? If it does, I'd then do a compression test to see if the piston and valve action is correct.
If all that pans out, you might want to try starting it with the rocker covers off, to see if oil is getting up to the top, and isolate any sounds. If you are the really careful type, you'll disassemble the engine, and check everything, including the stuff mentioned above. This is the slow, but possibly cheapest way to go.
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Rick -69 GMC 910 Long Box, 350 -98 Chev Silverado 1500, 350 Vortec 4L60e -08 Mustang GT Convertible |
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#17 | |
Registered User
Join Date: Nov 2012
Location: Mexico, NY
Posts: 559
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Re: First motor start, terrible knocking
Quote:
What did you all have done to the heads? If he cut the valve seats did he shorten the stems too? Did he deck the heads, how much? What is your quench distance? What pistons are you running, flat/dished/dome?
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'84 K10, SM465, NP208, 3.42 Gears, 33x12.5-15 GM 4 bolt 880 roller block, 062 Vortec Heads Comp Cams XR258HR-10, MSD Street Fighter HEI Edelbrock: Performer Intake 2116, 1405 Carb Long tube headers, 2.5" duals to Flow Master Super 40's Vortec Engine Build |
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#18 | |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
Quote:
I had the original heads magnafluxed and they were found to have hairline cracks, so the machine shop give me a different set of heads and performed the valve job on those.
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1972 C/20 LWB, 350/350 |
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#19 | |
Registered User
Join Date: Nov 2012
Location: Mexico, NY
Posts: 559
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Re: First motor start, terrible knocking
Quote:
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'84 K10, SM465, NP208, 3.42 Gears, 33x12.5-15 GM 4 bolt 880 roller block, 062 Vortec Heads Comp Cams XR258HR-10, MSD Street Fighter HEI Edelbrock: Performer Intake 2116, 1405 Carb Long tube headers, 2.5" duals to Flow Master Super 40's Vortec Engine Build |
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#20 | |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
Quote:
Using flat top pistons. I do not know how much deck clearance I had or what the cam is.
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1972 C/20 LWB, 350/350 |
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#21 |
Senior Member
![]() Join Date: Mar 2012
Location: Chesapeake, Va
Posts: 1,275
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Re: First motor start, terrible knocking
.039 thickness as stated
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Mike 72 C-10 Cheyenne off frame resto and Upgraded to 4 wheel disk, Tilt, Dakota Digital Dash / Rear slider. 421 SBC / TH350 3000RPM Stall Progression Ignition /Holley 750 DP/3:73 gear Eaton Limited Slip unit / 2 1/2 exhaust glasspacks ![]() |
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#22 |
Farmtruck desciple
Join Date: May 2009
Location: 90605
Posts: 158
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Re: First motor start, terrible knocking
Always start with the easy low cost stuff before tearing everything all apart;
In order - 1) Rent a bore-scope. Pull the spark plugs and look inside all of the cylinders for loose parts and scarred pistons from valves touching. Also check the oil pan if it's emptied of oil for loose parts. 2) Confirm all of the valve retainers are in place. Confirm the pushrods are equal length and in place. 3) Use a long screwdriver and electric drill to prime the oil system from the distributor shaft hole. 4) Re-adjust the rockers - adjust all to zero lash plus 1/3 turn, turn the motor 45 degrees and re adjust. Do this 6-8 times turning the motor 45 degrees each time you adjust. 5) Confirm firing order / plug wires. 6) Check all ancillary equipment (alternator, A/C, power steering, flywheel, clutch or torq convertor, etc) for proper installation or loose parts. 7) Check oil level. Try starting 'er again. |
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#23 |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
I will start going down that checklist, suprachrgd82. Thank you.
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1972 C/20 LWB, 350/350 |
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#24 |
Registered User
Join Date: Jul 2001
Location: Youngstown, OH
Posts: 95
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Re: First motor start, terrible knocking
I had a valve get stuck in the guide once after an engine rebuild and waiting a few months to fire engine. The valve bent and hung open creating dead cylinder condition. Had to pull head and replace valve and the guide to remedy. check compression to see if a cylinder is way off from others.
Was the water pump replaced? Someone advised check ancillary components or remove them from equation when restarting engine. |
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#25 | |
Registered User
Join Date: Dec 2015
Location: San Diego, CA
Posts: 51
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Re: First motor start, terrible knocking
Quote:
I did not replace the water pump. Just cleaned it, painted it and put it back on.
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1972 C/20 LWB, 350/350 |
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