![]() |
|
![]() |
#1 |
Registered User
Join Date: Jun 2017
Location: Austin TX
Posts: 12
|
Loud knock at idle!!
I have my 71 c10 with 454 swap in it. Today I was making a dump run and when I pulled into the bay to dump my trash I noticed a knock that just got louder and louder.
Metal on metal, quite loud and irregular. Like something is floating around bagging side to side. I pulled out of the dump and drove her home and noticed that there’s no knock or any irregular sounds when she’s under load. Just while idling... Any ideas what this could be??? Thanks guys Posted via Mobile Device |
![]() |
![]() |
![]() |
#2 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,217
|
Re: Loud knock at idle!!
It might be something got into a cylinder. A hunk of carbon might have broke loose or an object came out of the carb or air filter. Also a fuel pump can make a noise like that.
George |
![]() |
![]() |
![]() |
#3 |
Registered User
Join Date: Nov 2014
Location: Bigfork, Montana
Posts: 1,137
|
Re: Loud knock at idle!!
Well, let's hope it's not in the motor. The first things I'd check are the exhaust pipes, BB exhaust can be a tight fit, the motor moves around causing it to hit. On that note, check the motor/trans mounts. (The BB trucks have different engine stands on the crossmember to give more clearance, if you used SBC stands things are going to be tight)
Check the torque converter bolts. Wrong bolts (too long) will bottom out & be tight but the converter is still loose. Also inspect the flex plate for cracks. I have had several flex pates crack over the years. they can cause odd, irregular sounds. |
![]() |
![]() |
![]() |
#4 | |
Registered User
Join Date: Jun 2017
Location: Austin TX
Posts: 12
|
Re: Loud knock at idle!!
Ok this is helpful. I don't think it's inside the motor since it runs perfect when accelerating or just cruising. It's when it's idling that it sounds like plate is getting bounced up and down, side to side, with no measurable rhythm. Its very loud too... like a ball bearing bouncing around a metal cup. I certianly hope is a motor mount or something to that nature.
Quote:
|
|
![]() |
![]() |
![]() |
#5 |
Senior Member
![]() Join Date: Mar 2003
Location: Colfax-California
Posts: 8,550
|
Re: Loud knock at idle!!
My money is on a cracked flex plate (flywheel) or loose torque convertor bolts
|
![]() |
![]() |
![]() |
#6 |
Registered User
Join Date: Jun 2017
Location: Austin TX
Posts: 12
|
Re: Loud knock at idle!!
|
![]() |
![]() |
![]() |
#7 |
Registered User
Join Date: Jan 2011
Location: Chattanooga, TN
Posts: 2,151
|
Re: Loud knock at idle!!
me too.
__________________
'83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project |
![]() |
![]() |
![]() |
#8 |
Registered User
Join Date: Oct 2008
Location: Marianna Arkansas
Posts: 7,270
|
Re: Loud knock at idle!!
My first thoughts were flexplate or converter bolts also
|
![]() |
![]() |
![]() |
#9 |
Registered User
Join Date: May 2017
Location: Parker, CO
Posts: 130
|
Re: Loud knock at idle!!
I had a 350 once that the flexplate bolts would loosen up over time. Just unbolted the torque converter and it would move back far enough to get to the flexplate bolts with a wrench. The knocking was only at idle and sounded very close to the noise a rod would make.
__________________
72 Chevy C10 383/465 69 Corvette convertible 454/650 |
![]() |
![]() |
![]() |
#10 |
Registered User
Join Date: Jun 2017
Location: Austin TX
Posts: 12
|
Re: Loud knock at idle!!
I figured out the problem is but I don’t know how to fix it. There’s a floating crankshaft bearing that’s just rattling back and forth. See video link.
I don’t understand the purpose of this part or how to make it stay put. Any insight ?? https://youtu.be/jfw1vDFuz5c |
![]() |
![]() |
![]() |
#11 |
Registered User
Join Date: Jan 2011
Location: Chattanooga, TN
Posts: 1,108
|
Re: Loud knock at idle!!
That is your harmonic balancer. It absorbs engine vibrations and you do need to replace it. There is supposed to be a rubber ring between the sections of metal. It is missing. You will have to remove the crankshaft pulley and belt and remove the large crankshaft bolt that holds the balancer (or dampener) and remove it using a wheel pulley.
I would replace it with a new, quality balancer. Summit Racing sells nice ones as well as NAPA. I would pick up a new keyway too to replace the old one. I hope this helps.
__________________
2016 RAM Laramie HEMI 1966 Fairlane GT/A, 390/335 HP If it costs you a dollar to make a friend, KEEP THE DOLLAR. If it costs you a friend to make a dollar, KEEP THE FRIEND. |
![]() |
![]() |
![]() |
#12 |
Registered User
Join Date: May 2017
Location: Parker, CO
Posts: 130
|
Re: Loud knock at idle!!
i would also replace the seal in the timing cover. Use a install tool to put the new balancer in as well. Most auto parts places like O'Rielley's have a tool loan program so you don't have to buy these.
__________________
72 Chevy C10 383/465 69 Corvette convertible 454/650 |
![]() |
![]() |
![]() |
#13 |
Registered User
Join Date: Jun 2017
Location: Austin TX
Posts: 12
|
Re: Loud knock at idle!!
Thanks guys. I think I’ll just hire someone to do the work since this is going to take some special tools and a good amount of time.
Thank you so much for the help |
![]() |
![]() |
![]() |
Bookmarks |
|
|