Engine Knock on fresh rebuild - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Locutus · 12-12-2004, 05:49 PM

Today we fired up the engine for the first time and ran it thru the break in. After we came back from lunch we fired it up again and it has developed a knock when I let off the gas. It not advanced and I don't think it is detonation since it only seems to do it when you let of the gas. Any ideas what it could be??? I already fear we are doomed to pull the engine and have to start over

cableguy0 · 12-12-2004, 05:52 PM

check the torque convertor bolts and just look for anything else that might be loose if you dont find anything. dont risk it and just pull the engine out its cheaper to fix now than after a catastrophic failure. also does the engine have good oil pressure?

Cat Fuzz · 12-12-2004, 07:21 PM

I was also thinking flexplate bolts. Gotta use thread locker on those or they will come loose and create quite a racket.

dwaite72lnghrn · 12-12-2004, 07:25 PM

If it knocks when you let off it might be a rod bearing. drain the oil and look for silver in it.

Brainchild · 12-12-2004, 07:35 PM

My first thought was converter bolts also.Lets hope for something easy

cableguy0 · 12-12-2004, 07:40 PM

i actually had something similar happened sounded definately like a rod knock turned out we blew the torque convertor b4 it got outta the garage power braking it. thought for sure the motor was done right then and there with 40 minutes running time on it till i unbolted the convertor

rodnok1 · 12-12-2004, 08:07 PM

It could be a wrist pin, take the plug wires off one by one and see if it clears up. A rod bearing should double up.

Broken_down? · 12-12-2004, 08:08 PM

I have the opposite from what cable was saying. Mine knocks when I get going about 35 to 40mph. The timing is not advanced dwell fine/rpm when I left off it stops knocking. I was just under the truck today and torque is not bad flex is not loose and the oil does not have any silver in it. any other ideas?

Rich

shortymac83 · 12-12-2004, 08:41 PM

is it definitely coming from the bottom of the motor? what is the oil pressure? If it's coming from the top, maybe you have an oil passage plugged and a lifter or rocker isn't getting any oil. If it's coming from the bottom, check the flexplate and torque converter first.

Broken_down? · 12-12-2004, 11:06 PM

mine personally has oil pressure in the 20 range for about 10 mins or so after sitting all night. Once it has warmed up it drops to 0 unless it is idleing down hill in which case it is about 5 to 10. Sounds like a lower knock.

Rich

68C15 · 12-12-2004, 11:49 PM

was this a engine kit from Northern Auto Parts? I have done 5 engines so far with no problem until I bought from them for the most recent one. has a knock at first startup after oil change & also when sitting from a heat soak. also has a floating wrist pin noise upon decell about 1100-1500 RPM. they also sent me stock lift springs to go with the cam (cam is a 435-465 lift). I asked them what they will do & they said they would sell me new parts (no discount)
check the converter bolts before a complete tear-down.

Locutus · 07-31-2005, 04:49 PM

Ok I haven't messed with this in months I was so frustrated by the engine knock. Could it be a stuck lifter if it only starts to knock after it warms up? Plus oil pressure seems a little low at idle but also only when it warms up.

bigjimzlll · 07-31-2005, 05:23 PM

If it only starts to knock after it warms up(thins the oil) then your looking at a rod bearing. It could be a lot of things..forgotton to tighten up the rod bolts..impropper installation of bearings...dirt under bearing cap(my vote) or impropper machine work.

**VetteVet** · 07-31-2005, 08:17 PM

Look at this website.

http://remanufactured.com/Engine_Noi...gnosis_101.htm

GMC AMI · 08-01-2005, 05:57 AM

Always check bearing clearance on any motor before installing as a cheap insurance.
I learned this lesson of Hard Knocks!

12-12-2004, 05:49 PM	#1
Locutus Registered User Join Date: Jan 2003 Location: Santa Fe, Texas Posts: 250	Engine Knock on fresh rebuild Today we fired up the engine for the first time and ran it thru the break in. After we came back from lunch we fired it up again and it has developed a knock when I let off the gas. It not advanced and I don't think it is detonation since it only seems to do it when you let of the gas. Any ideas what it could be??? I already fear we are doomed to pull the engine and have to start over

12-12-2004, 05:52 PM	#2
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	check the torque convertor bolts and just look for anything else that might be loose if you dont find anything. dont risk it and just pull the engine out its cheaper to fix now than after a catastrophic failure. also does the engine have good oil pressure? __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

12-12-2004, 07:25 PM	#4
dwaite72lnghrn Registered User Join Date: Jun 2002 Location: central pa Posts: 1,525	If it knocks when you let off it might be a rod bearing. drain the oil and look for silver in it. __________________ 72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne

12-12-2004, 07:35 PM	#5
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	My first thought was converter bolts also.Lets hope for something easy __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

12-12-2004, 07:40 PM	#6
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	i actually had something similar happened sounded definately like a rod knock turned out we blew the torque convertor b4 it got outta the garage power braking it. thought for sure the motor was done right then and there with 40 minutes running time on it till i unbolted the convertor __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

12-12-2004, 07:21 PM	#3
Cat Fuzz My son, my joy. Join Date: Sep 2003 Location: Spokane WA Posts: 463	I was also thinking flexplate bolts. Gotta use thread locker on those or they will come loose and create quite a racket.

12-12-2004, 08:07 PM	#7
rodnok1 Registered User Join Date: Jun 2003 Location: Linden, North Carolina Posts: 617	It could be a wrist pin, take the plug wires off one by one and see if it clears up. A rod bearing should double up. __________________ 64 Panel Rebuild Pics Clutch Replacement and Borg Warner T10 Trans Rebuild 64 Panel 1/2 Ton 350cubes/400hp BorgWarner t-10 3:73 Auburn Posi

12-12-2004, 08:41 PM	#9
shortymac83 hmm... Join Date: Jan 2004 Location: Culver, Indiana Posts: 1,631	is it definitely coming from the bottom of the motor? what is the oil pressure? If it's coming from the top, maybe you have an oil passage plugged and a lifter or rocker isn't getting any oil. If it's coming from the bottom, check the flexplate and torque converter first. __________________ 1983 Oldsmobile Delta 88 1967 Chevy C-10 stripper www.fcrperformance.com - wanna go...faster? talk to FCR.

12-12-2004, 11:49 PM	#11
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	was this a engine kit from Northern Auto Parts? I have done 5 engines so far with no problem until I bought from them for the most recent one. has a knock at first startup after oil change & also when sitting from a heat soak. also has a floating wrist pin noise upon decell about 1100-1500 RPM. they also sent me stock lift springs to go with the cam (cam is a 435-465 lift). I asked them what they will do & they said they would sell me new parts (no discount) check the converter bolts before a complete tear-down. __________________ Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card

07-31-2005, 04:49 PM	#12
Locutus Registered User Join Date: Jan 2003 Location: Santa Fe, Texas Posts: 250	Ok I haven't messed with this in months I was so frustrated by the engine knock. Could it be a stuck lifter if it only starts to knock after it warms up? Plus oil pressure seems a little low at idle but also only when it warms up.

07-31-2005, 05:23 PM	#13
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	If it only starts to knock after it warms up(thins the oil) then your looking at a rod bearing. It could be a lot of things..forgotton to tighten up the rod bolts..impropper installation of bearings...dirt under bearing cap(my vote) or impropper machine work. __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

07-31-2005, 08:17 PM	#14
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,717	engine noises Look at this website. http://remanufactured.com/Engine_Noi...gnosis_101.htm __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

08-01-2005, 05:57 AM	#15
GMC AMI Registered User Join Date: Apr 2004 Location: The Other Maine! Posts: 2,236	Always check bearing clearance on any motor before installing as a cheap insurance. I learned this lesson of Hard Knocks! __________________ 1968 Chevy 4x4 307 4 speed Last edited by GMC AMI; 08-01-2005 at 05:58 AM.



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