Engine Noise - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dave2953 · 07-06-2006, 09:41 PM

I have an unusual engine noise that I'm can't seem to diagnose. I have a 68 c10 with an 86 305. The noise is sort of a rapping noise, like a rod knocking. The noise is most pronounced when there is a load on the engine, like if you're headed uphill and let off the accelerator. I took the oil pan off and found no metal, etc. I haven't checked the bearings yet because I wasn't sure what to look for when I got them apart. I know it could be a million things, but I don't really know where to start. Thanks for any help you can provide.

*rage'nrat638* · 07-06-2006, 09:49 PM

305's are know for lifter problems..bad cams,
might be time to start looking for that 350 sbc. while she's still running.
not trying to be a d _ _ k, just speaking the truth.
hope you get this worked out

**Boog** · 07-06-2006, 10:36 PM

305's are well known for timing woes (detonation). They don't take advance well. Pinging under acceleration or part throttle with regular grade gas.
Retard the timing a few degrees or run highest grade gas in it and see if it makes any difference. Carbon buildup on the tops of the pistons can also cause some knock type sounds. The factory installed knock sensor is an engine saver for the 305's.

**VetteVet** · 07-06-2006, 11:20 PM

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

Go here and it may give you some ideas.

**Ron 586** · 07-06-2006, 11:45 PM

Check for a loose or cracked flex plate. It has fooled a lot of people and it don't cost anything but a little time.

grayw0lf · 07-07-2006, 02:17 PM

I have similar noises from the '84 305 in my 70 C-10. Readjusting the valve lash & running 20w50 helped a bit.

dave2953 · 07-07-2006, 05:06 PM

Thanks for the suggestions. Since I have the oil pan off I'm going to replace the oil pump. I figure it's cheap insurance. I checked the flexplate but didn't find anything loose/broken. I'll check the valve adjustment tomorrow and drive her and see what happens.

cdowns · 07-07-2006, 05:15 PM

another place i've found a knock is from a worn harmonic balancer alot of times looking at it running it will have a wobble to it

**john** · 07-07-2006, 07:28 PM

You can open the oil filter and check for metal if you are concerned with the bearings.

355 · 07-08-2006, 07:42 AM

I had a lifter sort of sound, it had a thudier sound though, adjusted the lifters and it would not go away. Listened for it thru a christmas wrapping tube to find the pinpoint and it was all over the block. To make this short it was the fuel pump spring had broken and the slider was being hit by the cam lobe and enough spring left to throw it back. SC

tcoop68 · 07-08-2006, 11:34 PM

It is possible if your motor has a lot of miles on it,it could be piston slap on your cylinder.If you drain your oil and get in direct sunlight you should be able to see metal flakes in your oil if its a bearring,also could be a wrist pin on a piston.You should go ahead and try to find a 350 and do away with your 305 anyway,thats what I have done in the past.You will getter figured out stay with it.

07-06-2006, 09:41 PM	#1
dave2953 Dave's not here, man Join Date: Jun 2004 Location: Winder, Georgia Posts: 2,000	Engine Noise I have an unusual engine noise that I'm can't seem to diagnose. I have a 68 c10 with an 86 305. The noise is sort of a rapping noise, like a rod knocking. The noise is most pronounced when there is a load on the engine, like if you're headed uphill and let off the accelerator. I took the oil pan off and found no metal, etc. I haven't checked the bearings yet because I wasn't sure what to look for when I got them apart. I know it could be a million things, but I don't really know where to start. Thanks for any help you can provide. __________________ - 2014 VW Jetta - 2015 VW Jetta - 1966 Ford F-250

07-06-2006, 09:49 PM	#2
rage'nrat638 Account Suspended Join Date: Mar 2003 Location: THE FALL GUY CHICAGO IL Posts: 5,883	Re: Engine Noise 305's are know for lifter problems..bad cams, might be time to start looking for that 350 sbc. while she's still running. not trying to be a d _ _ k, just speaking the truth. hope you get this worked out

07-06-2006, 10:36 PM	#3
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,453	Re: Engine Noise 305's are well known for timing woes (detonation). They don't take advance well. Pinging under acceleration or part throttle with regular grade gas. Retard the timing a few degrees or run highest grade gas in it and see if it makes any difference. Carbon buildup on the tops of the pistons can also cause some knock type sounds. The factory installed knock sensor is an engine saver for the 305's. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

07-06-2006, 11:20 PM	#4
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,717	Re: Engine Noise http://remanufactured.com/Engine_Noi...gnosis_101.htm Go here and it may give you some ideas. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

07-06-2006, 11:45 PM	#5
Ron 586 RIP Mr Ron Join Date: Dec 2005 Location: Big Sandy, Tn. 38221 Posts: 8,166	Re: Engine Noise Check for a loose or cracked flex plate. It has fooled a lot of people and it don't cost anything but a little time. __________________ Ron (Mr Round Tuit) Be kinder than necessary, for everyone you meet is fighting some kind of battle TN Message Forum TN Facebook Group SETN Truck Show My Photobucket

07-07-2006, 02:17 PM	#6
grayw0lf Registered User Join Date: Apr 2004 Location: Clanton, AL Posts: 1,253	Re: Engine Noise I have similar noises from the '84 305 in my 70 C-10. Readjusting the valve lash & running 20w50 helped a bit. __________________ 85' CUCV M1009!!! The newest addition! 6.2diesel, Th400, NP208, & only 36k miles! 70' C-10 LWB Fleetside - Looking good these days! 05' Dodge Neon 88' Winner Escape Sport 1750 - 4.3v6 94' Seadoo SP 84' Honda TRX200, bare nekkid. Just a frame & tires. Always looking for another project or any good deal!

07-07-2006, 05:06 PM	#7
dave2953 Dave's not here, man Join Date: Jun 2004 Location: Winder, Georgia Posts: 2,000	Re: Engine Noise Thanks for the suggestions. Since I have the oil pan off I'm going to replace the oil pump. I figure it's cheap insurance. I checked the flexplate but didn't find anything loose/broken. I'll check the valve adjustment tomorrow and drive her and see what happens. __________________ - 2014 VW Jetta - 2015 VW Jetta - 1966 Ford F-250

07-07-2006, 05:15 PM	#8
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Engine Noise another place i've found a knock is from a worn harmonic balancer alot of times looking at it running it will have a wobble to it __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

07-07-2006, 07:28 PM	#9
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Re: Engine Noise You can open the oil filter and check for metal if you are concerned with the bearings. __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/

07-08-2006, 07:42 AM	#10
355 Registered User Join Date: May 2005 Location: South Mississippi Posts: 81	Re: Engine Noise I had a lifter sort of sound, it had a thudier sound though, adjusted the lifters and it would not go away. Listened for it thru a christmas wrapping tube to find the pinpoint and it was all over the block. To make this short it was the fuel pump spring had broken and the slider was being hit by the cam lobe and enough spring left to throw it back. SC __________________ 1969 C10 Long Step,355,700r4w/lockup, HEI,Weiand,750 Performer,1.6 rockers,Camel Humps,Comp 262Extreme,Hedman,2 1/2"pipes, tele/tilt,SunRoof,ps,Disc pb,ac,Cragar,eaton,Corvette style roll pan, Bowtie louvered tail gate,lowered 2/2.

07-08-2006, 11:34 PM	#11
tcoop68 tcoop68 Join Date: Jan 2006 Location: Cushing Oklahoma Posts: 226	Re: Engine Noise It is possible if your motor has a lot of miles on it,it could be piston slap on your cylinder.If you drain your oil and get in direct sunlight you should be able to see metal flakes in your oil if its a bearring,also could be a wrist pin on a piston.You should go ahead and try to find a 350 and do away with your 305 anyway,thats what I have done in the past.You will getter figured out stay with it.



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