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From: jim on 9 Jul 2010 20:22 willy wrote: > On Jul 9, 1:26 pm, jim <"sjedgingN0Sp"@m(a)mwt,net> wrote: > > > Does the vibration damper (crankshaft pulley) look like it is running > > true? or does it wobble? Rubber does tend to fall apart after 35 years > > and they can knock when that happens. > > > > -jim > > On a that year engine, the vibration damper, (harmonic balancer), and > the crankshaft pulley are two separate pieces. They may be two pieces but they are not separate. They're bolted together. > > > Never had one make a "knocking" sound on a small block Chevy. Never > had one come apart. The outer part of the balancer will "spin", > throwing the timing mark off, or, if on a 400 small block, it will > make the engine vibrate. I agree that the odds are not good that the noise is coming from the vibration damper, but unlikely as it may be, if that is the problem it should be something the OP can find an fix. He made it pretty clear that he isn't going to be able to deal with anything that involves tearing the engine down. > > > Even if the outer ring slid all the way back, it won't make a knocking > noise. It will make a "scraping" sound. (hits the "tin" timing chain > cover) If the rubber is that bad, the ring would come of. Usually the > rubber dry rots or gets soft from people putting the balancer in the > parts washer. The solvent softens the rubber. I could be wrong but it is my recollection that the outer ring can't come off to the timing chain cover side. If the outer ring is going to come off the inner hub, it will go the other way and knock against the pulley. -jim > > > A "knocking" sound, coming from the bottom, and going away at constant > RPM is a rod bearing, possibly a wrist pin.
From: willy on 9 Jul 2010 21:53 On Jul 9, 8:22 pm, jim <"sjedgingN0Sp"@m...(a)mwt.net> wrote: > I could be wrong but it is my recollection that the outer ring can't come > off to the timing chain cover side. If the outer ring is going to come off > the inner hub, it will go the other way and knock against the pulley. > > -jim Yea, I shouldn't have said "come off", cause it won't/can't come off. It'll just make a lot of noise. It could seperate, but I've never had one/seen one on a small block, or big block. By his description, it sure sounds like a rod bearing.
From: Paul on 9 Jul 2010 23:21 BSAKing(a)hotmail.com wrote: > I have a 1976 vette with about 120K miles on it. > Today the noise is back. But now It sounds morelike a banging/knocking > sound. The frequency increases with engine RPM. If I bring the engine > up to a modest rpm and hold it there , it seems to go away. It seems > worse when I first start it. Rod bearings tend to knock on decel when the load is off. Mains knock on accel under load.
From: BSAKing on 10 Jul 2010 08:45 On Jul 9, 11:21 pm, Paul <P...(a)Houston.com> wrote: > BSAK...(a)hotmail.com wrote: > > I have a 1976 vette with about 120K miles on it. > > Today the noise is back. But now It sounds morelike a banging/knocking > > sound. The frequency increases with engine RPM. If I bring the engine > > up to a modest rpm and hold it there , it seems to go away. It seems > > worse when I first start it. > > Rod bearings tend to knock on decel when the load is > off. Mains knock on accel under load. FWIW, the other day when I ran it - I was on the driveway in park with no load. It was knocking and rattling, and then I held it at about 2300 rpm and it went away. When I took my for off the gas, it still appeared to be gone for the most part. It will take me a few days to get to it due to other things going on here. I think I will take off the fan and all belts so I can get in there with better safety with a chunk of pool hose to see what I may be able to determine.... Keep you posted...... BSA
From: Nate Nagel on 10 Jul 2010 09:02
On 07/10/2010 08:45 AM, BSAKing(a)hotmail.com wrote: > On Jul 9, 11:21 pm, Paul<P...(a)Houston.com> wrote: >> BSAK...(a)hotmail.com wrote: >>> I have a 1976 vette with about 120K miles on it. >>> Today the noise is back. But now It sounds morelike a banging/knocking >>> sound. The frequency increases with engine RPM. If I bring the engine >>> up to a modest rpm and hold it there , it seems to go away. It seems >>> worse when I first start it. >> >> Rod bearings tend to knock on decel when the load is >> off. Mains knock on accel under load. > > FWIW, the other day when I ran it - I was on the driveway in park with > no load. > It was knocking and rattling, and then I held it at about 2300 rpm and > it went away. > When I took my for off the gas, it still appeared to be gone for the > most part. > > It will take me a few days to get to it due to other things going on > here. > I think I will take off the fan and all belts so I can get in there > with better safety with > a chunk of pool hose to see what I may be able to determine.... > > Keep you posted...... > > BSA Is it possible that something in the exhaust system shifted and is rapping on the frame? How are your engine mounts? Nice and fresh or soft and gooey? I like the harmonic balancer idea too. Had one ring walk right off the hub on a Packard engine in an old Studebaker Golden Hawk, that sounded like the engine was going to fly right apart. nate -- replace "roosters" with "cox" to reply. http://members.cox.net/njnagel |