1979 DeVille knocking noise upon startup!

[AtlantaMc]

Well guys,,, something new and not so improved after getting the car back from the shop to have the rear main seal re-replaced, and the intake seals re-replaced; as both were still leaking/burning/smoking after the first freeway voyage... Now, there is a banging sound upon start-up that lasts about four to five times(bangs) and smooths out; but still hearing something different on the freeway. Not the usual ticking from the lifters. Any ideas on what this surprise might be? Thanks in advance for your time...

[TJ Hopland]

Seal re replaced?  Were there any problems before other than leaks? 

What else was has been done?

Was the timing chain done one of the times it was apart?

What weight of oil was used each time?

I don't remember if the oil pickup has an O ring or anything like that on it that could have been disturbed.   

[60eldo]

   Is this banging when car is hot?  Does it do it when car is cold? I had a similar problem, It  did it when it was hot, I changed thermostat to a 160  now its fine.

[Tim Pawl CLC#4383]

Sounds like carbon build up on top of Pistons. Will hammer for awhile until warmed up.  Try putting GM Top Engine cleaner down carb with engine running it will clean the carbon off.     Tim Pawl #4383

[AtlantaMc]

This just started last weekend. Haven't done anything to it other than just having all of the outer seals replaced. The shop found gunk in the oil pan and burnt on crust in the valve covers which they cleaned. My Aunt apparently didn't maintain very well after my Uncle passed away... The car idles a little rougher now too. Tried to attach the sound it makes but not allowed on this site. It stops the loud banging after the first 5 or 6 times. Tried it again at lunch. I used 10-30 which helps the lifter ticks versus the 5-30 everyone else has gone with. It has 5-30 now.  Never made this latest noise before though.

[AtlantaMc]

Found a video on youtube for 1979 with the identical noise. His knocking doesn't go away though after start-up... https://www.youtube.com/watch?v=UTDBmkKyBCY

[waterzap]

I had a weird knock thing coming from my exhaust on my eldorado at start up. When they replaced the timing chain, the sound went away

[Two Crabs]

On a cold start, hearing engines noises like that usually means connecting rod bearings are not holding oil due to excessive clearance or it could be the wrist pins in the pistons.
If it goes away within the first 10 - 20 seconds it is oil pressure related.

[R Schroeder]

That video sounded like rods to me, but could be exhaust or  a bad timing chain.
Maybe the fuel pump arm slapping on the cam.
Maybe starter hitting fly wheel for a bit.
Hard to say without being there.

[AtlantaMc]

Thanks guys for the replies. Was heading to work this morning and was hearing a little more noise, which normal ticking vanishes, so turned it around and headed for the shop. The verdict thus far without pulling the pan was either a wrist pin or rod bearing on number 7. They are going to drop the pan and research further; and get back with me... Just curious, what would cause this? 

[Eric DeVirgilis CLC# 8621]

Based on one of your earlier posts, it strongly suggests the classic case of a low mileage car that was driven short distances without the engine having gotten a chance to reach full operating temperature - accompanied by mileage-based oil change intervals. In other words, she probably didn't change the oil enough for her driving habits.

I've witnessed many occasions whereby a low mileage engine was sent to an early grave due to a lack of oil changes when a car had regularly been driven short distances. Even moreso in colder environs. In such cases, the time honored 3,000 mile oil change interval is grossly insufficient. 

The reason for this is the formation of condensation within the crankcase which results in sludge, which makes oil changes all the more critical. The condensation does not have a chance to boil off when the engine isn't fully warmed up - and preferably for a good 20 minutes at that. Not as critical during warm weather.

Newer vehicles are designed with a oil life indicator system for this exact reason. These systems calculate the effective oil life based upon real world conditions of trip distance, engine & ambient temperature and other factors.

Therefore under some conditions, oil change might not be needed in as much as 6,000 miles while for others, perhaps as little as 500 or even less.   

[Dan LeBlanc]

That's why, regardless, I always change the oil in my antiques in the fall before I put it away and when I take it out in the spring.  I know it's fresh when I put it away, but I like that feeling of knowing my oil is always minty fresh.

[TJ Hopland]

Did they find any small plastic chunks in the pan?

If the pan is coming off again it would be another chance for doing the timing chain if it has not already been done.   Mileage and age are not at all kind to the originals.  Who knows maybe its hanging by a thread and its part of your noise?   

[Aaron Hudacky]

I agree with Tim Pawl.  I have had two 425 cars develop this sound; one a very clean 42,000 mile car and the other a 175,000 mile example.  Both sounded exactly like the video you linked.  The low mileage car started the noise after being parked during winter.  The high mileage car did it after a plug change.  On that car, the noise went away after revving the engine in idle to show my causing what it sounded like, with the expectation that it was going to throw a rod.  It didn't.  After a few rpm increases, the thick would completely disappear in the higher ranges but come back as the engine slowed.  I revved it repeatedly until the knock would reappear at a point lower and lower in the rev range.  After about 15 minutes there was a large black carbon spot in the snow and the knock was gone. 

With the lower mileage car, I did a similar procedure, but I did not rev it as aggressively.  I drove the 175k car for another year before I sold it with the engine running perfectly.  The low mileage car I still own and the sound never came back.

I have spun rod bearings in a 500, and that sound is completely different.  The carbon sound is always loud and comes on very abruptly but does not change in intensity, just speed as you rev the engine.  The rod noise got louder and worse over time, and came on much more slowly and progressively.  Before you have someone disassemble the engine, try seeing if it might be carbon.  If the sound worsens, you know it is unlikely to be carbon.  The top end cleaner Tim recommended would probably be a much better procedure to use than the one I did. 

[Eric DeVirgilis CLC# 8621]

Top end cleaner is certainly worth a shot.

Mark- I'd also switch to 10W 40. 5-30 is far too low viscocity in the 425 - IMHO - unless you're regularly driving in sub freezing temps.

[AtlantaMc]

Thanks guys for all the info/support. Never new that about the oil life(driving habits) Eric. But totally makes since with her driving short distances. I started using the 10-40 which did quiet the ticking versus the 5-30 everyone uses now. Doesn't get that cold here in Atlanta either thank goodness! Question- at this point, should I just replace the part they come back with? Or, opt for an overhaul? Or a new rebuilt engine? Just don't want to keep throwing money away or spend most of my life back and forth with shop repairs due to past maintenance issues. Going on 6 weeks of this now and want to do so much more with my own repairs to the car. But those don't really matter much unless it's drivable and dependable... Uh Oh,,, starting to whine!  Hehe!!! 

[Eric DeVirgilis CLC# 8621]

I wouldn't consider anything so drastic such as a rebuild at this point - there are still many options to consider. 

I have heard of couple of old tricks involving running kerosene in the crankcase and other "flush" products that are added to the oil which can help with excessive sludge removal. Apparantly some of these solutions have proven very effective in some cases; less so in others. I've also heard that occasionally a large enough piece can break off further complicating issues. So as you can see it can be quite a quandry.

Others here may have more to contribute on the subject as I have no direct experience with any of these approaches.

It's defintely something worth looking into.

[waterzap]

I am a bit skeptical of these magic potions when the engine is really dirty. For my Seville I pretty much opened the engine up and cleaned it out with pics and brushes. There was so much gunk. No way some chemical was going to clean it up. If you open the intake manifold, valve covers, lift the engine a bit and get the oil pan out, you should be able to get out a lot of gunk if there is any in there.

[R Schroeder]

you said your engine was still leaking after you got it back from having the seals done. Don't know if that was fixed again or not.
But, here is my 2 cents. Running cleaners in the crankcase , or kerosene isn't good in my book.
If this engine has that much sludge in it your asking for problems. This all happened because of poor maintenance and it isn't going to be reversed by cleaning.

Also the only way I would rebuild the engine is if the car was absolutely mint. You wont get your money back out of it, if it isn't a perfect car.

Just my 2 cents.
Roy

[AtlantaMc]

Well looks like chambers 7 and 8 are messed up and the chambers are pretty charred. He said it could have been driven without oil? Anyway, looking at a re-manufactured engine verses repairing and not knowing what will go next. Anyone have experience with different vendors out there?