I need some help with my 350 Chevy engine...
My first post after doing my intro.
I purchased a 350 rebuilt engine 3 years back for my 1992 Chevy van.
After 15K miles the engine suddenly developed a knock. The knock occurs when the engine is just beginning to shift into second gear.
The engine burns no oil and runs and starts well.
I removed the engine and have begun starting to take it apart.
So far I have found no problem except for one thing:
Cylinders 2 through 8 had spark plugs that looked white and clean.
Cylinder #1 had a jet bleck spark plug.
After I removed the heads I saw that cylinders 2-8 had identical brown color on the exhaust valves. Cylinder #1 all valves are jet black.
Cylinder walls look OK, but I have not removed the pistons and rods yet. Engine is very clean inside. No sludge, metal particles or any sign of damage anywhere. I removed the oil pan and all looks OK there as well.
Anyone have an idea of what I need to look for to ID this knocking? I really am in need of help here........pg
Hi and welcome to the HR forums.
On the knock, i may have been more inclined to ck the trans or flywheel first before getting into the engine.
As far as #1 being black, it could be oily black or too much gas black. Is it carb'd or injected?
Thanks for the quick reply.
I thought to check the flywheel carefully for cracks, but it looks good.
My description of it knocking when it gets ready to shift may have been a little misleading. When I sit there in neutral and bring the rpm up to about 2500 the knock begins. And it sounds like a rod knocking too.
Maybe when I get the rods off the crank I will see some kind of damage. This is not my first time to work on a Chevy, but it is the most serious problem I have encountered.
In other words, I am in deeper than ever before and I still don't have the pistons out yet. :sweat: ........pg
Sounds like you have your work cut out for you! Hope it's not hot and humid where you're working!
Piston pin knock like rod knock happens as the piston and rod assembly change direction and the slack of excessive clearance is taken up. Piston knock is typically from a cracked skirt which flexes every time the piston changes direction and the skirt snaps across the bore clearance between its thrust and non-thrust sides.
It's often hard to tell the difference between these unless you've heard them a lot.
Jmark and Bogie.....
Hot and humid in Houston Texas? Ha-Ha, no worse than living in a swamp 347 days out of the year. I had the engine in the garage part of the shop after I got it out of the van. I have a 30 inch wall fan there and noticed sawdust on my motorcycles that are parked in there. The fan is swirling the dust around and it is humid!
So my first activity on the engine was to roll the engine on the stand to the air conditioned shop in the next room. Ah-hhhh. Better now, and no dust!
Thank you for the comments.
This knocking may happen for a few seconds when I crank the engine cold, then it goes away until the engine gets to around 2500 rpm.
The knocking is not a heavy thud-thud-thud, but rather a higher pitched clacking sound. I had a harmonic balancer come loose on an old 318 Dodge I had and this sound a bit like the same kind of noise. In fact I crawled under the van to check the torque on the balancer when I first heard the knocking. It was/is tight though.
Now what you say about a possible piston crack or wrist pin problem has my interest because of the #1 cylinder looking so black compared to the other 7 which look all alike and are tan colored. I would post a pic if I knew how to do that.
So, when I get the rods out I will look at #1 first and closely.
I will let you guys know what I find. I am hoping to find something, and as bad as it sounds, it would be a blessing to find a cracked piston.
Got the ridge reamer today....
The Lisle 36500 ridge reamer showed up today. I know it is a reamer, so I should only turn it clockwise. I assume I use a generous amount of cutting oil too? The cutter is carbide so I am not sure.
Nothing in the instructions tells me to lube it.
I am really eager to have a look at the #1 piston.......pg
Pictures of that piston would be nice. The way I know how to up-load them, is to scroll down to "Manage Attachments"(while posting), and click on it. This will take you to a upload page. You need to make sure your pictures are downsized, edit in your picture manager, then simply hit "browse" and click on the picture/pictures, and click on "upload". These will show up under your "post" when you are done.
How others on here, get their pictures in their post, I have not figured out yet. :sweat: :welcome:
I am going to see if I can get this photo to load, so this is a test only.......pg
edit note: That seems to work, so on to getting that piston out.
yep, right when the trans shifts it knocks. Basically when there is little load on the engine and the revs are around 2-3000. Had this happen a couple of times. Ended up to be a weak oil pump (spring was bad not holding enough psi).
The fact that #1 is black would make me think a different problem. Hope you dont have to dig to deep and come up with maybes :sweat:
Just having 15000 should not need ridge reamer.
OK, I got the number piston out this morning.
To start with:
I checked the crankshaft end play and it was .015. The book tells me it should be .002 to .006, so that is a negative.
I checked the side clearance of #1 rod and it was .015 gap. Book says .006 to .014, so I am just a little wide on that.
You guys were correct in saying I did not need a reamer. But I used it anyway and one rotation cleaned it to the metal.
Now for some photos:
The first pic is of the insert in the cap. It is stamped .010. Does this tell me the bearing is .010 oversize (that the crank journal has been ground down) .010?
The next two pics are of the rod inserts. They look really worn, considering the engine has only 15K miles on it. Half of the ebarings have copper color showing and the other half have silver showing.
Can anyone give me an idea if the bearings may be bad or not? They look very bad to me, but I hae no experience with this kind of thing.
I will do another post with photos of the piston and bore. Hang tight.....pg
Here are the shots of the piston and bore.
The piston looks really good to me. No cracks. No scuffing, and the skirt walls look like I just took the piston out of the box.
The bore looks good too. Hard to take a photo of it, but the walls are smooth top to bottom. There are a couple of light lines on the wall which seem to match light lines on the piston.
Back to the crank: I forgot to mention that the journal feels a bit rough if I drag a fingernail over it. I did not get a shot of it, but it certainly is not smooth as it would be if it were freshly ground. Again, I do not know what 15K miles will do to the surface. Oil has been changed every 3K miles.
I sure hope you guys have something to tell me about this. Meanwhile, I will continue to remove rods and pistons I guess.......pg
Wow, the rod bearing looks nasty. Will be interesting to hear with the pro builders have to say on that.
The center piston pic shows ( to me atleast) a lot of crusty oil down in the ring groove, like it's been burning a lot of oil in that cylinder.
More pictures of other cylinders/pistons/ and bearings would be nice.
That cylinder, and rod bearing looks to me that the rod is bent, or the rod journal on the crank, is ground crooked. The rough scoring on the crankshaft, and bearing is from debree, or some lack of oil pressure at some point. It does not look blackened from lack of oil over a long period of time.
Number one cylinder is the last to get oil pressure in a SBC, or BBC for that matter.
From what I can see of the top of the piston, it does not look like a ring problem. If it was, the quench area would be washed clean of carbon. I would look more into a valve guide, valve seal, or intake gasket leak.
In my experience that looks like bad oil pump or oil pressure but like carsavy said we kinda need more pics of other pistons and rods.
I bought a bbc that was supposed to have 10k when i got it and drove about 5k or 3 mnths before a rod bearing halved up on me and destroyed a crank.......welll **** happens so that motor was a 454 when that happened now 468 with edelbrock performer package and that thing lopes boy sounds almost to big of cam but there is no such thing as to much heheheheh.
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