Steve's Nova Site is an automotive enthusiast website dedicated to the 1962 - 1979 Chevrolet Nova, Chevy II and Acadian automobiles. We work together to preserve, restore, drive, show, race and provide fellowship for these classic cars. This is one of the best places to find information about parts, rebuilding, restoration and racing. This website is not affiliated with GM, General Motors or Chevrolet in any capacity.
I have a 383 SBC that was in a wreck several months ago. After reassembling the engine, it developed a vibration around 2500-3000 RPM's. Suspecting the crank, I took the engine out and these are what the upper bearing halves look like. Do the bearings look like there is a vibration, or this wear normal? Engine has approximately 300 or so miles on it. Oil pressure cold at idle was ~60 PSI, and when hot it would get down to 40 PSI at idle. Steadily increased as RPM did.
This is in response to the other thread I had started, but related to the bearings now. I was told that the blue spots on the bearings were from the factory. It looks like heat marks from either a journal being out of round, or the phantom vibration? Can anyone confirm? I haven't gotten any real solid guesses/answers, and I have no clue. I have looked at a couple bearing damage guides, but nothing really fits.
Is this even worth trying to fix?
Thanks.
Last edited by mrdreex; 23rd-October-2009 at 01:38 AM..
On my phone so can't see the pics till morning, but having just destroyed an engine, I'm keeping my fingers crossed that this will be something inexpensive to fix.
I have a 383 SBC that was in a wreck several months ago. After reassembling the engine, it developed a vibration around 2500-3000 RPM's. Suspecting the crank, I took the engine out and these are what the upper bearing halves look like. Do the bearings look like there is a vibration, or this wear normal? Engine has approximately 300 or so miles on it. Oil pressure cold at idle was ~60 PSI, and when hot it would get down to 40 PSI at idle. Steadily increased as RPM did.
This is in response to the other thread I had started, but related to the bearings now. I was told that the blue spots on the bearings were from the factory. It looks like heat marks from either a journal being out of round, or the phantom vibration? Can anyone confirm? I haven't gotten any real solid guesses/answers, and I have no clue. I have looked at a couple bearing damage guides, but nothing really fits.
Is this even worth trying to fix?
Thanks.
what kind of oil pan are you using ? it looks like its starving out on oil a little , what do the crank journels look like , do you have a pic of the crank ?
what kind of oil pan are you using ? it looks like its starving out on oil a little , what do the crank journels look like , do you have a pic of the crank ?
Using a Moroso 20191. Oil pressure has never gone down past 30. It does leak oil like a ***** out the rear and front seal. I will be honest, I did run the engine when it was low on oil, but only ONCE. I did not notice the oil pressure start to go down until I stomped on it, but I didn't stay on it. I babied it home where I promptly added oil.
What I REALLY want to know is if this wear is indicative of a bent crank. The wear seems uniform across all the mains, and the bottom of the mains look literally nothing like the tops. Most of the bottoms look just fine, with little to no wear, or atleast, normal wear.
No pictures of the crank, but the main journals all looked polished and just like when I had dropped it in. No pitting, that I could see, but a picture could probably help me alot more as well. I will get one when I can.
Last edited by mrdreex; 23rd-October-2009 at 01:59 AM..
how much clearance do you have between the bearing and the crank , take some plastigauge and mic it , or put the main caps on mic the bearings with a telescoping mic or a dial bore mic/gauge and then mic the crank
how much clearance do you have between the bearing and the crank , take some plastigauge and mic it , or put the main caps on mic the bearings with a telescoping mic or a dial bore mic/gauge and then mic the crank
should have at least .001 - .002 for clearance
When originally put in, it was in between .001 and .002", but I do not remember exactly where. I will check tomorrow. I don't have plastigauge, but I do have a set of Starrett inside mic's and a 2-3" Starrett outside micrometer. Thanks for your help.
its possable that the main bolts or studs cam loose or lost there torq if you say the crank looks good and so does the main caps , what kind of main bolts /studs are using ?
its possable that the main bolts or studs cam loose or lost there torq if you say the crank looks good and so does the main caps , what kind of main bolts /studs are using ?
Can't remember the brand name, but it isn't ARP. It's something like BPG...it was cheaper at the time, only ones he had in stock and said 'they do the exact same thing as ARP', when I bought them from my short-block machinist. I guess it is possible. Maybe I over-torqued them after I took it apart, after my wreck. I will re mic the clearances tomorrow and see what it comes to. It's been a while since I have measured anything.
Could the oil starvation be because of too much torque? I don't remember the torque rating of the bolts, or whether or not there was any to begin with.
Are the bearings toast? Or can I still use them?
Here are some pics of the lower bearing halves. I don't remember which ones went where, but I think they're all there.
Are we in agreeance that the lower mains look a fair bit better than the uppers? If it were bent, wouldn't I see wear on these bearings as well? Atleast some copper shown?
Thanks again.
EDIT: Forgot to include they are bolts, not studs.
I don't see an obvious problem and solution. You said this engine was in a wreck? The vibration happened after the wreck? Is it at that RPM regardless of throttle position? Did you replace the harmonic balancer or reuse it?
I would first put the crank on some precision V blocks and check run out with a dial indicator. Crank may be bent.
Check bearing journals with a mic that goes to 10 thou. Check in two axis and sides for four measurements total each journal. Record these on a spread sheet. You'll want to check rod bearing ID as well and calculate true bearing clearance and out of round. Plastiguage won't do it.
Clearance shouldn't be tighter than .0018" and no looser than .0023" on the rods.
Check the main caps while torqued to actual bolt specs. ARP has a different torque value than stock bolts. I don't know what the spec is for these "same as" bolts. I wouldn't assume anything on that. Block may be distorted from the crash.
In fact don't assume any part is ok just by a visual look.
I would inspect and precision measure everything. Make a list and check things off line by line. Process of elimination will find the most elusive gremlin.
__________________
Quote:
Originally Posted by Paul Wright
Building a small, high rpm engine
with the perfect bore, stroke and rod ratio is very impressive...
like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar.
Cubic inches is like Indiana Jones with a cheap pistol..
Last edited by Paul Wright; 23rd-October-2009 at 10:24 AM..
I don't see an obvious problem and solution. You said this engine was in a wreck? The vibration happened after the wreck? Is it at that RPM regardless of throttle position? Did you replace the harmonic balancer or reuse it?
I would first put the crank on some precision V blocks and check run out with a dial indicator. Crank may be bent.
Check bearing journals with a mic that goes to 10 thou. Check in two axis and sides for four measurements total each journal. Record these on a spread sheet. You'll want to check rod bearing ID as well and calculate true bearing clearance and out of round. Plastiguage won't do it.
Clearance shouldn't be tighter than .0018" and no looser than .0023" on the rods.
Check the main caps while torqued to actual bolt specs. ARP has a different torque value than stock bolts. I don't know what the spec is for these "same as" bolts. I wouldn't assume anything on that. Block may be distorted from the crash.
In fact don't assume any part is ok just by a visual look.
I would inspect and precision measure everything. Make a list and check things off line by line. Process of elimination will find the most elusive gremlin.
Yes, engine was in a wreck and the vibration started after the wreck. I replaced the harmonic balancer with the exact same one. It's an internally balanced rotating assembly, and the balancer is a neutral balanced Pioneer something or other. Can't remember the part # off the top of my head. It is always at that RPM regardless of what gear I'm in, and can feel it while neutral revving the engine. That takes everything behind the engine out of the picture except for the flywheel/pressure plate/clutch. Transmission is new.
I can remember atleast one instance where I was running it through the gears, got into fourth gear on the highway, slowed down to roughly 2700 RPM's, and the vibration was GONE. Accelerated up a bit to around 3500, and still gone. I was dumbfounded. It came back later though when I slowed down. This was a few months ago, but I do distinctly remember that the vibration went away while in the RPM range it usually showed up in. Since then I haven't been able to reproduce it.
I will be doing all the clearances again tonight. It's been too long since I measured them and am making a list as I type. Thanks for the tip. Is .001" - .002" a good tolerance for the mains? Not sure where to get a set of V blocks, but would removing the upper bearing halves from the 3 middle mains and rotating it on the front/rear halves be as effective?
Thanks for the help Paul.
Last edited by mrdreex; 23rd-October-2009 at 10:43 AM..
It's funny you mention that, because I remembered looking at this some time ago from a post you made. I actually searched for that thread and have been through it a couple times now. That and about every single google search result for a bearing damage guide.
It looks either like oil starvation, or it's the wear on the coating of the bearings. That would be normal wear because there are just not many miles on them at all. I am fairly certain there would be copper showing, or at least alot more wear if there was a bend in crank and it was causing any sort of damage.
Thanks veno.
Last edited by mrdreex; 23rd-October-2009 at 10:59 AM..
hey.. some of the internal balanced cranks for scat and Eagle are not truly neutral balance..
I dont recall it specifically but either the harmonic balancer or the flex plate is counter weighted and the other is neutral... but they call it neutral balance
__________________
If ya say HIGHER and throw the Peace sign up it will do you no harm. Sly.
hey.. some of the internal balanced cranks for scat and Eagle are not truly neutral balance..
I dont recall it specifically but either the harmonic balancer or the flex plate is counter weighted and the other is neutral... but they call it neutral balance
When the local shop I had my machine work done at was open, they bought the crank and internally balanced it. The counter-weights are drilled in several spots. I will have to look at that a bit more though.
If the clearances check out OK tonight I'm going to take it to get wet magged, etc. If it's ok, then I will have it rebalanced if it needs it.
Linear Mode
