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Recently switched from an 8.5psi to a 9.5psi procharger pulley. Didn’t rag on the car as it hasn’t been tuned up to that level of boost, but after a few miles I started hearing a knocking noise at low revs.
Though at first it may have been the procharger idler, but now I’ve disconnected the procharger the noise is definitely coming from the engine.
But again that dont sound just right at all even at cold.
Its definitely coming from the passenger side of the engine, I think from near the top-end. I’ve had the valve cover off and the springs all seem ok.
Im not sure what my next step should be. I’m not a mechanic by any means, and being as I’m in the U.K. I don’t have access to a wealth of shops that specialise in vettes.
Is there anything more I can do before getting it sent across the country probably never to see it again?
Unless you can work on it probably not. Might be a bent pushrod... Also might need to pull the head and see what's going on.
Originally Posted by jimxms
Its definitely coming from the passenger side of the engine, I think from near the top-end. I’ve had the valve cover off and the springs all seem ok.
Im not sure what my next step should be. I’m not a mechanic by any means, and being as I’m in the U.K. I don’t have access to a wealth of shops that specialise in vettes.
Is there anything more I can do before getting it sent across the country probably never to see it again?
Its definitely coming from the passenger side of the engine, I think from near the top-end. I’ve had the valve cover off and the springs all seem ok.
Im not sure what my next step should be. I’m not a mechanic by any means, and being as I’m in the U.K. I don’t have access to a wealth of shops that specialise in vettes.
Is there anything more I can do before getting it sent across the country probably never to see it again?
I put money it is # 7 push rod are you good enough to see if it is coming from the front are rear of the motor. But what ever you do don't get it running in no more high RPM range.
If you can see if it is the rear # 7 more than not. PULL THAT ROCKER ARM OFF THEN check that push rod. All check all the push rods on that side. If no problem with ONE are more being JUST A LITTLE BENT replace those & back together. IF NOT THEN I would pull that side of the head off the car & really check the valve springs out TO MAKE SURE THAT THEY ARE HOLDING THE WEIGHT that it needs to hold....
This c7 is really bad with a boost car to drop a valve are bend a push rod. I think you got a bent push rod & it is not closing the valve all the way & is hitting the top of your piston..... Robert
It doesn't sound good, but to narrow it down, take off the other belt and run it for a minute. Keep in mind the water pump will not be turning, so don't run it for long as it will over heat.
I'd also do a compression check. That will hopefully identify bent push rods.
If you have an air compressor, you can do a leak down test, but that it more complicated and requires a more expensive tool than a regular compression check.
If you pull the valve cover off again, put a dial indicator on each rocker and rotate the engine by hand noting the total movement. Pull the plugs to make it easier. I suppose it may be pretty easy to just remove the push rods and check for any bent ones, but then you wouldn't know if it's a collapsed lifter.
At the very least, I would pull the plugs and valve cover then rotate to see if everything seems to move the same.
I put money it is # 7 push rod are you good enough to see if it is coming from the front are rear of the motor. But what ever you do don't get it running in no more high RPM range.
If you can see if it is the rear # 7 more than not. PULL THAT ROCKER ARM OFF THEN check that push rod. All check all the push rods on that side. If no problem with ONE are more being JUST A LITTLE BENT replace those & back together. IF NOT THEN I would pull that side of the head off the car & really check the valve springs out TO MAKE SURE THAT THEY ARE HOLDING THE WEIGHT that it needs to hold....
This c7 is really bad with a boost car to drop a valve are bend a push rod. I think you got a bent push rod & it is not closing the valve all the way & is hitting the top of your piston..... Robert
On the passenger side of the car I would say it is coming from the piston/valve not closest to the firewall, but the one in front of it.
I had the intake manifold off, and put a camera down into the valves. I couldn't see anything obviously wrong. Can I just unbolt the rocker arms and pull the valves out? Do they need tightening a specific way when re-assembing them?
I will get the plugs out of the car tomorrow and try and get the camera in there on top of the pistons. If a valve is hitting a piston should there be visible damage?
It doesn't sound good, but to narrow it down, take off the other belt and run it for a minute. Keep in mind the water pump will not be turning, so don't run it for long as it will over heat.
I'd also do a compression check. That will hopefully identify bent push rods.
If you have an air compressor, you can do a leak down test, but that it more complicated and requires a more expensive tool than a regular compression check.
If you pull the valve cover off again, put a dial indicator on each rocker and rotate the engine by hand noting the total movement. Pull the plugs to make it easier. I suppose it may be pretty easy to just remove the push rods and check for any bent ones, but then you wouldn't know if it's a collapsed lifter.
At the very least, I would pull the plugs and valve cover then rotate to see if everything seems to move the same.
I will try taking the belt off (I assume to rule out any accessories causing the noise?) and I'll get the valve cover off too and rotate the engine to see if everything is moving the same. The compression test is beyond my skill level I think.
It doesn't sound good, but to narrow it down, take off the other belt and run it for a minute. Keep in mind the water pump will not be turning, so don't run it for long as it will over heat.
I'd also do a compression check. That will hopefully identify bent push rods.
If you have an air compressor, you can do a leak down test, but that it more complicated and requires a more expensive tool than a regular compression check.
If you pull the valve cover off again, put a dial indicator on each rocker and rotate the engine by hand noting the total movement. Pull the plugs to make it easier. I suppose it may be pretty easy to just remove the push rods and check for any bent ones, but then you wouldn't know if it's a collapsed lifter.
At the very least, I would pull the plugs and valve cover then rotate to see if everything seems to move the same.
Better to do a leak down test. OP see if you can rent one of these from like a shop in your town are a parts store like auto zone if you have one in town....Robert
It could be an artifact of the video but I'd swear you can almost see synchronization between the sound and the accessory drive. I guess we'll find out when he pulls the belt!
Probably a bit off topic, but if I get the engine stripped and rebuilt, are the parts to strengthen the engine for boost just drop-in replacements? Roughly how much would
it cost to proof the engine against 800hp?
I have found an engine builder but they aren’t Chevy experts. I think they can strip and rebuild with new parts but not much more.
Probably a bit off topic, but if I get the engine stripped and rebuilt, are the parts to strengthen the engine for boost just drop-in replacements? Roughly how much would
it cost to proof the engine against 800hp?
I have found an engine builder but they aren’t Chevy experts. I think they can strip and rebuild with new parts but not much more.
First do the leak down test buddy no need to rebuild something that really not needed. If it is running like it is it is a push rod are a valve spring just replace those.
But if you are going to have to do a rebuild GET FORGED PISTONS a small cam with good valve spring after market stuff. Really the forged stuff is not that much more than the stock crap.
Use your stock crank but if me for 800 rwhp I would also get a good rod & for sure pistons also. Robert
First do the leak down test buddy no need to rebuild something that really not needed. If it is running like it is it is a push rod are a valve spring just replace those.
But if you are going to have to do a rebuild GET FORGED PISTONS a small cam with good valve spring after market stuff. Really the forged stuff is not that much more than the stock crap.
Use your stock crank but if me for 800 rwhp I would also get a good rod & for sure pistons also. Robert
Thanks for the info man. Is there an idiots guide to valve spring and push rod removal?
I remember watching Engine Masters and seeing how the rocker bolts need to be tightened to a certain torque and then slackened off a bit to get the ideal spring tension...or something like that?
Unless things have changed, you take off the top bolt and can pull the rod out. roll it on glass or something super flat. If it waddles, it's bent. To replace, drop in the new push rod and torque the nut to 22 lbs. Torque and loosen are not in the book for the PRs.
I just loaned my manuals to a friend so the 22 lbs is from memory so don't take it to the bank! Look it up!
Unless things have changed, you take off the top bolt and can pull the rod out. roll it on glass or something super flat. If it waddles, it's bent. To replace, drop in the new push rod and torque the nut to 22 lbs. Torque and loosen are not in the book for the PRs.
I just loaned my manuals to a friend so the 22 lbs is from memory so don't take it to the bank! Look it up!
Elmer
Thanks man, I'll give that a go tomorrow.
I think what I was getting confused with on the torque and loosen was the lash adjustment.
I will try taking the belt off (I assume to rule out any accessories causing the noise?) and I'll get the valve cover off too and rotate the engine to see if everything is moving the same. The compression test is beyond my skill level I think.
Yes. Pull the belt to rule out the accesories.
Compression checks are actually very easy. Pull the plugs, screw the hose of the compression gauge into the sparkplug hole and crank the engine several revolutions. The gauge will hold the reading until you press the releif button. You will see some variation, but you are looking for one reading that seems out of place with the others. If you have autoparts stores that lend tools, they probably have one.
#7 is definitely bent. Bent enough to cause problems, you guys tell me?
#8 isn’t perfect but I don’t think my glass table is perfect either.
I also pulled the spark plugs while I was there. The picture goes 5,6,7,8. 7 and 8 are lighter brown whereas 6 and 7 are darker. Would this indicate a leaner burn? More air in cylinders from improperly closed valves? Again, I’m interested to hear what the experts say.
I tested compression on 5,6,7,8 and they were all between 210-220 PSI.
Finally I got a scope down into the cylinders. The pictures are crap as it’s an eBay special scope, but I couldn’t see anything really bad. Can you?
#5
#6
#7 - the scratches are from the camera. The piston was right at the top of the cylinder and the camera scratched away a load of the carbon deposits when I inserted it
05-18-2018, 06:09 AM
Has my engine just taken a sh*t??
OP see if you can rent one of these from like a shop in your town are a parts store like auto zone if you have one in town....Robert
