Engine knock, where should I start?
Thread Starter
Melting Slicks
Joined: Oct 2004
Posts: 3,117
Likes: 0
From: St. Louis, MO
Engine knock, where should I start?
MTI 383 engine, only 40k, rarely ran hard.
Last fall, left a stop sign and spun it too about 5k, engine developed a miss. Rough idle, low on power, wanting to stall. I knew I had a bad wire due to touching a header , and didn't think much of it. The miss persisted, however, so I took it to a GM friend's house to run a hand held on it.
No codes.
Thought possible MAP needed as I had a previous oil problem near that area. However, as I limped home, I heard a slight knock as I pulled in the driveway.
Now, the knock is louder and has me freaking out that it's down low.
Good oil pressure, still no codes.
I'm thinking (hoping) broken valvespring.
SO do I start by pulling a valve cover to look at the springs, get a compression gauge on it first, or what?
I'm a little nervous as the last internals of an engine I saw was replacing a cam on a carburetored 350 about 10 years ago.
Any advice would be appreciated.
Last fall, left a stop sign and spun it too about 5k, engine developed a miss. Rough idle, low on power, wanting to stall. I knew I had a bad wire due to touching a header , and didn't think much of it. The miss persisted, however, so I took it to a GM friend's house to run a hand held on it.
No codes.
Thought possible MAP needed as I had a previous oil problem near that area. However, as I limped home, I heard a slight knock as I pulled in the driveway.
Now, the knock is louder and has me freaking out that it's down low.
Good oil pressure, still no codes.
I'm thinking (hoping) broken valvespring.
SO do I start by pulling a valve cover to look at the springs, get a compression gauge on it first, or what?
I'm a little nervous as the last internals of an engine I saw was replacing a cam on a carburetored 350 about 10 years ago.
Any advice would be appreciated.
Melting Slicks
Joined: Aug 2000
Posts: 2,618
Likes: 5
From: Overland Park KS
I'd drain the oil pan and check for needle bearings from a lifter or rocker arm. This is the easiest way to find something broken and doesn't take much time. I went the valve cover route and found nothing out of place and THEN drained the oil and found some needle bearings. Then removed the oil pan and found a few more!...
If everything is clear (including the filter, take it apart). I'd take off the valve covers and have a look. If everything "looks" okay then you need someone who knows a bit about engines to check the rods, valves, remove heads etc. Not knowing your experience maybe you're fine with taking it to these steps....
Sorry I can't be of more help.
If everything is clear (including the filter, take it apart). I'd take off the valve covers and have a look. If everything "looks" okay then you need someone who knows a bit about engines to check the rods, valves, remove heads etc. Not knowing your experience maybe you're fine with taking it to these steps....
Sorry I can't be of more help.
Safety Car
Joined: May 2006
Posts: 3,799
Likes: 1
From: Northern Virginia
St. Jude Donor '08
I'd drain the oil pan and check for needle bearings from a lifter or rocker arm. This is the easiest way to find something broken and doesn't take much time. I went the valve cover route and found nothing out of place and THEN drained the oil and found some needle bearings. Then removed the oil pan and found a few more!...
If everything is clear (including the filter, take it apart). I'd take off the valve covers and have a look. If everything "looks" okay then you need someone who knows a bit about engines to check the rods, valves, remove heads etc. Not knowing your experience maybe you're fine with taking it to these steps....
Sorry I can't be of more help.
If everything is clear (including the filter, take it apart). I'd take off the valve covers and have a look. If everything "looks" okay then you need someone who knows a bit about engines to check the rods, valves, remove heads etc. Not knowing your experience maybe you're fine with taking it to these steps....
Sorry I can't be of more help.
Did your friend run a Tech II on car?
Do you know the type of valve springs on car? I have read about a lot of Comp Cam 918 springs failing and wonder if this is the problem?
Thread Starter
Melting Slicks
Joined: Oct 2004
Posts: 3,117
Likes: 0
From: St. Louis, MO
Not sure about springs, but before the knock, this is what we were thinking.
I just don't understand what would have caused a knock to start 100 miles after the initial miss.
Pro
Joined: Aug 2007
Posts: 619
Likes: 1
From: ATLANTA GA
I had a knock a few months ago.. It turned out to be cylinder #5 had a spun bearing..
Let it get to operating temperature... and slowly rev increase the rpms.
Is the knock linear(increase With Rpms)? My knock was in the VERY early stages, I diagnosed it very fast and could have turned the crank but i opted to replace it.
My knock was increasing with rpm, and it had a clanging rattle kinda sound to it.
Let it get to operating temperature... and slowly rev increase the rpms.
Is the knock linear(increase With Rpms)? My knock was in the VERY early stages, I diagnosed it very fast and could have turned the crank but i opted to replace it.
My knock was increasing with rpm, and it had a clanging rattle kinda sound to it.
Tech Contributor
Joined: May 2008
Posts: 2,843
Likes: 16
From: Howell Michigan
St. Jude Donor '09-'10-'11
Plaster,
Sorry to hear about your sick vette! That sucks!
I would suggest looking at the valvetrain, like bent push rod. If the engine still feels like it is missing then one of the cylinders isn't producing its share of the power. A spun bearing typically will cause a drop in oil pressure and will not make the engine feel like it is missing, but will make noise.
When you say it is making a “slight knock”, is it truly a knock or could it be a tapping sound? Have you heard a bad lifter before, and if yes, is it sound something like that?
If the engine is missing at idle, pull the power supply wire to each coil one at a time. The engine idle rpm will change for any cylinder producing power. When you find the coil that doesn't change the idle speed, this will be the cylinder that has the problem. This will allow you to focus on its rockers, push rods, spark plug or maybe even the injector.
Let us know what you find.
Regards,
Eric D
Sorry to hear about your sick vette! That sucks!
I would suggest looking at the valvetrain, like bent push rod. If the engine still feels like it is missing then one of the cylinders isn't producing its share of the power. A spun bearing typically will cause a drop in oil pressure and will not make the engine feel like it is missing, but will make noise.
When you say it is making a “slight knock”, is it truly a knock or could it be a tapping sound? Have you heard a bad lifter before, and if yes, is it sound something like that?
If the engine is missing at idle, pull the power supply wire to each coil one at a time. The engine idle rpm will change for any cylinder producing power. When you find the coil that doesn't change the idle speed, this will be the cylinder that has the problem. This will allow you to focus on its rockers, push rods, spark plug or maybe even the injector.
Let us know what you find.
Regards,
Eric D
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Safety Car
Joined: May 2006
Posts: 3,799
Likes: 1
From: Northern Virginia
St. Jude Donor '08
Let us know what you find out.
Hope it is something that is easy and inexpensive to fix.
Thread Starter
Melting Slicks
Joined: Oct 2004
Posts: 3,117
Likes: 0
From: St. Louis, MO
Plaster,
Sorry to hear about your sick vette! That sucks!
I would suggest looking at the valvetrain, like bent push rod. If the engine still feels like it is missing then one of the cylinders isn't producing its share of the power. A spun bearing typically will cause a drop in oil pressure and will not make the engine feel like it is missing, but will make noise.
When you say it is making a “slight knock”, is it truly a knock or could it be a tapping sound? Have you heard a bad lifter before, and if yes, is it sound something like that?
If the engine is missing at idle, pull the power supply wire to each coil one at a time. The engine idle rpm will change for any cylinder producing power. When you find the coil that doesn't change the idle speed, this will be the cylinder that has the problem. This will allow you to focus on its rockers, push rods, spark plug or maybe even the injector.
Let us know what you find.
Regards,
Eric D
Sorry to hear about your sick vette! That sucks!
I would suggest looking at the valvetrain, like bent push rod. If the engine still feels like it is missing then one of the cylinders isn't producing its share of the power. A spun bearing typically will cause a drop in oil pressure and will not make the engine feel like it is missing, but will make noise.
When you say it is making a “slight knock”, is it truly a knock or could it be a tapping sound? Have you heard a bad lifter before, and if yes, is it sound something like that?
If the engine is missing at idle, pull the power supply wire to each coil one at a time. The engine idle rpm will change for any cylinder producing power. When you find the coil that doesn't change the idle speed, this will be the cylinder that has the problem. This will allow you to focus on its rockers, push rods, spark plug or maybe even the injector.
Let us know what you find.
Regards,
Eric D
Your first paragraph is kinda what I was thinking, hoping it's somewhat easy to handle and not a spun bearing.
Pulling the wires makes sense, thank you.
Pro
Joined: Aug 2007
Posts: 619
Likes: 1
From: ATLANTA GA
Pulling the wires made little to no change when I had the spun bearing trying to determind what cylinder it was. I ultimately had to discover that on the teardown..
most v8's because of having 8 cylinders if you take one down itll still idle about the same unlike say a 4 cylinder(less mass)
Theres a clear difference between lifters tapping, and a knock.
You will be able to hear the noise prevail up top.. With a spun bearing knock youll kinda be able to tell its deeper down in the engine..
most v8's because of having 8 cylinders if you take one down itll still idle about the same unlike say a 4 cylinder(less mass)
Theres a clear difference between lifters tapping, and a knock.
You will be able to hear the noise prevail up top.. With a spun bearing knock youll kinda be able to tell its deeper down in the engine..
