Valvetrain noise after tune and dyno Ls 4.8
12-09-2018, 07:07 PM
#1
Teching In
Thread Starter
Join Date: Oct 2017
Location: Southern Indiana
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
Valvetrain noise after tune and dyno Ls 4.8 Ok so I had my engine tuned and dynoed when I got the car because someone had put in a cam in it but did not have the right tune. After it put down 5 dyno passes I noticed a tick from the valve train on the driver side. It’s got a big cam and dual springs, but I don’t know the specs. Listening with a mechanics stethoscope it sounded like 5 & 7.
So I have checked torque on the rockers and I have pulled the rockers to inspect them and the pushrods. I don’t see any issues aside from and almost impercievable bow in the push rods.
When rolling them on the granite countertop (wife loves it) I can just barely tell that one of them rolls slightly smoother than the other two. How much runout is allowed on a push rod? And is that little bit i described enough to cause a tick?
i have heard that ls engines with a big cam will have valve train noise but how much is ok?
My my next step is to pull the head to check the lifters.
Any my input is appreciated.
So I have checked torque on the rockers and I have pulled the rockers to inspect them and the pushrods. I don’t see any issues aside from and almost impercievable bow in the push rods.
When rolling them on the granite countertop (wife loves it) I can just barely tell that one of them rolls slightly smoother than the other two. How much runout is allowed on a push rod? And is that little bit i described enough to cause a tick?
i have heard that ls engines with a big cam will have valve train noise but how much is ok?
My my next step is to pull the head to check the lifters.
Any my input is appreciated.
12-09-2018, 07:26 PM
#2
TECH Senior Member
If you detect ANY out-of-straight in a pushrod, it is DONE. Then find out how/why it bent.
12-10-2018, 06:16 AM
#4
Moderator
iTrader: (4)
Join Date: Jul 2014
Location: My own internal universe
Posts: 10,446
Received 1,836 Likes
on
1,145 Posts
For pushrods, I normally put one end in a drill and trigger the drill. If it's bent, it wobbles. if it wobbles, check that hole for eyebrows. OP, which lifters and pushrods, and how much preload? Sometimes just using not quite long enough pushrods makes the system pretty noisy.
Which is why it is best to always err on the side of heavy pushrods, so they don't flex and pole-vault.
It's possible they used the stock pushrods with heavy springs causing them bend.
12-10-2018, 09:34 AM
#5
Stock push rods on a large cam is terrible to begin. Heavy dual springs on an old used GM lifter also less than ideal
rockers could be spitting rollers out as well Lastly if the springs weren’t setup properly AND crappy push rods it quite possibly went into valve float and could have tagged pistons with valves which likely bent that pushrod and others
rockers could be spitting rollers out as well Lastly if the springs weren’t setup properly AND crappy push rods it quite possibly went into valve float and could have tagged pistons with valves which likely bent that pushrod and others
12-10-2018, 09:49 AM
#6
TECH Fanatic
iTrader: (7)
I'd like to see zero "runout" on a pushrod...the fact you can see any with the naked eye is enough reason throw them all away and start with at least 3/8th's...
EDIT: You can get Brian Tooley 3/8th's chromoly .080" wall for about a hundred bucks. Cheap insurance.
12-10-2018, 11:11 AM
#7
TECH Senior Member
And yes, stockers with heavy springs is a recipe for pushrod failure in some cases. At which point they too will be tossed.
Trending Topics
12-10-2018, 01:43 PM
#8
Teching In
Thread Starter
Join Date: Oct 2017
Location: Southern Indiana
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
For pushrods, I normally put one end in a drill and trigger the drill. If it's bent, it wobbles. if it wobbles, check that hole for eyebrows. OP, which lifters and pushrods, and how much preload? Sometimes just using not quite long enough pushrods makes the system pretty noisy.
Which is why it is best to always err on the side of heavy pushrods, so they don't flex and pole-vault.
Which is why it is best to always err on the side of heavy pushrods, so they don't flex and pole-vault.
I have a pushrod length checker and the plastic rocker for a SBC will that work for a ls head?
12-10-2018, 02:37 PM
#9
Moderator
iTrader: (4)
Join Date: Jul 2014
Location: My own internal universe
Posts: 10,446
Received 1,836 Likes
on
1,145 Posts
i don’t have a lot of detail on this motor as it was already in the car when I bought it, but these sure look like factory pushrods. No markings and ball type. I haven’t checked preload yet ran out of time yesterday. Going to go buy a set of 12” calipers to check current length and then I’ll check preload settings.
I have a pushrod length checker and the plastic rocker for a SBC will that work for a ls head?
12-10-2018, 06:35 PM
#12
TECH Senior Member
12-10-2018, 09:16 PM
#13
Teching In
Thread Starter
Join Date: Oct 2017
Location: Southern Indiana
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
12-10-2018, 09:59 PM
#14
This reminds of the old days. Mishiftin my L-82 vette with the big cam to 8000. Going home and rolling out the pushrods on a glass table top tossing the bent ones for straight ones so I could get back on a lonely back woods road so I could cook up the tires for those two hundred foot burnouts again. I miss that Muncie stone crusher.....
12-11-2018, 10:40 PM
#16
This reminds of the old days. Mishiftin my L-82 vette with the big cam to 8000. Going home and rolling out the pushrods on a glass table top tossing the bent ones for straight ones so I could get back on a lonely back woods road so I could cook up the tires for those two hundred foot burnouts again. I miss that Muncie stone crusher.....
come on man....bring it in for the real deal.....
12-16-2018, 02:15 PM
#19
Teching In
Thread Starter
Join Date: Oct 2017
Location: Southern Indiana
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
Ok so here’s the data. Used pushrod measure 7.385-7.39 even the bent ones. Using my pushrod checker which only would go down to 7.37 at zero lash took just short of one whole turn to seat the rocker. So by my math that’s just about right with .050 preload.
That means a 7.375 pushrod would be what I want. I think comp does them in.025 increments. Or should I just go back with a 7.4? But that would be close to .075 preload.
The interesting thing is that I thought that I would see more length difference in the bent rods that would be causing the valvetrain noise I have.
That means a 7.375 pushrod would be what I want. I think comp does them in.025 increments. Or should I just go back with a 7.4? But that would be close to .075 preload.
The interesting thing is that I thought that I would see more length difference in the bent rods that would be causing the valvetrain noise I have.