lifters pumped up odd bank only ls7
07-19-2019, 05:56 PM
#1
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
lifters pumped up odd bank only ls7 I have an LS7 with an unusual problem. No compression on the odd bank of cylinders due to lifter pump up. I've gone to absolute minimum practical lash after extensive troubleshooting and still having problems. Even cylinders are fine. Used compression tester to verify. Cam Motion Stage 1 cam. Texas speed roller tipped 1.82 rockers. Engine rebuilt completely and has 9.7 : 1 compression for marina 87 oct gas. Pushrods vary 7.700, 7.750, 7.800 based upon each individual valve gap check. Cylinder heads are WCCH. When the rockers are pulled, leakdown test is fine. The LS3 I ran in the boat last summer worked so great that I opted for an LS7. HELP?
07-19-2019, 09:45 PM
#2
ModSquad
iTrader: (6)
Are you using an adjustable push rod to find your pr length? You currently are using equal length pushrods on both banks? Have you verified your actual pushrod length with a caliper to ensure that they are all same length?
07-19-2019, 09:45 PM
#3
ModSquad
iTrader: (6)
Welcome to LS1Tech!
07-19-2019, 11:11 PM
#4
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
pushrods are different lengths for each valve. I have 4 full sets: 7.8, 7.75, 7.7, 7.65. Measured .140-.180 gap from zero lash on top of each valve when lifters will compress fully (takes a day or so). base circle and/or valve stem height seem to vary. Same method both even and odd banks and only the odd bank pumps up. Most of the valves took 7.7, some 7.75, and couple of 7.8s to get the same lash at each valve either head. Many hours into this already. Started the process with pushrod length checker and quickly discovered measurements varied throughout each head. Lifters pump up enough to open valves just by turning the engine over on the starter with coils disconnected, injectors disconnected, and oil apparent through the pushrods and out the weep holes on the rockers.
07-19-2019, 11:21 PM
#5
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
pushrods are different lengths for each valve. I have 4 full sets: 7.8, 7.75, 7.7, 7.65. Measured .140-.180 gap from zero lash on top of each valve when lifters will compress fully (takes a day or so). base circle and/or valve stem height seem to vary. Same method both even and odd banks and only the odd bank pumps up. Most of the valves took 7.7, some 7.75, and couple of 7.8s to get the same lash at each valve either head. Many hours into this already. Started the process with pushrod length checker and quickly discovered measurements varied throughout each head. Lifters pump up enough to open valves just by turning the engine over on the starter with coils disconnected, injectors disconnected, and oil apparent through the pushrods and out the weep holes on the rockers.
Trending Topics
07-22-2019, 12:59 PM
#9
heads were milled with a potato crinkle cut tool?
First Ive ever read about an engine taking "multiple" sizes of pushrods. I dont know if im just that uneducated or if thats actually possible.
First Ive ever read about an engine taking "multiple" sizes of pushrods. I dont know if im just that uneducated or if thats actually possible.
07-22-2019, 04:40 PM
#10
The motor should run with incorrect sticks, although it may misfire. The OP states the entire bank is not firing, which suggestions an electric issue.
07-22-2019, 08:11 PM
#11
ModSquad
iTrader: (6)
That happens. Its usually slightly different for each head. One head's milling and or casting when made can be slightly thicker or thinner than the other bank. But, since the entire bank is out, I think the problem is electrical. As in the coil pack connector, the pin outs, harness or loom.
The motor should run with incorrect sticks, although it may misfire. The OP states the entire bank is not firing, which suggestions an electric issue.
The motor should run with incorrect sticks, although it may misfire. The OP states the entire bank is not firing, which suggestions an electric issue.
I use a solid LS7 lifter that I modified to find my pushrod lengths, using an adjustable length pushrod. I add my wanted lash and done. I’ve never seen anyone find pushrod length the way the OP is doing in this situation.
07-23-2019, 03:58 PM
#12
Yeah, I don't know whats going on except the PR length seems long. I know he said it was a 7 and they have offset rockers, but I don't know why one bank would be so different than the other that it wouldn't fire. That suggests an electrical problem. The PR lengths are OK for one bank but not the other? No cam or valve train should have that much difference between banks where the bank won't even misfire.
I think its something else, although I have experienced some truly weird motors over the years.
I think its something else, although I have experienced some truly weird motors over the years.
07-24-2019, 11:00 AM
#14
Stock LS7 pushrods are 7.800
Running all the different length pushrods was unnecessary. The lifters have ( I don't recall the exact number) but something like a .050 preload variance that is acceptable (unless they are short travel). So if you had say a .005-.010 variance it wouldn't matter, even if it was .020 it would be fine to use all the same length pushrods. That's what people normally do. Unless like Scott said it's a short travel and you aren't landing in the acceptable zone.
OP how are you checking this? You said you have .140 lash but based on what measurement push rod are you finding that .140??
What lifters are you using?
Are the rocker arms adjustable or no?
Running all the different length pushrods was unnecessary. The lifters have ( I don't recall the exact number) but something like a .050 preload variance that is acceptable (unless they are short travel). So if you had say a .005-.010 variance it wouldn't matter, even if it was .020 it would be fine to use all the same length pushrods. That's what people normally do. Unless like Scott said it's a short travel and you aren't landing in the acceptable zone.
OP how are you checking this? You said you have .140 lash but based on what measurement push rod are you finding that .140??
What lifters are you using?
Are the rocker arms adjustable or no?
Last edited by 00pooterSS; 07-24-2019 at 11:08 AM.
08-22-2019, 10:41 AM
#15
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
checked springs (after market dual) and looked fine. Then swapped back to the stock rockers and the engine ran great. Not sure why the rockers would cause lifter pump up. The roller rocker tips looked fine on the valve stems. Sent the rockers back to Texas Speed, no issues found. Still stumped.
08-22-2019, 10:57 AM
#16
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
08-22-2019, 11:05 AM
#17
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Also, pushrod lengths vary cylinder to cylinder, not just left to right bank.
Cam motion base circle only varied approx .015" intake to exhaust lobes and were fairly consistent.
08-22-2019, 11:08 AM
#18
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Stock LS7 pushrods are 7.800
Running all the different length pushrods was unnecessary. The lifters have ( I don't recall the exact number) but something like a .050 preload variance that is acceptable (unless they are short travel). So if you had say a .005-.010 variance it wouldn't matter, even if it was .020 it would be fine to use all the same length pushrods. That's what people normally do. Unless like Scott said it's a short travel and you aren't landing in the acceptable zone.
OP how are you checking this? You said you have .140 lash but based on what measurement push rod are you finding that .140??
What lifters are you using?
Are the rocker arms adjustable or no?
Running all the different length pushrods was unnecessary. The lifters have ( I don't recall the exact number) but something like a .050 preload variance that is acceptable (unless they are short travel). So if you had say a .005-.010 variance it wouldn't matter, even if it was .020 it would be fine to use all the same length pushrods. That's what people normally do. Unless like Scott said it's a short travel and you aren't landing in the acceptable zone.
OP how are you checking this? You said you have .140 lash but based on what measurement push rod are you finding that .140??
What lifters are you using?
Are the rocker arms adjustable or no?
08-22-2019, 11:12 AM
#19
Teching In
Thread Starter
Join Date: Jul 2019
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
checked springs (after market dual) and looked fine. Then swapped back to the stock rockers and the engine ran great. Not sure why the rockers would cause lifter pump up. The roller rocker tips looked fine on the valve stems. Sent the rockers back to Texas Speed, no issues found. Still stumped.
Last edited by tyeegs; 08-22-2019 at 12:21 PM. Reason: signature added
