Stuck valve? or stuck lifter?
#1
Member
Thread Starter
Join Date: Jul 1999
Location: Indianapolis, IN
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Firebird
Engine: 412ci/sb
Transmission: Built 700R4
Stuck valve? or stuck lifter?
I am bending an intake pushrod. The other cylinder I checked is fine. The car was ran for the twenty minute cam break in no problems. Come back the next morning and start motor and the car is backfiring out of the carb. Pulled valve covers and checked all the valve lash. The #1 cylinder both rockers were loose. Fixed those and all others were ok. Started the motor and it ran fine for 5 min or so and the backfiring began to get worse. Shut it off and the rocker was loose again. Checked the pushrods this time and the intake pushrod on #1 was bent no others were. So is it either a stuck valve or a lifter? what do you guys think? Thanks
------------------
------------------
- 412ci/sb
#3
Supreme Member
Join Date: Dec 1999
Location: Reno, NV
Posts: 1,237
Likes: 0
Received 1 Like
on
1 Post
Car: yep
Engine: uhuh
Transmission: sure does
As stated above, back another rocker off and check spring hieght.
Did you lube the cam real good with assembly lube??
When you have it back together, check the lift by watching the rocker in the problem cylinder, how does it compare to the others??
Its not very common, but I have seen cams go flat right after break in. (unless its a roller, you didnt specify)
------------------
ASE Mechanic/Machinist/Smog Tech
1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...
R.I.P. #3
"He can see air"
[This message has been edited by Engineboy (edited October 14, 2001).]
Did you lube the cam real good with assembly lube??
When you have it back together, check the lift by watching the rocker in the problem cylinder, how does it compare to the others??
Its not very common, but I have seen cams go flat right after break in. (unless its a roller, you didnt specify)
------------------
ASE Mechanic/Machinist/Smog Tech
1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...
R.I.P. #3
"He can see air"
[This message has been edited by Engineboy (edited October 14, 2001).]
#4
Member
Thread Starter
Join Date: Jul 1999
Location: Indianapolis, IN
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Firebird
Engine: 412ci/sb
Transmission: Built 700R4
They are hydraulic lifters. I will try that and a compression test as well to see if a valve is sticking. It will show up. Thanks
#5
Member
Thread Starter
Join Date: Jul 1999
Location: Indianapolis, IN
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Firebird
Engine: 412ci/sb
Transmission: Built 700R4
I am going to put another pushrod in and see if it acts up again. If it does it will be because of a bent valve most likely and I will pull the head and go from there.
#6
Supreme Member
Join Date: Jul 1999
Location: Loveland, OH, US
Posts: 18,457
Likes: 0
Received 15 Likes
on
15 Posts
Car: 4
Engine: 6
Transmission: 5
What cam, valve springs, and rockers?
I'd say the likelihood of a bent valve causing that is somewhere between slim and none. Valves and lifters don't "stick" with enough force to bend metal parts. I'd suspect a spring reaching coil bind.
------------------
"So many Mustangs, so little time..."
ICON Motorsports
I'd say the likelihood of a bent valve causing that is somewhere between slim and none. Valves and lifters don't "stick" with enough force to bend metal parts. I'd suspect a spring reaching coil bind.
------------------
"So many Mustangs, so little time..."
ICON Motorsports
#7
Member
Thread Starter
Join Date: Jul 1999
Location: Indianapolis, IN
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Firebird
Engine: 412ci/sb
Transmission: Built 700R4
The heads are Sportsman II's assembled the springs say max lift .560 My cam is a comp reduced base circle .480/.480 230/230 112 seperation. I have 1.6 rockers as well. Non of this points to coil bind. Pushrods are .100 longer to compensate for reduced circle.
Trending Topics
#8
Supreme Member
Join Date: Jul 1999
Location: Loveland, OH, US
Posts: 18,457
Likes: 0
Received 15 Likes
on
15 Posts
Car: 4
Engine: 6
Transmission: 5
Do the heads have guide plates, or slots, or large holes? Are the rockers self-aligning?
------------------
"So many Mustangs, so little time..."
ICON Motorsports
------------------
"So many Mustangs, so little time..."
ICON Motorsports
#9
Member
Thread Starter
Join Date: Jul 1999
Location: Indianapolis, IN
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Firebird
Engine: 412ci/sb
Transmission: Built 700R4
I am using guide plates. The rockers are full rollers. I am not sure if they are "self aligning"
#10
Member
Thread Starter
Join Date: Jul 1999
Location: Indianapolis, IN
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Firebird
Engine: 412ci/sb
Transmission: Built 700R4
I installed another pushrod in and ran the motor it did fine no problems as of yet. Ran for about 10-15 minutes no clacking sounds or backfiring. Will keep you all updated to see if it re-appears again. Thanks
------------------
------------------
- 412ci/sb
- Edelbrock RPM
- custom tuned Q-jet by Damon
Thread
Thread Starter
Forum
Replies
Last Post
RyanJB
Engine/Drivetrain/Suspension Parts for Sale
0
09-14-2015 03:39 PM
355tpipickup
Tech / General Engine
9
09-13-2015 11:35 PM
dimented24x7
Tech / General Engine
4
09-06-2015 03:51 PM