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

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I' am for the lifter. If you loosen a rocker on a known good valve and check the heigh you will know. If it is the same on both valve you have a stuck lifter.

 

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)


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[This message has been edited by Engineboy (edited October 14, 2001).]

 

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

 

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.

 

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.

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"So many Mustangs, so little time..."
ICON Motorsports

 

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.

 

Do the heads have guide plates, or slots, or large holes? Are the rockers self-aligning?

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"So many Mustangs, so little time..."
ICON Motorsports

 

I am using guide plates. The rockers are full rollers. I am not sure if they are "self aligning"

 

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

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