393W stroker issues

[RnrdTheFox]

I've had my new 393W stroker up and running for about two weeks now. I have about 300 mi on it. Yesterday morning on the way into work as I take off and turn at a stop light, the engine stumbles and starts to miss and shake. I'm only a couple miles from the house so I turn around and take it home.

Tonight I run codes and everything checks out for both KOEO and KOER. Since it acts like it's missing, I run a cylinder balance test. It shows that #6 is weak. I run it two more times and get #6 flagged. I check spark plug and wires and everything looks and measures ok. I run a compression check on it and the first time it shows 90 psi, second time it doesn't even pump up. I check #5 and it shows 150 psi. I didn't check anymore at this point.

So, here's the question: what is most likely to have gone wrong? I will pull the valve cover tomorrow and take a look at that. If I don't have compression that would either be a broken ring or valve not closing right?

It sucks to be me. I'm going to have a chat with my engine guy tomorrow. Any ideas or suggestions are appreciated.

thanks,
Renard

 

[Crude dude]

You are on the right track, I bet you will find the issue under the valve cover. Possibly a bent push rod on the intake valve or a broken valve spring? Are they press in studs or screw in? Did the engine run good up until that point and is it making any ticking noises from that bank of cylinders?

 

[Bronco73]

Could also be a wiped out cam/lifter, if its not a roller cam set up. If the new cam was not broken in correctly this can happen.

 

[barronj]

I would almost guarantee it's in the valvetrain. I had THE most random thing happen to me about a year ago, the stud broke in 1/2 just under the rocker, and caused something similar.

 

[RnrdTheFox]

You are on the right track, I bet you will find the issue under the valve cover. Possibly a bent push rod on the intake valve or a broken valve spring? Are they press in studs or screw in? Did the engine run good up until that point and is it making any ticking noises from that bank of cylinders?

They are AFR 185 heads. I think they are screw in right? The engine was running good after getting the initial ideal set. I had the hardest time with the idle. It really didn't like to idle below 800 rpm. I wonder now if something in the valve train was causing a rough idle. It was VERY smooth off idle and cruising. I have noticed a ticking noise from time to time, but not consistent or loud and sounded more exhaust related?

 

[RnrdTheFox]

Could also be a wiped out cam/lifter, if its not a roller cam set up. If the new cam was not broken in correctly this can happen.

It's a roller cam setup. 94 351 roller block with Comp Cam 35-514-8. I ran it for 10 min at about 1200 rpm for break in.

 

[barronj]

about a year ago, the stud broke in 1/2 just under the rocker, and caused something similar.

This happened on AFR185's, with screw in studs (factory hardware), and a mild roller cam (E303)

I sourced a new stud from a machinist who had a few extra for whateve reason. I needed one, he gave me two, I changed it out & I've never had the problem reoccur.

 

[RnrdTheFox]

This happened on AFR185's, with screw in studs (factory hardware), and a mild roller cam (E303)

I sourced a new stud from a machinist who had a few extra for whateve reason. I needed one, he gave me two, I changed it out & I've never had the problem reoccur.

Ok, thanks. I'll know here in a bit. I'm pulling the intake off now so I can get to the valve cover.

 

[RnrdTheFox]

Well, the intake rocker stud snapped just below the nut. That would explain the snap/ding that I thought I heard when it happened.

So, here is the question. Is this just crappy luck on my end with a bad stud or something maybe the builder did? I know I can order another stud and replace this one. But I don't want to have to deal with this again. My builder did call comp cams and asked about the springs, rocker and cam combo.

Thoughts?

Thanks,
Renard

 

[Broncobowsher]

Put in a set of ARP rocker studs and be done with it.

 

[Apogee]

Put in a set of ARP rocker studs and be done with it.

X2...sounds like you may get out of this relatively cheaply. ;D

 

[Mountain Ram]

Was there no damage to the rocker? Glad it turned out rather simple... Can't believe they would use crappy studs like that... Two members on here with the AfR heads experience the same failure...

 

[bmc69]

What rockers are you running?

 

[TwoDalesDad]

I had the keepers fall off, On number 6...I pulled over after the same stumble/cough...lifted the Vcover off...and the keepers were layin there...So I took the spring off lifted the valve up as high as I could get it then black tapped it in place....As it turned out....The Installed height was a Cu t hair long.....And That is Why The Engine From the Start didnt idle right to begin with...

 

[RnrdTheFox]

Was there no damage to the rocker? Glad it turned out rather simple... Can't believe they would use crappy studs like that... Two members on here with the AfR heads experience the same failure...

No damage from what I can see. Everything is smooth and no galling. Yeah, they should put good studs in for what you pay for the heads.

 

[RnrdTheFox]

What rockers are you running?

comp cam 1442 roller tip 1.6 rockers

 

[bmc69]

Good rockers..I use those a lot.

Well heck...nothing looks "wrong". And the location of that stud break means it almost certainly had to be purely a tension failure. I assume you've made sure that your rocker geometry, as determined by push rod length, is correct and that the rotation is well within the design range for that rocker....

 

[nvrstuk]

Change all the studs to ARP. If you follow the "go fast" Mustang forums you will find that very, very few don't upgrade all hardware in the heads... doesn't matter what brand. Make sure you upgrade the keepers too because when one of them fail your new engine is toast...

 

[RnrdTheFox]

I assume you've made sure that your rocker geometry, as determined by push rod length, is correct and that the rotation is well within the design range for that rocker....

Can you explain what you mean here? I had my engine guy do the long block in hopes that this kind of thing would not happen. If I swap out the studs, etc. I will be doing it myself most likely and need to understand what I need to do to do it right.

Thanks.

 

[bmc69]

Can you explain what you mean here? I had my engine guy do the long block in hopes that this kind of thing would not happen. If I swap out the studs, etc. I will be doing it myself most likely and need to understand what I need to do to do it right.

Thanks.

What I was referring to is the correct pushrod length that assures that the rotation of the rocker through full range of valve lift is "centered" in the rocker slot and thus not binding at either the fully open or fully closed rotation positions.