New 351w Fired up Today but 7 and 8 not firing **Solved**

[73azbronco]

He has got to be hot down there.

 

[nvrstuk]

So what are #7 & 8 doing now? Same no spark fire issue?

A Q jet built for a 302 will work fine on a 351W unless it's built, like really built. Are those 2 plugs wet? Are they getting fuel? You will need to probably (maybe) change metering rods on the qjet but for an easy test of the carb ROTATE it. Turn it 180 on the intake and fire your engine up. Obviously you won't be driving it unless you swap your throttle linkage but it will rule out the potential carb issue ( w/o being there but I don't think that's it)

Did you double check the resistance of those 2 plug wires? I have bought new wires and most will be 1-2K ohms and then the rest over 5-10k ohms. GARBAGE is what's sold today so rule out the plugs not getting spark and make sure they are wet with gas if they aren't firing.

 

[Ol'Blue]

I spoke to Bruce for a while. He said:

• Runing great at first couple of miles - he said the choke was probably on masking another issue.
• Make sure to torque the carb bolts to 8-10 ft lbs as the qjets are particularly sensitive to warping from over torque - check
• Spraying carb/brake cleaner around the carb will change the RPM even with no leaks, What, What Bruce?! He said there is some draw around the butterfly rods and the carbs are tuned to make up for this. Never heard that before but I trust the man.
• The one that shocked me is he said to pull the driver PCV out and spray carb cleaner into the PCV port and to do the same on the passenger side breather. This is to test if the intake manifold gasket is leaking. No change in RPM so gasket should be okay. Note when doing this test on the breather side, make sure the PCV is removed from the oposite valve cover or you can draw the vapors through PCV changing the RPMs.
• Jetting - He noted that the primary jets for the qjet on a Chevy 350 and 454 are almost identical. Second only slightly different so my jetting should be okay but to get it running right and check plug health later. I may need to play with the idle screws a little but got to get the vacuum/carb issue resolved first.
• He mentioned the carb sitting could have goobered things up inside so he said try driving it and maybe it will clear.

I think 7 & 8 are firing about the same as the rest of the cylinders now and maybe at my first post I got bad readings in the temp gauge.

Tomorrow I will try swapping around spark plug wires around but Im still thinking its a carb/vacuum issue.

 

[Ol'Blue]

Have done a bunch of testing over the past week including just about everything suggested except for rotating the carb and even replaced the intake manifold gasket and number 8 still running cold. Number 7 seems fine now, but it may have been fine all along and maybe I just got a bad read.

The only other thing I can think of is valves on number 8 are not adjusted right or a stuck lifter.

Ive never adjusted valve before. Anyone got a good how to for adjusting hydraulic roller lifters and roller rockers?

 

[DirtDonk]

Yes, but first you have to determine if they are even adjustable.
I don’t remember seeing any aluminum heads on that engine. Have you posted pictures of the heads or rocker area yet?
If they are stock cast-iron heads and stock rocker arms, they’re probably not adjustable.
If not sure you’ll have to pull the valve cover off and verify.
Of course if you already know that they are in fact full roller rockers, and adjustable, then it’s all pretty straightforward.

 

[Ol'Blue]

I believe they are adjustable. I pulled the valve cover off and looked for any signs of damage, poor installation or looseness when #8 is at TDC. The only thing I noticed was the small pin that holds the roller in place for the #8 intake sticks out a little more than all the others. See pics circled in red. The other photo is of the exhaust valve with the pin in farther. Searched the internet for image and saw similar variations in how far that pin sticks out.

They are Crane Cobra 1.7 roller rockers F3ZE.

As I mentioned earlier, compression on #8 is good at about 170 lbs. but Bruce was saying a valve or cam lob issues may not show low compression when on the starter but have the issues once the motor is running.

Im so stumped.

 

[Ol'Blue]

Here is a video turning it over.

 

[nvrstuk]

Carbs do not in any application distribute equal amounts of fuel to each cyl. They do surprisingly well but that's as close as it gets.

Adjusting adjustable rockers is real easy, just messy.

-Engine at temp

-Pull off valve cover

-Hopefully you have a cover with the center cut out or you can use a rag to help keep oil from squirting 2-6" above the rocker and on to the headers

-have an extra clean rag handy to swap rags if the first one gets saturated. All you're trying to do is keep oil from squirting everywhere. The entire operation for 2 studs should take 30sec.

I always do this outside and have a hose and fire extinguisher handy. 99% chance nothing happens but...

- loosen the intake rocker nut slowly until it makes a very noticeable clicking/clacking noise then tighten it up appr 1/2-5/8 of a turn for stock 3/8" diameter studs.

-repeat for the exhaust rocker

That's it.

 

[DirtDonk]

How are those adjustable? I haven’t looked up that particular model, but I don’t see studs with nuts in the center, or adjusters at the push rod.

I’m just looking on my phone, but it looks like a simple bolt down pedestal mount.
Can you tell from a different angle whether the roller tips are rolling on the valve stem tips, squarely and in the center?

Maybe I’m just not familiar with that style, but it’s worth listening to what others have to say about it.

 

[nvrstuk]

I think you're right Paul. I am glad I said "Adjusting adjustable rockers is real easy, just messy" and didn't say, yeah, those are adjustble!!!

Pic is blurry. Can you take a pic that is clearer?

 

[Ol'Blue]

Not adjustable

 

[DirtDonk]

Then, to my way of thinking, “adjustable“ is done by modifying the length of the pushrod.

 

[DirtDonk]

Which means hopefully they are already adjusted correctly!
So, I’ll reiterate to get a good shot of the roller tip as it hits the valve stem tip.
Specially handy if you can mount a camera and take a video of it while you are turning the engine over. if they are rolling back-and-forth just over the center, then the set up of the rocker arm is generally correct.

Then I guess after that, the only way of checking, if a pushrod is too long and holding the valve open, would be to back off the bolt until you feel lash. Then get it down to zero lash, and count the number of turns before the bolt is torqued tight.

But that’s really more trouble than it’s worth at this point. With a reading of 170 psi it’s a good bet that the valve is not being held open in anyway.
And since it’s not ticking, the lifter has not collapsed and the rocker is not loose.

Which means you’re probably back to fuel mixture in an imperfect manifold through an imperfect head through an imperfect carburetor.
Which is probably something that has gone on all along, and we were just blissfully ignorant of it, because none of us had infrared thermometers back in the day.

 

[nvrstuk]

Yup, what Paul said.

 

[ba123]

You had compression on that cylinder, so your valves must be closing, right?

 

[Broncobowsher]

Compression, confirmed.
Fuel. Carburated and the other cylinders are running, so there is fuel.
Spark. We know there is spark at the coil and to many of the cylinders. Unless I missed something, this is what I would be looking at. Until I see confirmation that the spark plugs have been swapped with known good cylinders. And the plug wires swapped with known good plug wires. It is the top of my suspect list.

 

[ba123]

What about your dist cap? Have you tried sanding the inside contact for #7?

 

[73azbronco]

Then, to my way of thinking, “adjustable“ is done by modifying the length of the pushrod.

Bingo. Was an adjustable pushrod checker used? Odd though to have just two cylinder not adjusted correctly, usually most are wrong when you change heads or rocker setup. Yeah I am pretty sure my eyes see hydraulic lifter rockers…

 

[Ol'Blue]

Here is a video of the rockers. Looks good to me. I also hooked up air compressor line to #8 at TDC. The valves seem to be holding closed since the compressor will turn the motor until one of the valves opens letting the air escape.

I was told you could get a good compression reading when turning the motor over with the starter but could lose compression at higher RPM.

Next test is to put the valve cover back on and fire it up and hold the relief open on the compression tester.

Then I’m going to move to spark again. Swapping plugs and wires again.

 

[Ol'Blue]

What about your dist cap? Have you tried sanding the inside contact for #7?

The cap, distributor, wires are all new. I realize that doesn’t mean they should be good. But I did pull the cap and all looks good.