High throttle miss

[Texasdoc]

From memory:
Bore - 4.030
Stroke - 4
Rod length - 6.2
Cylinder cc - 72
Piston dish - 15.8
Piston to deck - 0.017
Head gasket thickness - .030
Head gasket bore - 4.060

Static compression - 9.55:1

AFR recommends those plugs "as a starting place" with these heads.

[jhv48]

Just a thought, have you checked the rev limiter in your msd box?
Might have been set to 4500 rpm.

[Jac Mac]

Originally Posted by jhv48

Just a thought, have you checked the rev limiter in your msd box?
Might have been set to 4500 rpm.

Coming up to five days of silence makes me wonder if Jim hit the nail on the head!

[DWRAT]

Originally Posted by Jac Mac

Coming up to five days of silence makes me wonder if Jim hit the nail on the head!

Not a chance I bet.

[Gaz64]

Originally Posted by jhv48

Just a thought, have you checked the rev limiter in your msd box?
Might have been set to 4500 rpm.

He says he a Mallory Hi-Fire.

Worthwhile checking, although hopefully already has.

Interesting the fault occurs at the lowest RPM limiter setting.

[Texasdoc]

No, it is not the limiter. As discussed previously in this thread, that has been checked. The Mallory box was even changed to a MSD digital 6AL2 without any change in the misfire. No news because the car is now in the shop. They have had it a week but I don't think they've gotten to it yet.

I will come back and report here when I get any more information. Just discussing it with them when I dropped it off, they think it is valve float. This is because I've replaced everything on the ignition. We will see.

[Texasdoc]

Ok, just got a call from the shop. At least one broken valve spring. He said these springs are only good for 6000 rpm and up to 600 lift. I need springs for 7000 (I run up to 6000) and 650 lift (I have 610).

Any spring recommendations? I will probably need new retainers, etc. Anyone have a good site where I can get info about spring size, height, shims, pressure, etc. Also info about how to correctly setup everything?

It's weird, AFR says the stock springs that come on these AFR 195 renegade heads can handle 7000 and 650... Maybe they changed them at some point.

[blykins]

You will need to measure your install height with those retainers. If I have an install height, I can recommend a valve spring.

Do you have a spring mic or does the shop have one?

[Texasdoc]

Originally Posted by blykins

You will need to measure your install height with those retainers. If I have an install height, I can recommend a valve spring.

Do you have a spring mic or does the shop have one?

I ordered one from Amazon. I'll get the car back tomorrow. Once I get the mic, I'll measure everything then give you a call.

[Texasdoc]

You think I did damage to the lifters or cam by using the stock AFR springs? If they are rated for 600 lift and I have 608, do I need to check the lifters? Or do you think the hydraulic lifters could/should have protected the system?

[blykins]

Very doubtful.

For one, you probably don't have exactly .608" lift. With pushrod deflection, valvetrain geometry, etc., you prob have more like .590" at the valve.

Also, the spring data is based on coil bind clearance. Most springs are rated at around .060" coil bind clearance. You can effectively run .050-.055".

However, I would be rolling the engine over and seeing now much coil bind clearance you have, how much retainer to valve seal clearance, etc.

How many broken springs did they find?

[DWRAT]

Originally Posted by Texasdoc

He said these springs are only good for 6000 rpm and up to 600 lift. I need springs for 7000 (I run up to 6000) and 650 lift (I have 610).

AFR 195 Renegade heads are rated to 7,000 rpms per ARF specs.
I'm betting you have a different problem causing your misfiring.

[Texasdoc]

Originally Posted by blykins

How many broken springs did they find?

They took the driver's side valve cover off and found "at least one" broken inner spring. I don't think they did any more than that. Once he found the broken spring he called me to see what I wanted to do. The labor alone on replacing them all was quoted as $1k. He was going to go"talk to the machine shop" to see what springs they recommended. I don't know anything about their machine shop, and I trust Brent, So I just told him to put it all back together and I would do the work myself.

Originally Posted by DWRAT

AFR 195 Renegade heads are rated to 7,000 rpms per ARF specs.
I'm betting you have a different problem causing your misfiring.

That's if AFR used the same springs when I bought these heads as they do now. Yes, the current springs are rated for 7k, but I read on other sites that previously the 7k springs were an option, not standard. They have since started using the better springs as standard. I don't know which springs I actually have.

The shop guy said a spring was broken. He said they were only rated to 6k and were weak. I didn't ask how he decided that. Either way the springs need to be replaced if there is a broken one.

When I get it back tomorrow, I'll see if I can figure out what springs they actually are, then find their ratings. They should be painted with a color stripe for identification.

[Jac Mac]

$1k to swap a set of springs..Phew. !!

[Texasdoc]

OK, here's the damage. This is the Cylinder 7 exhaust spring. What's left of it anyway. It is the only broken one I've taken off so far. 7 intake is good. I'll get the spring mic and measure installed height later this week. I can see that the outer spring of Cylinder 3 exhaust is also broken.

There are no color markings on these springs anywhere to tell me what springs they actually are.

[jhv48]

If you want to do the job yourself without removing the heads, go to youtube and watch a couple of videos. Key to success is preventing a valve from falling into the cylinder once the springs are removed. Buy a good valve spring compressor tool and once you have the correct parts, R&R should only take half a day. While you're at it, pull the pushrods and make sure they're still straight and not damaged on the ends.

[Texasdoc]

Originally Posted by jhv48

Key to success is preventing a valve from falling into the cylinder once the springs are removed. Buy a good valve spring compressor tool...

Yeah. I learned that today the hard way. You can only take one off at a time. Was able to get the valve back up and reattach the good intake spring.

I have a nice spring compressor - that's how I was able to get the broken one out. Thanks.

[Gaz64]

That's right, only one cylinder at a time at TDC for that cylinder.

[cobrakiwi]

Ouch!
Have not done this job in years, but we used to use a modified spark plug with a compressed air hose fitting welded to it, fill cylinder with compressed air to hold the valves up, one cylinder at a time.
You were lucky not to drop a valve there
Good luck on your repairs.

[Texasdoc]

Yeah, I had the compressed air running, but the intake valve slid down the guide when I tried to compress the exhaust spring. Lucky for me, I had the piston most of the way up, so it caught the valve before it fell completely into the cylinder. I was able to slowly raise the piston until I could grab the valve.