Head pitting in combustion area

Without getting into any specific case in point, what are the possible results of running heads with pitting in the combustion area? Are we talking detonation possibilities? Are there ways to repair heads with pitting??

Would like to talk theory and how it would effect the combustion itself as well as how various compression ratios may amplify any problems ***ociated with pitting.

Thanks performance gurus!

Scooter

 

Let's see your acne kid.

 

yep, would love to see pictures. how's the piston look?

-scott noteboom

 

YAH! So get off your damn ***!

 

Uh hum....

Yes I have some pitted heads, and it's the reason that I'm interested in the subject, but I want to learn more about the general THEORY here. Since we talk about old engines around here, I figured that this might be a useful subject to expand our knowledge. I really didn't want to get into a specific case in point.

 

**sigh**
Depends on to which degree they are pitted. SO let's not get into SPECIFICS, but let's go with SAMPLES.

 

majority of cases that i've seen this in are due to bad long term detonation. basically because the ignition of this remaining "end gas" occurs after normally timed combustion, it occurs at very high heat / pressure that causes huge pressure, irregular heat and thus damage focused towards the combustion chamber. seen this much worse with aluminum heads too... on a steel head, you'll usually see piston damage as well, if it gets to that degree. piston top and top ring gland.

-scott noteboom

 

It seems to me that pitting would be less of a problem than little high spots like when you get carbon deposits that start curling up and hanging there, or like the protruding part of a spark plug or bumps caused by casting imperfections. The inside of the pit would probably be cooler than the surface of a bump.

If you look at the roof of the combustion chamber in cross section, little protrusions would be the hottest points probably, and then the flat areas would be mostly a consistent temperature, and then the pits would be even less temperature because they're in a little deeper in the cast iron. There's a big temperature gradation going from very hot at the combustion chamber side to much cooler on the water jacket side. The pits would be in there slightly closer to the water jacket side, so it seems like they should be cooler. Unless maybe carbon winds up deposited in the pits and stays hot because it doesn't conduct heat as well as the surrounding steel.

But pitting might lead to other problems like cracking of the cast iron. And pitting might naturally make a place for carbon deposits to get a grip on the surface that you wouldn't have with a polished smooth combustion chamber. A polished combustion chamber tends to reflect heat in towards the center of the chamber more than a rough or pitted surface.

I guess if the pitting's not too terrible, and you're not running at high compression and not using really ****py low octane gas, and your timing and fuel/air mixture is correct, it probably won't be a problem. The pits will increase the volume of the chamber slightly and lower compression slightly -- probably not enough to make much of a difference unless the pits look like big caves.

I'm just tossing out ideas though.

 

Which means that NO Scooter, you would not run them without doing some porting/polishing and possibly even changing your seats out, ESP on older engines.

When an engine gets to that degree of heat, it starts to also cause warpage.

 

AH HA! Now were talkin'! However... I should have taken the specifics a step further. Pitting due to rust. Thinkin' about those guys whose engines who have had water in the cylinders at some point and caused corrosion pitting. Good point about the detonation pitting though.

For Brandy...


These are HD Sporty (ironhead obviously) and they are not mine and don't know who's they are. I'm not posting a picture of my heads because I don't want this thread to turn into a discussion (or non-requested opinions) of "s**** 'em or keep 'em". I'm interested in the performance effects (if any) ***ociated with engines that have corrosion in the combustion chamber. I've been noticing more and more people talking about engines that they're digging up out of fields and surely some of these will have some pitting issues. So let's talk about the effects.

 

THIS is what I'm talking about! Thanks for kicking that off!

MORE!

 

yeah, that looks like rust breaking down. i'd bead blast the ****ers, valve job em and run em. i've rebuilt some performance motors (used to get combustion chamber pitting quite a bit w/ a bad run on high boost turbo vw drag motors) after just bead blasting, crack inspection, and lightly cleaning up pitted combustion chambers (couldnt take too much out, as it would affect cc of chamber.) Seemed to cause no problems.

-scott noteboom

 

If we need more examples... here is combustion chamber of an AMC 304 head.


Looks to be a cast finish in the combustion area.

Also, I think it's fair to say that whenever a seat is pitted it either needs to be replaced or machined. So, let's stick to the combustion chamber itself.

 

Ack, NOW you're starting to fill in some blanks dummy! See, you said pitting, we asked for pics to make it more specific...ala RUST.

My inner nerd spends hours reading the ******** at www.eng-tips.com

Having an equal/smooth surface will help keep the heat even thru the head. Like Rusty said, it will create a cooler area. Creating a cooler area is not what you want in an efficient setup, it will also impede air flow which will kill your horsepower in the long run.

Then you leave yourself open for carbon buildup, which lead to sharp edges, then which lead to detonation issues.

Either that or it's late and I'm babbling.

 

I'd bead blast those before worrying about it too much. I bet they'll look better than you think after you bead blast them. If the pits don't wind up too deep, you could use a die grinder and smooth up the combustion area and use them.

If you don't have a bead blaster, you could buy a gallon or two of some stuff called "Evaporust" and let them sit in that stuff for a few days in a bucket, and that stuff will dissolve all the rust without hurting the metal at all. Then they'll just have a sooty black coating on them that will rinse off with water and a little scrubbing with a toothbrush. I left some rusty trim parts in that evaporust for a few months by accident and it didn't hurt the parts at all. It really does just etch the rust -- unlike the acid types of rust strippers which can also etch the steel if you leave it in there too long.

 

You've (somewhat) answered your own question....in that many OE heads use an as-cast chamber & work just fine. Carbon buildup tends to mask any pitting/roughness anyway, although it may cause issues of its own.

Oddly enough, some newer designs might suffer more, in the event of pitting/damage, simply because the chamber is so efficient that there is little buildup...the Kaase P-51 comes to mind, and certain AFR chambers.

Chambers can always be ground or coated to eliminate problems, up to a point.

Squish grooves tend to defy the whole theory of hot spots in the chamber being bad....the benefits seem to outweigh the potential hazards. Depends on the chamber design & a whole slew of other things, though.

 

I ran 354 heads on a 392 that had rust pitting in one chamber. Never noticed any differance between that chamber and the others. Worked fine for me.

 

What you say "coated", what can be used to coat a combustion chamber?

You're babbling, but you've babbled good info! SEE! That wasn't so tough!! LOL! Did you need pictures to say that?? (elbow, elbow)

Speaking of pictures...

Those heads aren't mine. Just grabbed the pictures off the net (mostly for Brandy), but I suspect that a lot of people may encounter similar rusty finds out there, so I thought it would be a good example. I'm sure those would clean up better then some.

 

YAH I needed pics. Sometimes, there is a SLIGHT pitting from rust bubbles. Stuff like that can be cleaned up with just a run of your tongue thru the chamber. Other times, it looks like an old prom date of mine.

You can coat them with an epoxy and then obviously zoom zoom on a lil port/polish.

 

I just had this hilarous vision of you in an 80's prom dress! BWAHAHA!!! I won't go into the vision of you and your tongue and the typical layout of a combustion chamber with valve seats... UHOH!!!!

 

Oh yeah... back to combustion pitting.

How about the effects of higher compression ratios? I ***ume aplification of any problems that may occur?

 

Oh My! that was an unexpected visual image to a tech question...you two are dirty, hehehe

 

She's the one licking combustion chambers!

 

And God Bless her for that, never a dull moment with Brandy...the drink or the girl...she's totally swoon-worthy...anyway, good luck with your questions, you sicko...hahaha

 

I'm as innocent as freshly driven slush. =O)

I'm having a brain freeze, but I do know the answer to that question.

 

LOL! Thanks! I need it!

Seriously though...

Anything else to add here?? I realize this has moved to a more "adult" thread, but is there still more we can learn? Anyone ever had there pitted areas coated or smoothed out?

 

For some reason, when she mentioned prom dates of the past....combined with the old rusty pic...a sudden image of "Stinky the Austin bum" flashed through my mind. I thought, "She should have better taste."

Then I started thinking about my own two daughters beginning to date in the next several years. Boys just like Stinky - in mindset, if not appearance.

Then I made a mental note to castrate any boy who sets foot within a 20 foot range.

Yes, this was a completely useless post by me....anyone with daughters will understand.


(Ahem) Swain Tech, a**** others, can coat chambers...it's a proprietary formula as a rule. The intent is to reflect heat back into the chamber, but it can help to fill pitting.

I have had some luck in doing this myself with Tech Line coatings...they are hard to find, though. I think Summit & Jegs stopped carrying them. You can apply & cure them yourself, though they aren't quite as effective.

VHT white high-heat will work for a little while, but it was used more to evaluate the combustion process in drag/circle track engines & I haven't seen anyone do it for a while. Aluminum heads are easier to evaluate & nowadays you can practically get them at Wal-Mart.

Scoot, one other thing that occurred to me, that you may not have run across, is the concept of "dimpling"...actually peening the chamber with a rounded punch. This looks something like a golf ball surface....it was done to increase turbulence, or sometimes to help reflect the mixture back towards the plug. With the introduction of better chambers this seems to have died, or been replaced by the "groove".


One final note: the "baking" process, as opposed to a regular hot tank or jet spray tank, will make even completely awful heads/blocks look nearly new....if you can find a machine shop to do it.

 

EXCELLENT INFORMATION!!!!! Now we're getting somewhere!

 

and in regards to how higher compression ratios come into play in causing pitting metal break down, etc.... well, everything bad becomes violently more bad with higher pressure (compression.) that includes higher compression ratio, boost or improved air/fuel efficiency (like nitrous, fuel.) having worked on a lot of high boost turbo stuff in the past, the damage becomes much more dramatic in lean out, detonation, timing related problems. Instead of blowing out a pit, it tends to blow out entire holes

what's *****en is that at times, especially if you actually muffle the exhaust loudness, you can briefly hear that particular frequency of sound that resonates through the motor and says very quickly "you're ****ed" right as the motor is melting down in the top end... It's a different frequency than your typical ping.

-scott noteboom

 

I hope I NEVER hear that on any engine I ever build!