The Stovebolt Site Forums The Shop Area Engine Shop hole in piston!! aaahhh!!!

haven't been on the forum for awhile, been too busy trying to make some $$, having a newborn is expensive (but I have to say it is a true joy, it's fantastic having a kid!).
but back to subject: awhile ago I had this post about overheating, breaking down and ending up with zero compression in one cylinder. a lot of good tips from everybody here, but everybody was wrong. it took me awhile to save up for a gasket set, a torque wrench and some odd parts, but I finally started last week, taking head off, checking valves, all that. turns out I got a hole about the size of a penny in my #5 piston! no one ever guessed that.
and again, this is something I never done before. my idea: drain oil, pull the oil pan, take connecting rod off, take out piston, install new piston, attach connecting rod, attach oil pan, put head and all that back on, add oil & coolant and we're driving again. yes or no?
few things I wonder about:
-is it really that simple?
-do I need to hone the cylinder?
-are the NAPA pistons any good (they seem to be the only one selling single pistons)
-am I on a road to disaster replacing just one piston?
and then the big one: why did this happen? my guess is: leaking manifold gasket caused running lean, combined with being too hot, and maybe a leaky exhaust valve (it had quite some carbon on it), and all this together caused meltdown.
alright, that's a long long post, hope I get the little truck running soon, this is no fun (although I am becoming a pretty good mechanic!)

I'm not the most experienced mechanic around here, and better ones are likely to jump in. My feeling is that you want to be sure you know why it happened before deciding how to proceed.

Yes you can replace just the one piston, and while that's not ideal, it should run better afterward.

I'd spend some effort flushing the oil passages to make sure nothing from that holed piston remains inside to cause more trouble. I'd worry that it may have already caused problems, so I'd check at least a few more bearings before putting it back together.

I think it would be a shame to have the head off and not do a valve job, unless it had one real recently and has no valve damage from the piston problem.

But knowing what caused that hole in the piston is the key. Fixing the symptoms but not the root cause can sure lead to frustration and more expenses.

Oh, and if you think newborns are expensive, just wait for college... A friend of mine recently joked college was costing him a sports car a year. As he did so I realized I paid more for last semester than I did for my Corvette.

You haven't been using starter fluid have you? That will blow a hole.

no starting fluid. I suffered a breakdown (right between Nowhere, MS and Nowhere, MS) while towing a 12' trailer full of parts. must've happened then, after that I only drove it about 50 feet into the carport.
and the valve job has been done, I agree with you Oldsub, if you take things apart anyway you should make sure they're fine. also discovered that valve springs on a 235 are way tougher than on a Buick inline 8. the Buick springs I could compress with a wood clamp, no chance on the 235. but I got the valves out, checked all clearances, installed new valve stem oil seals, lapped all valves and cleaned them all. razor blade and paint thinner does miracles on carbon deposit.

Holed piston problems are usually caused by detonation. Detonation is caused by overheating, over advanced ignition timing or too low octane fuel. Not likely to be a problem with the fuel unless someone's shaved a lot off the head. But you know you had the overheating, Fixing that has to be a good thing, I would check the ignition timing when the motor's back together too.

Good luck with the truck, Stuart.

Seetz, your summary steps to changing the piston are correct in principle, but simple steps have a way of becoming complicated. First, what engine do you have? Are the pistons aluminum? If this is a 216 or early 235 engine, the connecting rods bearings are babbited and will likely have shims under the caps. Pay attention to the shim stacks and return them to the same place. Also, if this is what you have, make sure you put the dipper on correctly- facing the oil spout in the pan- or toward the cam shaft. If you have a 235 with insert bearings, there may also be a shim under the bearing shell. If there is, make sure it stays where it is when you assemble the rod. I don't remember with any certainty, but the wrist pin may be pressed into the piston, or it may be held by a clamp bolt at the small end of the connecting rod. The early engines had the clamp bolt, but I don't recall on the later engines. With the clamp bolt, the wrist pin floats in the piston, so make sure the pin is centered in the piston and won't extend beyond the piston diameter when you move the rod the full extent of its side play, about 1/16 inch either way. If you have aluminum pistons, there may be a notch that indicates the front of the piston. Don't put it backwards on the rod and in the cylinder. If you have the clamp bolt on the rod, I believe that bolt should face the cam shaft when the assembly is installed in the engine, and the piston should be installed with the notch to the front of the engine. Check the other rods and pistons before you take everything apart. I don't think the cast iron pistons have a 'front' position. Determining the cause of the puncture is of high importance. Detonation is the primary cause of that condition, so make sure you have the correct initial timing and correct timing advance in the distributor. From your description of towing the trailer, you may have had the truck overloaded, and that was the cause of your trouble. Although, if the power piston in your carburetor was working properly and the timing advance mechanisms were working correctly, you shouldn't have had any that trouble. But overheating certainly would be a factor, which may have been the result of overloading the truck and driving at a low speed with that load. Driving with a 3-speed transmission in the top gear, at low engine speed with a heavy load would certainly promote overheating. Check the condition of all the spark plugs. If they are very clean and white, that would indicate a lean fuel mixture, which would also contribute to overheating and detonation.

You may also have to buy a set of rings for the new piston. In principle, you could use the old rings, but you may break them, or bend the rails if you are not careful when removing them from the old piston. If you have to buy a whole set of rings, you might as well re-ring all the pistons. And lightly honing the cylinders, glaze-breaking, is customary practice. Also, you may have to remove a ridge at the top of the cylinder before removing the piston. Don't try to remove the old piston if the ridge is more than barely detectable.

Hope this helps.

Harvester

harvester, thank you so so much. that is exactly all what I needed to know. I have the notched aluminum pistons, so that seems to be good. I'm also sure it's the original 1959 engine (235), and I am so sure because I've spoken to all previous owners. as for the reason, my guess right now it's a combination of overheating, a leaking manifold gasket and carbon deposit on the valves.
I'm going to have a little practice run tomorrow on my Buick 248 straight 8, it's quite similar to the 235, and then asap do the big repair on the truck.
thanks!!!

Seetz, if the carbon on your valves in on the port side, that indicates valve guide leakage. If the build-up is on the combustion chamber side, there is oil consumption from rings or head gasket leakage. If the engine is a '59, there is an oil passage going through the head; sometimes the head gasket leaks there, but that usually only affects cylinders 3 and 4 (I think). That oil passage supplies oil to the rocker arms. Also, the '59 engine has insert bearings for the connecting rods, so shims would be under the bearing shell, if any were used. There weren't any originally, but sometimes they are added after the fact.

Harvester

Shims 'under' the inserts...boy, that is a new one on me. I didn't think that was possible, but I guess anything IS possible.

Stuart

Stuart, shims under a bearing shell were used to some extent, but it wasn't considered good practice- the desperate last resort, so to speak. There were tapered shims commercially available that were thicker in the center and tapered toward the ends. I don't know if those shims served the intended purpose very well, but they were commonly available in the past. Also, I don't know if the tapered shims came in different thicknesses, but I think they did. Also, I have known aluminum foil to be used under the shell, to take up a thousandth or so of clearance- a last resort again.

Harvester

I had so much fun today. I practiced piston removal on my Buick straight 8. so much fun. I started slow, but the last one I got out in about 30 seconds. that is so simple! so I went to NAPA and ordered a piston, it'll be here in a week. said it was a direct factory order, factory is in Kentucky (??Chevy engine factory in KY??). so now I'll have to wait a bit. I'll go ahead and do some more work in the meantime. found a nice AC glass bowl fuel filter that I want to install, will paint the side cover, things like that

Thought, If you decide to grind valves and such it may step up the compression to the point whet the engine will smoke and take oil. I have been there.

I have been know to take shortcuts more often than not, but I'd worry about where that penny sized piece missing from your piston ended up.
I don't know but was wondering if maybe Ross or Egge made pistons and sold singles. Egge especially likes to claim they make pistons for rarer and/or vintage stuff.

I just did an autopsy on a small block 350 that made about 550 HP on my dyno. It burned two pistons recently. The owner of the engine, who is one of my former students, told me he found the spark plugs on the #3 and #5 cylinders with the electrodes burned away, and discovered a couple of loose intake manifold bolts. He retorqued the manifold, replaced both plugs, and got about another 1,000 miles out of the engine before the tops of the pistons went away. It's no fun at all to get a vacuum leak at full throttle. The damage is extensive, and immediate!
Jerry

so Jerry, what you're saying is, he first found the plugs damaged and the manifold bolts loose, then did the easy fix, and after that he burned the pistons? because of a vacuum leak?
if I understand that order correctly, that is pretty much what will have happened to me. been driving top speed (about 65 mph) with a big load, running a bit hot, and then it all shut down. the first thing I found was a broken manifold gasket (= vacuum leak I'd say (?)).
I'm curious, did you find any damage done to the engine internals? my guess is that there'd be no residue from the hole in the piston, the hole melted but I think the molten metal would not come apart from the piston.
I'll pull the oil pain on wednesday or thursday, when my piston gets in at NAPA. am planning to clean that very thoroughly, but my guess is that should be all I need to do

I suspect the beginnings of the piston damage happened at the time he smoked the plugs. Generally, here's the sequence of things- - - - -a lean condition develops, either from wrong carburetor jetting, a clogged jet, or possibly a vacuum leak, and the cylinders affected by the lean condition start burning hot enough to melt things. Usually, the plug conductors, both insulated and ground, melt and/or vaporize. There's enough hot oxygen in the cylinder after all the fuel is gone that it starts eating aweay at whatever's handy, plugs, valves, and piston crowns. Once anything inside the cylinder gets hot enough to ignite the incoming fuel (pre-ignition) during the compression stroke, the hammering action of the burning fuel opposing the upstroke of the piston (detonation) starts melting and/or breaking away small pieces of the piston crown. Most of these are small enough to find their way past the exhaust valve, or sometimes they will weld themselves to the cylinder head somewhere. I suspect the engine in question here began the piston damage during the initial vacuum leak, and even though the leak was stopped, the damage progressed from there. In the case of severe detonation, like in an alcohol-fueled blower engine, the cylinder head can actually be blown off the block.

Hot oxygen is like a sailor on shore leave- - - -it's definitely going to combine with something- - - -RIGHT NOW! The piston is the closest thing, and it also has the lowest melting point. If you're obsessed with either maximum performance, or maximum fuel mileage, remember that gasoline is cheaper than pistons! Don't go too lean!
Jerry

I truly enjoy this, thanks everyone. I know a lot about chemistry, physics and all (got a masters degree in that stuff) but what it all comes down to in the real world is a different thing. Harvester and Jerry, thanks a million. this is stuff you don't read in books, but I love it.

On the topic of a hole in a piston, I've seen a blown head gasket lead to a hole in a piston. Does the steam cause pre-ignition, detonation? Interesting topic.

thanks

temperature at which water will start to break down into its elemental components is 4939 fahrenheit. which are hydrogen and oxygen, both of which would help burning holes. that temp will be considerably lower under high pressure (as in an engine). I might do the math tonight. and I also seem to remember something about water injection to make engines run better on the salt flats. california bill's book on stovebolt speed. any old hotrodders that know more? this IS getting interesting..

Seetz, I don't think water leakage into a cylinder would lead to detonation or pre-ignition. Water injection has been used routinely to suppress detonation by reducing combustion temperature. Depending on where it is injected, it can also cool the intake charge, making it more dense. Alcohol can be added to the water to prevent freezing when that is a possibility. Charge-air coolers are the current technology for reducing intake charge temperature, and so reducing combustion temperature. And that also increases power. Water/alcohol injection was used on some production turbo-charged automotive engines in the past, but drivers would forget to refill the resevoir, and get into your situation. It was called Anti-detonation Injection Fluid. Water/alcohol injection was also used in piston-engine airplane engines for extra power- combat power, it was called, but operation under that condition was limited to a few seconds at a time, lest you lose all power at a bad time. It was also used to increase take-off power. Since you asked...

Harvester

The B-52's and KC-135 tankers I worked on in the Air Force used water injection for increased takeoff power. It allowed much higher rates of fuel flow without burning holes in the burner cans of the jet engines. One incident I recall was an air show on Armed Forces day at Bunker Hill AFB (Later named for Gus Grissom). A B-58 Hustler was supposed to do a low-level Mach 1 pass by the reviewing stand as the high point of the show. A KC was airborne at about 10,000 feet on a routine training mission, and the pilot had made a long takeoff run and didn't use his water injection. As the B-58 rolled in to make his low level pass, the tanker driver put his plane in a steep dive, firewalled the throttles, and hit water. As the B-58 passed the reviewing stand the tanker PASSED THE B-58! BTW, in case the military designation doesn't ring any bells, that's the same airframe as a Boeing 707! The pilot got grounded for overspeeding the plane, and the plane stayed grounded for several weeks for stress inspections! Water injection makes a plane scoot, for sure!

We used to mix water in with the alcohol/hydrogen peroxide fuel mix in the flathead Ford powered dirt track racer Dad ran back in the early 1950's. One 6-ounce Coke bottle into an 8-gallon beer keg fuel tank on a humid day, two on a normal day, or three on a dry day! It kept the highly corrosive oxygen-bearing peroxide from burning little wormholes in the pistons.
Jerry

I checked some stuff, and we're about 3800 degrees short of making oxygen and hydrogen in a combustion engine.
but that's very interesting to read those water stories. never been close to planes, they quit the draft around the time I turned 18 (which is 18 years ago, I'm speaking Dutch military here).
funny how the worst trouble with my truck turns into the best topic I've ever read..

Just a quick note on the single piston replacement.

Many years ago , I had a '39 Chevy sedan.
One weekend a bunch of us guys went on a road trip. About 100miles from home the chev tossed the top off a piston , came off right 'round the oil ring groove.
We left the car on the side of the road (engine partly dismantled) and got back to it the next weekend.

During the week I went to a local wrecker and bought a 2nd hand cast iron piston , complete with rod. That was all I could afford on apprentice wages.

Back at the car I pulled the sump, changed out the rod etc, refitted the head and spent hours trying ( in vain) to get the sump back on with some gaskets intact.

Finally , after sleeping in the car for the night , I got it going and rushed off home . We stopped at every garage to scrounge another couple of gallons of used oil , such was the size of the leakage from the bad gasket job on the sump.

It never even occurred to me to check the bore or bearing size , I just stuffed it in .
What a total fluke that it worked .



The next week it tossed the top off another piston.

Replaced the original 216 with a hotted one from a '50. Whole 'nuther story.

One more lean-out story, and I'll let somebody else shovel the manure! About 15 years ago, I got into building tractor pull engines. A neighbor had a Super Stock class 4WD Dodge truck, and he wanted a little more power. I built him a .060" overbored Dodge 440 engine with a lot of high performance prep work, ported & polished heads, high compression pistons, roller cam, etc. We had to run one 4-barrel carb and gasoline, but otherwise, engine modifications were wide open. I wound up making several dyno pulls at over 700 HP, at around 6,500 RPM. During one max-power run, I heard a little rattle, which must have actually been pretty loud, since I was wearing earplugs, and muffs on top of the plugs. Before I could get off the throttle and the load valve, maybe 10 seconds or so, one piston had developed a hole the size of a half dollar! The measured HP just before the meltdown was 714. I had to do a complete teardown and new buildup to get the piston debris out of the rest of the engine. I still don't know why just one piston failed, but I suspect there was a momentary lean condition on that hole for some reason.
Jerry

Jerry,

Can you comment a little further about the connection between a lean condition, and overheating in the cylinder? In other words, a lean condition means a fuel/air combination that is too far to the air side, so does air make the combustion burn hotter? This seems counter-intuitive to me . . . (?)

Also, I'm now paranoid about a leaky intake manifold gasket. What is the best way to verify that the proper mixture (what's it called? Stochiometric or something?) is reaching the cylinders? Is there a test for vacuum leaks into the manifold? I'm thinking I heard someone suggest an unlit propane torch held around the manifold would reveal leaks . . . or maybe that's a bad idea . . .

Thanks as always,

-Michael

OK, here's how I've been teaching fuel/air mixture for almost 40 years:

Air is about 20% oxygen, which is what combines with fuel to burn it and release the thermal energy to power an engine. Since virtually all fuels are hydrocarbons, the oxygen combines with the hydrogen to form water vapor, and the carbon to form C02. If there's a shortage of oxygen, the incomplete combustion also allows carbon Monoxide to form (CO). The whole point to computer-controlled fuel injection is to constantly monitor the oxygen content in the exhaust stream, and instantly adjust the fuel/air mixture for the most efficient combustion efficiency. Since that adjustment can happen several times a second with a properly-programmed computer, electronic fuel injection is far superior to a carburetor for wringing the best efficiency and performance from an internal combustion engine.

Anything that drastically alters the mixture away from a 14.7:1 air/fuel ratio (by weight) affects performance, and can do major engine damage. Gravity makes our atmosphere weigh 14.7 pounds per square inch, which is just a coincidence, I think. Look at it this way- - - -the atmosphere extends to about 100,000 feet above sea level, and the force of gravity acting on the air makes a 1 square inch column of air 100,000 feet tall weigh 14.7 pounds. Combine that column of air with 1 pound of gasoline, and we've got the perfect air/fuel mixture. Since gas weighs about 6 1/2 pounds per gallon, it takes a column of air about 3 1/2 inches square, and 100,000 feet tall to burn a single gallon of gas.

If there's too much air for the available gasoline, all the fuel gets burned early in the power stroke, and the remaining hot oxygen has to burn something- - - - -like spark plugs, valves, pistons, etc. A lean mixture gets extremely hot, which heats up any exposed metal or foreign material in the cylinder- - - -spark plug electrodes, carbon deposits, and/or exhaust valves, for instance. Once those things get hot enough, they become the source of ignition for the fuel instead of the spark plug, and the fuel begins burning early in the compression stroke.(Pre-ignition) Cylinder pressure rises abruptly, and the piston material, which has been softened by the high cylinder temperature, gerts blown away by the pressure spike. (Detonation) Gasoline detonation is the second-most powerful destructive force, pound for pound, known to man, exceeded only by a nuclear explosion. It's more powerful than Dynamite, TNT, C-4, etc.

Bottom line- - - - -don't let an engine run lean for any reason. A vacuum leak can be terribly destructive to your engine!
Jerry

EDIT: I use an unlit acetyline torch to check for vacuum leaks, but Propane would work just as well. Unscrew the burner head from your Propane torch, add a couple of feet of rubber fuel line, Open the gas valve a little, and explore any suspected leaks around manifold gaskets, vacuum lines, carb base, etc. When you find a leak, the RPM will rise, and/or a rough idle will smooth out.
Jerry

Thanks for the thorough reply. I'm still paranoid, but at least now I'm less ignorant!

Amazing to think how much air these engines use, and mind-boggling to think how FAST this is all happening!

-Michael

Yep, even at the relatively sedate pace of 2,500 RPM, each cylinder is firing 21 times per second! When I've got a roundtrack race engine up near 7,000 things really happen in a hurry!
Jerry

The 'Stoichiometric' air-fuel ratio for gasoline is 14.7:1, and is the ratio at which all of the fuel is consumed. In reality, a tiny amount of gasoline is released in the exhaust as hydrocarbons, 14, I think altogether, and carbon monoxide. Methane is one of the more common hydrocarbons released, and acetlyne is another one, I don't remember the others. Ideally, at the stoichiometric point, there is only water, heat, and carbon dioxide being produced. Richer fuel mixtures than stoichiometric increase fuel consumption and the raise the various components of hydrocarbons in the exhaust stream, but they also give more power. The rich-best-power mixture is about 12.7:1, although that varies slightly with the gasoline blend. A typical cruise mixture for an automotive engine with a properly tuned carburetor was in the range of 13-13.5:1. Some would go leaner than that, but rarely beyond 14.7:1.

In the past, with airplane engines, one method used to reduce fuel consumption for a cruise condition was to lean the fuel mixture beyond 14.7:1 until cylinder head temperature began decreasing, but a flight engineer was watching cylinder head temperature for 72 cylinders- four engines, 18 cylinders each.

But in the real live world of cars and trucks, the best way to determine fuel mixture is to watch the spark plug colors: very clean and white along with slightly bluish electrodes usually indicates too lean; dark brown or dry black indicate too rich. Black and wet indicate oil consumption. Beyond that, both light and dark conditions can be the result of the wrong spark plug (wrong heat range) for the engine.

Harvester

Hotrod Lincoln,
I just wanted to let you know I appreciate your knowledgeable replies. I'm retired from the Air Force, and currently attending my local Vo-Tech auto mechanics class. I gotta say I've learned lots from your replies on this forum. By the way, did you ever serve at Minot or Grand Forks during your B-52/KC-135 days?

Nope, never got that far north! My stateside assignments, after tech school at Chanute, Ill. were at Little Rock AFB, Ark. and Castle AFB, Ca. I got to Okinawa, Thailand, (twice), the Phillipines, and TDY's all over the place. Most of the time, I was in some sort of SAC outfit, other than Korat, Thailand, where I helped supervise avionics maintenance on five types of aircraft I'd never worked with!

"SAC sucks, but a suck for SAC is a blow for freedom!"


Jerry

Copy that. I spent most of my active duty time up North. 11 Years in Minot's missile field, a year in Iceland, then my last 7 at Forks. Most of my time was as a SP, but my last years were as a training manager for a TRANS, then a KC-135 AMXS unit. My experience is that some of the best and hardest working people are wrench turners and maintainers. I should have been one, but I thought I wanted to be a cop on the outside. That dream died a long time ago. Can you believe those old aircraft are still flying.