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29ft rear gas pusher RV with 440 about 1976 vintage engine open chamber heads, standard bore. Bought this thing a couple weeks ago, has about 5k on 15yo engine build. KB hypereutectic pistons probably about 10:1 not sure- VERY few miles on the build, because it quit on him and then he left this world shortly after. So I tear it down and there's a burned piston just ONE all others look just fine so I figure it was a vacuum leak or a fluke and replace the piston. Runs fantastic for about 200 miles, then it burns ANOTHER ONE, right next to the one I replaced. Again, no other pistons show sign of pre-det that I can see. Sooo, anyone have any ideas here? Seems to me that the compression is just too high for 92 pump gas and stock timing, and It's a new carb/distrib too. What I can't understand is why it's taking out one piston at a time (adjacent pistons) with others not showing any signs of damage? Any thoughts appreciated please see photo.
 

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Classic detonation/preignition damage. I presume you don’t hear it ping, but it is.

Could be an intake leak as you considered. But anything that causes the mixture to be lean, the engine running too hot, too much spark advance. Too hot a spark plug heat range, hot carbon build up, overheated exhaust valve, pulling a lot of oil either around the rings and or down the valve guides or even missing or failed valve stem seals.

Thees older big block Chrysler’s with excessive squish/quench clearance and open combustion chambers are really detonation prone when they are worked hard. What you see here is the result.

Bogie
 

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Discussion Starter · #3 ·
Classic detonation/preignition damage. I presume you don’t hear it ping, but it is.

Could be an intake leak as you considered. But anything that causes the mixture to be lean, the engine running too hot, too much spark advance. Too hot a spark plug heat range, hot carbon build up, overheated exhaust valve, pulling a lot of oil either around the rings and or down the valve guides or even missing or failed valve stem seals.

Thees older big block Chrysler’s with excessive squish/quench clearance and open combustion chambers are really detonation prone when they are worked hard. What you see here is the result.

Bogie
Yes, I can't hear a thing with it in the back like that tho I could block the tires and try and emulate a load. I'm going to get rid of the KB's or at least go with a lower compression KB piston... any recommendations? Just a hypereutectic flat top, forged? I need a builder/machinist who really knows these engines, can calculate compression ratios, what HG to use etc and don't think there's anyone around here that fits that description. Thank you.
 

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What is your timing doing under a load? If you are running champion plugs find a substitute. Tape your wife's phone to the engine and set it to record audio then play it back to see if you hear any pinging. If you need help cleaning up the recording I'll see what I can do with it.
Maybe go up on octane level from what you're running? What oil are you using?
 

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Discussion Starter · #5 ·
What is your timing doing under a load? If you are running champion plugs find a substitute. Tape your wife's phone to the engine and set it to record audio then play it back to see if you hear any pinging. If you need help cleaning up the recording I'll see what I can do with it.
Maybe go up on octane level from what you're running? What oil are you using?
I had Valvoline "premium blue" 15/40 in it, they were autolite coppers... did it (killed a piston) with a stock dizzy and a holly 650 spreadbore, and this time it was a pertronix diz with matching coil and new edelbrock performer 650. Didn't check total advance just set the base timing I was only driving 200 miles to get the thing home. I'm already running premium pump gas, if I need more n' that, I need a different configuration- thanks for the idea on the phone.
 

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Discussion Starter · #6 ·
I had Valvoline "premium blue" 15/40 in it, they were autolite coppers... did it (killed a piston) with a stock dizzy and a holly 650 spreadbore, and this time it was a pertronix diz with matching coil and new edelbrock performer 650. Didn't check total advance just set the base timing I was only driving 200 miles to get the thing home. I'm already running premium pump gas, if I need more n' that, I need a different configuration- thanks for the idea on the phone.
Some wisdom from another FMC owner "
Race parts are not suitable for heavy truck, bus, RV use.
The Dodge INDUSTRIAL engine 361HT/413HT had a cast iron ring made into the piston for the top ring land,
The heads had changeable seats for the exhaust valve, which were sodium filled, and it had valve rotators on those exh valves also.
It had a much bigger water pump which returns water from a big port on the END of the head (not down to the block) to the H2O pump.
Gear drive on the camshaft, and a Water heated intake manifold, and huge 7 bolt LOW exhaust manifolds.
They were used in 50,000 lbs GVW Trucks, as well as lower weight trucks (but NOT in Pickups)
Picture is of the Dodge Industrial 413HT installed in a FMC. It is still running today."
Motor vehicle Automotive exterior Electrical wiring Gas Automotive fuel system
Wheel Tire Vehicle Car Hood
 

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Looks like some damage down the side of the piston exposing the ring and ring gap. Now follow that up to the top of the cylinder. Is that a crack? Was that the beginning of the piston damage or the result?
 

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Discussion Starter · #8 ·
Looks like some damage down the side of the piston exposing the ring and ring gap. Now follow that up to the top of the cylinder. Is that a crack? Was that the beginning of the piston damage or the result?
Blazer, that appears to be a deposit not a scratch... I'll know for sure soon gonna pull that piston now. So seems that's the result.
 

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Discussion Starter · #9 ·
More clues, I noticed that these pistons which are already not "low" compression pistons, actually stick OUT of the bores. Not the hump, the deck of the piston is out of the bore.
 

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Yeah when the side of the piston melts out the cylinder wall typically gets pretty gouged.

For the kind of use you would give this engine I’d recommend stepping up to a forged piston and the purchase of aluminum head’s.

The forged piston can take more detonation beating without failure.

Aluminum head’s move heat faster so they are a lot more resistant to detonation even getting a start in the chamber.

Bogie
 

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KB shows two different heights for those step head pistons.....with a full point of compression difference between them.
One has a compression height of 1.992"(#KB184), the other one is 2.057"(#KB236.

Compression height is distance from top deck surface of piston that isn't dish or dome.

Find out which you have and list the casting number off the cylinder heads so we can find out what the combustion chamber volume is ...and then we can figure out exactly what you compression ratio range achievable with that piston is.

Difference amounts to this - the taller piston makes nearly 10:1 compression with an 88cc open chamber....the shorter piston makes 9:1 with the 88cc chamber.
If you've got the 10:1 combination there is no wonder why it keeps eating pistons....too much compression ratio for the no quench smogger chamber and pump gas when working hot and hard under the back of that bus.
I'd consider 9:1 the high limit, ......and that might need pump super to stay alive in hot weather or mountain grades.

Bogie pretty much nailed it, that is classic detonation/pre-ignition damage.

Why it is adjacent cylinders could be several factors....might be hottest section of block due to water flow paths, leanest cylinders due to carb or manifold mixture distribution, might relate to cylinders next to each other in the block but also adjacent to each other in the firing order.....hard to say at this point.
Was it cylinders 5 and 7?

Aluminum heads would be a huge plus, and I'd have forged pistons in it regardless of what head is on it.
I'd also say a seperate engine oil cooler would be a mandatory upgrade if it doesn't have one. With it's own electric fan if you can't put it directly in an air stream.
 

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Discussion Starter · #13 ·
Hey guy's thanks for the feedback. Well, the original pistons have been *conspicuously discontinued, I didn't ask why but have the feeling it was related to the problem I'm having. They were/are TALL (humps) (KB 278?) meant to be custom shaved. I sinned a little and just replaced the first burnt with closest modern piston just to go the 200 miles home - KB Automotive Hyper - Chrysler/Dodge 440 / 7.2 - KB236. The problem is, think I mentioned already but the deck has been shaved considerably because these pistons are proud of the deck by (I haven't measured" at least .010 maybe twice that so all bets are off with what the comp would normally be with the 236 piston... no? I need to measure how far they are out! I used btw, the middle thickness cometic AND a copper felpro under. I'm considering slapping a good running 400$ industrial 413 in there just to make it mobile while I take my time with this 440. I may end up just getting another block and have it machined for forged pistons and reuse most of what I have on the existing engine... it's a low miles build, such a shame. Sorry if I missed answering any questions if so please remind me- Thanks!
 

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Discussion Starter · #14 ·
KB shows two different heights for those step head pistons.....with a full point of compression difference between them.
One has a compression height of 1.992"(#KB184), the other one is 2.057"(#KB236.

Compression height is distance from top deck surface of piston that isn't dish or dome.

Find out which you have and list the casting number off the cylinder heads so we can find out what the combustion chamber volume is ...and then we can figure out exactly what you compression ratio range achievable with that piston is.

Difference amounts to this - the taller piston makes nearly 10:1 compression with an 88cc open chamber....the shorter piston makes 9:1 with the 88cc chamber.
If you've got the 10:1 combination there is no wonder why it keeps eating pistons....too much compression ratio for the no quench smogger chamber and pump gas when working hot and hard under the back of that bus.
I'd consider 9:1 the high limit, ......and that might need pump super to stay alive in hot weather or mountain grades.



Why it is adjacent cylinders could be several factors....might be hottest section of block due to water flow paths, leanest cylinders due to carb or manifold mixture distribution, might relate to cylinders next to each other in the block but also adjacent to each other in the firing order.....hard to say at this point.
Was it cylinders 5 and 7?
Was #6 and 4.
 

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Was #6 and 4.
That location points to excessive heat due to paired exhaust ports ....a small block Chevy has the same type of problem because of the same design layout of paired center exhaust port locations.

Reason for asking if it was 5 and 7 is that 7 follows 5 in the firing order.....so that means those two adjacent cylinder therefor follow each other in intake charge inhalation order too....one robs from the other making one of those cylinders lean.
 

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That location points to excessive heat due to paired exhaust ports ....a small block Chevy has the same type of problem because of the same design layout of paired center exhaust port locations.

Reason for asking if it was 5 and 7 is that 7 follows 5 in the firing order.....so that means those two adjacent cylinder therefor follow each other in intake charge inhalation order too....one robs from the other making one of those cylinders lean.

Interesting. I keep hearing random anecdotal accounts of 440's running really hot in motorhomes, too hot frequently. I wonder tho, if I had a block that wasn't shaved and used the lower comp version of that 236 piston, if that would be "enough"? I don't want to gamble, but it's got to be possible. One issue is this is a rear pusher, does though, have two radiators that run in series. Thanks
 

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Discussion Starter · #18 ·
Interesting. I keep hearing random anecdotal accounts of 440's running really hot in motorhomes, too hot frequently. I wonder tho, if I had a block that wasn't shaved and used the lower comp version of that 236 piston, if that would be "enough"? I don't want to gamble, but it's got to be possible. One issue is this is a rear pusher, does though, have two radiators that run in series. Thanks
I guess as stated above, forged would be a better choice.
 

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440’s ran hot period, they were originally designed for 100 plus octane leaded fuels. The factory approach back then when faced with emissions was to reduce compression by enlarging an already lazy combustion chamber or adding height to the squish/quench clearance either through a thicker head gasket or dishing the piston. I had a 71 Challanger, California version, 440 with a 4bbl it ran miserably hot and even with High Octane fuels it was pingy. In spite of Vanishing Point and Kowalski, I found it to be a pretty miserable car with a lot of problems I ditched it in a couple years and went back to Fords and Chevy giving up on Ford by the mid righty’s as this was a point in my life where I just didn’t have time to fix Detroit’s mistakes as there were so many. When you go to the dealer for what should be warrantee work and you hear ‘their all like that’ this is not an answer to the problems.

The R and RB block engines, like the Ford FE in a different thread on this channel we’re designed around high octane fuel and high compression and no emission systems. The addition of emission requirements really should have gone a different technical direction in top end design. But ever cost before science Detroit tried all sorts of Mickey Mouse ways to meet emissions with no substantive design changes and got themselves into a disaster. It never had to go that way. The technology we take for granted today of heart shaped combustion chambers, high swirl mixtures, high amounts of squish and quench were all know solutions that even work with carburetors. This knowledge had been around since WW-II if not before. But Detroit decided to cheap it out with what they had ending up American Motors going out of business, Chrysler going bankrupt, Ford narrowly missing going out of business, and GM finally going bankrupt. I find it absolute incredible that when faced with critical business decisions everyone of these companies took the cheap way out, and as I’ve said on this forum many times that “the cheap way out of problems leads back in to them“. Yet time and again these companies followed that path. You should get the idea that America’s business leaders are not as great as they advertise themselves to be when faced with anything more complicated than laying off workers they have no solutions.

But anyway off the soap box, your 440 needs to be rethought to bring modern or contemporary solutions to the fact that 91-93 octane fuel will not work without top end modernization. You really need to look into aftermarket head’s with as much of a heart shape chamber as possible. The key features being the spark plug moved as far to the center of the cylinder as the valve position will allow. This is pretty much on a tangent line drawn between the intake and exhaust valve, the further fron that line the bigger the combustion headaches the engine has. This reduces time needed to burn across the chamber which nets more power on less advance which nets greater resistance to detonation getting started. The other feature is a generously large squish/quench step. This in squish as the piston closes on TDC forces the far side mixture into the valve pocket where the spark plug is. This violent expulsion of mixture really breaks up fuel globules and mixes them with the available air so the burn is quick and through. The quench function of these same parts of the chamber step and a flat surface of the piston is at the end burn where temperatures and pressures are at a point that without effective quench they will ignite before the flame front gets there. In quench we want to tighten this clearance between piston and the chamber step to close to .040 inch, this includes the head gasket thickness. What is happening is there is a lot of surface with little volume so this sinks the excess heat that would otherwise result in spontaneous ignition of the end fraction mixture. This is detonation and preignition combined, the detonation hits hard often holing the piston in the middle the preignition burns torch hot melting the piston through the ring lands.

Pistons, the OEMs have a bad habit of using a round dish piston as a means of lowering the compression ratio and reducing cost as the same piston can be used on either bank. The round dish extends under the squish/quench deck thus increasing the volume to surface area which reduces both the squish and quench effects. The most effective piston in terms of burn control is the flat top as it minimizes the volume to area ratio for maximum effective squish and quench while unlike a domed piston offers no impediment to flame travel. But depending on what volume combustion chamber is needed to satisfy the squish/quench requirement the builder can get into excessive compression ratio situations. A solution to this is either a D shaped cup under the valve pocket or a stepped crown or head piston where this feature is under the valve pocket. Basically I make my choice if there is one to be made in that if the chamber is open to the bore on the exhaust side of the head (common to Chrysler head’s) then it’s fine to use a stepped crown piston. If the head has a secondary squish/quench step on that side then a D dish let’s you take advantage of another squish/quench pad. But either will work in either chamber almost equally, I’m slicing hairs here.

So inorder to walk into a builders shop and know if they understand the science behind all of this you need to do the math first on where the volumes go as you mix different head’s, gaskets and pistons. You will probably note that your head’s are cupped all the way to the bore extreme toward the valley side of the engine, Uncle Tony’s love for Chryslers aside, this is a design that encourages detonation. It was passable in the good old days when you could dial up 115 octane with enough lead to solder plumbing pipes, but today that is just an impossible form to force on unleaded fuels.

I guess you need to offer up a budget to see if we can get to the needed changes and or what compromises need to be worked out to arrive at a solution that doesn’t blow up again.

Bogie
 

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Discussion Starter · #20 ·
440’s ran hot period, they were originally designed for 100 plus octane leaded fuels. The factory approach back then when faced with emissions was to reduce compression by enlarging an already lazy combustion chamber or adding height to the squish/quench clearance either through a thicker head gasket or dishing the piston. I had a 71 Challanger, California version, 440 with a 4bbl it ran miserably hot and even with High Octane fuels it was pingy. In spite of Vanishing Point and Kowalski, I found it to be a pretty miserable car with a lot of problems I ditched it in a couple years and went back to Fords and Chevy giving up on Ford by the mid righty’s as this was a point in my life where I just didn’t have time to fix Detroit’s mistakes as there were so many. When you go to the dealer for what should be warrantee work and you hear ‘their all like that’ this is not an answer to the problems.

The R and RB block engines, like the Ford FE in a different thread on this channel we’re designed around high octane fuel and high compression and no emission systems. The addition of emission requirements really should have gone a different technical direction in top end design. But ever cost before science Detroit tried all sorts of Mickey Mouse ways to meet emissions with no substantive design changes and got themselves into a disaster. It never had to go that way. The technology we take for granted today of heart shaped combustion chambers, high swirl mixtures, high amounts of squish and quench were all know solutions that even work with carburetors. This knowledge had been around since WW-II if not before. But Detroit decided to cheap it out with what they had ending up American Motors going out of business, Chrysler going bankrupt, Ford narrowly missing going out of business, and GM finally going bankrupt. I find it absolute incredible that when faced with critical business decisions everyone of these companies took the cheap way out, and as I’ve said on this forum many times that “the cheap way out of problems leads back in to them“. Yet time and again these companies followed that path. You should get the idea that America’s business leaders are not as great as they advertise themselves to be when faced with anything more complicated than laying off workers they have no solutions.

But anyway off the soap box, your 440 needs to be rethought to bring modern or contemporary solutions to the fact that 91-93 octane fuel will not work without top end modernization. You really need to look into aftermarket head’s with as much of a heart shape chamber as possible. The key features being the spark plug moved as far to the center of the cylinder as the valve position will allow. This is pretty much on a tangent line drawn between the intake and exhaust valve, the further fron that line the bigger the combustion headaches the engine has. This reduces time needed to burn across the chamber which nets more power on less advance which nets greater resistance to detonation getting started. The other feature is a generously large squish/quench step. This in squish as the piston closes on TDC forces the far side mixture into the valve pocket where the spark plug is. This violent expulsion of mixture really breaks up fuel globules and mixes them with the available air so the burn is quick and through. The quench function of these same parts of the chamber step and a flat surface of the piston is at the end burn where temperatures and pressures are at a point that without effective quench they will ignite before the flame front gets there. In quench we want to tighten this clearance between piston and the chamber step to close to .040 inch, this includes the head gasket thickness. What is happening is there is a lot of surface with little volume so this sinks the excess heat that would otherwise result in spontaneous ignition of the end fraction mixture. This is detonation and preignition combined, the detonation hits hard often holing the piston in the middle the preignition burns torch hot melting the piston through the ring lands.

Pistons, the OEMs have a bad habit of using a round dish piston as a means of lowering the compression ratio and reducing cost as the same piston can be used on either bank. The round dish extends under the squish/quench deck thus increasing the volume to surface area which reduces both the squish and quench effects. The most effective piston in terms of burn control is the flat top as it minimizes the volume to area ratio for maximum effective squish and quench while unlike a domed piston offers no impediment to flame travel. But depending on what volume combustion chamber is needed to satisfy the squish/quench requirement the builder can get into excessive compression ratio situations. A solution to this is either a D shaped cup under the valve pocket or a stepped crown or head piston where this feature is under the valve pocket. Basically I make my choice if there is one to be made in that if the chamber is open to the bore on the exhaust side of the head (common to Chrysler head’s) then it’s fine to use a stepped crown piston. If the head has a secondary squish/quench step on that side then a D dish let’s you take advantage of another squish/quench pad. But either will work in either chamber almost equally, I’m slicing hairs here.

So inorder to walk into a builders shop and know if they understand the science behind all of this you need to do the math first on where the volumes go as you mix different head’s, gaskets and pistons. You will probably note that your head’s are cupped all the way to the bore extreme toward the valley side of the engine, Uncle Tony’s love for Chryslers aside, this is a design that encourages detonation. It was passable in the good old days when you could dial up 115 octane with enough lead to solder plumbing pipes, but today that is just an impossible form to force on unleaded fuels.

I guess you need to offer up a budget to see if we can get to the needed changes and or what compromises need to be worked out to arrive at a solution that doesn’t blow up again.

Bogie
Bogie, that's some knowledge there. Well, I'm pretty sure for the time being i'm abandoning this ill-conceived 440 and plunking a stock 413 HT (industrial) engine with low miles in it... friggin cheap too. Not going to burn up the hills but I at least it can "take the heat". I'll putt around for a while like that come back to this issue at a later time. I do appreciate your offer to hash this out with me but for now I'm bowing out of the overheating, self-destructing 911 RB RV.
 
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