A engine rebuild theoretical discussion...Piston Sealing

[James_Douglas]

Ok,

I need to get on with my building of a 265 that will live in the big Desoto until I am dead. Say 20 years or so.

 

We will be driving this car as our daily driver. We have, as you may or may not know, no “modern” car.

 

Over the last 20 years I have been taking compression readings every 2 or 3 years. A pattern has emerged. Every 10K the compression pressure drops about 6 PSI. It started at about 140 and after 70K miles it is in the 70 to 80 psi range.

 

When I had the head gasket fail in 2017, a decade after it was rebuilt, I measured the tops of a couple of bores and I could see a fair amount of tapper. I have checked all 4 of my other engine blocks and they all show a good amount of tapper.

 

I talked with Tony about this as well as a couple of engine rebuilders I know. The consensus is that the heavy pistons combined with the very long stroke generate a lot of side thrust on the bores. This causes wear and tapper and the loss of piston seal.

 

Tony has pistons that are a more modern shorter and lighter design. My question has to do with the bore material.

 

The optimum thing would be to get a bore material that was engineered to match the ring material and that is harder than the stock walls. Let me digress for a moment. The early Jaguar XKE engine that was in my 1964 XKE, an inline six, had sleeves made by a special process that was used in WWII fighter engines. The stuff had hardly any wear. Many XKE guys hunt for those early blocks just for that reason.  They stopped making those sleeves by 1968. So, I know that bore material can be a factor in these longer stroke engines.

 

My question for discussion is what the benefit – cost ratio is for spending the money to sleeve all six bores. Would the lighter pistons alone be enough to slow that wear or should I consider the expense of sleeving the bores and using the lighter pistons.

 

Like I said, this is to be our daily driver for the next 20 years. This is a heavy car. We plan on extensive travel in it. 

 

A discussion on the relative merits of how to maintain piston to wall seal over the long run would be instructive.

James

Edited November 26, 2021 by James_Douglas

[Sniper]

Did you talk about rings as well?  I have found moly rings to wear very little on my 318's.  Now granted that's about an inch and a half difference in stroke though, 3.31 vs 4.75.  But plain old cast iron rings are bore eaters. 

 

While I cannot speak specifically on the 265, in general integral cylinders are part of the strength of the block, cut them all out and sleeve it, some of the strength goes away.  How this might affect the 265. I dunno, it's fairly over built as is and may not.  Of course, the real question is this, are the sleeves made out of a material that is better than what is already there?  If not then the question is answered.  If so then you at least know what ever the cost is you won't just spend money to end up where you are.

 

One last thing, oiling.  What are you running for oil, how often are you changing it and I assume you will have a full time filtering system as well.  Another thought here is that the oilers for the cylinder walls might be a bit undersized or misaimed?

[kencombs]

IMHO, the longer stroke doesn't contribute to taper wear, it actually is better than a short stroke.  Due to the rod to cylinder angle created at the mid point and higher in the travel being less thus creating less side thrust.   But the heavy piston probably creates a very large 'rocking' moment at both ends of the stroke.  Again, IMHO, the biggest contributors to bore wear are cylinder wall and material.

 

Early short stroke V8s with really short pistons wore the cylinders much worse than our old flatties.   I've seen 265 chevies with horrendous bore wear at 50k or so.  Many with the skirts broken off all the pistons too.  I've always attributed that to the severe rod angle.  Maybe wrong, but seems reasonable.

 

Cast iron on cast iron is the worst combination.  So better rings and matched walls would be the first steps to reducing wear.  Lighter custom pistons will allow higher rpm, lower stress on the bottom end and provide the opportunity to tailor the crown to pin height.

[Bryan]

Dang...y'all going to make me have to study.  One would think at the top of the piston, rings would be the major point of contact. I'd have to check. I know the piston skirts and lower sides definitely contact the cylinders.   With metals, the harder metal always wears the softer metal.  A lower contact area rubbing on a surface with the same force behind it wears more than the same force spread over a larger area. Lubrication would be critical..I won't say the Synful oil word.

[Bryan]

Page 2 was interesting.   Stroker Motors Basics and Theory - FordMuscle

[Bryan]

A little over my head..   Piston Motion: The Obvious and not-so-Obvious, by EPI, Inc. (epi-eng.com)   " From that it is clear that piston acceleration is important because many of the significant forces exerted on the pistons, wristpins, connecting rods, crankshaft, bearings, and block are directly related to piston acceleration. Piston acceleration is also the main source of external vibration produced by an engine. (Torsional vibration is discussed separately on another page.)"   "Contemporary piston engines tend to have R / S ratios in an approximate range of 1.5 to 2.0. Note that a rod / stroke ratio less than 1.3 is, for practical applications, not possible due to physical constraints such as the need for piston rings and a wristpin, sufficient piston skirt length, and the inconvenience of having the piston contact the crankshaft counterweight, not to mention the excessive side load such a small ratio would produce."  

[James_Douglas]

Nice article. I think the 265 engine has a rod ratio of 1.64 which is right at the lower end of what the writer sites and the optimum ratio...

 

James

[Loren]

You can't really change the material of the block without sleeving it.

The closest thing would be hard chrome plating and the only way to do that is at a shop with a huge Barnes Drill Hone. Which are kind of rare these days. Grinding is out of the question as an I.D. grinder would have to be huge to swing an in line 6 block, a "wobble grinder" would be the best bet and they are super rare. There is only one outfit I know of that chrome plated automotive cylinder bores (Chevy Vega) as a regular business. Chromall in Los Angeles. I know they are still in business because a month ago I had them do the cylinder shafts from the tilt on a forklift that was vandalized. The cost might be unacceptable however.

 

Chrysler made the 237 DeSoto, 251 and 265 Chrysler engines, keeping the same pistons but altering the crank and the rods. Each longer stroke got shorter rods. Since the bearings were all the same, you could put longer rods in to help with the rod angle then move the wrist pin up to accommodate the stroke. Longer rods with the longest stroke might not be doable because of clearance issues at the bottom of the bore.

 

Next Item I'd look at are piston rings. New materials enable you to use fewer rings lessening friction and wear. Auto makers have tried Low Tension Rings to accomplish fuel economy goals but they have been a disaster with oil consumption (1 quart in 600 to 800 miles is not unusual!)

The pistons themselves have potential for lessening cylinder wear. New engines have shorter skirts with low friction coatings on them.

Cast Aluminum comes in new flavors as well. Silvolite uses a special alloy for their Keith Black pistons which bridge the gap between cast and forged.

 

There's lots of new stuff that can be done to improve reliability and longevity.

[James_Douglas]

I looked into all of that Loren. Tony has pistons and rings that are an improvement and I will also have him re-work my rods. The Desoto 8 inch rods will not clear the block at the bottom...

 

So about the only thing left to do would be sleeving. LA Sleeve would not warranty their work even if I paid them to do the sleeving. So if they screw up a block or a sleeve moves 5 years down the road...

 

A sleeve with a lip in theory cannot move as the head keeps it in place.

 

Babbitt Bearing Company in San Jose are the folks that did my second gear on the Desoto 15 years ago. They can do an ID up to 30 inches. I am wondering if had chrome may be a better choice that sleeves?  I have no idea what the thermal issues may be.

 

Hummmm....You are always around with things to ponder.  Thanks, James.

[Bryan]

20 minutes ago, James_Douglas said:

Babbitt Bearing Company in San Jose are the folks that did my second gear on the Desoto 15 years ago. They can do an ID up to 30 inches. I am wondering if had chrome may be a better choice that sleeves? 

Nikasil?   Cylinder Bore Surfaces- Kevin Cameron Insights | Cycle World   "In two-stroke motorcycle racing, chrome-plated cylinder bores gave way in the 1980s to Mahle’s Nikasil, which is a layer of electroless nickel containing 5-percent super-hard silicon carbide particles. When diamond honed, this produced an oil-retaining textured surface that was extremely resistant to wear."  

• "Guest

  11 February, 2016

  You don't hone or bore Nikasil. You send the cylinders to any number of companies here in the US, they remove the "old" Nikasil with an acid bath, then simply replate it with a fresh Nikasil coating. Cost is around $200."

   

[Bryan]

Automotive Engine Performance Coatings and Treatments • Muscle Car DIY   end of article....2016 prices

Nikasil, on the other hand, is very consistent for thickness and hardness uniformity. Because Nikasil allows tighter clearances and its oil retention is much higher, you can get away with creating a smoother finish. Typical Nikasil cylinder finishes are in the Ra range of6 to10.

Rings

It’s absolutely critical to use the correct type of rings in conjunction with Nikasil-coated cylinders. The top ring is typically moly or PVD; the second ring is ductile iron. Chrome rings cannot be used (including oil control rails) because chrome and Nikasil react to each other and result in scuffing. So just run plasmamoly top rings, ductile-iron second rings, and unplated oil rails. Ring seating occurs very quickly. Nikasil and other cylinder coatings are applied to aluminum or iron walls (on parent bores or on liners).

Typically, the coating is about .008 inch and can be sprayed on between .012 and .015 inch thick. This type of coating visually appears to be chrome, very shiny and difficult to scratch. In order to touch up Nikasil in order to re-ring, a 150-grit aluminum-oxide stone usually suffices, just to clean and remove any high points. However, if you find excessive wear or if new sleeves are to be installed, finishing requires a 500-grit diamond stone.

Cost

For a four-cylinder block, cost could typically be around $750 for coating the metal bores, or $200 per liner if you need sleeves. Coated liners for an eight-cylinder block may run about $1,600.

[Sniper]

I imagine the rings would be tricky to find if he went nikasil

[kencombs]

Way back when, Henry built some engines with steel, not cast sleeves.  Very thin wall and manufactured from rolled sheet, butt welded together.   Using sleeves of that type would open up a lot of material choices.   Probably would require a large investment in equipment needed for the process, unless it exists in some other industry.

[Loren]

You'd think those thin wall steel sleeves would have been a real good thing.

The hot rodders couldn't wait to push them out and install Mercury pistons.

I guess cubic inches were thought to be more important than reducing internal friction and longevity.

Ford didn't use them for very long as they must have been costly.

[Sniper]

2 hours ago, Loren said:

Ford didn't use them for very long as they must have been costly.

 

Or didn't work as expected, or both.

[Loren]

I believe the purpose was to differentiate the then new Mercury from the Ford on the spec sheet.

1939 being the first Mercury which was a one year only model. The critique of the 39 Merc was that it looked like a fat Ford.

The 1940 (at least to me) looked quite a bit different. By 1949 the Mercury had established its own identity (only to be lost again later).

The V8 guys I knew never said anything about how the thin sleeves performed and they only talked about removing them for Mercury displacement.

Think about it. You drive your car till the bores wear out and it smokes then you punch the sleeves out replace the pistons and you've got a new Mercury engine in your Ford!

Another interesting thing Ford tried were steel pistons. As light as aluminum but stronger. They didn't stay in production long either.

On diesel engines it is very common to see an steel ring cast into the piston for the compression ring groove. They also will cast a salt ring in them, then wash the salt out leaving a channel for the oil jets to squirt into.

Ring placement has a lot to do with reliability and compression. Closer to the top of the piston increases the compression BUT....too close to the combustion chamber and the compression rings get hot and loose their tension. I've worked on cars that the compression ring was too close and they were fine unless overheated, then they had no compression. On later versions they lowered the compression rings and they never had any problems. 

[James_Douglas]

I have several blocks...

 

Makes me wonder if I could get a deal with LA Sleeve if I did two or three blocks using their thick sleeve (1/8) on them. They do charge less for each additional hole after the first one.  I like the chrome or Nikasil idea but in the end I think it would cost more and be more trouble down the line than just using good liners...

 

Of course this could be crap as well...that is why I started this thread to tease out ideas and thoughts.

 

LA sleeve has the sleeves for our engines, if one looks into the dodge truck list, so I do not have to pay for custom sleeves.

 

James

[Sniper]

Just in time for the holidays and semi relevant.

 

 

https://www.facebook.com/thefreewheelingtonysmith/photos/pcb.4809499449071273/4809464029074815

Edited November 27, 2021 by Sniper

[Loren]

Beautiful stuff!

That is definitely a "Needs vs Wants" discussion item!

Those rods are way over kill unless you're going to use a blower!  lol

The pistons are very modern and likely the best you can get.

I definitely want it but....need it? Well maybe not. But I still want it!

 

[kencombs]

4 hours ago, Loren said:

I believe the purpose was to differentiate the then new Mercury from the Ford on the spec sheet.

1939 being the first Mercury which was a one year only model. The critique of the 39 Merc was that it looked like a fat Ford.

The 1940 (at least to me) looked quite a bit different. By 1949 the Mercury had established its own identity (only to be lost again later).

The V8 guys I knew never said anything about how the thin sleeves performed and they only talked about removing them for Mercury displacement.

Think about it. You drive your car till the bores wear out and it smokes then you punch the sleeves out replace the pistons and you've got a new Mercury engine in your Ford!

Another interesting thing Ford tried were steel pistons. As light as aluminum but stronger. They didn't stay in production long either.

On diesel engines it is very common to see an steel ring cast into the piston for the compression ring groove. They also will cast a salt ring in them, then wash the salt out leaving a channel for the oil jets to squirt into.

Ring placement has a lot to do with reliability and compression. Closer to the top of the piston increases the compression BUT....too close to the combustion chamber and the compression rings get hot and loose their tension. I've worked on cars that the compression ring was too close and they were fine unless overheated, then they had no compression. On later versions they lowered the compression rings and they never had any problems. 

I'm not sure what all the reasons where, but they used them in tractors for a while too.  Makes me think they expected longer life from them.

[Bryan]

2 hours ago, Sniper said:

Just in time for the holidays and semi relevant.

 

 

https://www.facebook.com/thefreewheelingtonysmith/photos/pcb.4809499449071273/4809464029074815

Bet these aren't any $200 a bore...?

[Sniper]

Maybe for the rings they are $200 a bore.  I talked with him some months back and he was estimating around $4500, iirc.

[Bryan]

28 minutes ago, Sniper said:

Maybe for the rings they are $200 a bore.  I talked with him some months back and he was estimating around $4500, iirc.

? ? You're going to have me do a Sanford "Elizabeth, this is the big one"...

[wayfarer]

The cast iron in the block hasn't changed a huge amount over the years except for what folks call hi-nickle but is/was it really some 'special formulae'?

Forged pistons with low tension metric sized moly rings should go a long way to making a 150k plus mile engine. Modern oil is a major factor as would be a 'premium' filter system. Recall that some of the new light weight oil needs corresponding very tight clearances.

As noted, long strokes and long rods are not adding much side loading at the piston.

 

What are you planning to use for bearings?

[Sniper]

3 minutes ago, wayfarer said:

Recall that some of the new light weight oil needs corresponding very tight clearances.

 

We just had a discussion about this very thing here.  Turns out the clearances really are not any tighter, in fact the specified clearances for our 230's is a hair tighter than the modern 5.7 Hemi. 

 

 

Edited November 27, 2021 by Sniper
can't spell, or maybe type, or both