KB's in a 318 with No Re-balance

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nm9stheham

nm9stheham

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Ironmike mentioned it being winter and his brain working overtime on gearhead stuph.... same thing here LOL

Dartfreak75's long decision making process led to this little project, and we've PM'd back and forth on solutions. He provided some of his 318 piston-rod assemblies for weighing to get a grip on bobweights, so he gets a big thumbs-up for helping.
  • Problem: The 318 LA's low compression pistons
  • Solution: Put in higher compression pistons like KB's; that opens up the cam selections for a torquey street engine
  • Next problem: The lighter pistons require a re-balance, and that damages the budget by $250-300.... that's almost as much as the KB167 pistons.
  • For the guys on a budget, that re-balance is just another barrier to improving the engine.
Soooo..... How about doing what the Mopar factory engineers did, to use the same crank with 273's and 318's? Namely, make the piston pins heavier for the 273 pistons to keep the bobweight the same.... then there is no need to re-balance when KB167's are put in.

Some bobweights first:
  • Stock 318 with the later heavy rod: 2169 grams with nominal component weights
  • Actual measured 318 parts with slightly heavier than standard rods: 2177 grams.
  • Put in KB167's as shipped and bobweight drops to 2093 grams... which is why a re-balance is normally needed
If we could increase the pin weight from 132 grams (from KB) to around 211-212 grams with KB167's, the resulting bobweight would be 2174 grams.... right on target.
 
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So how to do this? Making new pistons pins is an involved and precise process…. not for the home shop gearhead. 273 2 BBL pins nominally weigh 211 grams, so those would work, but I seriously doubt you will find NOS, and using used ones has one issue: they are ¼” shorter than the KB pins, and so may not work right with the pin locks. So the approach of adding a mild steel sleeve inside the existing pin has been taken.


It works out that a mild steel sleeve turned down from .75”ODx.51”ID DOM tubing (.120” wall thickness) adds just the right amount of weight for the KB167 for the 318 bobweight. If different pin weight changes are desired, like for KB399 domed 318 pistons, then a different wall thickness DOM tubing can be used.


The ID of the tool steel KB pin for the KB 167 piston is .730” so the tubing has to be turned down. I don’t have a lathe but made a mandrel from a 6” long grade 5 bolt, set up to chuck 3” tubing lengths into a ½” chuck hand drill. When the drill was spun at low speed, and the tube held against a grinding wheel, this acts as a crude lathe grinding setup up. It took very frequent checking to correct tapers with this sort of deal, but it worked. The end result was a very good fit, at .001-.003” clearance inside the KB pin.


Sleeve length was set at 2.990” which is .020” shorter than the 3.010” KB pin length. This is to make sure the sleeve’s ends will be slightly recessed in the pin, so that only the pin rides on the pin locks when installed.

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Next problem is how to secure the sleeve inside the pin for good. 2 candidates seemed to be good. (But there may be others; I’m open to suggestions.)
· Tack welding at the end
· Using sleeve retainer compound, like used for cylinder liners, valve guides, small motor winding on their shafts, bearings in housings, etc.

The welding has not been tried. Some effort has to be made to do proper preheats and cool downs, to deal with the different steels: mild steel in the sleeve, and tool steel in the KB pins. The weld has to be recessed so as to not interfere with the pin locks. And, it has to be done so as to not distort the pin’s diameter, as that has to be controlled to well under .001”.

So the sleeve retaining compound has been tried. The .001-.003” clearance is very good for the Loctite 640 and Permatex 64000 Hi Temp Sleeve Retainer compounds; they will fill up to .007” diametrical difference. After a quick hone of the inside of the pin to clean it up, and multiple cleanings of the sleeve and pin, the retaining compound flowed on easily and seemed to wick in and fill very well when the sleeve was inserted with a twisting motion.

The pin was set horizontal during curing, and cure was at room temp for 24 hours per mfr’s instructions. Afterwards, the pin was solidly held in place. To test, a 360 block was suspended just from the sleeve while the pin was clamped in wood blocks. After 2 hours, the load was removed, and the end clearance of the sleeve to the pin was re-checked with a depth micrometer; it was still as before the load was applied, at .0113” so no creepage occurred with this load.

To give you an idea of the ultimate strength in this configuration. I went through the MIL test specs for these compounds in detail and confirmed what I had read elsewhere, that the total shear strength is the bond area times the compound strength in psi. Since this is rated at 3000 psi at room temp, and the bond area here is just over 6 square inches, that is 18,000 lbs….! So even if you got 1/10th of that number, you would be good for this application as there is no actual load on the sleeve; it just has to be kept from moving. This particular long cylindrical configuration is very good for this retaining compound.

How this sleeve retainer compound will work over temperature is a very good question. It is rated to work from -65F to +400 F. Per the Loctite Tech Data Sheet, if held at 350F for over 500 hours, the strength will drop to about 50%. The product’s strength is not effected by hot oil. And the disassembly instructions on the Permatex product package reads: “To disassemble parts, weaken cured Sleeve Retainer by heating above 500F and then use pullers to separate parts.”

So things seem pretty good over engine operating temperatures.

Is there a hidden problem with the weight or the sleeve retainer compound? Well, if I knew, it wouldn’t be hidden LOL. But as always, ideas are welcomed.

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I think it'll work. I think you better be really careful making the sleeves, but in theory it should work. Not sure it'll be good for high rpm racing, but maybe for the street it'll be ok. Build it! I wanna know how it turns out.
 
Welding adds weight that is super hard to keep at the same weight. The welding would work though. But I think it a “Going around the long way” only to re spend money on balancing.

Best just to have a shop expertly balance it IMO.

I do like the thinking out of the box though.
 
I would go 9 % lighter than what the crank was balanced to, and never look back. Ed Hamburger told me this years ago, a 10% difference was not to worry. I did it on a 340 with solid engine mounts no vibes
 
Seems like a lot of work/time without a guaranteed outcome of proper engine balance. All that to save a few hundred bucks? You'd be further ahead in the long run by having it professionally balanced. IMO 65'
 
i don't know.. adding weight just doesn't sound right to me..

$300 to balance is breaking the budget? work some OT or sell a few things and just have it balanced if you are so worried about it being balanced correctly.

personally i'd throw it together like a million other people have over the years and never had a problem without re-balancing...
 
All this so you get 1-1.5 points of static compression? What's the actual power increase you expect to realize here? 10% on a 300ftlb engine is 30 pound feet of torque. And I'd bet the price of pistons and balancing that you don't realize 10% from that specific change. So this is worth risking taking out the block when (I don't feel this is an "if" situation) the pin augmentation works it's way out? Have you ever had the pin move and put a gouge in the bore? I've seen it on pressed and retained pins and I'm no pro doing it every day.
With all due respect you guys really amaze me. Never have I seen so much time taken to avoid spending on things that have such little effect on how an engine runs or lasts...lol.
 
You're way over thinking this. Piston weight is an entirely different thing than rod weight...and big end rod weight is entirely different than small end.
Stick the pistons in there and don't give it a second thought.
 
Putting additional weight out on the small end of the rod, is, in my opinion, is not a good idea..........I always thought that the idea was to remove as much mass off the small end as possible to reduce inertia loads on the rod.....it is alot less stressful to slow a 132 gram pin down vrs 212 gram pin, that is 80 gram difference, or call it almost 3 oz......I think that is alot

FWIW.....my "Mean Teen" as I call it started life in a 1971 D600 Medium duty truck, cast crank, 2899496 rods (340 rods), cast pistons...I'm sure that as a truck engine, the pistons were heavy as hell for durability reasons, I pulled out the rods and replaced them with a set of lighter 273 rods and replaced the pistons with a "give me" set of cast rebuilder Sealed power pistons, didn't balance, actually didn't even check, never noticed any bad vibration all the way out to 7000 rpm, maybe some day I'll pull a bearing to see if any tell tail information has been left behind
 
Good idea in theory. Hell, mass produce those and sell them to the stock car guys. LOL The street stock/ hobby stock guys love to throw a cheap engine together. I think I'll continue to have weight removed from the other end

. Although taking a stock piston out that weighs 2169g. and replacing it with one that weighs 2093g. and a "adapter" that weighs 76g. is all the same weight in damn near the same place. KB could thicken the heads of the pistons by 76g and it would be the same as stockers. A +.030 would weigh more anyway so it's a mute point.
 
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My old bracket motor was a 440 with pistons 70 grams heavier than stock. No balance ran 11 years. Pulled the bearings and they looked like new so I reused them. Its setting in the corner of my garage for a back up motor. Ran its quickest times when I pulled it. high tens, low 11s. New motor is balanced cant see a difference in smoothness.
 
C130 Chief said:
Wait... you're talking about intentionally increasing reciprocating mass?!?
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This method keeps reciprocating weight exactly the same as it was with the stock pistons. Same method as for the factory designed reciprocating weight for the 273/318. It just moves weight between the piston and pin.

And it does not change the inertial weight on the rod.... it stays the same.
 
moper said:
All this so you get 1-1.5 points of static compression? What's the actual power increase you expect to realize here? 10% on a 300ftlb engine is 30 pound feet of torque. And I'd bet the price of pistons and balancing that you don't realize 10% from that specific change. So this is worth risking taking out the block when (I don't feel this is an "if" situation) the pin augmentation works it's way out? Have you ever had the pin move and put a gouge in the bore? I've seen it on pressed and retained pins and I'm no pro doing it every day.
With all due respect you guys really amaze me. Never have I seen so much time taken to avoid spending on things that have such little effect on how an engine runs or lasts...lol.
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LOL, I agree on the odd things that are thought about.

But I'll disagree over the value of the compression change.... It is not the peak torque gain just from the CR change... it is the ability to put in a larger cam without killing the low RPM torque and making a dog out of the engine for street use. The chronic 318 dilemma..... You increase the cam without killing the low end torque AND that will increase the peak torque and peak HP more than stated above. There is nothing new in this....

As for risk..... LOL. There are SO MANY ways to harm an engine. We all know that just flipping the rocker shafts upside down will kill the valvetrain in short order; we see engine mess-ups here every week or so. Now if you can identify a way in which these inserts will likely move and fail, then I am all ears. But just raising a 'strawman' failure without a good rationale.......
 
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aaronk785 said:
My old bracket motor was a 440 with pistons 70 grams heavier than stock. No balance ran 11 years. Pulled the bearings and they looked like new so I reused them. Its setting in the corner of my garage for a back up motor. Ran its quickest times when I pulled it. high tens, low 11s. New motor is balanced cant see a difference in smoothness.
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And this I can see, and won't gainsay any of the experiences related about not balancing and engines working fine; I honestly believe all those stories. But if someone came on here and said they were putting in KB167's and did not mention re-balancing, then there would be all sorts of comments that is SHOULD be balanced.

So, which is it? Is balance important or not, and to what tolerance? I think this all is a testament that the actual effects of some level of imbalance are not all that well understood, at least at the hot-rodder level. All I know to go with is the wisdom and targets developed over years, that the harder you run and the higher you go in RPM, the more important it is and the tighter the balance tolerance needs to be. (Nothing new or earth-shaking in that statement LOL)
 
And if you're rebuilding your teen and need to bore it .030 you are going to need new pistons anyway. Might as well use the KB's and get the compression where it needs to be. With your adapters balance wouldn't be an issue.
 
toolmanmike said:
Good idea in theory. Hell, mass produce those and sell them to the stock car guys. LOL The street stock/ hobby stock guys love to throw a cheap engine together. I think I'll continue to have weight removed from the other end

. Although taking a stock piston out that weighs 2169g. and replacing it with one that weighs 2093g. and a "adapter" that weighs 76g. is all the same weight in damn near the same place. KB could thicken the heads of the pistons by 76g and it would be the same as stockers. A +.030 would weigh more anyway so it's a mute point.
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FWIW... I DID email UEM a couple of weeks ago asking about heavier piston pins, and explained this aspect of the KB line, and that the Speed Pro H116CP's were a no-brainer for the lower $$ 360 builders since they are stock weight. Got an answer last night... no dice on the heavier pins, but it will be passed on to Engineering. I would not count on anything changing, and have no idea of the the market value to them for such a change, but it was nice that they replied at all. I figured it would go into the 'circular folder'... 'Here's another on of those nutty suggestions' LOL.
 
nm9stheham said:
FWIW... I DID email UEM a couple of weeks ago asking about heavier piston pins, and explained this aspect of the KB line, and that the Speed Pro H116CP's were a no-brainer for the lower $$ 360 builders since they are stock weight. Got an answer last night... no dice on the heavier pins, but it will be passed on to Engineering. I would not count on anything changing, and have no idea of the the market value to them for such a change, but it was nice that they replied at all. I figured it would go into the 'circular folder'... 'Here's another on of those nutty suggestions' LOL.
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You just hope someone gets a "ah ha" moment. "Gee, why didn't I think of that" LOL
 
Very nice work nm9stheham. Im glad to part of it and have thoroughly enjoyed talking and learning with you. This project is perfect for guys who dont have the extra money or frankly the time to fool with a machine shop. Every machine shop I have talked with have a few month waiting period. If you want or need to get a engine put together as cheap and quick as possible this is the ticket imo. I have looked and studied alot of different options. Not just the 318 but other engines too. And all the aftermarket piston are either lower compression height or lighter. After my 360 is complete and running i still plan on building my 318 for a truck project and i will be using this method.
 
whitepunkonnitro said:
You're way over thinking this. Piston weight is an entirely different thing than rod weight...and big end rod weight is entirely different than small end.
Stick the pistons in there and don't give it a second thought.
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I bored a 360 out .030 over and stuck the speed pro pistons in there and didn't even weigh 'em. No issues, ran it, raced it for 4 years and ran great when I sold it.
Not that it think weighing and balancing isn't a good thing
 
I recall a 360 build by some magazine. It was some time ago. They used the KB107'S and did not balance rotating assembly. It was a cheap type build. They ran car to get some times after break was done. And claimed that engine ran surprisingly smooth @ all rpm's.
 
QuickDart360 said:
I recall a 360 build by some magazine. It was some time ago. They used the KB107'S and did not balance rotating assembly. It was a cheap type build. They ran car to get some times after break was done. And claimed that engine ran surprisingly smooth @ all rpm's.
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That could very well be. Most replacement pistons are lighter than the stock ones. Then you make them .030 bigger and they may be close to the standard stockers. My .030 over Egge pistons were 68 g. lighter than the stock ones. The pins were different though so we balanced it. I wanted it right.
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