L2355 piston to wall clearance?

[RTsehibb]

Hi guys, this is my first post here and I am a very appreciative fan of this forum.  Thanks to all for the great reads and advice.

I'm just getting back into the hobby after many years and you guys have been a great help with my 69 RT/SE I have owned for over 20 years.  Special thanks to Challenger 340 for the piston info - The original owner put the low compression KB 1263's in my 440 during the 1980's when it was once rebuilt. 

I recently went in the motor due to valve train noise, went to do a cam change, didn't like the cam bearings, pulled the heads prior to motor removal (Very small garage), and sure enough, flat top pistons .100 down in the hole.  I can turn a wrench but I am not an experienced engine builder as many of you are, so I seek your advice.

So now all is out with the block bored .040 at the machine shop and Speed Pro L2355F 40's ready to go in.  I have researched and even called Federal Mogul tech line who say the piston to wall clearance on these newer high silicone content coated pistons require only a fit of the bore to 4.400 - 4.401 max (They have a .0015 recess built into the skirt so piston to wall clearance is only .0025 on these?).  My shop wants the piston to wall clearance no tighter than .0035 as I will be running lousy California pump gas in this # matching mostly restored Charger (And for street use).

What do you engine guys think a safe piston to wall clearance should be on these newer forged Speed Pro's?

Thanks in advance.

RTsehibb   



 

[ws23rt]

I'm not the right guy for advice on this but from what I have read about this issue is that the clearance should be VERY close.

BTW welcome to the group of posters.

If Speed Pro calls for 0.0015" for their pistons I would say to make it a larger clearance at the advice of your shop guy is a mistake.

Ask your shop to reconsider their recommendation. -- They may need to have a chat with the tec. guys at Speed Pro before they make your bores larger and perhaps waste time and money just cause they are nervous.

Edit. This got my interest and with a little looking around I found this.http://www.hughesengines.com/TechArticles/2clearancerequirementsforhypereutecticpistons.php

[RTsehibb]

Thanks for the response.

You are probably right, and that tight clearance is what the speed pro tech line guy said after he looked it up.  I understand why the machine shop guy is hesitant to go that tight as forged pistons always went with at least a .004 PTW clearance?  Thanks for adding Hughes chart - good info.  Maybe these are more like hyper instead of forged?  By the way, a torque plate was used on the bore to .040 if it makes a difference.

Anyone else with L2355F experience? 

[firefighter3931]

My last build with the 2355's used .006 piston to wall...but that was several years ago. Typically you want at least .001 clearance for every inch of bore diameter. So with a 4.36 bore you would expect a clearance of .005 to be in the ball park ?

Perhaps the alloy being used now has less thermal expansion ?

Send a PM to Bob (Challenger340) for his thoughts... He is a top shelf builder and will point you in the right direction   


Ron

[Challenger340]

No need to pm, I'm here.
Tech-Line "computer screen readers" always say that...... they get paid to drink the kool-aid
Nonetheless,
when pushed far enough regarding different "applications"..... they will then always default to "an additional .001" to .003" may be required" given factors like Compression Ratio, RPM, or Boost.
And in your case.... and given high heat loads, with potentially lower fuel qualities, and some intended performance application...

I would agree with your Shop (smart guys  ),
no tighter than .0035" measured above the skirt coating as a safety factor to the high heat/performance application.  

I would also recommend your shop check and adjust(if they haven't already), the Pin-Fit of the Pins in the Pistons to around .0006" to .0007" clearance for street use ? (6 to 7 TEN-Thousandsths)
which,
if you are then going to beat it like a "red-headed step child" closer to 6000+ rpm ?, we then adjust the Pin Fit up closer to .0009" to .0010".

You are really going to wake up your 440, it will run like it's "apposta"  

[RTsehibb]

Wow!  First time poster and I already got 3 replies including ones from the 440 experts on this site! 

Thank you Firefighter and Challenger 340, I have been reading your posts for months and planned my engine work based on your combined advice.  I will forward your specific recommendations to my Machinist with great relief. 

After driving the car with low compression for so many years, it's going to be a blast with the correct pistons.  The car is so original I am running stock manifolds, 906 heads, 727, stock converter, original 355 gears and will install a Lunati Voodo #702 (With Johnson lifters of course).

I bought this 69 RT/SE from the original owner that I worked with.  Thanks to your advice, I expect this car will preform better than when new.  I will post pictures when I figure out how to configure them.   

I have gotten so much information from this forum, I'm even doing the grille restoration (thanks to all who have posted on that topic as well).

Thanks to all on this forum who share their expertise on the coolest cars ever made.

RTsehibb 

   

[BSB67]

The .0025 has been the recommendation for years. I don't understand it. They may or not scuff at that installed clearance. I do exactly what you machine shop recommends, 0.0035. There will be a slight piston slap when cold but will get quiet when warmed up. 

[ws23rt]

When I first read in this thread about a recommended 0.0015" clearance it got my attention.
My instincts from my work (not engine building) is that -at that bore size that would be a light press fit. --(depending on the kind of oil used at assembly).

The other thing that comes to mind is being able to know for sure if all bores are indeed at (for example) 0.0015" and not 0.001"
I do understand and get that going to a little larger clearance just for assurance is not a bad thing.

The question comes back to --why does Speed Pro call for that tight a fit if it is not used in the real world?

[John_Kunkel]

Measure the actual piston diameter and deduct that from the nominal bore dimension....that's the clearance the piston manufacturer intends you to run.

[Challenger340]

Measure the actual piston diameter and deduct that from the nominal bore dimension....that's the clearance the piston manufacturer intends you to run.

Yep it is, that is the "intent" John.
Problem being,(and I have taken this up with FM), I can have 2 sets of exactly the same coated FM pistons on the bench "side by side", same micrometer, same temps, and I can still sometimes see variances smallest to largest in one set of pistons up to .0005", and I have even found .0007 to .0008" between 2 identical sets !

So, if just Honing bang on nominal dimension for all ?  would result in different clrc on different pistons ?

When I took this issue up with FM... again here, IMO, their tech guys like top spew the "propaganda" until pushed.... then the back-pedalling ensues from the provided Sizing directions, and claims of coating thickness variance that "won't hurt anything", and as always.... with the disclaimer "additional clrc as deemed by the Machinist depending upon application"

NOT trying to tell anyone how to do anything here, as always.... anyone should do as they see fit.
just say'in... IMO
FM's recommended sizing instructions to "nominal" bore dimension for their coated Pistons, for all applications, again, IMO.... is flawed at best, and should include more clarification regarding applications.

[John_Kunkel]

Didn't know that the 2355's are now available coated.

[aerolith]

Piston clearances, what an issue indeed!
Obviously it all depends on piston type and material...
Most old skool forged are a minimum of 4 thou up to 6 thou.
New age forged are running tighter but not less than 3 thou I would say?
Famous engine builder back in the 70's ran factory cast at 4 thous and made huge gains over stock clearances!

When it comes to hypers then 'run 'em tight' and keep dem fingers crossed lol...

[metallicareload99]

Piston clearances, what an issue indeed!
Obviously it all depends on piston type and material...
Most old skool forged are a minimum of 4 thou up to 6 thou.
New age forged are running tighter but not less than 3 thou I would say?
Famous engine builder back in the 70's ran factory cast at 4 thous and made huge gains over stock clearances!

When it comes to hypers then 'run 'em tight' and keep dem fingers crossed lol...

Newer L2355F are made out of 4032 Aluminum apparently, so the piston to wall clearance can be tighter.  At any rate my 440 with coated L2355F30 never seemed to have any piston slap when cold?

Measure the actual piston diameter and deduct that from the nominal bore dimension....that's the clearance the piston manufacturer intends you to run.

Yep it is, that is the "intent" John.
Problem being,(and I have taken this up with FM), I can have 2 sets of exactly the same coated FM pistons on the bench "side by side", same micrometer, same temps, and I can still sometimes see variances smallest to largest in one set of pistons up to .0005", and I have even found .0007 to .0008" between 2 identical sets !

So, if just Honing bang on nominal dimension for all ?  would result in different clrc on different pistons ?

I thought all machine shops would hone cylinders to fit the pistons?

[Challenger340]

Piston clearances, what an issue indeed!
Obviously it all depends on piston type and material...
Most old skool forged are a minimum of 4 thou up to 6 thou.
New age forged are running tighter but not less than 3 thou I would say?
Famous engine builder back in the 70's ran factory cast at 4 thous and made huge gains over stock clearances!

When it comes to hypers then 'run 'em tight' and keep dem fingers crossed lol...

Newer L2355F are made out of 4032 Aluminum apparently, so the piston to wall clearance can be tighter.  At any rate my 440 with coated L2355F30 never seemed to have any piston slap when cold?

Measure the actual piston diameter and deduct that from the nominal bore dimension....that's the clearance the piston manufacturer intends you to run.

Yep it is, that is the "intent" John.
Problem being,(and I have taken this up with FM), I can have 2 sets of exactly the same coated FM pistons on the bench "side by side", same micrometer, same temps, and I can still sometimes see variances smallest to largest in one set of pistons up to .0005", and I have even found .0007 to .0008" between 2 identical sets !

So, if just Honing bang on nominal dimension for all ?  would result in different clrc on different pistons ?

I thought all machine shops would hone cylinders to fit the pistons?

NOPE !
With Engine Machining... you GET, exactly what you PAY for !

Ever wonder why after having your Engine "Bored & Honed", the open Piston Box has only ONE Piston out of it's bag ? or, if they are installed on the Rods... none are "numbered" ? Just go by the numbers on the rods right ? Don't you think if all 8 were measured it only takes a few seconds extra to felt pen the sizes on each they would do it..... or heaven forbid "adjust" Cylinders slightly for each and number the Pistons, or put the small pistons in the front holes in the block(coller/tighter running)
or,
when you receive that shiney new pre-Balanced Stroker Kit, that only cost $150 to balance(GREAT DEAL HUH ?), that all the Rods save one, are still sealed in their unopened bags ? Pistons same/same ?
And when you open the rods from their bags ? DAMN those Piston Pins are TIGHT in the Rods ? Wonder why ?
And like WHAT/WHO's Harmonic Balancer/Timing Gear(spacing) or Flexplate was installed when they "spun" the Crank to whatever Bobweight ?
Shit will run.... "close" as in Horseshoes and hand grenades.
Few grams here.... few grams there... a couple more grams where-ever.... it's called "stacking" tolerances. But hey.... dumb-dumb will never "feel" it in the Car, and what's 10-15 hp he'll also never feel seat of the pants, and WHO CARES if the Bearings fail prematurely in a few years, he probably checked his bearing clearances with plasti-gauge right ?

The Boring/Honing with the shorter skirt Piston Stroker Kirts is the most hilarious !
NO T/Plate, NO fitting.... $175 Job....
and literally hundreds of guys on the internet afterwards.... even posting VIDEO's on youtube wondering WHY is my Motor so NOISEY ?
Bwaaahahahaha !
Answer: because the pain of poor quality that was cost effective at the time, lives on, far after the glee of initial cost savings has been forgotten.

[John_Kunkel]

There don't have to be extremes. Somewhere between BillyBob's machine work described above and the big-buck builds Challenger340 advocates, there is a world where rebuilds are done without honing plates and balancing to the nanogram isn't necessary.

[c00nhunterjoe]

I have friends that spent 15 grand looking for a 5 horsepower increase. I also have friends that assemble engines in dirt floor garages with impacts. So i fully understand both extremes.

[Challenger340]

My point is the "middle road" Shops seem to have dis-appeared over the last 10 years, and IMO, we are indeed now left with the extremes at either end ?

Dunno about where you live, but around here it's gotten absolutely brutal.
We don't typically let any "new" customers through the door, we just don't have the time ?
And "if" we do ? and they are willing to wait ?  strictly NEW builds from scratch with Parts WE select, complete & Dyno'd... NO exceptions !

But that doesn't stop the usual 60-80 phone call horror stories a month.... and "can you look at it ? or FIX it" ?
I don't recognize the number ? I don't even answer the phone anymore.

[c00nhunterjoe]

I have a reputable "middle of the road" machine shop local to my area. They are a big outfit and are swamped 24/7. My "pro" builders are the same way. Im sure i have fly by night shops but i dont know where or how they operate as i dont use them. My pro shops operate very similar to you, its a start to finish with dyno job. They will fix other people screwups, but top to bottom, no "bandaids" if its broke and they fix it, its getting fixed.

[Challenger340]

I have a reputable "middle of the road" machine shop local to my area. They are a big outfit and are swamped 24/7. My "pro" builders are the same way. Im sure i have fly by night shops but i dont know where or how they operate as i dont use them. My pro shops operate very similar to you, its a start to finish with dyno job.

"They will fix other people screwups, but top to bottom, no "bandaids" if its broke and they fix it, its getting fixed."

We just won't get into repirs of someone else's problems anymore.... at ANY price.
It invariably ends up costing more than the headaches are worth, and no matter what you tell the customer up front ie: BY THE HOUR ! They somehow in their melons still believe they have a bunch of just "slightly" used parts that just need tweeking for a cheap fix ?
They just don't get it.... that if we're doing it ? It's going on the DYNO, and that ain't happening until I am happy with it, and it meets OUR criterion. And I don't shiv a git what anybody else said should still be fine ?

True Story:
I had a 57 year old grown man CRYING on the phone once !  NOT kidding, I wish I was !
Blubber'in away about have $67K in his HEMI, 3 attempts... 12 runs in total....
And all I did was politely "decline" it ?

went like this
"Awefully sry mate, but it's just NOT something we want to get into, we didn't build it, and it sounds like far more problems than we want to tackle.... why not just take it BACK wence it came from" ?
silence....
sniff...
sniffle....
BWAAAAAA BWAAAA....

WTF
After that I had new found respect for Dr. Phil ?  Like WTF do you some guy blubber'in away on the phone ?

To make matters even worse....
a few months later one of the partner Shops we deal with ships us a HEMI ?
GUESS WHO's ?
So as a courtesy we took it apart, assessed it, and politely DECLINED again !

[alfaitalia]

Don't blame you...Im a keen amateur, obviously nowhere near your knowledge and ability, but im ex motor trade (the kind you probably don't like when they bring poorly motors to you that they've "tuned"!) and I help out friends with there, usually rough running, cars occasionally  ....mainly slightly more modern stuff to be honest. But I really don't want to help a soon as they say its been played with in any way. You really don't know what you are starting with unless its stockish...and I don't want to guess and risk making it worse!! More difficult to turn down mates though!!

[c00nhunterjoe]

By fix someone elses screw up, i meant start from scratch. If its broke and put together wrong, its broke and put together wrong. No bandaids, sorry for your bad luck and lost fortunes.