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426 pistons in a .060" over 413 - WTF?!

62 Dart Convertible

62 Dart Convertible

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Well I finally pulled out my engine (1962 Chrysler 300H 413 wedge) and have it all stripped down, and found two problems.:icon_shaking:

Problem 1. Previous engine builder:jerk:mixed up upper and lower no 5 main bearing shells, so no 5 main and no 7 & 8 big ends were not getting oil supply. These bearings were toasted, yet surprisingly, the crank looks OK. I haven't fully miked it up yet but visually the (already .020 under) journals look no worse than any other so I'm hoping I dodged a bullet here. Not a big problem either way...

Problem 2. Scratched off the carbon on pistons and found part no L2184 STD. Scoured internet and found these are std size crowned 11:1 pistons for a 426 wedge (with an intended bore size of 4.25"). I measured my bore and found it taken out to 4.2475" (which is 0.060" over std 4.1875"). So it seems these pistons are .0025" tighter in the bore than they are designed for.
The pistons and bore are still clean and tidy with surprisingly very little scuffing.

I am after some advice on what folks think I should do wrt problem 2.

Should I leave it as is and let sleeping dogs lie as it seems to working OK, OR have the block honed the extra .0025" and get the piston/bore clearance right? (I know 11:1 is pretty high, but it seemed to run OK on Premium 98 fuel.)
 
Well, let's examine this sentence.

"So it seems these pistons are .0025" tighter in the bore than they are designed for."

No need to call emergency management. Your figure is two and a half thousandths. That's nothing. You could have made that mistake measuring the bore. The pistons could have been cast that much smaller requiring that size bore. The bore IS 4.250, technically. Sounds like all somebody did was punch it .060 to a 426 and put high compression pistons in it. Leave it alone if it's run fine this far.
 
The 426 Wedge is a 0.060" over 413....
 
Sonny has a ..............413, 426 Wedge is a 0.060" over . not too shabby, it can get up and go. well sort of:sleepy2:


Vito (1).jpg
 
I am a little astounded at the responses so far.

I measured the bore size with internal micrometer with accuracy plus/minus .001", no mistake measuring bore.

2.5 thou isn't nothing, it is 2.5 thou.

426 isn't a .060" over 413, it's a .0625" over 413.

So when it comes to machining accuracy of bore size, would you be happy if your machinist works to tolerance of plus/minus .0025"? I know I wouldn't be.
 
62 Dart Convertible said:
I am a little astounded at the responses so far.

I measured the bore size with internal micrometer with accuracy plus/minus .001", no mistake measuring bore.

2.5 thou isn't nothing, it is 2.5 thou.

426 isn't a .060" over 413, it's a .0625" over 413.

So when it comes to machining accuracy of bore size, would you be happy if your machinist works to tolerance of plus/minus .0025"? I know I wouldn't be.
Click to expand...

Have you taken the engine apart and measured the piston? If not, you might do that before condeming possibly good maching work. What if the pistons came in .0025 under spec? It happens all the time. And yes, It would not bother me one iota as long as the piston to bore clearance was in spec. THAT is the figure that's important here, not quibbling over a .0025 "discrepancy". Again, the piston to bore spec is the important factor here. Find out what that is and get back to us.
 
RustyRatRod said:
Have you taken the engine apart and measured the piston? If not, you might do that before condeming possibly good maching work. What if the pistons came in .0025 under spec? It happens all the time. And yes, It would not bother me one iota as long as the piston to bore clearance was in spec. THAT is the figure that's important here, not quibbling over a .0025 "discrepancy". Again, the piston to bore spec is the important factor here. Find out what that is and get back to us.
Click to expand...

Fair point Rusty. Finding any info on this piston was hard enough, so finding the recommended clearance is so far imposssible. This piston is listed as a NHRA approved TRW replacement piston for 11:1 426 MW, that's all I could find. TRW probably stopped supplying them 20 years ago.

If I were to leave it as is, what would you recommend for piston rings for this odd bore size? 4.25" and file back or you think that would that not be necessary?
 
I guess it's a forged piston? It probably is. I would say piston to wall clearance of .003-.004 would work. I've run over .010 before and not had trouble. lol Forged pistons are strong. They'll hold up where a cast piston would crack a skirt at those clearances. The ring gap is most critical there. Yeah I think the 4.250 rings would be the way to go. Maybe set the gap up about .025 top and 2nd ring. I know with the KB hyper pistons, they get up and over .030. lol That's where the ring gap will be in my 383.
 
I will come back to this post tomorrow. I will try to look up the pistons in a old Sealed Power catalog I have at work. As far as the rings go, a 0.005" OS set so you can file fit will be fine. Or, just use a regular set. You can use a set of 0.060" OS Hastings 437 cast rings, or 2M437 Moly rings. I will look up a set of rings for a 426W tomorrow.

A good machinist will measure the pistons to set up the bore clearance, and not just assume it is the bore plus 0.060". Or for that matter, 4.250" for a standard 426W, the piston always needs to be measured.
 
Thanks for the help guys. I would love to know the recommended clearance for this piston as well as whether it's forged or cast. I would imagine a TRW MW replacement piston would be forged?!

I have scoured the internet and came up with very little. This is the best I could find -
http://www.collectorsautosupply.com/Engine%20Parts.htm
Scroll down to Chrysler 1963-1964 426 wedge head

Any further help would be much appreciated.
 
Am I the only one who thinks this is **** cool! I would be thankful I dodged the bullet, clean it back up and put it back together if it works out well

Mike

Modified by management.......your language was modified to a permissible level
 
Last edited by a moderator:
Very easy to determine if the pistons are forged. When you get the engine apart, look at the underside of the piston. If it is all one uniform color, they are cast. However, if they have a "grain" to them of light and dark "streaks" they are forged. They are most likely forged which will set up like I said between .003-004, but more will not hurt a thing.
 
Cheers Rusty. Tomorrow I will measure the pistons and determine the piston to bore clearance. I'll have a closer look at the "grain" too..
 
Piston to wall clearance can be any where from .002" to .010", depending on intended usage. The factory sets them up pretty tight new, to keep it quiet, and improve ring seal due to less piston rock. And this will also tend to prolong ring life. These stockers seldom see much over 5000 RPM. But a high revving drag strip motor needs closer to .008 or even .010 piston to wall clearance. My sons 383 has .010 clearance and it runs great! But you sure hear alot of slap when its cold. I think a 4.25 diameter ring would work fine. What are the ring widths? A 383 uses 4.25 " bore, 5/64, top, 5/64, and 3/16 oil ring. Those should work in your motor.
 
69Bee said:
I will come back to this post tomorrow. I will try to look up the pistons in a old Sealed Power catalog I have at work. As far as the rings go, a 0.005" OS set so you can file fit will be fine. Or, just use a regular set. You can use a set of 0.060" OS Hastings 437 cast rings, or 2M437 Moly rings. I will look up a set of rings for a 426W tomorrow.

A good machinist will measure the pistons to set up the bore clearance, and not just assume it is the bore plus 0.060". Or for that matter, 4.250" for a standard 426W, the piston always needs to be measured.
Click to expand...

Hastings Rings:
413 Motor: 437 Cast, 2M437 Moly, 2C437 Chrome
426 Motor: 683 Cast, 2M683 Moly, 2C683 Chrome

For the piston L2184, the L designates it as a forged piston. As far as the clearance goes, I can find no information, and after calling Sealed Power, they had no info. Pistons are normally made undersize for the clearance required, so this is what I would do:

1) Measure the piston perpendicular to the pin axis
2) Subtract that measurement from a std. bore of 4.25"

This should give a close figure for the bore clearance. They did say that 0.0045" to 0.0065" was normal for forged pistons back in the day.
 
If it's not scuffing it's happy. These pistons can be run loose and will work. My bet is they have the slotted oil ring returns. They don't like to be as loose. What is your piston to wall? I'd like to see no less than .004" no more than .008". The looser you run them the more oil it will use. Lets face it these are not state of the art pistons. Will they run, you bet. Race em, be carefull to keep the RPM to 6000 max, they're heavy and old.
Would I use em in a street car/ocasional strip,yup.
Doug
 
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