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Discussion Starter · #1 ·
a few years ago I was sold a set of alum. forged 71mm JE pistons (with rings, pins, clips) said to be for CB450. From my brief research, I've found that the pistons are custom made job lot. Anyone know ways to identify the appication(s) for a JE piston set? TIA, danWI

p.s. i probably wont be using these pistons so they'll be FS once I figure them out
 

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Discussion Starter · #2 ·
I emailed JE pistons direct and they were nice enough to cross references the ID # on the piston. Im happy to report the response below:

Dan,

We are showing this for a Honda CB 450 with 12.5:1 compression.

Regards,

Brian Weaver
JE Pistons, Inc.
Technical Sales
TEL: 714-898-9763 ext 218
FAX: 714-897-5636
Email [email protected]
 

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Dan,

Then those would be 4'th oversize.

But 12.5:1 compression ratio - holy cow !!
Must have radical domes - they'd blow out your head gasket in no time at all, you'd have to get one of those copper gaskets...
 

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tbpmusic said:
12.5:1 compression ratio - holy cow !!
Must have radical domes - they'd blow out your head gasket in no time at all, you'd have to get one of those copper gaskets...
considering the stock ratio is 9:[email protected], I wonder what a compression gauge would read on those 12.5's?
 

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jayel said:
considering the stock ratio is 9:[email protected], I wonder what a compression gauge would read on those 12.5's?

Couldn't say....

There used to be a guy at the old MSN DOHC450 forum named "dinosaurthatroars" - I think his name was Paul Jones - he's still in my address book. He didn't migrate over here like a lot of guys did after that group closed down.
Anyway, this guy has done everything it's possible to do on a 450.
He would be able to answer you......
 

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we've gotten as high as 210 PSI on a freshly rebuilt stocker.....and isn't pressure an inverse square deal?.... Math-wise, it should be somewhat above 300 PSI.... Wouldn't that self-detonate (diesel)?
 

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Could those be some bastardized pistons used to combine CB500T head with 450 lower ends or something?? :oops:

GB :mrgreen:
 

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Discussion Starter · #8 ·
Well, this morning I slid these 71mm forged pistons into a 500T cylinder... they fit! I do wonder if these pistons are 12:1 to compensate for a "thicker" copper gasket. I'll assume this would bring the compression down to a reasonable/usable pressure.

BILL: would you mind passing Paul's email to me? I'll contact him direct and as for advice. Thanks man!
danWI
 

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danWI said:
Well, this morning I slid these 71mm forged pistons into a 500T cylinder... they fit! I do wonder if these pistons are 12:1 to compensate for a "thicker" copper gasket. I'll assume this would bring the compression down to a reasonable/usable pressure.

BILL: would you mind passing Paul's email to me? I'll contact him direct and as for advice. Thanks man!
danWI

I sent you his email address.

Stock bore on both 450 and 500T is 70 mm, so it's a little confusing now......
 

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Discussion Starter · #10 ·
Maybe my 500T cylinders are at 4th over then? Thanks for the addy, I'll let ya'll know the results. danWI
 

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Discussion Starter · #11 ·
Well, here i am few weeks later with no word from Paul... so I'll ask here, how thick would the rocker head gasket need to be to lower the compression on these 12:1 pistons? is there a formula or measuring method? i would like to get the info prior to posting these for sale next week. thanks for advice, danWI
 

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You can figure out the "squish" from the bore stroke calculations..... On a stock 450, the bore X the stroke displaces 222cc per cylinder ...At 9:1, that means the compressed volume is 1/9 of the original 222, or 24.66666666 cc. The stroke is 57.8mm...
Assuming the same stroke, and a 1mm larger bore, the displacement is ~228.8cc....
For a 9:1 ratio, the compressed volume would have to be 25.42cc.... You have 24.666 of that, so the head gasket would have to have a thickness (h) to provide the additional volume of .74cc.....
Volume equals area of the circle X height ( Pi X r X r x h).... r is now 35.5mm, so the gasket would have to be 1.92mm thick......
I'd just run a 1.5mm base gasket and get about a 10.5/10.75 ratio...LOL....

That isn't as big as it sounds, the stock gasket is about 1 mm before torquing and about .75mm after.....
 

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nothing wrong with a little more compression :) anything low enough to run on 93 pump gas (less than mid 12 to 1) is probably safe just keep her tuned up!
 

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Rod...I believe if you actually measure, the "deck height" is the same (or very close, certainly within the "squish of the gasket)).... The 450 piston is too long to go in a 500, it would "hit" the crank flywheels (Or you could cut the skirt down).....I believe you CAN run the 500 piston in a 450, but the shallower dome would decrease the compression ratio...... I always assumed the gudgeon diameters were different, but they appear the same in your pic....
 

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The deck height should be measured as the centerline of the wrist pin the deck of the piston (not the crown).

In the picture above it looks like the right 2 pistons have longer skirts and are giving a false impression. If the
wrist pins are the same diameter on all the pistons you could just measure from the top of the wrist pin to the deck.
 

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Discussion Starter · #18 ·
these are 450 pistons that happen to fit a 500 cylinder i have here. still have not verified that the bore is 71mm tho....

ALSO, HUGE thanks Steve! that info is incrediable valuable and appreciated :)

danWI
 

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