HarleyTechTalk

"Most moly-coat processes recommend a minimum of 5 microns to a max of 25 microns, with 18-20 microns as the best coating thickness to shoot for to get the max benefit and durability. If you are fitting things that close...." If ?

Shame on you if your not."[/i]

How are measuring to get within 5-25 microns? Can you let us in on your tool(s) to do this? And if it's ok, we will be sending all our cylinders and pistons to you for micron sizing. 

1 micron ~= 0.00004" or 4 x 10 ^-5 so 20 microns ~= 0.0008 (0.000787)" --- about the minimum clearance spec for a stock coated HD piston to wall ... yes?

0.0008 (0.000787)" --- about the minimum clearance spec for a stock coated HD piston to wall ... yes?

NO. TC cast are .0006" 

>>NO. TC cast are .0006"<<

Shoot, looks like I fit 'em too loose! (Bailiff, wack his ......!)

How are measuring to get within 5-25 microns? Can you let us in on your tool(s) to do this? And if it's ok, we will be sending all our cylinders and pistons to you for micron sizing

I use a Standard Gage Company Bore Gage, increments on it are 2.56 microns (.0001"), that I set with Pratt & Whitney gage blocks, that are periodicaly calibrated with standards traceable to the N.I.S.T.

If your not in a big hurry sure, but I will warn you, I'm not cheap.

Damn Ed! Am I the ONLY one who actually reads/follows the instructions?

yet the stock pistons have a " clean " spot to use as a measuring point

That's the only spot to "size" .

Better it be bare then somebody messing up the coating with a micrometer anvil or spindle.

>>That's the only spot to "size"<<

Yup. And there are various approaches to the sizing issue with coated pistons. Some OEM's and piston makers (MAHLE is one) state explicitly that coated pistons are not to be measured and provide a "bore to" size ... and you had best do as they say. There are also different types of coatings that may require some special considerations. Bottom line?   

Just an FYI and point of interest on the difference(s) in coating types.
These are the actual listings of 02 specifications for the GM LS6 Engine with teflon coated pistons ... notice anything "strange" by HD standards or what we work to with moly/graphite coat pistons?

Piston Outside Diameter - Non Coated Skirt - at Size Point
98.969-98.987 mm
3.8964-3.897 in

Piston Outside Diameter - Measured Over Coating - at Size Point
99.989-99.027 mm
3.897-3.899 in

Piston to Bore Clearance - Non Coated Skirt - Production
0.013-0.049 mm
0.0005-0.0019 in

Piston to Bore Clearance - Non Coated Skirt - Service
0.013-0.074 mm
0.0005-0.0029 in

Piston to Bore Clearance - Coated Skirt - Production
-0.027 to +0.029 mm
-0.001 to +0.0011 in

Piston to Bore Clearance - Coating Worn Off - Service
0.013-0.074 mm
0.0005-0.0029 in

Back to the origanal problem of comp, I warmed up the engine and it check 178 rear and 175 front, so I guess all the panic by me was for nothing huh.

Wellll .... maybe. If'n it was me I'd still want to do a leakdown test. Like I said, a motor can "pass" the compression test and still have leakdown issues. Just one more thing in the process of elimination as to why it doesn't seem to be meeting your expectations. Your call.

Reply # 36 ...... hit the nail on the head.NO SHORTCUTS !!!!!!!!!!!!!!
John

I just hope you checked the cam timming, as this will cause a decrease on 1 cyl if out bye a tooth , or vacumme leak etc ,you have done the right thing through out your build, its just sad you were decieved bye improper pistons, but as you say the bore was right on , like the S/E ones off the shelf,i get my mate to bore mine and always spot on , but mostley around 1 thou  clearance ,i like a tight fit but longer running in periods,good luck, cheers Barny

What I'm going to do is put some new exhaust on this winter and redyno this spring, see I haven't dynoed since I fixed the sumping or at least got the oil in the crank from 12oz to 6oz, that may have hurt me some, going to get rid of the V&H's tru duals and rush mufflersa(which sound awesome by the way) and put Rineharts or a D&D with the quiet baffle, we'll see but the bike runs great it was just down a little on what I thought it should do, 81hp and 93.5tq, with new exhaust and the oil issue should pull a few more ponies and may excert a little more tq.
Thanks to everyone except the guy who said I was a liar. (I was telling the truth so help me God.)

Back to the origanal problem of comp,

I kinda sorta thought we were discussing the original problem.

Apparently I am totally in the dark, perhaps you could start at the beginning and explain the part that sounds like you had identified a bad bore as the problem, and yet re-used them for the next assembly anyway, the "fix" as you put it is +.01" SE flat pistons and a bore job that has not yet been done. I am assuming you still have bad ring seal, and bad bores, and the pistons remain a mystery. Comp and leak testing is to determine what?

Posted below is what I read (a little paraphrasing).

Post #1

the indy that did the bore job fitted the pistons with the wrong clearence

after 1200 miles ordered new pistons…..  reuse my old rings,…. apparntly there in lies the problem, 

I guess I'll go 10 over with flatop SE pistons and might shave a little off the heads while I'm at it.

Reply  #3

engine builders said to reuse the old rings since they were going back in the same cylinders

Red,

If you can't keep up ... take notes! :>)

that's a joke,son, that's a joke

notice anything "strange"

yes, this -

Piston to Bore Clearance - Coated Skirt - Production
-0.027 to +0.029 mm
-0.001 to +0.0011 in




unless I am misinterpreting the negative value it indicates that the bore can actually be .001" smaller then the piston.
Most of these tolerances are +/+ (plus, plus)

Yepthir! Give the man a ceegar :>) The concept of forcing a piston into the bore with an "interference fit" sent more than a few folks sideways and had them wrapped around the axle for awhile. But they work just fine. "It ain't yer Daddy's Oldsmobile no more"

See, ya can keep up, after all!

QuoteBut they work just fine.

I would hope the motor is run real softly until it was good and warm. Yeowch!

It has more to do with measuring over the coating IMO. The coating may be thicker but the piston size isn't.

I default all the time to the OEM engineers on most things, but I admit I would have a hard time wraping my mind around the concept of a .001" press with a .0006" coating thickness.


Piston Outside Diameter - Non Coated Skirt - at Size Point

3.8964-3.897 in


Piston Outside Diameter - Measured Over Coating - at Size Point

3.897-3.899 in



.0004" on a diameter that large? WOW! GFL!

Id have to attend the seminar, it would take more then the sales man.

!LOL!

I've seen some that look like the coating was sprayed on with a spray can. Thick. Measure twice. Cut once. I'm sure you can agree with that.

>>It has more to do with measuring over the coating IMO. The coating may be thicker but the piston size isn't.<<

That's true. These are teflon coated pistons, and the "coating" is really more like a pad on the thrust faces of the piston as opposed to a fully coated moly/graphite coated piston. Still makes some folks go but Z06 vettes with the LS6 motors do just fine with 'em.

Ed, if you look at worst case the interference is .001" and the coating is .0006" there is potential for your .0004" to be metal to metal.

That's the part I would struggle with, I could accept teflon/metal contact, but the metal/metal, that's a tough one.