I found my problem with a compression check.

[metaliser]

Well I finally broke down and went to sears last night a bought a comp. checker and what I found explains the problem, my bike runs good but is not doing what it should do, it's a 95" KB flatops, 30 thous cometic gasket, 9.5 comp, HQ 0034's BigBoyz streetport, V&H's tru duals and rush mufflers with 2"baffles, dynoed 80hp and 93.5tq, not good.
I've talked to everybody about this, I also found a little sumping, I had 12oz of oil in the case, tore that back down and now have 6oz of oil so here's the kicker, rear cylinder-172psi front-152psi, so now what, this initself is a long story, see the indy that did the bore job fitted the first set of pistons with the wrong clearence, KB's should have 1 1/2 thous and I had 3.5 clearence, piston slap, tore it back down after just 1200 miles and ordered new pistons and had 1 1/2 thous but was told by several to reuse my old rings which I did, apparntly there in lies the problem, the bike never seemed to have the umph that it did after the first build and I have been chasing the problem every since.
No more KB's for me, I guess I'll go 10 over with flatop SE pistons and might shave a little off the heads while I'm at it.

[mayor]

I feel your pain.  I paid a MMI trained buddy to put together a build for me last year (using KB pistons and SE jugs). I asked him three different times if he: would check the piston fit, are going to check the piston clearance, had checked the piston clearance. He said yes each time.  I developed a piston slap after about 300 miles.  To make matters worse, he wanted to charge me to look at it so I just tore the engine down myself- .004" piston clearance.  The pistons were sloppy loose, to the point where I had oil blow back in the combustion area.  I switched to SE pistons and cut the larger intake valve relief with a ball end bur on a dremel. 

I'm curious, you ordered new pistons but reused the old rings?  why?  didn't the new pistons come with rings? 

[ederdelyi]

Glad to hear you found the problem. FWIW, the KB pistons are usually O.K., i don't see where this is the fault of the piston. A good cast or hyper piston can be run with pretty tight tolerances if things are done right. Stock cast piston clearance spes are 0.0008 to 0.0016", IIRC.

As to the rings ... well, ya learn form experience that some things are just not worth trying to save a few bucks on. If ya do this for a living, it's cheap insurance to use new, quality components rather than having to eat a comeback.
Cost of a set of rings, a bearing, etc. is a lot less than having to do it over ... even for the customer if you think about it a bit.

Freshen up the bores, make sure the fit is right, break it in right ... enjoy!

[metaliser]

Yes they did come with new rings, two engine builders said to reuse the old rings since there were no miles on them and since they were going back in the same cylinders I thought it would be ok, this was a big topic once on the v-twin forum, some say yes and some say na, I say never again but after talking to a freind of mine thats a service manager at a HD dealer he said to warm up the bike and recheck the comp ans as long as it is within 10% of each other it is ok, is that correct.

[Admiral Akbar]

"KB's should have 1 1/2 thous and I had 3.5 clearence, piston slap, tore it back down after just 1200 miles and ordered new pistons and had 1 1/2 thous"

So you are telling us that the same brand pistons had 0.002 difference in size?  How did the skirts look on the ones that came out? Something smells fishy...

Rings are like spark plugs... When in doubt replace. Max

[metaliser]

The bottom of the skirts had a very tiny line where it was shiny, I called KB tech line and spoke with a rep and he's the one who told me what to look for, the front cylinder had 2 1/2 thous but both jugs were dead nuts on 3.875, my theory was they had a mixed set of pistons and just bored the jugs without checking each piston, the next set were on the money, I was there when they were checked and the jugs also, after I replaced them no more piston slap but poor performance, I could do a roll on against my freinds fatboy with 37 cams and run off and leave him, after the new pistons he could stay right with me.

[ederdelyi]

>>after talking to a freind of mine thats a service manager at a HD dealer he said to warm up the bike and recheck the comp ans as long as it is within 10% of each other it is ok, is that correct.<<

Yes and no. HD's take for a stock motor is that a variance of 10% and a minimum of 90 PSI is "O.K" (service limits). That's pretty normal criteria, but it does not address the possibility of leakdown problems and IMO, 10% variance on a hi-po engine is unacceptable. I do agree that doing a baseline cold then "hot check" is a good data point to have and a well built motor should show little change from cold to "hot". As time goes on, periodic checks compared to baseline will be a good indicator of engine health. Usually, both a compression test and a leakdown test are needed to verify engine seal. Low compression can be an indicator of leakage, but engines with leakdown problems can and do pass compression tests. When in doubt ... do both.
Engine seal is just too important for good performance to just say "close enough", IMO. YMMV

As I was typing your other post showed up. It could have been an undersize piston ... or the skirt collapsed a bit. While not as common with cast/hyper pistons as with forged it can happen.

[Don D]

I used to do a lot of 95" top ends. All of the KBs I used were VERY close to identical in terms of size. I tell my machinist to set them at .001 (unless I know the guy will be hammering it) and have had good results there. I have had some from others and one of the "signs" there may be a size issue is just a quick ring end gap check (with .001 I usually see about .016 end gap, or in that neighborhood). The rings are usually very close from Hastings and if I see an anomaly there almost always the piston to wall is not right.

[ederdelyi]

Don,
Barring QC/manufacturing screw ups most all of the pistons i use are closer to spec than most will have the abilty to measure accurately ... same goes for bore size, out of round, and taper. Not trying to pee in anyone's cornflakes, but with modern manufacturing most of the stuff we get is pretty damn good. Still gotta check 'em .... "measure twice, cut once" :>)

[Don D]

Ed I couldn't agree more! I didn't want to insinuate that if my machinist did the boring I just would run them if the gaps were right. I just used the gaps to quickly spot a bad one before pulling out the gauges. Just a little flat rate deal I suppose.
Hell yes measure everything! Use good tools to do that.

[ederdelyi]

Don, I understood what you were saying. We all have our little tricks ... they may not work for others who don't do other things that you or I would normally do in the build process ... 'nuff said.

[metaliser]

Dewey and Ed I understand what your saying, I don't know what happened to the pistons but the tech at KB told me to hit the skirts with a hammer and bring them back to spec  , well needless to say I did not do that, I'm not saying that KB's are bad pistons it's just I've had problems every since the replace of the pistons with the ole rings and I think that this is the problem, don't you guys think that the comp is down a bit even cold.

[mayor]

"KB's should have 1 1/2 thous and I had 3.5 clearence, piston slap, tore it back down after just 1200 miles and ordered new pistons and had 1 1/2 thous"

So you are telling us that the same brand pistons had 0.002 difference in size?  How did the skirts look on the ones that came out? Something smells fishy...

I can't speak for metaliser, but I can tell you based on my own experience - the KB pistons I bought were under sized based on the published specs.  Someone mentioned before that they thought they recently moved the manufacturing out of the U.S. into Mexico, and the quality seemed to suffer at that point.  who knows?  I gave the ones I took out to Sonny, and he also confirmed by measuring them that the pistons were indeed under sized (with no real noticeable wear on the skirts).  I had a set of take off cylinders bored for the SE pistons that I replaced the KB's with.  The SE's checked in at .0015" clearance in the bored cylinders and the SE cylinders, while the KB's came in at a little over .004" in both (using a feeler gage against the skirt and cylinder wall).   Neither were checked with torque plates (just so my good friend PHR doesn't flame me  ). 

[ederdelyi]

>>the tech at KB told me to hit the skirts with a hammer >>
Please tell me you're joking! YtheF would a tech rep make such a statement to a customer ... even as a joke?

>>don't you guys think that the comp is down a bit even cold.<<

Yes, a bit. It's enough to warrant a leakdown test, IMO. I would not be happy with those results on a build or my own motor.

Mayor: Not saying it doesn't happen. Generally, machined parts in this day and age are very good on tolerances. I can remember when replacement parts were such that the odds of winning the lotto were better than expecting a part to fit properly without fitting, honing, etc ... it's what you had to do. Ever file a babbit bearing rod cap to get the right clearance? :>)

EDIT: As in a poured or cast in place babbit bearing. Better clarify that befoer the "nit picker " patrol jumps my case :>)

[metaliser]

Ed it's sad but it's the Gods honest truth, he said put it in a vice or someway to hold them and lightly tap on the bottom of the inside skirt to knock them out  , I didn't say it but I thought you idiot, well anyways I'll warm the bike up and redo the comp test and then I'll have the HD shop do a leakdown test to be sure but as far as I'm concerened I'm ready to pull it down now!!

[mayor]

I agree Ed.  I think the wildcard could have been changing manufacturing sites (if that did indeed happen). 

[FLTRI]

"I don't know what happened to the pistons but the tech at KB told me to hit the skirts with a hammer and bring them back to spec"
Ok. up til now we were with you but to ask us to believe that a piston mfg's tech even indicated to you that a piston could be straightened, resized, or anything like that with a hammer, is just too much to swallow.
This is something like trying to shave your balls with a chainsaw. Look, the guy was pulling your leg, pure and simple.

[Billy]

KBs have been off my list since the last 2 sets I purchased I couldn't use. One set for A 95 TC were .024 short in compression height another set for a EVO the CH was .010 different one slug to the other.

[PanHeadRed]

>trying to shave your balls with a chainsaw<

NOW you tell me.

[metaliser]

"I don't know what happened to the pistons but the tech at KB told me to hit the skirts with a hammer and bring them back to spec"
Ok. up til now we were with you but to ask us to believe that a piston mfg's tech even indicated to you that a piston could be straightened, resized, or anything like that with a hammer, is just too much to swallow.
This is something like trying to shave your balls with a chainsaw. Look, the guy was pulling your leg, pure and simple.

Look dude I have nothing to gain by lying to you guys and I'm not going to, I called my freind up as soon as I hung up the phone with the tech and told him what he suggested and like me he said he's F***ing crazy and I agreed, I also told my indy that and that was what he said also, now personally I could care less whether you beleive me or not but I hope you understand I have nothing to gain by lying or making up stories and sometimes the truth is stranger than fiction.

[ederdelyi]

Hmm, why would you want to shave yer .... let alone with a chainsaw? Never mind, I really don't wanna know!

All: I don't work for KB, don't sell 'em, and don't use them as a rule unless asked specifically to do so. The ones I have used were fine. Over the years I have had screwups from reputable vendors and not just pistons... $hit happens and things change. If I stopped using parts from every vendor who made a boo boo I would have a rather limited selection to choose from.
Not defending poor QC or manufacturing. If they truly continue to make crap one would hope that lack of business will eventually take them out of the market.

[Sonny S.]

On coated skirt pistons do ya'll bore the cylinders based on the piston measurement with or without the coating ?

[ederdelyi]

I fit 'em based on the actual measurement of the piston as it will be installed in the cylinder. Never caused a problem for me.

EDIT: 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 ... good on ya!

[PanHeadRed]

>If you are fitting things that close<

If ? Shame on you if your not.

[ederdelyi]

Dang it! I knew that wasn't gonna come across right. I meant if one was trying to compensate for the small amount of wear to the coating that will occur ... aw Hell, go sit in the corner Ed!

[FLTRI]

"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. 

[ederdelyi]

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?

[PanHeadRed]

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

NO. TC cast are .0006" 

[ederdelyi]

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

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

[PanHeadRed]

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.

[PanHeadRed]

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

[Sonny S.]

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

[PanHeadRed]

That's the only spot to "size" .

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

[ederdelyi]

>>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?   

[ederdelyi]

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

[metaliser]

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.

[ederdelyi]

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.

[jsachs1]

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

[barny7655]

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

[metaliser]

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.)

[PanHeadRed]

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

[ederdelyi]

Red,

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

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

[PanHeadRed]

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)

[ederdelyi]

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!

[Faast Ed]

But they work just fine.

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

[wfolarry]

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

[PanHeadRed]

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!

[wfolarry]

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.

[ederdelyi]

>>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.

[PanHeadRed]

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.

[ederdelyi]

Not "my" specs, those are actual '02 specs from GM. I do recall a revision for the '03's, but I don't have them here. They do run them quite tight, but not metal to metal :>) I'll look for the revised '03 specs when I head up north next week. May take awhile before I get back on the forum as I will be very busy ... good news to some I suspect!

EDIT: Online full engine specs that match what I posted ... still can't find the revision that I was speaking of.

http://www.lbfun.com/warehouse/tech_info/C5/LS6Specs.pdf

[metaliser]

Heres what happened, put the engine together and it was a little loud then it got louder, piston slap, talked it over with the indy and he said I had 1 1/2 thous clearence, after 1200 miles I tore down the engine again, rechecked the  bores and they checked 3.875, both of them and the pistons were 3.871.5 and 3.872, that gave me to much clearence, I called the tech at KB and the indy called the tech also and they would not give us new pistons, indy ordered new pistons and when they came in they were at 3.873.5, both of them, we rechecked the bores and we had 1.5 thous clearence on front and back, thats why I reused the rings, the pistons were the problem not the bores, or they didn't mike the pistons right and bored wrong, but in the end all was right.

[ederdelyi]

On Topic: That's the chain of events that i got out of your posts. Glad i got that much right! So, are you gonna pursue this further or have you decided that the results of your hot compression test are good enough to preclude any seal problems?

Off Topic:
Red,
I can be a little slow on the uptake sometimes :>) The specs include dimensions and clearances for two piston types. Use the specs for either coated or uncoated, don't try to mix and match. Mid year change is why both specs are there. In no case will the final metal to metal minimum clearance be less than the specified service limit. Try those numbers and see if that makes more sense to you. i know I have the '03 coated only specs some damn place, CRS sucks!

[metaliser]

Ed I posted that back  for Red so he could see where I was coming from, anyway I guess I'll leave it alone, the dyno guy said I had to good of a midrange to have much wrong, maybe the light sumping and new exhaust will help.
Thanks.

[ederdelyi]

10-4, ride it!

[PanHeadRed]

Ed, I interpreted this as the before coating and after coating dimensions of the same piston.

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

Interesting info none the less.

[PanHeadRed]

met, I got it now, I was focused on:

> the bore job fitted the first set of pistons <


And I must have missed the part where the guy who checked the pistons checked the bore, and this time it was right.

Like Ed sez, Ride it!

[ederdelyi]

Red,
I knew that there two different piston types listed going in, and I should have caught the confusion in this post:

>>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<<

And when Larry was commenting on the coating thickness. A case of having MHUMB ... no excuse. I'll give myself some corner time!

Mahle makes these pistons and the newer coated pistons have a new barrel shape that actually let's them tighten things up a RCH. No matter how you slice it, 0.0005 or less minimum clearance on a bore that big for a production motor water cooled or not is pretty impressive, IMO.

[PanHeadRed]

I knew larry was posting about the coatings but I did not know if it was to you or me. I am not a coating expert and probly don't have the experience with it he has so I did not have much to comment any way.


No matter how you slice it, 0.0005 or less minimum clearance on a bore that big for a production motor water cooled or not is pretty impressive, IMO.

Absolutely, and that's what drives me nuts about Poo-Pooing SE/HD. If the guys bashing could wrap their mind around .0006" on air cooled, with no special approach needed, just make your hole to tolerance, make your piston to tolerance, DONE. I won't get into all the "he said, she said" internet tech.