Author Topic: KB Super Duty Piston expansion.  (Read 560 times)

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Offline 838

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KB Super Duty Piston expansion.
« on: June 10, 2021, 03:47:54 PM »
I typically let my bike get very warmed up when I ride. Last weekend I rode with a buddy who does not. My bike is a twin cam 117Ē with KB super duty pistons. I noticed when operating temps were low (warm but not fully) the bike would make a sound (similar to valve train with an aggressive cam) starting at about 2800. I only reved to 3k cause the sound was getting louder as rpms built. Once up to operating temps the noise was gone. Iím assuming forged piston expansion, but my question is this:

In this situation would revving higher be detrimental? These dudes will park for 20-30min then hop back on and  immediate aggressive riding... Iím cool with that 😎, but could there be damaging effects to the piston or cylinder wall, or is this speced in  the tolerances when honing to fit?

Offline joes124

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Re: KB Super Duty Piston expansion.
« Reply #1 on: June 10, 2021, 06:47:21 PM »
My guess is the sound is piston slap.

Offline 838

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Re: KB Super Duty Piston expansion.
« Reply #2 on: June 10, 2021, 07:33:20 PM »
I agree. They are forged pistons, so what Iím wondering is if I have to take off with the bike not completely warmed up to operating temps (and/or the pistons not fully expanded) will that be harder on the components, or are they specíd to tolerate this? Iím not talking about a completely cold engine either (see original post, 2nd paragraph for scenario).

Offline FXDBI

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Re: KB Super Duty Piston expansion.
« Reply #3 on: June 10, 2021, 08:05:16 PM »
I agree. They are forged pistons, so what Iím wondering is if I have to take off with the bike not completely warmed up to operating temps (and/or the pistons not fully expanded) will that be harder on the components, or are they specíd to tolerate this? Iím not talking about a completely cold engine either (see original post, 2nd paragraph for scenario).

No engine should be pounded on until full operating temp.  That being said it will warm up to that temperature riding it easy until it fully warmed up.  Abuse=shorter life cycle. If its anything of a performance
with compression you will blow a head gasket eventually hammering on it cold. I always warm mine up before riding dont care what the next guy does its my $$$ no one elses to fix it.  Bob

Offline 838

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Re: KB Super Duty Piston expansion.
« Reply #4 on: June 10, 2021, 09:20:43 PM »
So then would riding easy mean to up shift before the slap begins (2800 rpm)?

Offline kd

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Re: KB Super Duty Piston expansion.
« Reply #5 on: June 10, 2021, 09:32:20 PM »
Are the pistons coated?  Is something like that a reasonable option to resolve the issue and bring back some reliability?
KD

Offline 838

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Re: KB Super Duty Piston expansion.
« Reply #6 on: June 10, 2021, 09:39:21 PM »
They are coated, line-2-line.

Offline HD Street Performance

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Re: KB Super Duty Piston expansion.
« Reply #7 on: June 11, 2021, 05:51:57 AM »
When they rattle cold that is piston slap, simple as that. They should never be clobbered cold. I have fixed many that have been cold seized.
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Offline 838

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Re: KB Super Duty Piston expansion.
« Reply #8 on: June 11, 2021, 05:58:00 AM »
When they rattle cold that is piston slap, simple as that. They should never be clobbered cold. I have fixed many that have been cold seized.

No clobbering. But would you say to try and avoid the slap when warming up (short shifting @ 2800RPM), or could I do easy roll ons to say 4k, even if she buzzes a little bit?

Is cold slap common/normal with these KB super dutyís?

Offline motorhogman

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Re: KB Super Duty Piston expansion.
« Reply #9 on: June 11, 2021, 07:48:03 AM »
I have road with lots of people who jump on fire the bike up, slap it in gear and go.. I watch them leave.. I check my brake, directional, tail lights, spots, and head light before every ride. She don't move until a good 2 minutes of warm up.. I say let them rip, you'll always catch up..
where's the points and condenser ?
Tom / aka motor

Offline HD Street Performance

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Re: KB Super Duty Piston expansion.
« Reply #10 on: June 11, 2021, 08:04:06 AM »
The line2line coating is a sacrificial coating. If the cylinders are straight and true the forged 4032 piston will run quiet when it is set up with the proper clearance to begin with. You actually have to scuff the skirts just to get the pistons in the holes. If you have piston slap there is too much clearance, simple as that. The cylinders distort, usually not wear. After they are get out of round and not straight the ring seal goes away and so does power, oil control (adds detonation), and cooling. The ductile iron sleeves seem to fair better in a twin cam.
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Offline 838

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Re: KB Super Duty Piston expansion.
« Reply #11 on: June 11, 2021, 08:56:47 AM »
The line2line coating is a sacrificial coating. If the cylinders are straight and true the forged 4032 piston will run quiet when it is set up with the proper clearance to begin with. You actually have to scuff the skirts just to get the pistons in the holes. If you have piston slap there is too much clearance, simple as that. The cylinders distort, usually not wear. After they are get out of round and not straight the ring seal goes away and so does power, oil control (adds detonation), and cooling. The ductile iron sleeves seem to fair better in a twin cam.

Will allowing the bike to reach operating temps delay or prevent the cylinders from going out of round? I have not herd this noise whatsoever until this last weekend when I got on the highway after a 30-45min break. I just short shifted till the temps got up where they need to be.

Offline kd

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Re: KB Super Duty Piston expansion.
« Reply #12 on: June 11, 2021, 10:00:06 AM »
The line2line coating is a sacrificial coating. If the cylinders are straight and true the forged 4032 piston will run quiet when it is set up with the proper clearance to begin with. You actually have to scuff the skirts just to get the pistons in the holes. If you have piston slap there is too much clearance, simple as that. The cylinders distort, usually not wear. After they are get out of round and not straight the ring seal goes away and so does power, oil control (adds detonation), and cooling. The ductile iron sleeves seem to fair better in a twin cam.

Will allowing the bike to reach operating temps delay or prevent the cylinders from going out of round? I have not herd this noise whatsoever until this last weekend when I got on the highway after a 30-45min break. I just short shifted till the temps got up where they need to be.


Going back on the thread, I am wondering if you can give a list of engine components, mileage, oil change interval, filter etc?   There seems to be a decision made that it is piston slap without any real factual info.  This last statement makes me think we are all jumping to conclusions with no real basis for it.  Piston slap will not just appear full on like that.  It will be something you think you can hear before it gets bad enough that you say "Oh yeah, that sound IS getting worse".   

Personally, after hearing you say how it suddenly occurred (and now continues to occur), I would first suspect poor oil flow to the lifters.  Maybe a piece of debris in the cam plate relief valve?  You already said it sounded much like valve train noise.  Your Spidey senses may have been correct.  The cam plate cools, the valve sticks, the cam plate comes up to temp and the valve moves as it should.  :nix:  How is the oil pressure?  Have you tried to find the area the sound is generated from yet?  A stethoscope type device can be your friend here.  IMO, there's no point in discussing pistons unless there is real evidence that's where the clatter is coming from. 
KD

Offline 838

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Re: KB Super Duty Piston expansion.
« Reply #13 on: June 11, 2021, 10:49:52 AM »
Not sudden, itís always done it. I just learned quickly it went away once up to full temps, so I landed on forged piston cold slap. I simply wait till the bike is at running temps before letting the rpms come up. The question was to see if waiting will extend the life, or can I ease her to 4k in this situation to get up to highway speeds?

Super mild 117. 10.3:1 s&s 570, headwork, s&s premium lifters, quickee pushrods, s&s plate and pump. It does have heavier springs and more seat pressure than necessary think they are kibblewhite .600Ē springs (came with the heads... I figured stock would be better).

Online Ohio HD

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Re: KB Super Duty Piston expansion.
« Reply #14 on: June 11, 2021, 12:26:34 PM »
What was the piston clearance set to?

Hopefully they didn't measure the piston over the line 2 line coating, and then add 0.0025" to 0.0035".....     :doh:
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Online Hossamania

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Re: KB Super Duty Piston expansion.
« Reply #15 on: June 11, 2021, 12:46:29 PM »
?
https://harleytechtalk.com/htt/index.php/topic,115271.0.html
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Offline jsachs1

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Re: KB Super Duty Piston expansion.
« Reply #16 on: June 11, 2021, 02:38:02 PM »
Generally, when using pistons that are Line to Line coated, the size of the piston is usually stamped on the wrist pin boss. Figure .0025" to .003" over that number SHOULD be the size of the bore. High spots need to be scuffed down. The pistons won't fall through the finished bore. They will need a little help getting through. I've never heard them rattle cold, and I always bore to .003" over.
John

Offline HD Street Performance

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Re: KB Super Duty Piston expansion.
« Reply #17 on: June 11, 2021, 07:50:10 PM »
At about .0045 they start to rattle cold.
Hot it goes away.
The nominal number that the bore should be theoretically is not what I use unless I have some coated pistons (wiseco) that have no measuring window. Often times to get the desired clearance the bore will end up short of the nominal bore size. On a KB forged LCA piston the skirt size under the Line2line coating at gauge point is scribed on the piston by the pin, as John described.
« Last Edit: June 11, 2021, 07:55:01 PM by HD Street Performance »
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Offline 838

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Re: KB Super Duty Piston expansion.
« Reply #18 on: June 11, 2021, 08:40:01 PM »
At about .0045 they start to rattle cold.
Hot it goes away.
The nominal number that the bore should be theoretically is not what I use unless I have some coated pistons (wiseco) that have no measuring window. Often times to get the desired clearance the bore will end up short of the nominal bore size. On a KB forged LCA piston the skirt size under the Line2line coating at gauge point is scribed on the piston by the pin, as John described.

If this is the case, and I wait until the pistons expand before operation, will the longevity of the pistons/cylinders be extended? Or am I looking at a new top end in the near future? Thatís assuming the noise is cold clap of course.

Offline HD Street Performance

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Re: KB Super Duty Piston expansion.
« Reply #19 on: June 12, 2021, 05:36:33 AM »
My belief is it won't fail. What happens is the rings wear at an accelerated rate.
Assumption is these cylinders were sized right to begin with plus true and straight. Unless you check them in plates with calibrated gauging no way of knowing.

The pistons expand at a different rate than the barrel, casting/liner, assembly. In theory that is what keeps them quiet. Problem is the barrels don't expand (cool) uniformly. Testing was done by Randy Torgeson that is very interesting. He heated the components and measured. The results were not pretty or how it is supposed to be. The results were explained when the barrels were cut apart and there were air voids. Apparently there were problems with the production process, centrifugal spun-cast iron, which is touted as drawing out the impurities including air.
The solution?
Ductile iron sleeves. Ductile iron is twice as hard and strong as grey iron. It also can be warped (uneven air cooling remember) and return back to its original size, metal memory.
Problem is how many people are going to spring for sleeved cylinders? It is a cost and downtime factor many will not swallow. This is mainstream for motors that are highly stressed with power adders. I have sleeved them for some of the local clubbers. they clobber the bikes.
« Last Edit: June 12, 2021, 05:42:05 AM by HD Street Performance »
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