# Keith Black pistons , ring fit?



## Lok (11 mo ago)

So I ordered a set of Keith Black pistons UEM-KB346KTM-STD with rings . 
Now the problem is the ring fit for these pistons is.
Top 0.0065 per inch x 4.12 = 0.02678" as per the instructions . 
Second .004 per inch x 4.12 = 0.01678" as per instructions 

The ring kit 4120AM8.STD came with the pistons are first off non file . 
The top ring fit as it would stand would be 0.018 measured in the bore
Second ring fit as it came is 0.026 measured in the bore

Ok my problem is not so much with the top ring(can always be opened up)
The second ring is way to big of a gap and you know as well as I can't add material to a ring. 

UEM who makes all the parts abouve as they own Keith Black and the rings are UEM branded. 

I have contacted summit and they are willing replace them , that's what I am gonna do , but UEM insist that the ring kit is correct. UEM is now on my no buying from list as that's just sloppy work 

What is your opinion on this ?

Thanks 
Mike


1970 GTO 13.2 in the quarter when it was 1320ft . All stock .


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## PontiacJim (Dec 29, 2012)

Lok said:


> So I ordered a set of Keith Black pistons UEM-KB346KTM-STD with rings .
> Now the problem is the ring fit for these pistons is.
> Top 0.0065 per inch x 4.12 = 0.02678" as per the instructions .
> Second .004 per inch x 4.12 = 0.01678" as per instructions
> ...


The pistons typically have an installation sheet that indicates what ring gap to use.

Forged pistons expand a little more than cast pistons, so you cannot use factory gap settings. If you use a power-adder like nitrous, you want even more gap. Hypereutectic pistons require bigger gaps as the rings set higher up on the piston and take more heat so they expand more.

So ring gaps can vary due to piston material, ring land placement, size of the bore, and power-adders.

I have the Keith Black FHR Icon forged pistons for my 455. The "General Clearance Guidelines" data sheet gives ring gaps and piston/wall clearances.

What I have is a formula of bore size X .004" ring gap factor.

So top ring is 4.12" x .004" = .0016"

Second ring seems to be the same, but states minimum gap.

For street towing - .0045" = .0018"
Nitrous - .0050" = .020"

However, going through a couple engine build books for ring gaps I get this:

H&O Pontiac Engine Blueprinting

For a good high performance engine - .0015"-.0018"
Some smog motors with higher piston/block temps can be up to .0045" gap

Speed-Pro Ring Gap formula

Moderate Performance
Top Ring - .004" = .016
Second - .005" = .020"

Drag Race
Top Ring - .0045" = .018"
Second - .0055" = .022"

1968 Factory Manual

Cast pistons -
Compression ring .020" 
Oil ring - .035"

1965 GTO 389CI AMA Factory Specs:
Cast Pistons-
Top ring - .021"
Second ring - .019"
Oil ring - .035"

1970 400CI
Top ring - .019"
Second ring - ..015"
Oil ring - .035"

OK, a little more from the web:

*JE Pistons Ring End Gap Recommendations*


High-Perf. Street-StripBore x 0.0045"Bore x 0.0050"

*The ring manufacturer suggests (based on a 4.44" bore) the top ring to be 0.020-inch and the second ring 0.004- to 0.008-inch larger.* 

The idea is to run a slightly larger gap for the second ring to prevent a pressure buildup between the top and second ring.

Using the above .0045" = .01854", .018/.019" Top Ring. Using the .004"-.008" for the Second ring, gap comes up to .022/.023"-.026/.027"

So *using the "modern" thinking *in preventing pressure to build up between the top and second ring so as not to unseat the top ring, your ring pack is correct. Using the old typical way of doing ring gaps, your ring pack may be a little wide.









Ask Away! with Jeff Smith: Calculating and Setting Piston Ring Gap for Your Engine Build - OnAllCylinders


I’m currently checking the gaps on a new set of first and second rings. I’m not building an all-out drag race motor, but have plans to be a weekend warrior. …




www.onallcylinders.com


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## Lok (11 mo ago)

Jim correct the piston build sheet is the instructions I am using. See the Keith Black pistons I am using is places the top ring higher in the cylinder, and a higher operating temp. I have attaches the piston build sheet here(I hope).
Thanks
Mike

After I posted the machinist I use called me back and said I did the right thing , he has used these pistons before.


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## lust4speed (Jul 5, 2019)

The key word here is "Hypereutectic". Ten years ago they were on their sixth formulation and the tech thought they were close to getting it right -- but I bet they have moved on through additional mixes of alloys. These hyper pistons transfer a massive amount of heat to the top ring and the piston manufacturer keeps trying to get things sorted out. Last set I did was for a .040 over 455 and their instructions at that time said a top ring gap of .032", but when I called the tech he said forget that and play it safe at .036" gap. The bore was 4.190 and dividing by the recommended .036 gap gives a .0085 factor or slightly above what they now recommend for towing. The super heated top ring expands and insufficient gap locks the ring to the cylinder wall, seizes, and pops off sections above the top ring land. I see by the photos that they have lowered the top ring land quite a ways down which won't heat the ring as much. While this seems like a massive gap, bare in mind that the ring expands with heat and ends up with a running gap about the same as any other ring.

Personally I prefer to stay with a more standard aluminum alloy and moderate gaps, but that last hypereutectic piston equipped engine I built for a club member is still tearing up the street and not a puff of smoke to give away the large top ring gap.

The concern with your rings is not nearly enough top ring gap and too much second ring gap. Second ring is just a little sloppy but the top ring can decimate your build. While the rings you are using are non-file, you can always file a ring for more gap. While they don't advertise it, file-to-fit rings are simply a standard ring that is .005" larger to give the installer room to grind it down for exact fit. I switched over to using nothing but file-to-fit rings simply because the drop-in rings were almost always .006" to .010" larger gap than spec. Here's a photo of the Keith Black Hypereutectic pistons in the 455 short block.


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## Lok (11 mo ago)

Thanks for the tips and info lust4speed, yea ordering a set of file fit today. I think the frustration for me was the kit should have come with file fit rings so I could give them the correct clearance and they did charge me for the rings (like 119 bucks) . It's just wrong to charge some one for a part that isn't right. 
Mike


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## Lok (11 mo ago)

Update 
At my machinist recommendation I purchased the uem 4125AM8.STD , his recollection on these pistons was to not venture wildly from materials of the recommended rings. He has built 4 engines with the hypereutectic pistons all with no issues. He showed me the old piston build sheet and the larger gap requirements, he agrees with lust that they lowered the first ring and must have changed alloys , more than likely. He always orders file fit and assumed I did when doing my research, I missed that one . He said he has seen dozens of article's about thes3 pistons seizing, and he always asks him self if they fit the rings right(he said most of these are from when they introduced them, not as much latley).
I want to thank Jim and Lust for putting info out there and sharing, always good to have confirmation these days with the interwebs so full of bad info.
Along Jim and Lust , asked over 20 engine builders , some old nhra team builders, some aircraft mechanics, some back yard mechanics, and one engine designer for a small company named Yamaha. Not one said the second ring gap was acceptable and all agreed that the first ring is needs to be filefit, some even did research into (on their company s time ) into the materials being used . 

So thanks guys 
Mike


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## BearGFR (Aug 25, 2008)

I recently spoke with the tech folks at well known ring supplier "Total Seal". I was in the process of file-fitting a set of their rings for my most recent build, and I had misread their gapping spec chart and had filed one or two of my second rings a bit too wide - my mistake.

Here's what their tech department told me, which I pass along for your own consideration. I'm not personally advocating one way or the other, just relaying information:

"The second ring is primarily for oil control. The ring seal for compression purposes is handled by the top ring, so don't worry about it too much if the second ring gap is a little wider. It'll be fine."

FWIW, I'm also running their gapless top rings and forged pistons.

Bear


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## PontiacJim (Dec 29, 2012)

Lok said:


> Jim correct the piston build sheet is the instructions I am using. See the Keith Black pistons I am using is places the top ring higher in the cylinder, and a higher operating temp. I have attaches the piston build sheet here(I hope).
> Thanks
> Mike
> 
> After I posted the machinist I use called me back and said I did the right thing , he has used these pistons before.


OK, got it. They hypereutectic pistons do require more ring gap due to the higher ring location which causes them to run hot, thus expand more. They early hyper's got a bad rap early on because engine builders were using what they knew as factory ring gaps and this cause the rings to butt together when they got really heated up and then break the top ring land right off the piston, or bust/crack the piston and engines were damaged/destroyed.

But as engine builders realized their errors and followed the required manufacturers ring gaps, broken piston issues went away. The Hyper's are a good middle ground between cast and forged and reasonably priced. Most new cars/engines use Hyper's from the factory. I installed a set in my brother's engine I rebuilt for him and he has had no issues. It is a street engine more than a race engine and I felt the Hyper's were adequate for his needs and as a means to save some money.

They may have made changes to the piston material or ring land location since all the bad raps of the early days - I don't know. But I would not hesitate to use them depending on the build and the engine's use.


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