Excessive piston to wall clearances on KB944s?

[SilverXJ]

When I orginally contacted Keith Black about the KB944 pistons I was told this:

Yes they are 2618 forgings.
I would run them about .004" clearance.
Piston weight is about 437 grams and the pin should be about 170 grams.

So based on that information, what the spec sheet said and what my machinist decided on the 2618 alloy they were installed with .004" wall clearance.

Recently I started seeing different information on different sites regarding the alloy. I contacted KB again for clarification. Now, Keith Black tells me different:

The IC944 is shown with the 2618 line but is made of 4032 alloy and forged in a 2618 style forging die.
Piston to wall is .0025”
Part number change this year from KB944 to IC944, same part.

So, what is going to happen with the greater piston to wall clearance? More piston rock? Shorter life? Broken skirts?

Its just one problem after another.

[gradon]

I really don't know what they're doing over there at KB, but they definitely have spread their share of misinformation on specs and other random issues. I was so hyped to get those pistons when I was building mine, but delay after delay, and then the first batch was bad. Why'd they change the name to Icons? Anyhow so you've already bored the cylinders based off what they first told you and now you're told that the clearances should be .0015" less? Hopefully that doesn't mean the piston slap won't go away once it's warmed up, excessive oil gets in the CC, excessive wear on the walls, and not ideal compression. Ross or Diamond seems the way to go, imo.

[SilverXJ]

KB got back to me after I voiced my concern. They said their first batch of pistons were 2618 alloy, so .004" should be correct for that (still waiting for verification). You can tell by looking on the underside of the piston (see pic below). The 2618 Alloy pistons have a R114 cast in them. The current 4032 alloy pistons have R114-2 cast on the bottom.

They said the spec was changed on 6/08. However mine were manufactured on 6/23/08. So I assume that the spec was changed while that first batch was run.

[SilverXJ]

I really don't know what they're doing over there at KB, but they definitely have spread their share of misinformation on specs and other random issues. I was so hyped to get those pistons when I was building mine, but delay after delay, and then the first batch was bad. Why'd they change the name to Icons? Anyhow so you've already bored the cylinders based off what they first told you and now you're told that the clearances should be .0015" less? Hopefully that doesn't mean the piston slap won't go away once it's warmed up, excessive oil gets in the CC, excessive wear on the walls, and not ideal compression. Ross or Diamond seems the way to go, imo.

I think what they are typing to do is differentiate their products more. Their Silv-O-Lite pistons are listed as just aftermarket pistons. The KB pistons are listed as performance 390 hypereutectic alloy pistons, and the Icon pistons are listed as Forged racing pistons 2618 alloy. They also have Icon FHR forged pistons, which I can't find what the FHR means. The install sheet still list the Icons as 2618 alloy and .004" for clearance. There is also no reference on their IC944 page as to what alloy they are made of.

[go4lo]

Just got my IC944s today and they have R114 on the inside. There are no other numbers?

[SilverXJ]

I don't know. This is just what I was told:

This is a 6-23-08 production date , at the time the R114 was a 2618. The current blank is a R114-2. It is a 2618 alloy that you have.

You may want to contact them yourself to get a straight answer.

[gonridnu]

I think what they are typing to do is differentiate their products more. Their Silv-O-Lite pistons are listed as just aftermarket pistons. The KB pistons are listed as performance 390 hypereutectic alloy pistons, and the Icon pistons are listed as Forged racing pistons 2618 alloy. They also have Icon FHR forged pistons, which I can't find what the FHR means.

That is exactly what they are dong and have for some time. Their Silvolite brand are stock or rebuilder replacement pistons. For a long time the only performance pistons they offered were the KB's and were a hypereutectic cast piston. When they started developing the forged pistons they naturally just assigned them KB numbers but as the line grew they wanted to differentiate them from the hypereutectic cast line so gave them the Icon brand name so as to eliminate confusion...."You have KB pistons, cast or forged?" FHR stands for Forged Head Relief and are dome pistons for Chevy's and Fords.

I will get to the bottom of the forging material/clearance questions today if possible...

I will say that I cannot recall seeing a forged piston from any manufacturer that runs super tight skirt clearances. While different manufacturers will have you measure in different places which affects the perceived clearance based on the shape of the piston (my B-1's are BME's and run .007"), forged pistons generally run bigger clearances due to the greater expansion of a forging vs. cast material. I am at somewhat of a loss why they did not make these out of a hypereutectic casting as it seems the vast majority are going in drivers and would benefit from the tighter skirt clearances. Likely they didn't want to duplicate product lines and chose the forged.

[lafrad]

Man.. I WISH they had a hypereutectic piston specifically for the 4.2 crank, 4.0 rods and 4.0 block. I wanted hypereutectics so much that I went to the 4.2 rod and 4.0 piston combo. I've had some forged piston V8 motors for the last few winters, and its downright annoying to wait for the pistons to quiet down at -10F.

[gonridnu]

When I orginally contacted Keith Black about the KB944 pistons I was told this:

Yes they are 2618 forgings.
I would run them about .004" clearance.
Piston weight is about 437 grams and the pin should be about 170 grams.

So based on that information, what the spec sheet said and what my machinist decided on the 2618 alloy they were installed with .004" wall clearance.

Recently I started seeing different information on different sites regarding the alloy. I contacted KB again for clarification. Now, Keith Black tells me different:

The IC944 is shown with the 2618 line but is made of 4032 alloy and forged in a 2618 style forging die.
Piston to wall is .0025”
Part number change this year from KB944 to IC944, same part.

So, what is going to happen with the greater piston to wall clearance? More piston rock? Shorter life? Broken skirts?

Its just one problem after another.

This is absolutely correct information. I contacted a buddy at KB yesterday and he confirmed it all, along with the fact that my pistons came with the wrong instruction sheet. He emailed me a corrected instruction sheet which i will post here for others. Please note that the underside marking on the piston IS NOT an indicator of the alloy used as they are using the same dies and did not change the die to the -2 number when the alloy changed. Only the manufacuring date printed on the box will tell you which alloy was used and since they changed it in '08 it is unlikely anything you buy today from a dealer is going to have the old alloy.

As for what increased clearances might do....well maybe a little rattle on start up and an extended warm up period but no catastrophic anything. If you were to supercharge, turbo, or nitrous the engine it would require even more clearance for the addditional combustion heat. Rings seal the oil so that is not a problem either. Really we are talking about .001" over the length of the piston so it's kinda insignificant....The bright side is you can overheat it without sticking a piston...LOL

[SilverXJ]

Only the manufacuring date printed on the box will tell you which alloy was used and since they changed it in '08 it is unlikely anything you buy today from a dealer is going to have the old alloy.

This is also stamped on the piston.
Its the PR number as seen here:

As for what increased clearances might do....well maybe a little rattle on start up and an extended warm up period but no catastrophic anything. If you were to supercharge, turbo, or nitrous the engine it would require even more clearance for the addditional combustion heat. Rings seal the oil so that is not a problem either. Really we are talking about .001" over the length of the piston so it's kinda insignificant....The bright side is you can overheat it without sticking a piston...LOL

I already have a rattle on cold startup, which doesn't bother me. My concern was having the correct clearance for the correct piston.

Post that sheet and I'll make it a sticky.

[Exos]

I also have piston slap on startup, and up until operating T. I bought those about a year ago. My machinist put a 0.0045 clearance on them. Am I good, or did KB misinformed me?

[go4lo]

Post that sheet and I'll make it a sticky.

Silver - here's a link to the pdf sheet on the KB website. This is the exact sheet that came with my pistons:

http://www.kb-silvolite.com/assets/icon ... lation.pdf

[SilverXJ]

I also have piston slap on startup, and up until operating T. I bought those about a year ago. My machinist put a 0.0045 clearance on them. Am I good, or did KB misinformed me?

You would need to contact Kb with the date code from the piston or box.

[gonridnu]

I have the sheets in my email and may or may not need help posting them.....gotta go the wife is waiting

[gonridnu]

Let's hope this works...if not I'll need to email them to someone. My buddy told me he sent a memo to the warehouse and had them correct the issue. If you get the instruction sheet with the blue border it is supposed to be the correct one. If you get the instruction sheet with the burnt orange border like I got, it is the wrong one....