LLY - Cracked piston

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
Figured out the piston oil ring was bent out of the box. New one came and all is good. Had to clean up a burr on the oil ring land but everything looked ok.
Moving on to piston protrusion, I had thought the performance cast pistons had .010” off of stock. With that, I planned GRADE C as the deck was milled .008” which usually calls for the “D” gasket which has +.010” thickness. Based on what I’m seeing, the pistons aren’t cut at all vs OEM unless my machine shop botched the deck process. I doubt that’s the case as everything else is right where it should be. 02B565E3-0A70-4730-9D40-2BA846790790.jpeg46DD874E-8F40-41BF-A99C-DC9A42B835BF.jpeg
Tallest protrusion I have is .019”. Most are .0170-.0180 on the top side and .0145-.0160 bottom.

Thoughts??
 

Fingers

Village Idiot
Vendor/Sponsor
Apr 1, 2008
1,663
15
38
White Oak, PA
By Spec, you measure across the pin. In real life, you measure the top and bottom and rock the piston to see the max protrusion. Not a big issue with cast since they don't rock much if the bore is in spec, but a big deal when dealing with Forged and the larger piston to wall clearances.
 
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NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
By Spec, you measure across the pin. In real life, you measure the top and bottom and rock the piston to see the max protrusion. Not a big issue with cast since they don't rock much if the bore is in spec, but a big deal when dealing with Forged and the larger piston to wall clearances.
Given the clearances I gave with rocking, would you run C? I will check along wrist pin this week.
 

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
only if you want to rescale and see boost beyond the stock 22 or 27 psi (what ever it is)
Only came to mind as I was only seeing about 18 in data logging even though we were pushing 42. I wasn't sure if it's reading correctly or not. No trouble codes came up though...
 

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
seems real tight but what is the numbers over the wrist pin? may not be an issue.
I’m getting .0125-.0145 on 1,3,5,7.. but I just hit .0180 on #2. If I just cycle the crank and measure TDC I’m seeing within spec but if I use my fingers to rock the piston front to back and side to side, this is when I’m seeing the higher tolerances. What’s the proper way?
 

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
seems real tight but what is the numbers over the wrist pin? may not be an issue.
Here are the numbers. First set is firm hand rocked with fingers. The numbers are in this order: Top, bottom, front, back. Front-back is along wrist pin.
1: .0180, .0160, .0135, .0135
3: .0180, .0140, .0145, .0140
5: .0170, .0145, .0130, .0135
7: .0170, .0140, .0125, .0125

2: .0185, .0180, .0170, .0170
4: .0180, .0190, .0175, .0175
6: .0180, .0190, .0170, .0165
8: .0165, .0180, .0155, .0140

Second set - cycled through without hand rocking - measured along wrist pin TDC. Numbers are in this order: Front, Back

1: .0070, .0070
3: .0075, .0075
5: .0065, .0065
7 .0045, .0055

2: .0090, .0090
4: .0105, .0095
6: .0100, .0090
8: .0080, .0070

I’m really scratching my head here on which numbers are right....
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
17,968
313
83
Phoenix Az
I’m getting .0125-.0145 on 1,3,5,7.. but I just hit .0180 on #2. If I just cycle the crank and measure TDC I’m seeing within spec but if I use my fingers to rock the piston front to back and side to side, this is when I’m seeing the higher tolerances. What’s the proper way?
i base off the wrist pin mainly because thats what easiest for me to base off of against what other guys are looking at (easiest way to keep things constant to what they are questioning). if you are hitting .018 on teh wrist pin on the even bank, i would be running the D gasket on both sides to keep things kosher. thats about .031 to .034 on the P to H clearance which is high BUT you wont have issue with clearances if you turn the wick up or get things hot inside.


Per your second post, i would run the D gasket on each bank. Otherwise, pull the pistons, have .005 cut off and run a C gasket on Even bank and B gasket on Odd bank but re-verify your protrusion numbers after re-assembly before going with that. I dont like the idea of going below .024ish on P to H clearance under higher HP engines (more to it based on HP level and piston type but you get the idea) just because things get tight, you dont gain much and id rather error on the side of caution for the abuse these engines can see.
 

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
i base off the wrist pin mainly because thats what easiest for me to base off of against what other guys are looking at (easiest way to keep things constant to what they are questioning). if you are hitting .018 on teh wrist pin on the even bank, i would be running the D gasket on both sides to keep things kosher. thats about .031 to .034 on the P to H clearance which is high BUT you wont have issue with clearances if you turn the wick up or get things hot inside.


Per your second post, i would run the D gasket on each bank. Otherwise, pull the pistons, have .005 cut off and run a C gasket on Even bank and B gasket on Odd bank but re-verify your protrusion numbers after re-assembly before going with that. I dont like the idea of going below .024ish on P to H clearance under higher HP engines (more to it based on HP level and piston type but you get the idea) just because things get tight, you dont gain much and id rather error on the side of caution for the abuse these engines can see.
So hand rocking is correct? My machine shop is saying they took .005-.008 off the deck. Pistons are .010” off. Should have netted +.002”-.005” clearance. If I look at not rocking, the tolerance stack looks good. It’s the hand rocking that had me confused...
 

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
i base off the wrist pin mainly because thats what easiest for me to base off of against what other guys are looking at (easiest way to keep things constant to what they are questioning). if you are hitting .018 on teh wrist pin on the even bank, i would be running the D gasket on both sides to keep things kosher. thats about .031 to .034 on the P to H clearance which is high BUT you wont have issue with clearances if you turn the wick up or get things hot inside.


Per your second post, i would run the D gasket on each bank. Otherwise, pull the pistons, have .005 cut off and run a C gasket on Even bank and B gasket on Odd bank but re-verify your protrusion numbers after re-assembly before going with that. I dont like the idea of going below .024ish on P to H clearance under higher HP engines (more to it based on HP level and piston type but you get the idea) just because things get tight, you dont gain much and id rather error on the side of caution for the abuse these engines can see.
Also, pistons are ceramic coated so definitely don’t want to go cutting them lol
 

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
Anyone with comments on how to properly (physically) measure the piston protrusion???? rock it hard back and forth and take maximum, or just move the crank through and measure TDC along wrist pin without trying to push firmly side to side??
 

Bdsankey

Vendor
Vendor/Sponsor
Feb 1, 2018
2,458
135
63
Neenah, Wisconsin
#1
Yes, you measure across the wrist pin.

Sent from my FlashScan V2 using Tapatalk
#2
By Spec, you measure across the pin. In real life, you measure the top and bottom and rock the piston to see the max protrusion. Not a big issue with cast since they don't rock much if the bore is in spec, but a big deal when dealing with Forged and the larger piston to wall clearances.
#3
i base off the wrist pin mainly because thats what easiest for me to base off of against what other guys are looking at (easiest way to keep things constant to what they are questioning). if you are hitting .018 on teh wrist pin on the even bank, i would be running the D gasket on both sides to keep things kosher. thats about .031 to .034 on the P to H clearance which is high BUT you wont have issue with clearances if you turn the wick up or get things hot inside.


Per your second post, i would run the D gasket on each bank. Otherwise, pull the pistons, have .005 cut off and run a C gasket on Even bank and B gasket on Odd bank but re-verify your protrusion numbers after re-assembly before going with that. I dont like the idea of going below .024ish on P to H clearance under higher HP engines (more to it based on HP level and piston type but you get the idea) just because things get tight, you dont gain much and id rather error on the side of caution for the abuse these engines can see.


Anyone with comments on how to properly (physically) measure the piston protrusion???? rock it hard back and forth and take maximum, or just move the crank through and measure TDC along wrist pin without trying to push firmly side to side??
See the three above posts/quotes from other members. Fingers designs pistons as well as built many engines and James has built many engines as well. I've always measured across the wrist pin and rocking the piston to get the highest values.
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
2,716
31
48
Central OH
My career consisted of mainly inline engines, but we never rocked the pistons back and forth in the bore. Yes the pistons will "grow" a touch from higher temps, but with the short distance of the compression height it's a non issue IMO

If you're worried about getting it too close, by all means put a thicker gasket in there. Nobody is going to harass you for it
 

NevadaLLY

Adam B
Feb 24, 2019
268
12
18
Reno, NV
#1


#2


#3







See the three above posts/quotes from other members. Fingers designs pistons as well as built many engines and James has built many engines as well. I've always measured across the wrist pin and rocking the piston to get the highest values.
I understood rocking for top and bottom, but looking for input on across wrist pin. I guess I'm just overthinking this... if I measure across wrist pin like I've seen in basically every youtube video/maintenance manual, they don't rock the piston - just rotate the assembly to TDC, measure front and back. If I take those measurements, A-gasket is called for. If I manhandle the piston (only small film of assembly lube is in the bearings, small film of oil on pistons) I can get the higher numbers mentioned above which call for going to C and D gaskets. Its a huge swing and I'm trying to learn from the best here on what is right. I've scoured the forums and most just say "measure across the wrist pin" - my question is how, exactly, do you do that to get measurements that are tried and true?? The engine service manual isn't depictive here.

Some of my problem is with rocking, the numbers don't make sense with the hardware I have as I mentioned earlier. I wasn't running D gaskets before and I should have actually picked up clearance. Measuring without manhandling shows that - but if I push the piston side to side/front to back - I get numbers that are out of spec - fairly drastically so I'm definitely puzzled on this one.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
17,968
313
83
Phoenix Az
im surprised you have that much swing between no rocking and rocking while over the wrist pin. are you rocking top and bottom while the indicator is over the wrist pin or pushing the piston front to back while the indicator is over the wrist pin?

what is your piston to cylinder wall clearance?
 

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