Piston mix match
01-02-2024, 05:14 AM
#1
Piston mix match So I recently purchased a truck with what I thought was a 5.3 flex fuel motor.
The truck had a miss in #7 cylinder that I couldn’t figure out so I pulled the heads. I have 7 flat top pistons and one dished???! The dished is in #7 cylinder so I’m assuming that’s where my low compression/misfire is coming from? I’ve always heard that 4.8s had flats and 5.3s had dished. Also driver side head was 706 and pass side was 862. I’ve heard they’re identical and I’ve heard the 706s have smaller combustion chambers? I guess I need to know whether or not I can mix match the 706/862s. Currently looking for a bottom end with matching pistons lol.
thanks in advance for the help.
The truck had a miss in #7 cylinder that I couldn’t figure out so I pulled the heads. I have 7 flat top pistons and one dished???! The dished is in #7 cylinder so I’m assuming that’s where my low compression/misfire is coming from? I’ve always heard that 4.8s had flats and 5.3s had dished. Also driver side head was 706 and pass side was 862. I’ve heard they’re identical and I’ve heard the 706s have smaller combustion chambers? I guess I need to know whether or not I can mix match the 706/862s. Currently looking for a bottom end with matching pistons lol.
thanks in advance for the help.
01-02-2024, 03:14 PM
#2
ModSquad
iTrader: (6)
So I recently purchased a truck with what I thought was a 5.3 flex fuel motor.
The truck had a miss in #7 cylinder that I couldn’t figure out so I pulled the heads. I have 7 flat top pistons and one dished???! The dished is in #7 cylinder so I’m assuming that’s where my low compression/misfire is coming from? I’ve always heard that 4.8s had flats and 5.3s had dished. Also driver side head was 706 and pass side was 862. I’ve heard they’re identical and I’ve heard the 706s have smaller combustion chambers? I guess I need to know whether or not I can mix match the 706/862s. Currently looking for a bottom end with matching pistons lol.
thanks in advance for the help.
The truck had a miss in #7 cylinder that I couldn’t figure out so I pulled the heads. I have 7 flat top pistons and one dished???! The dished is in #7 cylinder so I’m assuming that’s where my low compression/misfire is coming from? I’ve always heard that 4.8s had flats and 5.3s had dished. Also driver side head was 706 and pass side was 862. I’ve heard they’re identical and I’ve heard the 706s have smaller combustion chambers? I guess I need to know whether or not I can mix match the 706/862s. Currently looking for a bottom end with matching pistons lol.
thanks in advance for the help.
The following 4 users liked this post by Che70velle:
01-02-2024, 03:39 PM
#4
ModSquad
iTrader: (6)
The following 2 users liked this post by Coal69:
Che70velle (01-02-2024), G Atsma (01-02-2024)
01-10-2024, 09:45 AM
#7
TECH Fanatic
This thread is making my day, boy these engines and their owners are starting to show their age when you see this kind of stuff, I mean the guy could have gotten another used flat top off FB marketplace for free or maybe 10 bucks, I find them still on the rod all the time ppl give them away, How hard would that have been to do while he had it apart? LMAO
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Woodylyf767 (01-11-2024)
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01-10-2024, 10:16 AM
#8
What generation of engine?
I thought it was the other way around:
4.8 = flat top pistons
5.3 = dished pistons
But they did make like a 5.3 HO with flat top pistons, apparently. See here: https://www.motortrend.com/how-to/4-...-engine-guide/
Either way, mixing and matching in this case is a bad thing. The compression ratio of the single different cylinder is going to be different than the other 7. Not to mention the balance is off now because the piston is different weight.
It almost sounds like your engine is a 4.8 based on the description above, and someone swapped a single dished piston from a 5.3? 🤔 That's probably not the case since you mention this is flex fuel engine? Is it a Gen IV?
I thought it was the other way around:
4.8 = flat top pistons
5.3 = dished pistons
But they did make like a 5.3 HO with flat top pistons, apparently. See here: https://www.motortrend.com/how-to/4-...-engine-guide/
Either way, mixing and matching in this case is a bad thing. The compression ratio of the single different cylinder is going to be different than the other 7. Not to mention the balance is off now because the piston is different weight.
It almost sounds like your engine is a 4.8 based on the description above, and someone swapped a single dished piston from a 5.3? 🤔 That's probably not the case since you mention this is flex fuel engine? Is it a Gen IV?
01-10-2024, 10:21 AM
#9
TECH Senior Member
The L33 had flat tops because it also had 243 heads with larger chambers than the 706/862 heads.
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strutaeng (01-10-2024)
01-10-2024, 10:42 AM
#10
TECH Fanatic
iTrader: (7)
GARANTEED this was what the guy said before the OP got it..."Throw it back together as CHEAP as you can, I'm gonna' get rid of it anyway."
I have a repair business and you can't believe how many times I've heard that!!
I have a repair business and you can't believe how many times I've heard that!!
The following 4 users liked this post by CattleAc:
01-10-2024, 10:49 AM
#11
man, sorry to hear that. Karma is a bitch tho !
and with shady **** like that, might as well go thru the entire motor and rebuild it the RIGHT way. I hope the transmission and rear axle are ok LOL.
and with shady **** like that, might as well go thru the entire motor and rebuild it the RIGHT way. I hope the transmission and rear axle are ok LOL.
01-10-2024, 02:06 PM
#12
ModSquad
iTrader: (6)
01-10-2024, 02:06 PM
#13
ModSquad
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Coal69 (01-11-2024)
