stock pistons...

[Shark]

there seems to be some confusion of how much a stock piston can be dished. do any of you have any experience with machining stock pistons? are there different piston castings? if so, which ones have the greatest amount of material to be removed? the price the KB's ended up being have me a little bummed. thanks, just something i was thinking about.

[Flash]

I agree, and this would be some grate info to add to the piston fact section.
From the Piston FAQ section, We already know the piston pin heights and the best one to dish do to it depth or thickness.

Is there a difference between thickness between the bottom of the bowl and the underside of the piston? in a factory installed piston?
Is that depth different between, say, a renix and a HO piston.............How about a Early HO piston compared to later design?
I remember someone saying that the late model piston was lightened up or that the rotating assembly what was lightened up.
Did they lighten up the piston by thinning up this area?

If any body has some old pistons laying around that could be measured, and we know what year they came out of ...............................


Flash

[John]

I have some 93 pistons that I will section and mike. Will report post results.
John

[John]

Regarding piston weights, I did a quick check through my factory manuals.
1989 piston weight less pin 510 - 514 grams
1990 piston weight less pin 510 - 514 grams
1999 piston weight less pin 417 - 429 grams

If someone has a FSM covering the 91 to 98 years please let us know what the piston weight is listed as.
John

[Flash]

Regarding piston weights, I did a quick check through my factory manuals.
1989 piston weight less pin 510 - 514 grams
1990 piston weight less pin 510 - 514 grams
1999 piston weight less pin 417 - 429 grams

If someone has a FSM covering the 91 to 98 years please let us know what the piston weight is listed as.
John

93,94,96,97and 98 FSM (couldn't find a 95) have a piston weight(less pin) of 563-567 grams
the 99 FSM i looked at confirms your # at 417-429 grams.

Thats all that i could find at this time.

Flash

[John]

So it appears we have at least 3 basic groups of pistons in the 4.0 blocks.
Renix 510_ 514 grams less pin
91 _ 98 563_567 grams less pin
99 _ ? 417 _ 429 grams less pin

Well, well, lets flesh this on out.
John

[Flash]

So it appears we have at least 3 basic groups of pistons in the 4.0 blocks.
Renix 510_ 514 grams less pin
91 _ 98 563_567 grams less pin
99 _ ? 417 _ 429 grams less pin

Well, well, lets flesh this on out.
John

What was the last year of the 4.0L?............got a idea hold on.

well found 01 spec. on dealer connect 663-671 Grams?
2000(00) had no piston weight spec but said that the top of pistons, top ring grove and crown are anodized and the piston skirt is coated with "molykoto" also said that head had a duel- quench?
sounds like they had intention of keeping the eng before they pulled the plug!!!!!!!!!!!!!!!
Look like we have one more to add

Flash

[SilverXJ]

For the 4.0l I6 my 2000 FSM says 417-429 g less pin. my 2004 WJ FSM say the same. The FSM also says the combustion chamber is dual quench, not specifically the piston. It also mentions molykote (black coating on the skirts) but mentions nothing of anodizing. What is dual quench?

For the 4.7L V8 2004 engine is says the top ring groove is anodized: "The anodized top ring groove and crown has
been replaced with a coated top ring that is blue in color on the bottom surface." Also, it says that the piston pin is full floating on the H) engine. Interestingly they only give a single weight for the piston, not a range like the 4.0L the 4.7L V8 weights in at 367.5 grams

[John]

My understanding is the tooling for the block was past prime and needed replaced/rebuilt, bean counters came up with the existing motors used in the soccer mom vehicles would be cheaper and would consolidate with the rest of their production platforms.
John

[John]

Known OEM piston data.

So it appears we have multiple basic groups of pistons in the 4.0 blocks.
Renix 510_ 514 grams less pin
91 _ 98 563_567 grams less pin
99 _ 2k 417 _ 429 grams less pin

01 spec. on dealer connect 663-671 Grams? I suspect this includes wrist pin weight.
2000(00) had no piston weight spec but said that the top of pistons, top ring grove and crown are anodized?
04 WJ FSM describes Molykote piston skirts

Keep em coming, I have a new crossover steering to put on the YJ tonight before I can autopsy the 93 pistons for thickness profile.
John

[John]

And before I go out to work on the heap, Dual quench, the photo is for a Corvette head but you will get the idea.

[Flash]

I will double check the spec's tomarrow, on the pin........and dig a little deeper on the 00 spec.


Flash

[Flash]

I will double check the spec's tomorrow, on the pin........and dig a little deeper on the 00 spec.


Flash

OK double check of spec,....... that was the weight of the Connection Rod

The piston is 417-429 for 2001

Flash

[John]

Gotcha, so 99 through 01, 417 _ 429 grams less pin. The connecting rod then equaled a butchers thumb.......
Notice the two pads in the head photo. Dual quench. Edelbrock is big on this. Check ads for some of their thoughts.
John

[Flash]

Gotcha, so 99 through 01, 417 _ 429 grams less pin. The connecting rod then equaled a butchers thumb.......
Notice the two pads in the head photo. Dual quench. Edelbrock is big on this. Check ads for some of their thoughts.
John

I was able aquire a 04 FSM(CD-FSM) that confurmed the above Grams.

So i would say that 99-04.... 417-429 Gram piston is a safe Assumption.

So it appears we have multiple basic groups of pistons in the 4.0 blocks.
Renix-------510_ 514 grams less pin
91 _98------563_567 grams less pin
99 _ 04k--- 417_ 429 grams less pin
Now all we need is a piston dish depth of each of the three groups above.

Flash.