kb 237 piston .30 over bore help

[yannick47]

hey im in he procees of rebuilding my 440 (1974 roadrunner).i bought a kb 237 .30 overbore piston set.the thing is my mechanic says i cant use it with my stock rods (part number LY 1851535)the piston information thing shows that it is ;S.any idea how long these rods are (6.768?)and since i live in qatar really hrd to find someone whos worked with old mopars engines(not realy sure about the mech might take it to another place.but i jus wated t mke sure tht if the rods would actually fit or they mech dosent know what hs talking about.....any help would be really appreciated

 

[Meep-Meep]

I'm running KB 237's on stock 6.76" rods in a 77 440 block. The pistons are set up for floating pins if you go that route but not required. Mine are pressed. These pistons will also give you nearly zero deck and will increase your compression to something similar to the 440 six pack. Be sure to follow the ring end gap instructions.

 

[yannick47]

I'm running KB 237's on stock 6.76" rods in a 77 440 block. The pistons are set up for floating pins if you go that route but not required. Mine are pressed. These pistons will also give you nearly zero deck and will increase your compression to something similar to the 440 six pack. Be sure to follow the ring end gap instructions.

hey thanks for the quick reply.. so the rods i have (LY 1851535 (df 56)are they stock ones with 6.76 length?are 77 440s same to 1974 440s? sorry if im asking stoopid questions jst im completely new to this

 

[yannick47]

and don't know if this matter but it has a stock crank in it with main bearings being .20 and connecting rod being .10

 

[Meep-Meep]

Yeah, they are basically the same rods. 6.76" center to center with a 1.094" dia pin. 10.7" block deck, 3.75" stroke and a 2.065" compression distance should yield zero deck.

 

[Cranky]

Ask him why he thinks the pistons won't work with stock rods....

 

[moparstuart]

Ask him why he thinks the pistons won't work with stock rods....

most likely the way the pins attach , some press fit and some use hardware

 

[yannick47]

Ask him why he thinks the pistons won't work with stock rods....

well he said the rods are longer(he just held both the pistons the 40 year old one and the new one and bang he said thre were long ;S)think i need to find a new mech ...prob is there hrdly any around here..anyways ill try taking it to another mech tomorrow morning and see how that goes ..

 

[yannick47]

another thing is the piston gap from what i got from the instructions that came with the pistons are ...4.350(.30).0065=0.28 gap for the first ring?and its says about .004 per bore for the second ring?im plannning to use this 3..4 tims week just around the city cruising and stuff...

 

[Cranky]

most likely the way the pins attach , some press fit and some use hardware

The rods are set up for either full floating pins or pressed. If they are stock, then they are pressed but the 237's will accept either like Meep said and yeah, full float has keeper or snap rings. His mechanic may or may not know the difference.

well he said the rods are longer(he just held both the pistons the 40 year old one and the new one and bang he said thre were long ;S)think i need to find a new mech ...prob is there hrdly any around here..anyways ill try taking it to another mech tomorrow morning and see how that goes ..

Yeah, I'd look for a new place to go to. The late model 440's used a piston that was a good .100 down in the bore and it's easy to see the difference when you get a piston that has higher compression. All the 440 rods are the same length. It's the piston that makes up the difference. Btw, when it comes to decimals, a .030 over size piston is what you have and not .30 Same with the crankshaft. Your main bearings are .020 and the rod bearings are .010 or if you want to convert to metric, .030" is 0.76mm so your pistons are .760mm oversize :headbang:

 

[jt4406]

Both pistons?

If you have the old pistons out and the new pistons available, take one of the old pistons, slide the connecting rod (and the pin) to one side as far inside the piston as it will go. Insert the new pin in the new piston, slide it out one side and into the old piston pin hole. Set them both upside down on a flat surface and see if the distance from the pin hole to the top is the same on both pistons (with the piston upside down it will be the bottom, next to the flat surface, but it is actually the top of the piston). Problemo solved! What you are actually comparing is called "compression distance" and there were some stock 440 pistons with different "distances". This effectively puts the piston farther down in the hole, or closer to the top, depending on what they intended for the engine's application, for example "six pack" pistons were closer to the top of the cylinder (greater compression distance) for increased compression on their performance engine.
jess

 

[moparstuart]

The rods are set up for either full floating pins or pressed. If they are stock, then they are pressed but the 237's will accept either like Meep said and yeah, full float has keeper or snap rings. His mechanic may or may not know the difference.

Yeah, I'd look for a new place to go to. The late model 440's used a piston that was a good .100 down in the bore and it's easy to see the difference when you get a piston that has higher compression. All the 440 rods are the same length. It's the piston that makes up the difference. Btw, when it comes to decimals, a .030 over size piston is what you have and not .30 Same with the crankshaft. Your main bearings are .020 and the rod bearings are .010 or if you want to convert to metric, .030" is 0.76mm so your pistons are .760mm oversize :headbang:

come to think of it now i have the opposite problem i have new H beam eagle rod and wanted to put them on old / nos pistons and they wouldnt mount so i had to buy KB pistons .

 

[Meep-Meep]

come to think of it now i have the opposite problem i have new H beam eagle rod and wanted to put them on old / nos pistons and they wouldnt mount so i had to buy KB pistons .

Say what???? How would that matter? Same 1.094" pin size right? Maybe a weight issue but that can usually be solved easily.

 

[yannick47]

Yeah, I'd look for a new place to go to. The late model 440's used a piston that was a good .100 down in the bore and it's easy to see the difference when you get a piston that has higher compression.

i had the piston and rod checked out by another mech he put the pins on both the old and new piston an set them both flat on the ground.....there is a tiny difference in height...could this be cause of the .100 down in the bore thing??and there is also a slight difference when he measured from the pin hole to the top on both pistons(the new kbs pop up a bit:S:S anywas having the crank mechanied getting it tommrow so were going to set in the new pistons and see if it goes out the bore????

and he told me tht if the pistons were going a tiny bit off the bore deck we could mil the piston a bit ?/can i do that ?

 

[yannick47]

here are some pics .....ill get some good ones tonight.......

 

[yannick47]

any chance if it wold fit?did anyone else have this problem?

 

[Cranky]

The compression height of the KB 237 piston is 2.067. The compression height of the stock piston is around 1.967 which is an estimate. It's probably worse. The 6 pack piston is 2.062 for example. Depending if the block deck has ever been milled, the KB's should be around .010 to .015" below deck. Factory deck height of the block can and do vary some because of production machining tolerance. You should be fine with those. What heads do you plan on using?

 

[Meep-Meep]

The above picture is not a correct method to check rod length.

The KB237's will work but you will have higher compression as I said in post #2 of this thread. I am running these exact pistons in a 77 440 with closed chamber heads and steel shim gaskets. I just need better than 91 R+M/2 gas is all. If you have open chamber heads you can drop about .4-.5 points of compression. Eddy aluminum about the same.

 

[yannick47]

im going off now too see if everything works out fine....i bought edlerbrock rpm heads 84cc chambers

(((((The above picture is not a correct method to check rod length. ))how do i check rod length?
thanks

 

[Meep-Meep]

Why do you need to check rod length? 440's all have the same rod as far as length goes. Length is defined as the distance from the center line of the pin hole to the center line of the rod journal. 6.76".