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Discussion Starter #1 (Edited)
Information regarding this seems to be lacking on the forum and I got tired of reading posts that said "maybe" regarding interchangeability. Let's remedy that. Thanks to JeepinPete for selling me these items which will hopefully be installed sometime this fall.



This is a 6BD1 SAE #3 flywheel housing on the left and a 4BD1T manual flywheel housing on the right. The 6BD1 and 4BD1 blocks and flywheel housing use the same bolt pattern. They are interchangeable. As previously confirmed through PMs with JeepinPete, the 4BD1T seal housing uses the same bolt pattern as that cast into the 6BD1 housing. There is one difference. Because the 6BD1 seal housing is cast in it does not have holes drilled to accommodate the locating pins found on the 4BD1T block. I'll have to remove the pins or drill the housing.



Here's the backside. The starter bolt pattern is the same on both housing, except the starter is tilted a few degrees inward at the top towards engine center-line on the 4BD1T. Height from flange to block mating surface is 4.125" on both.




The 6BD1 housing has a drain plug on the bottom and a large drilled hole further up the side. Possibly for installing a mag pickup and hold down plate.



6BD1 starter at the top with the 4BD1T starter at the bottom. I still have to get numbers off of both and confirm voltage on the 6BD1 starter.



This should interest some people. A 6BD1 flywheel on the left and a manual 4BD1T flywheel on the right. The crank bolt patterns are identical. The pressure plate bolt patterns are not. Pressure plate bolt circle on the 4BD1T is 13.75" (350mm?) and 12.625" (320mm?) on the 6BD1. Outer diameter on the flywheel is 14.5" on the 4BD1T and 14.438" on the 6BD1.



The 6BD1 flywheel has much more material along it's outer diameter. Good news if you want a heavier flywheel. I need to locate a scale to weigh the two. However, I won't know if that extra material will or will not interfere with the flywheel housing mounting bolts until I have it installed.



Lastly, the starter ring gear teeth are wider on the 6BD1 flywheel on the left.
 

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Excellent information, thanks for sharing.

The 6BD1 flywheel housing on the left appears to be the same item fitted to the very early 4BD1's in the US market with the SAE pattern.
Do you have weights and tooth counts on those flywheels? Also starter tooth count?

There is a variation in starters with 9T on the 2 bolt 24v 4BD1T starters and 11T on the 12v 3 bolt starters.
 

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Discussion Starter #3
4BD1T and 6BD1 starters have 11 teeth on the pinion.

4BD1T flywheel - 127 teeth
6BD1 flywheel - 129 teeth
 

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Sorry to semi revive this old thread, but does this mean you could swap all of the 4BD1T items onto the 6BD1 and be good to go? Basically use the 4BD1T flywheel and flywheel housing as well as starter on the 6BD1 then choose your adapter that works for the 4BD1T?
 

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Sorry to semi revive this old thread, but does this mean you could swap all of the 4BD1T items onto the 6BD1 and be good to go? Basically use the 4BD1T flywheel and flywheel housing as well as starter on the 6BD1 then choose your adapter that works for the 4BD1T?
Yes. But many 6BD1's are SAE #3 and easier to adapt than 4BD1T's.
 

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One other part you will need is the rear main seal adapter from the 4BD. Take a look at the pictures above, you will note that the SAE housing is also the seal housing.
 

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so from what I can tell from the different size flywheels and starter tilt between the two, If you swap the housing, you will need the matching flywheel and starter to have it all work?
 
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