L20 swap problem / Transmission not matching up.

[birdboy48]

Gang,

A trusted friend is helping me drop an L20 into my dearly beloved 72 510 wagon.

The motor we have is (in theory!) a recently re-built L20 from a 1974 710 automatic.

We were hoping to use my L16 flywheel on the L20 (as mentioned above the motor was origionally mated to an automatic) but apparently the L16 flywheel has 5 holes, while the end of crank on this motor has 6 holes.

Ummmm.....does this sound like how an L20 crank should be ??

Or....Would the number of holes on the crank end be different in an automatic ?

In any case, a 6 bolt resurfaced flywheel was obtained at a reasonable price from the kind folks at the junkyard, with the assurance it would fit our motor, and sure enough, it bolted to the L20 just fine.

But....now it apparently won't mate with the old L16 4 speed.

The problem seems to be that the new flywheel is simply of too large a diameter to fit inside the bellhousing of the old transmission.

My understanding was that this swap was *very* straightforward, but now it seems like we are looking for a new transmission.

Any idea what's going on here ??

It sort of seems as though we were given the wrong sized flywheel ?

Does it sound reasonable that this motor would take various diameter flywheels, and we simply did not get the right one ?

If so....which one might we need ??

Any insights would be greatly appreciated,

Bob, in Bend Oregon

[dimefury]

yes the L16 and L18 used a different flywheel than the L20b
L16 L18 have a 5 bolt and L20b has a 6 bolt
as for your trans fit issue, i've never heard of this problem before. i have had (in the past) a 510 with an L20b and a stock 4 speed and never had this problem, my current dime has a L20b and a 280z 5 speed

sounds like you have a weird flywheel, because (to my knowledge) all L-series blocks (fours and sixes) will mate up to all datsun trannies from L-powered cars. same bolt pattern. if the bell housing bolts are all the same pattern it would seem odd that you would have a flywheel that wouldn't fit

look into another flywheel

[birdboy48]

Dear Fury,

Thanks so much for taking the time to respond.

Yes, I suspect life would have been simpler if the L20 we are swapping had not been an automatic, and had come with it's own flywheel.

As "luck" would have it , the one that was given to us at the junks had to have some locating pins removed before it would bolt to the crank, and now that the pins are gone, they won't take it back.

While we are at it, the swap to the dogleg 5-speed......

Not too much is involved in that swap ?? Same driveshaft, etc ??

If I want to retain a conventional shift pattern, I need to go with the 280 and shortened driveshaft....right ??

Those are the two most common options ??

Thanks again,

Bob

[dimefury]

the dogleg 5 speed is the same length as the stock 510 auto or 4 speed transmissions (refered to as "short tail" transmissions) and will install using the stock 510 driveshaft.

the 280z 5 speed is what is refered to as a "long tail" transmission and would require you to shorten your stock 510 driveshaft to install it in a 510, but it does have a conventional shift pattern

these aren't your only choices, but as you said before, they are the most common swaps. for more info on other datsun transmissions and swaps go to jason gray's 510 tech page/tranny ratios (link is on dimequarterly or search google) last time i tried to access this site the browser couldn't locate it, but if you can get to it, print it as it has lots of info

as for the rest of the swap..........i know that the 280z/zx transmissions require a special trans crossmember that must be fabricated, i don't know what the dogleg 5 speed uses for its trans crossmember or what modifications will be required to mount it in a 510

i have a friend with the dogleg 5 speed, i called and left a message, i'll try and find out how his crossmember is mounted.

[system_02]

i have a dogleg 5 speed strait from japan that matched perfectly but it actually was shorter and lighter than every other 5 speed out there, i needed to make my driveshaft 5 inches longer because of it and i needed to put 1 inch spacers on the trans mount to drop it lower.