4age to Aisin AZ6 bellhousing adapters - LEEN & Niteparts

[Sam-Q]

There is an existing thread on this however I have some new information on the Niteparts adapter so I thought I would put this all in one thread.

This is about adapting the Aisin AZ6 to a 4A/7A engine. This is same basic model of gearbox as the Mazda MX5, RX8, Nissan S15/200SX and probably some others. But not S2000, that has something different. The housings change and as do the ratios but it's all variations on the same model. This Aisin gearbox is known to handle a decent amount of power and feel great in shifting. I can also personally verify these things are unusually light for what they are, I didn't get to weigh mine but if I had to guess it's between a T50 and a W55 at about 35kg.



LEEN offering:

The most well known and the original option is the full billet LEEN kit:



This makes the conversion very simple, is very professional, proven to work well, looks great if you're into the machined block look but is on the heavy side and is very expensive.

The original and normal model they offer is for the SXE10 Altezza variant, however they advertise they can on request make it suit S15 and RX8 variants as well.


Niteparts offering:

The second more crude option is from the New Zealand company Niteparts



Unlike the above option which is a whole billet machined bellhousing / front gearbox housing it's instead an adapter plate in between that existing part of the geabox and the engine. Catch is that the front half of the box needs to be taken off and 16mm machined off of it. It also only suits the Altezza variant.

The best part is it's only 600NZ.

Nitepart's very minimal website, doesn't even have this adapter on there:





There would be other things that would need to be done such as a custom tailshaft, gearbox crossmember, speedo drive, hybrid clutch and possibly something to do with the bearing carrier.

The housing has provision for two shifter positions and can be moved forward from it's original use with only basic tools and no extra parts. This puts it further back than a T50 shifter which is useable but it can be moved further forward with a lot of trouble, LEEN conversions do offer this service though.


LEEN's speedo cable offering:
More about this in the BEAMS thread:

LEEN's very professional looking shifter position modification:


Interested to hear about anyone who has any extra information that I missed such as in regard to speedo drive, clutch, clutch release and so on. Or has feedback / experienced with either of the above.


Disclaimer: I have no financial interest or have anything to gain from either of these companies.

[Vaughn]

Im not 100% sure about that, never heard of anyone doing that? i may be wrong

Do you mean as in the bell housing needs to be machined down to compensate for the extra length the adaptor adds?

[Admiral Ackbar]

That is very common with gearbox conversions. Normally it's just the bellhousing that needs to be machined but the AZ6 doesn't have a separate bellhousing - it's combined with the front half of the gearbox case.

There is a third option which is the lightest, stiffest, cheapest and imho best:

Step 1. Remove crank from block and input shaft from gearbox.
Step 2. Turn up a shaft that is the same diameter as the main journals at one end, the input shaft at the other end and is the correct length.
Step 3. Chop approx. 100mm off the engine end of the AZ6 "bellhousing" and 100mm off the engine end of the 4A bellhousing. Keep the 100mm part of the 4A housing.
Step 4. Put front half back on gearbox, bolt shaft to gearbox, place 4A bit over shaft, bolt shaft into main bearings, bolt 4A bit to block.
Step 5. Preheat alloy bits with oxy/propane/MAP torch. Tig together.

[Sam-Q]

Admiral Ackbar I have heard of people making adapter but they used the spigot to line things up, making a shaft on a lathe to locate a large part of the input shaft is quite clever and I like the idea. It would hold it really true and it's one more usefull thing I know. The only issue I see is the warpage.

I know someone who adapter a Daihatsu 3 cylinder diesel onto a VW transaxle for his Fiat van (interesting conversion!) and he said when he did it it moved when being welded and was useless in the end. What he did is weld them to a plate each, face the plate and then bolt the two plates together. Sounds messy though and I know someone else who does this with Supra gearboxes so I shall ask if he does any extra work to make sure they don't move.

[Admiral Ackbar]

The shaft should be thick walled or even solid. One end is held by the main bearing caps, the other is held by the input shaft bearing. A flange is machined at the input shaft bearing to ensure it doesn't move axially. This flange is also bolted to the gearbox via the bolts that normally hold the bellhousing on. I assume the front casing of the J160 is held on in a similar way. If this is done correctly there will be zero misalignment when welding and as good as an oem bellhousing machined on a massive mill.