Differences in irons. Need FC REW swap help
 

Hello everyone,

So I'm preparing for a REW swap into an FC. I've chosen to go the route of boxing the existing subframe to use the stock FD mounts. The donor motor is a 95 Auto, and it's going into an 87 T2. To figure out mounting alignment with the stock transmission, I've got the REW rear iron stacked with a rotor housing and the 13B-T center iron so I can use the FC mounts to approximate mounting locations. Dowel pins and a tension bolt were used. You can tell which is which because of the drastically different port locations...

https://cimg5.ibsrv.net/gimg/www.rx7...983c1229d7.jpg

I'm running solid mounts, so I don't really have to worry about slop in the rubber. The transmission is already bolted into place. I'm running into an issue though:

https://cimg9.ibsrv.net/gimg/www.rx7...455c09ad4a.jpg

With the bellhousing bolts tightened up completely, there's a noticeable difference in length of the block. You can see the separation between the rear iron and the rotor housing (the tilt is due to the back of the transmission being pressed up by the transmission jack supporting it).

This is the first I've heard of anything like this. I'm not sure if I should attribute this to differences in bellhousing length, auto vs manual rear iron lengths, 13B-REW vs 13B-T rear iron length differences, etc. Any ideas? I'm replacing the rear iron with one from a manual REW, and if they're different lengths, I'd rather have the mounts built using that iron instead. Or is there something else I might be missing?

Bolt the rear and intermediate housings together.

What you're seeing is 100% normal. The solid engine mounts aren't machined precisely (it actually looks like you may have the passenger side one installed incorrectly too - the studs are not coaxial - and if they are coaxial on your mount, it was made wrong), the subframe can shift around, the body is flexing into a different spot if it is on jackstands vs. on the wheels, the trans mount is moving, the trans crossmember is moving...


All of this is exactly why solid engine mounts shouldn't ever be used! It turns the drivetrain into a stressed member as the car flexes around it. Nothing you can do about it but accommodate it.

Aghhhhhhh.

Aghhhhhhhhhhhhhh.

Aghhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh-

Well ok. My old rubber mounts sheared clean in half. I was recycling these aluminum pucks I got free with another car and they use a thru bolt, so yeah, I guess it's made wrong. Weirdly enough, I assembled the drivetrain just fine last time and I ran them for a bit on the 13B-T. The bearings came out looking perfect. Didnt really run it for long though...

I can see now that the gap on the passenger side is larger. I'll see if any locals are willing to lend me mounts in good shape for a bit to get this figured out.

I don't have bolts long enough to fasten just the intermediate and rear irons together, besides the stock thru bolts which are way too long. The transmission mount is also solid at the moment, so I doubt that's flexing. For the mock up, would it make more sense to have the vehicle on wheels or on stands for the measurements? I can do either, i.e. stands like its on currently or put wood blocks under the wheels.

Well, there's two different ways you can approach this.

The first way is that you have to put the engine in precisely the same place that Mazda did.

The second way is that, it's your car, not a theoretical "perfect" car, you can put the mounts wherever you want to. So don't sweat it too much, just make sure the engine is level side to side (although, mine isn't, few are really) and your turbo manifold/plumbing will clear the strut and chassis rail. Heck, if you had clearance problems before, now would be a good time to fix them, you know?

In doing engine swaps I have had to move engines up, down, left, right, fussing around to make certain things clear. On my own car, my engine sits further to the right than Mazda intended. But then I also have a completely different subframe and the front axle centerline is also an inch forward than stock.

One of the beauties of fabricating your own hardpoints is that you can put things where it most benefits you, instead of the assembly-line workers/robots or legacy components designed twenty years earlier or multiple applications that don't concern you. (My car isn't RHD, so I didn't need the engine to be cocked way over to the left to clear the steering!... I didn't want it there either... the L/F corner is crazy-heavy on 1st-gens)

a small caution to the above. my REW-FC has the engine straight, and i'm going to have to go back in there and make it more crooked.

first thing is that the trans mount isn't happy, its twisted. long term, bad.

the other thing is more subtle, but things like an off the shelf exhaust don't fit anymore. i thought my DP was a POS for quite a while before i put a stock precat in to smog it, and the exhaust was still crooked.

the stock clutch fan flat out doesn't fit...

i'd suggest letting the trans mount line the engine up, and then you're good to go

If you want to use the stock clutch fan (I didn't think one could do that with an FD engine... full FC front accessories then?) then that would be one of those "hard" dimensions you'd need to accomodate.

IMO if one is fabricating engine mounts and stuff, doing a little exhaust tweaking is minor in comparison :)

I'm recycling the parts bundled up with the FD engine, which includes a small-ish FMIC and FD-sized aluminum radiator which I'm going to use for a V-mount setup, so clutch fan... eh. I didn't properly check, but you'd probably have to either see if the fan bolted to the water pump pulley (they might be different sizes) or use the FC front cover and go from there since I don't believe the water pump housings interchange. I remember looking at them and thinking "no way" because I wanted to reuse my almost brand new water pump housing assembly off the S4.

Exhaust, same thing, I'm having a custom downpipe made by the same guy welding the subframe, so I'm not too concerned about that. And even then, I'm having the rest of the exhaust done up differently as well. I'm also going straight to single turbo conversion and standalone, so I've plenty of flexibility in that respect. Though, if I really wanted to enjoy the headache of completely new hardpoints, I'd have made a new transmission crossmember as well. I'm just going to leave that stock.

I think I'll just go with that then. Align it as it is using mostly the transmission crossmember and then approximate the pitch with the FC mounts. Would it make sense to leave the car on jackstands and then remove the subframe to weld?

i did a fair amount of research after i had mine running, and i discovered that the JDM tuners rarely swap in an FD engine in its entirety. although they do like to use all the upgraded FD bits, the CAS's, upper intake/TPS, coils, water pump, belts.

this allows the engine to bolt in the car, without having to fab anything.

due to the way the HKS F-con V Pro works, they also get to keep the stock harness, and just add whatever they need too.

food for thought...