1.6l Miata mechanical bits rebuilding/reconditioning advice

So I have this Lotus Elan plus 2 sitting in my shop not doing anything. Actually the body is hanging from my shop ceiling while the frame and other mechanical bits are sitting in the loft. The original engine and transmission are gone. The plan is to use the drivetrain out of a 1992 Miata to replace the original bits. We may actually end up putting the entire Miata suspension under the Elan shell. I know this would kill the purists but it eliminates the fussy trunnion front end, rear inboard brakes and the rotoflex rear axles. This should leave me with a nice running Miata with the looks of a Lotus Elan. Simple plan right?

I'll eventually start documenting this project but for now I'm looking at the Miata drive train. The donor had 250k or so miles on it. I have no documentation proving that this is the original drivetrain but there wasn't any evidence of it being pulled out prior to me taking ownership. So here's my question. I plan to pull the engine apart and do a full rebuild. I'm comfortable with doing this work but I have less experience when it comes to the transmission and rear end. What should I expect as far as wear and tear on these items? I didn't get a chance to drive the donor before it came into my care. The transmission shifts smoothly between gears and both the input and output shaft turn properly. Should I just clean them up and hope for the best or should I start digging a bit deeper?

I would start here:

http://www.amazon.com/Build-High-Performance-Mazda-Motorbooks-Workshop/dp/0760337055

If you decide on any headwork..... I'll be happy to massage it for a reasonable fee....

Just to clarify my goals here. I'm not looking at building a high horsepower beast. I've done that to death and I really just want a pleasant street car that I can use for nice weather driving. I already have a track toy.

I would start by throwing away the worthless 1.6 motor, and the paper mache rear diff.

Based on your goals, if there is no perceptible play in the input and output bearings I'd throw it in, change the fluid and see how it shifts. Ditto on the rear, see if it's whining first. You'll probably have the engine and trans out at some point in the build after it's drivable anyhow.

Even at 250k, the Miata bits probably function better than the original stuff did new.

Kenny_McCormic wrote: Based on your goals, if there is no perceptible play in the input and output bearings I'd throw it in, change the fluid and see how it shifts. Ditto on the rear, see if it's whining first. You'll probably have the engine and trans out at some point in the build after it's drivable anyhow.

1.6 diffs dont whine, they just break.

In reply to Leafy:

We're talking about a street car that will probably end up lighter than the donor here.

Kenny_McCormic wrote: In reply to Leafy: We're talking about a street car that will probably end up lighter than the donor here.

Yup. Stock 1992 Miata weight 2200lbs, Lotus Elan+2 1850lbs give or take.

I rebuilt the 1.6 in my Spec Miata earlier this year. Fun experience. First time rebuilding an engine ever. Turned out quite nicely. It started out as a 180k mile short nose motor. Was well cared for and the engine internals were all still quite good. The only unusable part was the crank from some slight wear where the pulley had loosened and wore the keyway slightly.

The trans has not been problematic but that will be dependent on the previous owner. The OE 1.6 diffs aren't known to be very performance oriented so not sure if you really want to use it.

It dyno'ed 117 rwhp during break-in. I documented my misadventures on my blog. Hope you find it helpful.
http://blog.miataracer.com/2015/01/lessons-learned-rebuilding-assembling.html

The finished product:

Is there enough structure in the Elan to do this? The big difference between the Miata and the Lotus "rollerskates" is that the upper shock mounting points on the Elan are on the backbone chassis, and they're on the unibody of the Miata.

Ignore the naysayers for the diff. It takes abuse to wreck one with a stock mill. You've got the parts, try 'em. If something's worn out, replacements are cheap and drop right in.

In reply to Keith Tanner:

It sounds like Wayslow has a decent Elan rollerskate already, so melding the two shouldn't be too bad.

My first '90 Miata had 196k miles on it when I turned it into a Spec Miata. I did nothing to the VLSD except change the fluid. That was in 2006, and it still has the same diff in it (with fluid changes every other weekend of racing). My second '90, which I drive on the street, auto-x, and do track day events with, has 237k miles on it now with the bone stock VLSD still in it. I've changed the fluid in it once.

I liked my 1.6 Miata, stock rear diff and all! Of course, I never drove any other Miata's.

What will you do about the obvious track width differences?

In reply to Keith Tanner: Thanks Keith. I was hoping you'd jump in. I understand what you're saying as far as the Miata vs Elan frame goes. This is where we're still contemplating what we want to end up with. The Elan is far from perfect. It was hit in the front end back in the 70s. A new frame was installed and a new front clip was poorly grafted onto the front of the shell. The car was mostly reassembled, excluding the engine, and then the whole thing sat until a couple of years ago when the Wife of the original owner gave it to us. Here's a picture of us taking it out through her neighbour's yard and a shot of the grafted on front clip.

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If we were to use all of the Miata underpinnings it would likely require us to build an entirely new frame because I'd hate to chop up a perfectly good factory original frame when there are people looking for them to do a proper restoration. The easy button is to swap the Miata engine and transmission into the existing frame and utilize all of the other original Lotus bits. Decisions, decisions.

In reply to RossD:

Surprisingly there isn't much difference between the two as far as track width goes. 56" for the Miata and 55" for the Elan.