Would you rebuild the engine before starting the swap?
 

Ive got a wrecked '94 GT that Im going to be pulling the engine and transmission from and Ill be transplanting it into a mid-90s Miata. The GT ive got has 116K on it, and it seems to run fine. I cant really drive it much because the wreck jacked up the passenger front wheel, but I can drive it to where I need it at my house.

I saw some oil coming from it. Looked like the rear main, but apart from that I didnt really see any leaks.

So would you completely tear it down and rebuild the bottom end? Im going to be putting A LOT of work into this project, so part of m wants to rebuild it and do it right, and part of me wants to save the money for other stuff. This is going to be a long project, I don't even have the Miata yet. Just doing it one piece at a time. Lol

When I had a '94 GT as my daily driver for like 6-7 years, I replaced or fixed pretty much everything on it. Gears, rebuilt transmission, head work, etc, so to be honest, the bottom end is pretty much the only thing I HAVENT worked on on these cars. That right there really makes me want to do it.

I have never rebuilt a bottom end of an engine, but I know I can do it. Just a matter or doing my research and making sure its all right. The fact that Ive never done pistons and stuff also makes me want to do it.

I plan on probably rebuilding it with stock replacement pistons, possibly a 347 stroker kit, but that's like an extra $500 right there.

My goals for the car are to be getting somewhere between 300-350HP after Ive had it up and running for a while. Probably wont go with a blower in the future, but who knows. The car will be track driven, but it will mainly be used as a fast street car to drive around town. So I don't want anything too crazy (yet).

Opinions?

I used an 80,000 mile motor. Tore it down, new bearings/rings. Better to start fresh. Bores still all had factory hatch throughout, but figured better to be safe. Journals were a little grooved so ended up with a ground crank/oversize bearings.

Since the oil pan will have to come off for modification, you'll be able to see the overall condition/cleanliness of the internals. I got mine from a 100k mile Mustang in a salvage yard that was supposed to be good and from the outside that seemed to be true. Internally it looked like the oil had rarely been changed. My initial plan was to rebuild it anyhow, so that didn't matter. For the amount of effort that goes into the project, I agree with Jason that its better to be safe and start fresh. Even if everything was good, I would still want to replace the timing set, oil pump and its pickup and driveshaft.

Rebuild it.

Yep, I did oil pump, driveshaft, timing set, cam bearings as well. You'd be surprised on how things look when you dig in.

I have mixed feelings. I bought a 93 Tbird that ran and drove, no oil usage, with 165K miles as a donor for my 91 BRG . I decided I would go ahead and transplant the motor as it was, reasoning that I would not have to deal with the startup issues of a newly built motor on top of the startup issues of the conversion. It's still running after many years and about 20K miles of more or less daily short drives. It is getting tired, but it still runs well. I installed Megasquirt with the intention of having that in place and debugged when I finally do install a rebuilt motor. The car ran fine on the original ECU, but I like Megasquirt's flexibilty.

On the other hand, I recently inherited an 02SE converted with a newly rebuilt 302 motor, cam, heads, intake etc. It was difficult for me to sort out all the issues and I recently switched it over to MS2extra for the tunability. I am finally getting it to the point that it can be driven as a daily, after several months of fiddling. Some of the issues were oddball things like having the wrong flywheel and balancer, fuel tank and pump problems, and insufficient cooling fans, plus the ECU didn't seem to like the cam. Things that make a proper break-in problematic.

So, there's always more than one way to skin that kitty.

Mike

I'll be rebuilding it to stock, that way I don't have to worry about tuning it when I'm getting it started up. I don't feel like adding the tuning on top of everything else. The power parts will come later once it's all up and running and I can get a new ECU.

Thanks for all the input guys. Looks like I'm gonna rebuild it.

Yeah, I'm running stock ECU. Motor has some good bolt-ons, so I have a MAF tuned for the 24 lb injectors I am running. Runs nice.

I picked up a truck 302 with a mustang t5 for $200 with unknown history. I had every intention of going through it but it was rough and a proper rebuild seemed almost as costly as a crate motor so I resealed them both and slapped it together with a new goal of purchasing a proper crate motor to drop in once I've worked out the bugs in the chassis/driveline.

There are indeed many ways of producing a reliable swap.

I would not drop in an unknown used engine with that many miles on it. If it turns out to be an oil burning turd, you've wasted a lot of time and money.

Crate 302's are pretty much falling out of trees these days, for almost no money. They are very cheap. Anything more than rings, bearings, and gaskets, and I would buy a crate motor.

I would tear the motor down to nothing, and clean it all out. Check all the clearances. If you can re-use the rotating assembly then it's probably worth doing it yourself, assuming you already have the tools you need. But if you need to bore the block or cut the crank, you should just start over with a new engine.

A rebuilt stock long block from Summit Racing is only $2K shipped to your door step.