ReneKennedy

Hello my fellow miata lovers! My low mileage black 96 miata was recently totalled but the engine is still good and I have since found a nice 99 that needs an engine. Is this an easy swap? Or does it require too many changes?

sixshooter

It isn't a difficult swap at all. The bottom ends of the engines are identical. There are a few minor changes to the sensor locations and the cylinder heads were improved starting in '99. A great swap would be putting your engine in the '99 and keeping the '99 cylinder head to put on it (if it is good). The improved design is worth about 15 horsepower.

ReneKennedy

Great! I think the head on the 99 is still good because the engine still runs good, just has a lot of bottom end noise. So what are the do's and dont's? What should be done or replaced during the swap? Any tips to facilitate this swap would be greatly appreciated.

sixshooter

Before you pull the engine out of the '99, change the oil and run some Shell Rotella T6 synthetic oil in it for a few miles. You would be surprised how badly a collapsed lifter will sound in a Miata engine (been there). It sounds quite a bit like rod knock and can come from not changing the oil often enough. It shouldn't hurt to try.

There were a couple of rare problems with '99 engines losing crankshaft thrust bearings for no apparent reason. This happened in '99 only. It usually ruins the bottom end of the engine.

But if you are absolutely sure the sound is rod knock (it gets louder under a load and significantly louder at higher RPMS), then the previous owner might have run it low on oil and starved the bearings. The BP engine in the Miata uses a forged crankshaft and you might get by with simply polishing the crankshaft journals and replacing the bearings. You should do a compression test before removing the engine to determine the overall health of the piston rings. It may be worth leaving the head on the block and just changing what is wrong in the bottom end. It may be a simpler process. If you start into the bottom end and it looks like hell when you get the oil pan off, you can still swap to your bottom end.

ReneKennedy

Yes the previous owner ran it low on oil, definitely a rod knock. We pulled the engine and tranny out of the wrecked 96 last night and have some questions;
Since I'm going to use the head from the 99 should I have it redone? Is it really easier to pull the engine with the tranny or since I have to take the intake and exhaust manifolds off can I put the 96 engine back in the car and then put the manifolds on? Lastly what do you recommend I should replace while doing this, motor mounts, belts, water pump etc.

sixshooter

Timing belt, water pump - yes
Timing idler and tensioner pulley bearings should be inspected but are usually good.
Check for signs of leakage at front crank seal and front cam seals.

The motor mounts - you have four to choose from. If you can't find two good ones, get a new mazdacomp pair. They will be slightly firmer than the standard ones for less motor/trans movement. Mazda Miata Competition Engine Mount Bushings-PAIR for Miata

Yes, it is easier to pull the engine with the trans for this. Consider changing the clutch while you are in there. Along with that the throw out bearing and pilot bearing. The rear main seal on the engine should be done too.

Check the cam angle sensor on the back of the head for oil leakage.

Drain the trans before pulling it or you'll have a mess. Don't forget to refill it when you get everything back in.

I can't think of anything else right now.

ReneKennedy

Six Shooter
I just drained the oil in the 99 and although it was dirty I didnt see any metal flakes. Maybe it is a lifter? I do know the previous owner ran it low on oil and the shop it took it to said it was a rod knock. Could I call you and let you hear it?

sixshooter

I forgot the '99-up heads were solid lifter and not a hydraulic lifter arrangement. It could have conceivably kicked out a lifter shim from under the camshaft (which would be able to be seen with the valve cover off). A lifter shim is a shiny, round steel coin that goes between the cam lobe and the top of the valve lifter. It would be laying somewhere inside the valve cover area and there would likely be damage to one of the camshaft lobes. This is a less likely condition than it having actual rod knock.

Sorry for not remembering that difference previously. It's tough to keep up with all of the differences.

ReneKennedy

Well yesterday I ran the car with T6 and while using a stethoscope to hear where the noise was coming from it locked up, so diagnosis complete, it's broke!
I care more about the easiest installation than about having extra power ( I get too many tickets as it is) so If I leave the 96 head on the 96 engine do I use the 99 intake manifold with all the proper plugs? Also the 96 had a nice stainless exhaust, will that fit the 99? I did notice the 99 exhaust has another sensor farther back.

Many thank you's for all your answers!

sixshooter

The head and intake manifold (and the wiring harness and sensors) will be different from '96 to the '99. The easiest conversion is to retain the '99 head with the '99 chassis. The exhaust side of the heads are the same so your exhaust would interchange just fine.

There are two O2 sensors on the '99 but there should have been two on the '96 as well. The second one is frankly quite unimportant and is only used to determine the effectiveness of the catalytic converter. Not having it may or may not trigger a check engine light. This can be overcome with a "dummy O2 sensor" for just a few bucks if it ever becomes necessary.

The '99 has a sensor for the speedometer and the '96 uses a cable. No big deal to use either trans by just swapping it over if needed.