MK Indy Engine Rebuild

Since I stripped the engine then repainted the main engine block and painted the camshaft cover I’ve been slowly completing the MK Indy Engine rebuild, ready for it to be mated with the gearbox and put in the car. This is how it looked when I last reported on it in March 22.

Since then I have rebuilt it with new seals, gaskets and other service parts back to a like new condition. This will be a quick run down of the work complete and a bit more detail on the areas where I have done something a bit different.

Before I collected my kit from MK I rebuilt the engine to the following state with a new water pump, new camshaft cover seal and new timing belt, bearings and covers. In then stayed in this state for many months while I started the build of my kit.

Coolant Reroute

In the meantime, I did quite a lot of research into different elements of the MX5 engine and decided I would do the coolant reroute option. This is quite common on MX5 engines and for the MK Indy engine rebuild it has a few additional advantages. Particularly giving you more space at the front of the engine where the standard thermostat housing gets very close to the chassis.

Remove Thermostat Housing

So I ended up stripping the engine back again to remove the thermostat housing and plug the old thermostat hole with a 30mm stainless freeze plug.

Fix Hole in Cover

This left a gap in the timing covers where the old thermostat would normally come out. So I created a blanking plate out of 1mm aluminium which I clamped in place with a single rivet. I’m quite pleased with the result!

New Thermostat Location

For the reroute at the other end of the engine, I have used the Skidnation thermostat spacer and housing from their reroute kit and a new thermostat. Skidnation doesn’t have the spacer on their website separately but if you email them they are very quick at responding and will sell you the spacer separately.

I know that the heater matrix pipe can be deleted completely, however, I decided to keep this pipe and just link it to the Skidnation spacer for a few reasons.

  • It gives me the option of adding a heater later if I start using the car more for touring.
  • It maintains the original coolant inlet in the side of the engine which saves cost. Plus my Dad did a great job of fixing it!
  • It maintains a level of coolant flow around the engine while the thermostat is closed.

To make it neater I added a slight bend in the existing pipe and added a 90deg silicone hose to attach it to the skidnation spacer. I managed to bend the pipe using an internal pipe bender spring and a bit of heat. I then cleaned the pipe by leaving it to soak in citric acid for a few hours then painted it with Simonez Satin Black paint.

Engine Breather

I then created a small bracket to mount the engine breather to. On the Mk2.5 NB2 engine, it is missing one of the threaded holes at the front of the engine normally used to clamp the breather hose to. So I created a small bracket to mount to the corner bolt of the engine.

This works quite well and it’s quite neat with the standard breather hose that comes in the hose pack.

Adding Some Colour

The final bit of the MK Indy engine rebuild was to add a bit more colour to complement the bodywork. I originally painted the VVT pipework on the top silver and realised it would be better (in my opinion) if it was orange. So I set about changing it by using the same RAL2009 Traffic Orange paint I had left over from the Brake Calipers.

I also added a bit of colour to the Mazda logo on the crankcase cover and the oil filler cap. I used some RAL2009 Traffic Orange brush on paint, thinned by 10% and then injected it with a syringe. This worked very well and filled the letters with little mess. I used a cotton bud with meths to clean up any over spill.

Maybe this is a little over the top, but I personally think it will complement the bodywork really well once it’s in the car.

I also created a CAD file and then a 3D Print of the MK Logo for the centre of the steering wheel. Once printed, I sprayed it with satin black to give it a nice smooth finish. I then used the same approach to fill the lettering with orange paint. Once dry I gave the whole logo a clear lacquer to provide a tough finish. I plan to use the same approach to create wheel centre caps which happen to be an identical size.

My oil dip stick was also broken, so the handle needed replacing. I decided to 3D print on I found on Thingiverse and paint it with the same orange spray from the Brake calipers. I’m pleased with the result.


I added a new alternator to the engine as the original one was seized and the casing cracked in several places. So I bought a new WAI self-regulating alternator from BOFI so that it is not reliant on the ECU regulating the charge. This makes it easier to move to an aftermarket ECU later on. It does mean I need to slightly adjust the wiring to accommodate. It was also about £20 cheaper than the direct replacement Mk2.5 WAI alternator.

Mounting the alternator was straight forward and I used a Gates 4PK868 ribbed alternator belt. This is an 868mm belt, which is very short. It needs the alternator mounting as close to the engine as it possibly can get. But it needs to be this short to avoid the alternator clashing with the steering column. This ends up being a pain to get in but if you get one edge on a carefully turn the pulley it pulls itself on OK with a bit of patience.

Oil Pan/ Sump

The final part was to install the oil pan/ sump onto the engine. Originally I provided this to MK to shorten it to provide the extra ground clearance. I picked up the modified sump when collecting my kit and painted it ready to install.

I installed the main bearing support plate baffle plate and oil pick-up tube (also shortened) using Wurth Silicone Special 250 Red liquid gasket. This had been recommended by some of the other builders.

Wrong Sump!

I added my original baffle to the bottom of the sump and went to test fit the sump and found a problem, it didn’t fit! Now this confused me, for some reason it didn’t fit over the main bearing support plate baffle. This well and truly had me baffled! The pan wasn’t wide enough. I went back to the photos of the pan I sent MK for modification and found that the design of the pan I sent to MK was different to the one I have now. Somehow MK had returned a different pan to me than the one I sent. You can see the differences below.

I then did some further research and discovered that the MK2.5 NB2 sump had been changed and was different from the Mk2 sump. The main thing is they have improved the Main Bearing Support Plate (MBSP) to provide a stronger bottom end and higher engine revs. Looking at some of the forums the optimum combination for turbo applications is a Mk2.5 bottom end and MK2 top end without VVT. A result of the improved MBSP is that you need additional scolops in the sum to allow for the additional width of the support bracket.

So the Mk2 and Mk2.5 sumps are not interchangeable. You can’t fit a Mk2 sump on a Mk2.5 engine. However, apparently, you can fit a Mk2.5 sump on a Mk2 engine if you also change the main bearing support bracket.

Getting the Correct Sump

I emailed Neil at MK, who responded quickly. He was just as surprised by the wrong sump being provided back to me. I was assured that they have quite good processes in the workshops to ensure that the original items provided for modification are returned to the original owner. He was also unaware that the MK2.5 sump was different to the Mk2. Neil was brilliant and we managed to sort out a way of finding the correct sump. Neil arranged for it to be shortened and swapped it out with the one that I had.

Once I had the correct sump delivered I cleaned it up, painted it and fitted it to the engine with the same Wurth Silicone Special 250 Red liquid gasket as per the MX-5 workshop manual. I used new Mazda original half-moon gaskets as I’ve heard that after-market ones don’t seal very well.

MK Indy Engine Rebuild Complete

I am pleased with the results, it looks like it’s a brand-new engine even though it has 100,000 miles on it! Once the engine is off the engine stand I need to replace the main bearing seal at the bell housing end. This is impossible to do when mounted to the stand by the bell housing bolts.

I have decided to leave the coolant routing between the water inlet, throttle body and oil heater at the oil filter. This then continues to help the circulation of coolant around the engine when the thermostat is closed. It also helps in more extreme weather to warm the engine. I’m not expecting to use the car in colder climates, however, I’d rather leave it in place for the moment. It can always be removed later on. The front of the engine is a lot neater now with the removal of the front thermostat housing and the coolant reroute.

Summary of Build Costs and Hours

Here is a summary of the costs and person hours (total number of hours for every person that has helped) for the build so far. This should hopefully help others with the planning of their builds, by providing cost and time actually incurred for this build. A more detailed breakdown of all the costs and hours worked on the build to date can be viewed here.

Person Hours Worked This Post
Engine Rebuild Estimated Hours20 hrs
Car Build Costs This Post
30mm Stainless Freeze Plug£3
Waterpump Inlet Gasket, MX5 Mk1/2/2.5£5
Camshaft Timing Belt Cover, Middle, IL Motorsport, MX5 Mk1/2/2.5£17
Thermostat Cover & Waterpump Outlet Gasket, MX5 Mk1/2/2.5£4
Inlet Manifold Gasket, Mazda MX5 Mk2/2.5 1.8£9
Camshaft Timing Belt Cover, Upper, MX5 Mk2.5 1.8 VVTI£46
PCV Valve Grommet, MX5 Mk1/2/2.5£4
Oil Filter, Genuine Mazda, MX5 Mk1/2/2.5£8
Camshaft Timing Belt Cover, Lower, IL Motorsport, MX5 Mk1/2/2.5£18
VVT Oil Pipe Gasket, MX5 Mk2.5 1.8£3
Camshaft Timing Belt Kit, Complete, MX5 Mk1/2/2.560£60
Throttle Body Gasket, MX5 Mk1 1.8 & All Mk2/2.5£5
Thermostat, Aftermarket, MX5 Mk1/2/2.5£13
Waterpump, Genuine Mazda, MX5 Mk1 1.8 & All Mk2/2.5£68
Mikalor Spring Clips 14mm£3
Mikalor Spring Clips 20mm£5
Gates Alternator Belt 4PK868£11
Silicone Hose 90 degree 16mm£13
T Bolt Clamps Stainless 26-28mm £12
WAI Alternator £140
Skidnation Coant Reroute Thermostat Spacer£36
Skidnation Thermostat Housing£31
Totals This Post To Date All Posts
Person Hours Worked 20 hrs 397 hrs 404 hrs
Car Build £514 £13,040 £13,202
Tools / Consumables £0 £459 £470
Total Cost £514 £13,499 £13,672

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