Engine Repairs

MX5 Project, May-2022

I don’t have the luxury of a caustic bath so had the clean the soot from the cylinder head ports by hand – this was a messy job and took ages but found that engine degreaser or white spirit and a toothbrush worked OK. I flushed the EGR valve by removing the motor and depressing the valve by hand the blowing it through with an air line after soaking it in white spirits for a while.

I numbered all of the cam buckets before removal then took each valve out one at a time for inspection & cleaning. A couple of valves had light pitting on the seats so lapped them in with some fine grinding paste. None of the valves had excessive play in the valve guide. Replaced each of the valves with a new stem oil seal.

New vs Old Valve Stem Oil Seal
Cylinder Head Re-Assembled

The inlet manifold was an oily/sooty mess too and was difficult to clean due to its internal contours. I used white spirits sprayed inside using a Shutz gun and a flexible tube – the type that’s used to inject cavity wax – to flush out the gunk. This cleaned out most of the mess.

With all of the block mechanical parts cleaned, cylinders given a light “glaze-breaking” hone and the oil ways flushed through with an air line, re-assembly was pretty straight forward, strictly following the procedures in the manual and the associated torque specs.

The piston rings were “gapped” in accordance with the manual but none needed adjustment.

Piston Rings Fitted, Making Sure Correct Way Up
Crankshaft In Position
Bottom End Complete

I didn’t measure it, but the crankshaft end float prior to disassembly was huge and very noticeable. On re-assembly, the end float came out at 0.18mm, well within spec and can hardly be felt. The crank & pistons turned over smoothly with no binding.

The rest of the assembly was pretty routine.

Engine & Gearbox Complete

The only issue in re-assembling the engine was getting the final 90 degree turn on the crankshaft bolt – took two of us and an extension on the breaker bar. Once the bolt starts to turn (overcomes stiction) it moves a lot easier, so best to try and get the 90 degrees on in one movement if possible. Took some jiggling to get the engine, gearbox & subframe back on the chassis mounting points but got there in the end.

Filled the engine with Asda’s finest 5W30 fully synthetic just for the first 200 miles or so. The theory behind using a cheap oil after a rebuild is that it allows the rings & bearings to bed in quicker as the the cheaper oils don’t have the same lubrication properties as the more expensive brands – if you believe the hype, that is. I’ll be using Castrol Magnatec or Edge in future – it’s mostly down to personal choice but I think (or hope) the more expensive oils help prevent sludge build-up in addition to improving lubrication.

Once everything was reconnected, cranked the engine to get oil pressure. When oil pressure came on, I was relieved to see it stayed on for a good while after cranking was stopped – indicating much better pressure than before.

On first start, there was a LOT of white smoke from the exhaust that caused me a bit of concern. However, it cleared after a few minutes – this was probably the remnants of all the cleaning fluids left over in the engine. But – no blue smoke!

Done nearly 100 miles so far. Engine running sweetly with no knocks or smoke. Plugs showing little sign of oil or soot.

In conclusion, so far, so good.

The parts used:

  • King CR4515SI big end bearings
  • King CR5442SI main bearings
  • Goetze 08-429400-00 Piston Rings
  • Elring head gasket
  • Elring front & rear crankshaft oil seals
  • Valve stem oil seals
  • Ajusa head bolts
  • Mazda crankshaft pulley bolt
  • Clutch & release bearing

Note that searching online for “Ford 1.8 Duratec” parts instead of Mazda MX5 NC can yield more results. The Goetze piston rings for example are listed only as Ford parts.