Changing MX-5 MK3 Big Ends With Engine In Car?
Discussion
Hello,
Recently my elderly mother asked me what I thought of a strange rattle her MK3 MX-5 was making. I started it up and got a brief clatter. I have experienced this before as big end failure. Oil pressure is there at idle but only about three bars off the stop on the gauge. When I took it around the block I found no noise under steady driving or acceleration, with good pressure in all conditions above idle.
Topping the oil up didn't help.
The car is parked on a sloping drive with the front downhill. I wondered whether this was causing brief oil starvation but got the same noise when I parked it on the flat and restarted.
My plan is to swap the big end shell bearings out before any damage gets done to the crank as I am pretty certain it is big ends. I have replaced the shell bearings on my Pinto powered Westfield before now by simply dropping the sump and doing them is situ. As the Westfield /Pinto is a fairly simple beast am I being optimistic thinking I may be able to do this on a MK3 MX-5 ? If it can be done, does anyone know of any guides online?
I'd rather not take the engine out as the drive is on a slope leading into the garage. This doesn't give us much space in the garage to pull the engine crane back. The other alternative is to pull the car up the drive with another vehicle as we lift the engine out. I see a disaster in the making with that idea though. I live too far away to drive the car to my house to do the work without fear of damaging the crank.
Thoughts?
Recently my elderly mother asked me what I thought of a strange rattle her MK3 MX-5 was making. I started it up and got a brief clatter. I have experienced this before as big end failure. Oil pressure is there at idle but only about three bars off the stop on the gauge. When I took it around the block I found no noise under steady driving or acceleration, with good pressure in all conditions above idle.
Topping the oil up didn't help.
The car is parked on a sloping drive with the front downhill. I wondered whether this was causing brief oil starvation but got the same noise when I parked it on the flat and restarted.
My plan is to swap the big end shell bearings out before any damage gets done to the crank as I am pretty certain it is big ends. I have replaced the shell bearings on my Pinto powered Westfield before now by simply dropping the sump and doing them is situ. As the Westfield /Pinto is a fairly simple beast am I being optimistic thinking I may be able to do this on a MK3 MX-5 ? If it can be done, does anyone know of any guides online?
I'd rather not take the engine out as the drive is on a slope leading into the garage. This doesn't give us much space in the garage to pull the engine crane back. The other alternative is to pull the car up the drive with another vehicle as we lift the engine out. I see a disaster in the making with that idea though. I live too far away to drive the car to my house to do the work without fear of damaging the crank.
Thoughts?
Can’t be done, subframe is In the way.
It’s an engine out job.
Note the ‘oil pressure gauge’ is not what it seems, it’s just made up by the ecu.
Idler pulleys can go bad so I’d check that isn’t the source first. Generally they need to be run pretty low on oil for bearings to fail.
Injectors can also be super noisy.
It’s an engine out job.
Note the ‘oil pressure gauge’ is not what it seems, it’s just made up by the ecu.
Idler pulleys can go bad so I’d check that isn’t the source first. Generally they need to be run pretty low on oil for bearings to fail.
Injectors can also be super noisy.
The fault is as evoluzione states, it's burning oil because the rings seize. This has caused the oil level to drop and it's spun the bearings, usually on 1 and 4 big ends.
It is an engine out job and needs new rings and bearings. But unfortunately the nature of the failure causes the bearings to spin in the rods. This mean the rods need changing too, but they are pressed in gudgeon pins so it's a rod/piston assembly.
I might have one or two spare piston and rod assemblies kicking around here.
Nc2 and 3 engines were improved, the big ends went to a tanged bearing which helps with the spinning issue, and they seem less prone to ring seizure, not sure why in fairness, but I firmly believe half the issue is the oil change interval which is far too long, the internal state of these engines is usually pretty dirty. Oil changes ever 5-6k and some blasts up to red line is a good recipe for long engine life.
Just to add to this, the comment about front pullies is worth a look, they can chunter, it's worth taking the aux belt off and starting it up, it's unlikely you will be that lucky, but they are an often neglected part that I end up changing a lot of as well.
I've got to say, mk3s are really good cars, very reliable and with the exception of the engine issue which doesn't affect all cars (and absolutely isn't mileage related, there are plenty of high mileage cars that are perfect), the rust in the rear sill/bulkhead area they are great. And those issues aren't that expensive in the grand scheme of things to sort.
It is an engine out job and needs new rings and bearings. But unfortunately the nature of the failure causes the bearings to spin in the rods. This mean the rods need changing too, but they are pressed in gudgeon pins so it's a rod/piston assembly.
I might have one or two spare piston and rod assemblies kicking around here.
Nc2 and 3 engines were improved, the big ends went to a tanged bearing which helps with the spinning issue, and they seem less prone to ring seizure, not sure why in fairness, but I firmly believe half the issue is the oil change interval which is far too long, the internal state of these engines is usually pretty dirty. Oil changes ever 5-6k and some blasts up to red line is a good recipe for long engine life.
Just to add to this, the comment about front pullies is worth a look, they can chunter, it's worth taking the aux belt off and starting it up, it's unlikely you will be that lucky, but they are an often neglected part that I end up changing a lot of as well.
I've got to say, mk3s are really good cars, very reliable and with the exception of the engine issue which doesn't affect all cars (and absolutely isn't mileage related, there are plenty of high mileage cars that are perfect), the rust in the rear sill/bulkhead area they are great. And those issues aren't that expensive in the grand scheme of things to sort.
Edited by wildoliver on Sunday 27th November 07:06
I have read that it's possible to drop the sump with the engine in situ, but you need to suspend the engine and drop the subframe. This sort of makes sense and I have done it on other cars but not an MX5 NC so can't speak for how easy it might be.
The MX5 NC can use oil, but then any engine can use oil. Oil consumption isn't a reason for engine failure, but not keeping enough oil in the sump is. I don't think people carry out regular oil level checks even though it's normally recommended as part of a weekly check, also the dipstick design was modified to make it easier to read on later cars. If the oil level is maintained at the recommended level there is no reason for bottom engine failure although ever increasing oil consumption could eventually cause its own set of problems.
The MX5 NC can use oil, but then any engine can use oil. Oil consumption isn't a reason for engine failure, but not keeping enough oil in the sump is. I don't think people carry out regular oil level checks even though it's normally recommended as part of a weekly check, also the dipstick design was modified to make it easier to read on later cars. If the oil level is maintained at the recommended level there is no reason for bottom engine failure although ever increasing oil consumption could eventually cause its own set of problems.
Thanks for all your replies.
I will probably take the engine out and rebuild it given the potential issue with the rings. My mother had a previous example which she drove a considerable amount. She never had any issues with it until someone pulled out on her and totalled that car. This example was bought as a replacement just before Covid hit so it has only been used for going to the shops.
I will get some other petrolheads to have a listen to confirm whether it is the big ends, though I am fairly certain it is based on previous experiences.
I will probably take the engine out and rebuild it given the potential issue with the rings. My mother had a previous example which she drove a considerable amount. She never had any issues with it until someone pulled out on her and totalled that car. This example was bought as a replacement just before Covid hit so it has only been used for going to the shops.
I will get some other petrolheads to have a listen to confirm whether it is the big ends, though I am fairly certain it is based on previous experiences.
Sounds like the best idea. I rebuilt an engine using oil (no crank or bearing issues) for a few hundred pounds, most of the bottom end components are Ford Duratec. Advice I received was that if the big ends are knocking you’re likely to need a replacement crank, but o can’t speak for the accuracy of that advice as I don’t have experience.
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