QUESTION
My Lotus Esprit has Nikasil liners and given it had done most of its mileage in the UK before the year 2000
I am concerned that some Nikasil wear may have occurred.
A recent dyno trip showed the power at the wheels was 149kw, not too bad, given it means the engine itself is probably still close to the 160kw it should be.
I am just wondering though, given I have a set of brand new A grade (ie all four are balanced and matched) original forged pistons (with new rings) and 4 x new Nikasil liners, if I'm worried about the power loss can I simply change the liners and pistons?
This would of course be in liu of an inspection of the bearings, if they are good can this be done?
Its much much cheaper to just do a pistons (with new rings) and liner swap than bearings as well, which would be practically a full rebuild.
At this point in time I believe the top end, the springs etc are OK.
B.C. - Sydney, New South Wales
ANSWER
The correct way to determine the internal liner and piston ring wear is to carry out a periodic cylinder leak-down test.
This is a non-invasive test where compressed air is introduced into each cylinder via a pressure regulator and combined orifice.
A cylinder leak-down test should not be confused with a compression test as it allows a quantitative measurement to be made.
It is worth noting a compression test does not take into account the following items -
1) Incorrect tappet clearance as this affects valve timing
2) Machined cylinder head (reduced head thickness) and in turn retards camshaft timing
3) Worn or re-profiled camshafts that alter the original valve timing
4) Barometric pressure
All of these factors affect volumetric efficiency and final compression figures
When an engine is freshly built with standard components it is reasonable to expect to see a cylinder leakage of less than 2%.
If you install a high quality Total Seal piston ring pack then a cylinder leakage significantly less than 1% is attainable (this results in more available power)
With normal use, both the cylinder liner and piston rings will wear and cylinder leakage increases over time.
Once cylinder leakage approaches 20% the engine efficiency is greatly reduced and it is time to replace the worn components.
To replace the pistons, rings, liners and bearings in your turbo-charged Esprit requires the engine to be dismantled.
At this point it would be advisable to overhaul the cylinder head as it has experienced to same amount of wear as the rest of the engine components.
Copyright © 2014 Lotus Marques
My Lotus Esprit has Nikasil liners and given it had done most of its mileage in the UK before the year 2000
I am concerned that some Nikasil wear may have occurred.
A recent dyno trip showed the power at the wheels was 149kw, not too bad, given it means the engine itself is probably still close to the 160kw it should be.
I am just wondering though, given I have a set of brand new A grade (ie all four are balanced and matched) original forged pistons (with new rings) and 4 x new Nikasil liners, if I'm worried about the power loss can I simply change the liners and pistons?
This would of course be in liu of an inspection of the bearings, if they are good can this be done?
Its much much cheaper to just do a pistons (with new rings) and liner swap than bearings as well, which would be practically a full rebuild.
At this point in time I believe the top end, the springs etc are OK.
B.C. - Sydney, New South Wales
ANSWER
The correct way to determine the internal liner and piston ring wear is to carry out a periodic cylinder leak-down test.
This is a non-invasive test where compressed air is introduced into each cylinder via a pressure regulator and combined orifice.
A cylinder leak-down test should not be confused with a compression test as it allows a quantitative measurement to be made.
It is worth noting a compression test does not take into account the following items -
1) Incorrect tappet clearance as this affects valve timing
2) Machined cylinder head (reduced head thickness) and in turn retards camshaft timing
3) Worn or re-profiled camshafts that alter the original valve timing
4) Barometric pressure
All of these factors affect volumetric efficiency and final compression figures
When an engine is freshly built with standard components it is reasonable to expect to see a cylinder leakage of less than 2%.
If you install a high quality Total Seal piston ring pack then a cylinder leakage significantly less than 1% is attainable (this results in more available power)
With normal use, both the cylinder liner and piston rings will wear and cylinder leakage increases over time.
Once cylinder leakage approaches 20% the engine efficiency is greatly reduced and it is time to replace the worn components.
To replace the pistons, rings, liners and bearings in your turbo-charged Esprit requires the engine to be dismantled.
At this point it would be advisable to overhaul the cylinder head as it has experienced to same amount of wear as the rest of the engine components.
Copyright © 2014 Lotus Marques