Entabeni: 2006 Gen 3 Pajero 3.2 DiD LWB GLS Auto 204,000 km
Measurement of the four cylinder diameters, with all pistons removed. 2014-02-14
I set my Mitutoyo Cylinder Gauge to read zero at a diameter of 98.50 mm. This was done with my Mitutoyo 100 mm external micrometer set to that size --- see Photo 1. The table therefore records deviations from 98.50 mm, positive values indicating wear and negative ones the opposite. The smallest graduations on the Cylinder Gauge's scale are at one micron intervals, i.e. 1 micro-meter. Photos 2 and 3 show me sitting in the engine bay and making measurements.
There had been no sharp metallic ridges that needed to be removed before the pistons could be extracted. However, carbon removal from the inside top edge of the cylinders with a triangular-cross-section scraper was physically awkward and not 100%, so variations of several microns are bound to occur.
The measurement locations in the cylinders are given as follows:
A is above the area reached by the rings
B is in the area just reached by the rings
C is in the middle, approximately
D is at the bottom of the cylinder
In line with motor is designated by 'i'
Across " " " 'a'
Cyl 1 2 3 4
Ai 0.004 0.002 0.018 0.000
Aa 0.010 0.003 -0.001 0.010
Bi 0.010 0.011 0.015 0.002
Ba 0.022 0.012 0.010 0.028
Ci 0.009 0.018 0.025 0.006
Ca 0.027 0.020 0.017 0.034
Di -0.005 0.015 0.023 0.004
Da 0.028 0.020 0.005 0.028
What is very surprising is the small amount of wear after 204,000 km. Even more surprising is that cylinder 2 with its cracked piston exhibits less wear than cylinder 4, for example! The maximum wear measured, 0.034mm in cylinder 4, corresponds to 1.34 thousandths inch, which is not too bad. Certainly a rebore and oversize pistons are not necessary. So I am inclined to replace only piston 2 with a new one. However, this depends on whether I can buy only one piston, whether pistons 1, 3 and 4 can be proved to be crack-free and what the ring gaps are when placed in the cylinders. It would be best of course to install a full set of new pistons and rings.
The reason for so little wear is probably the care Mitsubishi has taken to lubricate the pistons and cylinder walls. First, there is a nozzle pointing up into each cylinder just above the throws of the crankshaft. This presumably sprays oil upwards --- see Photo 4. Secondly, there are the vertical holes in the piston undersides which allow oil to get into the 'cavity' in the piston crown and possibly into the grooves of the piston rings. (I described the piston structure in a previous posting.)
Photo 1 Cylinder Gauge zeroing
Photo 2 Sitting in engine bay
Photo 3 Measuring a diameter
Photo 4 Oil nozzle pointing up into cylinder
Hi Entabeni,
Thanks for keeping us fascinated - I have great respect for what you are doing.
Is there a way to verify that the spray for cylinder #2 is working as it should before you reassemble?
Are you going to weigh the 3 good pistons (after marking them, of course, for cylinder number and thrust direction) to get a good balance match for the replacement piston (assuming you can get a single piston to suit)?
Thanks for keeping us fascinated - I have great respect for what you are doing.
Is there a way to verify that the spray for cylinder #2 is working as it should before you reassemble?
Are you going to weigh the 3 good pistons (after marking them, of course, for cylinder number and thrust direction) to get a good balance match for the replacement piston (assuming you can get a single piston to suit)?
Hello again Andrew, and thank you,
When I asked a Mits purveyor of spares if I could buy just one piston he replied with a jolly tone that I certainly could, but it would cost the same as a set of four!!! Nice joke! So I have decided to play safe and buy a set of new pistons and rings. This means that I will have three slightly used spares! I will think about a way to check the oil spray nozzles.
I am not sure if the new pistons will require reassessment of the cylinderhead gasket thickness required.
Entabeni.
When I asked a Mits purveyor of spares if I could buy just one piston he replied with a jolly tone that I certainly could, but it would cost the same as a set of four!!! Nice joke! So I have decided to play safe and buy a set of new pistons and rings. This means that I will have three slightly used spares! I will think about a way to check the oil spray nozzles.
I am not sure if the new pistons will require reassessment of the cylinderhead gasket thickness required.
Entabeni.
Hi Entabeni,
Wondering how you are getting on with your rebuild?
Wondering how you are getting on with your rebuild?