re. About Maintenance
Discussion
Calvin,
I think your maintenance post is excellent and good advise for everyone with an Esprit. There are a couple of areas which need clarification though.
You state that: "Valve clearances are critical on our engines... The time the cams stay in contact with the valves are used to cool the valves off. If they get too out of whack they over heat and will burn..."
Actually. it is the off-cam duration which is critical to cooling the valves as the only way the valves can shed heat is to conduct it through the valve seat and into the head to be carried off by the oil and coolant flow which, of course, can only be accomplished when the valve and seat are in contact with one another. This is expecially important to remember when custom profiling a camshaft. Regardless of the lift desired, it is critical that this off-cam duration be maintained.
Also, the 910 engine has valve clearance tolerance of 0.002", 0.005"-0.007" (Intake) and 0.010"-0.012" (Exhaust). You will always find that the gap of 0.002" becomes smaller rather than larger as the valves drive their way deeper into the valve seats. Be sure to set the valves to the 'outside' or maximum tolerance. This will extend the time, or more correctly, mileage, between adjustments.
And, remember, while your cam opens the valves, it is the valve springs which close them. Valve springs on these cars are really only good to about 35-40k mi. After that mileage, the springs lose some of their ability to close the valves quickly and tightly. Spring pressure spec is 80-90 Lbs. This is critical for correct sealing and cooling to take place. Valve guides also have about the same service mileage.
Also, to clarify, when you state: "I think back to recent drive last fall when a friends car, (Jim) blew a puff of smoke out the tail pipe. Still had lots of power but he felt something was wrong. We took his engine apart in the winter. His main piston ring on #4 had failed. This enabled blow by gasses to migrate to the oil control rings which still held a lot of compression. Hot blow by gases then entered the holes on the oil control ring lands that act as scuppers for the oil to flow back when scraped off the cyl wall by the oil control rings. The hot blow by gases entering these holes shot right on to the connecting rod end as evidenced by the blow torch scarring effect.... So do things by the book or the car will end up as either your or someone elses problem child. .."
This is somewhat misleading as it reads. It lends one to perceive that the cause of this failure was poor maintenance. The fact of the matter is that my 1985 M.Y. Esprit Turbo suffered from a design flaw which Lotus was aware of and addressed in the very next model year. That flaw consisted of not upgrading the pistons when the turbocharged Esprit was introduced. Lotus continued to use a cast aluminum piston which had been successfully used on the n/a S1,S2 & S3 models. However, once exposed to the much harsher environment created by the introduction of turbocharging, it was found that the cast pistons would, over a number of heat cycles, which translated roughly to about 36,000 mi., start to 'crown'.
This 'crowning' has the effect of pulling the rings away from the cylinder wall which of course compromises the seal between ring and liner. Once this occurs, the damage you describe will occur. Lotus sucessfully addressed this shortcoming the following model year (1986) with the introduction of the matched forged aluminum pistons w/ Nikosil aluminum liners.
I was fully aware of this phenominon and had in fact detected it a year earlier as evidenced by much lower than spec compression readings. It was always my intent to rebuild the motor and install forged pistons which as you know I did with a great set from JE Pistons. But, you have the cause and effect mixed up. It was the blow-by from the piston 'crowning' which forced the ring land to fail, not the opposite. And, this failure is not limited to my Esprit. Every '80-'85 Esprit Turbo will suffer the same problem. It is not a matter of 'if' it is only a matter of 'when'.
Btw, Calvin, they are forecasting very nice weather for Sunday, 11/17, and as of this writing, Brenda and I are planning another run to the Wisconsin hinterlands. We'd love to have you along... let me know...Jim '85TE
>>> Edited by lotusguy on Tuesday 12th November 08:47
I think your maintenance post is excellent and good advise for everyone with an Esprit. There are a couple of areas which need clarification though.
You state that: "Valve clearances are critical on our engines... The time the cams stay in contact with the valves are used to cool the valves off. If they get too out of whack they over heat and will burn..."
Actually. it is the off-cam duration which is critical to cooling the valves as the only way the valves can shed heat is to conduct it through the valve seat and into the head to be carried off by the oil and coolant flow which, of course, can only be accomplished when the valve and seat are in contact with one another. This is expecially important to remember when custom profiling a camshaft. Regardless of the lift desired, it is critical that this off-cam duration be maintained.
Also, the 910 engine has valve clearance tolerance of 0.002", 0.005"-0.007" (Intake) and 0.010"-0.012" (Exhaust). You will always find that the gap of 0.002" becomes smaller rather than larger as the valves drive their way deeper into the valve seats. Be sure to set the valves to the 'outside' or maximum tolerance. This will extend the time, or more correctly, mileage, between adjustments.
And, remember, while your cam opens the valves, it is the valve springs which close them. Valve springs on these cars are really only good to about 35-40k mi. After that mileage, the springs lose some of their ability to close the valves quickly and tightly. Spring pressure spec is 80-90 Lbs. This is critical for correct sealing and cooling to take place. Valve guides also have about the same service mileage.
Also, to clarify, when you state: "I think back to recent drive last fall when a friends car, (Jim) blew a puff of smoke out the tail pipe. Still had lots of power but he felt something was wrong. We took his engine apart in the winter. His main piston ring on #4 had failed. This enabled blow by gasses to migrate to the oil control rings which still held a lot of compression. Hot blow by gases then entered the holes on the oil control ring lands that act as scuppers for the oil to flow back when scraped off the cyl wall by the oil control rings. The hot blow by gases entering these holes shot right on to the connecting rod end as evidenced by the blow torch scarring effect.... So do things by the book or the car will end up as either your or someone elses problem child. .."
This is somewhat misleading as it reads. It lends one to perceive that the cause of this failure was poor maintenance. The fact of the matter is that my 1985 M.Y. Esprit Turbo suffered from a design flaw which Lotus was aware of and addressed in the very next model year. That flaw consisted of not upgrading the pistons when the turbocharged Esprit was introduced. Lotus continued to use a cast aluminum piston which had been successfully used on the n/a S1,S2 & S3 models. However, once exposed to the much harsher environment created by the introduction of turbocharging, it was found that the cast pistons would, over a number of heat cycles, which translated roughly to about 36,000 mi., start to 'crown'.
This 'crowning' has the effect of pulling the rings away from the cylinder wall which of course compromises the seal between ring and liner. Once this occurs, the damage you describe will occur. Lotus sucessfully addressed this shortcoming the following model year (1986) with the introduction of the matched forged aluminum pistons w/ Nikosil aluminum liners.
I was fully aware of this phenominon and had in fact detected it a year earlier as evidenced by much lower than spec compression readings. It was always my intent to rebuild the motor and install forged pistons which as you know I did with a great set from JE Pistons. But, you have the cause and effect mixed up. It was the blow-by from the piston 'crowning' which forced the ring land to fail, not the opposite. And, this failure is not limited to my Esprit. Every '80-'85 Esprit Turbo will suffer the same problem. It is not a matter of 'if' it is only a matter of 'when'.
Btw, Calvin, they are forecasting very nice weather for Sunday, 11/17, and as of this writing, Brenda and I are planning another run to the Wisconsin hinterlands. We'd love to have you along... let me know...Jim '85TE
>>> Edited by lotusguy on Tuesday 12th November 08:47
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