QUESTION
Can you please confirm the bearing journal sizes on the two converted Datsun crankshafts Lotus Marques has just supplied.
Have the main and big-end journals been ground to the standard Ford dimensions?
M.P. - Perth, Wester Australia
ANSWER
The L18 (77.62mm stroke) crankshaft has been ground so the main and big-end journals are per the standard Ford dimensions.
The L16 (72.74mm stroke) crankshaft has been ground so the main bearing journals are standard but the big-end journals are -0.010" (under-size)
The under-size big end journals are the only way to obtain a "legal stroke" to race say in Group NC (Historic)
The bearing clearance has been ground to 0.002" to 0.00225"
This should be checked on assembly with Plastigage.
This is a mid-point tolerance and we have proven over the years its ideal for race/competition engines.
Occasionally its possible to move bearing shells around to optimise the bearing clearance.
However from experience ACL are achieving tighter bearing manufacturing tolerances these days.
Copyright © 2012 Lotus Marques
Can you please confirm the bearing journal sizes on the two converted Datsun crankshafts Lotus Marques has just supplied.
Have the main and big-end journals been ground to the standard Ford dimensions?
M.P. - Perth, Wester Australia
ANSWER
The L18 (77.62mm stroke) crankshaft has been ground so the main and big-end journals are per the standard Ford dimensions.
The L16 (72.74mm stroke) crankshaft has been ground so the main bearing journals are standard but the big-end journals are -0.010" (under-size)
The under-size big end journals are the only way to obtain a "legal stroke" to race say in Group NC (Historic)
The bearing clearance has been ground to 0.002" to 0.00225"
This should be checked on assembly with Plastigage.
This is a mid-point tolerance and we have proven over the years its ideal for race/competition engines.
Occasionally its possible to move bearing shells around to optimise the bearing clearance.
However from experience ACL are achieving tighter bearing manufacturing tolerances these days.
Copyright © 2012 Lotus Marques