Rover SD1 Snippety Bit - Testing for Rover SD1 Efi V8 Camshaft Wear
The Diagnostic Process.
# Warm up the engine and set the idle to a steady and easy to remember speed (say 800 rpm).
# Using suitably insulated grips/pliers, remove one spark plug lead at a time from the distributor (or spark plug) and observe the drop in idle speed for each cylinder.
# Note down the results for each cylinder in turn from No 1 thro 8.
# Removing the plug lead from a normally functioning cylinder will cause a drop in idle speed of approximately 250 rpm (so, from the suggested speed, down to about 550 rpm).
# Removing the plug lead from a cylinder with a badly worn cam will cause a drop in idle speed of approximately 100 rpm (to about 700 rpm).
# Intermediate results between 250 and 100 drop in rpm indicates a degree of partial cam wear.
# It's possible, of course, that a smaller amount of change in idle speed can be caused by a spark plug/lead malfunction which must be eliminated by substitution before blaming the cam.
# Detection of a small (say 100 rpm) drop in idle speed (not due to spark plug/ lead issues ) now really warrants a visual inspection of the cam function. See rationale, below.
# So only if found to be necessary, removal of a rocker cover will confirm any faulty valve lifting issues (on Efi models this is only possible on the L/H bank after removing the plenum chamber).
# Dealing with any intermediate results may warrant dismantling further as explained, but might also be taken together with assessing further symptoms of probable cam wear as follows:
o Idling seems to be OK but raising the engine speed to (say) 2000 rpm induces significant jerking/vibration (as if a plug lead is removed) which then partly diminishes at higher rpm.
o Not easy to detect, but a general loss of all round performance over long periods of time.
o the spark plug on a cam-affected cylinder may be partially fouled with oil/carbon deposits.
# Obviously, not all engines are the same and a degree of judgement is going be called for but if the specified dynamic test process causes the idle speed to fall by the approximate maximum 250 rpm on all eight cylinders, then its very unlikely that the camshaft is worn.
On a normally functioning engine, each cylinder contributes an equal amount of energy or torque to the overall output of the engine enabling it to idle smoothly at the chosen test rpm. Removing a spark plug lead has a significant effect on the output rpm fo two reasons.
1) One eighth of the total amount of energy has been lost and 2) The other seven functioning cylinders now have to work harder to compress the fuel/air mixture in the non working cylinder as well as keep the engine ticking over at the best speed it can achieve. Usually, a drop of 250 rpm.
When an engine has a badly worn cam, whilst it's still possible to adjust the idle speed to the chosen test rpm, the idle may not be perfectly smooth because the cylinder with the worn cam is making little or no contribution of energy/torque to the overall engine output. Disabling a good cylinder still has an effect similar to that described above, but removing the spark plug lead from a cam affected cylinder detracts very little from the test rpm.
At the same time, the energy required to compress the fuel/air mixture in a non functioning cylinder is less because either the induction and/or the exhaust valves are only opening a small amount. With this double jeopardy, the drop in idle speed is much less than that caused by disabling a good cylinder. Usually falling by typically 100 rpm.
The partial fouling of the spark plug on a cam affected cylinder is expected, especially on an Efi engine, because of a potentially rich mixture due to the inadequate induction of a full volume of air whilst at the same time the normal amount of fuel has been injected into the inlet tract by the ECU.
By performing the dynamic test process it's possible to pre-assess the condition of the camshaft without recourse to removing the plenum chamber or ant other parts of a Rover SD1 Efi V8 engine.
Please feel free to critique, comment and/or improve upon this process and let me have any considered corrections as you deem appropriate. Otherwise also feel free to contact me regarding Errors and Omissions.
For more Rover SD1 Snippety Bits, click here:
A Major Review of Rover SD1 V8 Electronic Ignition System
Description & Analysis Here:
Components & Testing Here
A disgruntled forum member had just been informed he may have a worn camshaft on his Rover SD1 Efi V8 Engine and was contemplating the follow-up advice to remove the Plenum Chamber in order to gain access to the LH Rocker Cover facilitating further removal to carry out a visual inspection of how much lift there is on each of the sixteen valves. Sometimes a person just dont wanna hear such devilish suggestions, all that stripping down only to find (perhaps) its all OK!
But Angel Gabrielle is at hand. "Fear not the mighty dread seizing a troubled mind. Just for thee, a cool worn camshaft test procedure without the need to dismantle any part of the engine!" First though, one has to set up an accurate rev counter on the engine because the cabin tachometer is not accurate enough. Some multimeters and strobe timing systems can be used for accurate rpm measurement and automotive multimeters are widely available at reasonable cost. Here then, a purely diagnostic process to detect a badly worn cam lobe on a Rover SD1 Efi RV8 Engine.
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