QUESTION
I am concerned about the constant tappet ticking noise coming from my Lotus twin engine after having the cylinder head rebuilt.
The valve gear on my Lotus Elan +2 now makes more noise than the Sprint I owned in the UK in the early 70's.
This is strange, since the head has been overhauled with new springs and shims via the local mechanic.
The engine seems to constantly 'tick' more loudly at idle speed.
Could you please advise if this is a shim related problem.
D.H. - Brisbane, Queensland
ANSWER
The ticking noise you describe not going to be fixed by changing shims to adjust tappet clearances.
From experience, this is a symptom of significantly worn cam followers and/or worn follower sleeves.
The followers have a barrel shaped characteristic wear pattern - in other words, they wear at the top and bottom but not in the middle.
Once there is 0.0025" to 0.003" clearance between the cam follower and sleeve, the follower will wobble causing the ticking noise.
The camshaft lobe is off-set to rotate the follower but is also responsible for the rocking action of the follower which in turn generates the ticking noise.
This is something that a mechanic may overlook if not experienced with component wear issues and the critical machining operations of the cylinder head.
The followers should be removed and checked for wear and at the same time the sleeve bores should be measured with an internal bore micrometer.
If the followers are original cast iron type and high mileage, then they should be changed at about 100,000 miles they have reached the end of their service life.
Copyright © 2014 Lotus Marques
I am concerned about the constant tappet ticking noise coming from my Lotus twin engine after having the cylinder head rebuilt.
The valve gear on my Lotus Elan +2 now makes more noise than the Sprint I owned in the UK in the early 70's.
This is strange, since the head has been overhauled with new springs and shims via the local mechanic.
The engine seems to constantly 'tick' more loudly at idle speed.
Could you please advise if this is a shim related problem.
D.H. - Brisbane, Queensland
ANSWER
The ticking noise you describe not going to be fixed by changing shims to adjust tappet clearances.
From experience, this is a symptom of significantly worn cam followers and/or worn follower sleeves.
The followers have a barrel shaped characteristic wear pattern - in other words, they wear at the top and bottom but not in the middle.
Once there is 0.0025" to 0.003" clearance between the cam follower and sleeve, the follower will wobble causing the ticking noise.
The camshaft lobe is off-set to rotate the follower but is also responsible for the rocking action of the follower which in turn generates the ticking noise.
This is something that a mechanic may overlook if not experienced with component wear issues and the critical machining operations of the cylinder head.
The followers should be removed and checked for wear and at the same time the sleeve bores should be measured with an internal bore micrometer.
If the followers are original cast iron type and high mileage, then they should be changed at about 100,000 miles they have reached the end of their service life.
Copyright © 2014 Lotus Marques