Well here’s something I’ve never encountered before. Going to set the tappets on the long - unused 1098 engine in my ‘54 every screw is seized solidly in place. The locknuts loosen easily but the screws won’t budge. They aren’t rusty, could this be caused by the pressed steel rockers deforming?
I freed one using mole grips but that damaged the end of the screw so now the locknut won’t go back on, although the screw is so stiff it hardly needs one now. Has anyone else had this?
Seized tappet adjusters
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philthehill
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Re: Seized tappet adjusters
Ian
A common problem.
The tappet adjusting screws get for use of a better word 'baked' into the rocker arm.
The oil sediment gets down into the threads and is baked solid with the engine heat.
The 948cc/1098cc 'A' Series tappet adjusting screw threads are 'Unified National Special' (UNS).
Once the screws are loosened the threads in the rocker can be cleaned up with a cycle thread tap which has the same angle profile as the UNS thread.
The cycle thread tap cleans the threads without removing metal.
To loosen the adjusting screws gently heat the end of the rocker which has the seized screw and then you should be able to undo.
A tip to make working on the rockers much easier without removing the head or loosening the head/loosing head torque:-
When reassembling the cylinder head the plate (Pt No: 2A515) that stops the rocker shaft locating peg from coming undone can be shortened so the plate is only secured under the 5/16" stud.
BMC did this modification and came up with plate Pt No: 2A259. Unfortunately BMC decided to secure the plate under the 3/8" stud which holds the head down.
Removing the plate secured by the 5/16" rocker pillar stud allows the rocker shaft peg to be removed and the rocker shaft (after backing right off the adjusting screws) to be slid forward allowing the rocker shaft and rockers etc. to be removed without disturbing the cylinder head/head gasket.
Assembly is the reverse.
Phil
A common problem.
The tappet adjusting screws get for use of a better word 'baked' into the rocker arm.
The oil sediment gets down into the threads and is baked solid with the engine heat.
The 948cc/1098cc 'A' Series tappet adjusting screw threads are 'Unified National Special' (UNS).
Once the screws are loosened the threads in the rocker can be cleaned up with a cycle thread tap which has the same angle profile as the UNS thread.
The cycle thread tap cleans the threads without removing metal.
To loosen the adjusting screws gently heat the end of the rocker which has the seized screw and then you should be able to undo.
A tip to make working on the rockers much easier without removing the head or loosening the head/loosing head torque:-
When reassembling the cylinder head the plate (Pt No: 2A515) that stops the rocker shaft locating peg from coming undone can be shortened so the plate is only secured under the 5/16" stud.
BMC did this modification and came up with plate Pt No: 2A259. Unfortunately BMC decided to secure the plate under the 3/8" stud which holds the head down.
Removing the plate secured by the 5/16" rocker pillar stud allows the rocker shaft peg to be removed and the rocker shaft (after backing right off the adjusting screws) to be slid forward allowing the rocker shaft and rockers etc. to be removed without disturbing the cylinder head/head gasket.
Assembly is the reverse.
Phil
Re: Seized tappet adjusters
Thanks Phil, a little heat from a blow lamp did the trick. I didn’t dismantle the rockers as I didn’t want to disturb the seal and torque of the head but ran each screw up and down the thread a few times until it moved freely. The damaged screw cleaned up with a small file to take the lock nut.
The clearances were more than twice what they should have been. Goodness knows when they were last done.
The clearances were more than twice what they should have been. Goodness knows when they were last done.
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philthehill
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Re: Seized tappet adjusters
Well done.
As an aside:-
Early BMC rocker shafts had a removable plug at the front of the rocker shaft so that when the plug was removed the inside/oil way of the shaft could be cleaned.
Later shafts just had a interference fit solid plug fitted so the shaft inside/oil way cannot be cleaned without removing the solid plug
Whilst it is relatively easy to drill out the solid plug the shafts are hardened and precision ground so it is near impossible to tap the oil way for the fitment of a removable plug.
Phil
As an aside:-
Early BMC rocker shafts had a removable plug at the front of the rocker shaft so that when the plug was removed the inside/oil way of the shaft could be cleaned.
Later shafts just had a interference fit solid plug fitted so the shaft inside/oil way cannot be cleaned without removing the solid plug
Whilst it is relatively easy to drill out the solid plug the shafts are hardened and precision ground so it is near impossible to tap the oil way for the fitment of a removable plug.
Phil