12-01-2022, 09:08 PM
Hi Henry,
This is a vital mod for the three bearing engine to push as much oil as possible towards the centre main bearing. The rear cam bearing of any A7 engine doesn't need restricting as the small running clearance between the bearing journal and bush forms a limiting restriction. The front cam bearing isn't as simple as the groove down the bush can dissipate oil. However, the splash of oil out of the front of the bush is what forms most of the lubrication for the timing gears so you have to retain some release. I've no experience of pressure fed engines but I use a drilling of 1.5mm for the front bearing of my three bearing splash engines. I drill and tap the oil feed hole of the bush and insert a brass screw with the 1.5mm drilling - looking very similar to a Zenith jet. The centre cam bearing can be blanked, an undrilled bearing shell effectively achieves this and it can be lubricated by a drain drilled from the tappet chest above it, a 3/16" drilling seems to give enough lubrication. The O ring mod is also a good one to make for any engine.
I hope that helps, Dave
This is a vital mod for the three bearing engine to push as much oil as possible towards the centre main bearing. The rear cam bearing of any A7 engine doesn't need restricting as the small running clearance between the bearing journal and bush forms a limiting restriction. The front cam bearing isn't as simple as the groove down the bush can dissipate oil. However, the splash of oil out of the front of the bush is what forms most of the lubrication for the timing gears so you have to retain some release. I've no experience of pressure fed engines but I use a drilling of 1.5mm for the front bearing of my three bearing splash engines. I drill and tap the oil feed hole of the bush and insert a brass screw with the 1.5mm drilling - looking very similar to a Zenith jet. The centre cam bearing can be blanked, an undrilled bearing shell effectively achieves this and it can be lubricated by a drain drilled from the tappet chest above it, a 3/16" drilling seems to give enough lubrication. The O ring mod is also a good one to make for any engine.
I hope that helps, Dave