The O series engine consists of iron block and aluminium cylinder head. The original manifold studs that are threaded into the head can snap off leaving very little of the stud to work with and more often than not mean the head would have to be removed and sent to an engineering company for repair.
Here we will show you a way of making this repair yourself with the engine in situ.
Firstly, you will need the following tools and parts:
5/16” UNF blind tap (to clean out remaining holes on head).
5/16” UNF thread repair kit (includes: HSS second tap. HSS drill bit, coil driver, tang remover and inserts)
Battery operated drill (variable speed with various drill bits)
Die grinder with a 40grit flapper wheel (or grinder with a 40grit flapper wheel)
Our engine is in the process of being fitted back together so we have a lot of space around the N/S of the engine. You may need to remove the carburettor, air box and manifold to gain access here. We were also lucky that the stud that snapped was at the front of the engine.
Start by cleaning out the remainder of the cylinder head stud holes with the 5/16” blind tap and measure their depths with a calliper gauge.
Next, you will need to use the flapper wheel to carefully grind down the stud so that it is flush with the face of the head. Get the stud small enough so that it protrudes slightly and use a file to flatten it down so not to damage the head.
Now take your drill punch and mark the centre of the old stud Make sure the stud is flat when you punch it in the middle
Carefully start drilling the stud with a 6mm HSS bit slowly. Check your alignment of the drill to the stud. The idea here is to eat into the old stud and remove it. You must continually check the depth and alignment of the hole as you do not want to go too far and drill into the oil gallery! Check depth against one of the other holes.
Move up a drill size once you have got the correct depth making sure you do not go above 5/16” at this point!
Clean out stud hole with a hoover
Once you are happy the stud is gone and the depth is correct, take the over-sized HSS drill bit from the repair kit. Centre your drill across the stud hole and drill out the hole.
Take the HSS second tap from the repair kit, centre it over the stud hole and carefully tap out the hole. You may want to use a light oil here to help lubricate the tap during this process. Wind the tap in and out a couple of times making sure that you have gone down all of the hole and removed all of the swarf. You may want to hoover out the hole before the next step.
Using the coil driver from the kit, carefully wind in the insert into the stud hole. Once you are happy that it is flush with the cylinder head manifold face take the tang removal tool and tap the end off the insert. The tang tool is magnetic and will hold onto the tang when it is extracted.
Test fit a new stud, or bolt.
You can now re-fit the manifold.