Hey all, awhile back I was talking to Tom on the phone and he mentioned drilling / tapping the rear oiling hole on each head for a set screw to prevent oil leaks in the rear of the motor. I've been searching for a good writeup on this and don't see it even mentioned. Is this not a common practice? Thanks, Mike
It is for me Mike. It's just a precautionary measure to keep the oil from weeping through the multi layers of composite head gaskets. It WON'T hurt anything to do this as the oil dead heads at the block & has no where else to go. I'd also be interested what others have to say. Tom T.
It makes total sense to me Tom and I see no reason not to do it. I was just looking to see if it was documented somewhere here. Do you drill and tap from the top or the bottom? Looks like I need to remove a valve spring if I do it from the top. I'll probably have my buddy who is a machinist and metal fabricator do it for me just to be safe.
From the top & no where near the valve spring Mike. Look where the rear bolt for the rocker support goes into. See the hole?? Drill with a #7 drill about 1" & tap.
My apologies if I sound ignorant... bt do you mean the small hole in the side of the larger hole where the arrow is ? What was that hole meant for in the first place ? So the idea is to plug it from the top ? This wont prevent the hole from a specific purpose ? Sorry I had never read up on this before.....
The early big blocks didn't oil through the pushrods, but oiled through the rocker shafts via the holes of each head shown in the pic. I either forgot that the other hole isnt necessary until I read this thread.
Plugging the unused oil passage in the rear of the head will eliminate a possible oil leak when using composition head gaskets.... Oil is fed to the rocker arm shaft from the front cam bearing, through a passage in the block, through the head gasket into the head, then through that passage you see in the head to the rocker shaft bolt. The bolt shaft is narrower than the rocker support stand, so oil flows around the bolt and up into the the rocker shaft and to the individual rockers. Since a cylinder head will fit either left or right side, that oil passage in the head is at both ends. But it's only needed in the front. If the oil passage in the rear of the head (not being used) is left open, oil from the rocker shaft will flow through the head to the block, where it dead ends and won't go anywhere..... IF you have the stock steel head gasket. If you have a replacement composition head gasket, oil may seep between the layers of the gasket and leak out somewhere.
Thank you Walt! I've seen that leak on Brian Clark's engine, maybe mine too. I've tried to prevent that leak with sealant on the gasket, but a more positive seal would be desireable.
All you have to do Ted is remove the rockers. Drill the hole with a #7 drill about 3/4", give or take. Use some grease on the end of the drill bit to catch MOST of the drillings. Use the appropriate tap, with some grease, for the set screw. Blow out the hole with compressed air. There is NO NEED to worry about filings as they have NO place to go & WILL NOT get into your engine. Install the set screw & oil leak fixed.
man I'm glad I read this thread. I've been trying to figure out my oil leak for quite some time now, thank you I can't wait to try this.
Rob, I don't see a "Nail" in your signature just a '68. I'm NOT sure of the early 400/430/455 engines. I would ASSUME they are the same since the early engines oil through the rocker shafts & NOT the pushrods as on the later engines as the heads can be swapped left-right on either. Someone will have to verify that
I've got a set of loose '69 430 heads laying around. I can look at them later tonight. I also have a '68 400 block so I can see if it has the oiling hole. That is if I can get to it.
So yes indeed the early gen 3 motors (400 and 430 at least) oil through the rocker shafts. the oil comes from the front, so you need to block the rear. When I looked at my heads, I found one hole on each blocked with JB Weld.
