Prepare for a bit of reading..
I have taken the liberty to cut an 885 head in half.. dont worry it was cracked. Straight down the middle of the tunnel/combustion chamber. It was a pain in the ass, but could be worth it. Plus its interesting.
this is down the inlet side..
here is where they crack on the 5th cyl underneath the tunnel. The aluminium is just as thick here as it is anywhere else.. Why it cracks here could be answered as this thread gets more involved.
Lets start with the small water gallery holes in between the combustion chambers. Because the hole is so small, over time it becomes clogged from corrosion/rust/debris floating around the cooling system. I had one completely blocked. Standard size they are 4.7mm unblocked.
They head up at an ANGLE into the main watergallery that runs under the cam tunnel. The circular upright you see behind it with the brace is what the headbolt runs through.
On the block side it runs down like so.
This is my idea to help improve the water flow. Feel free to add your opinion.
Drill out the hole to 5mm instead of 4.7mm
or even 6mm
Then you would need to drill out the headgasket to suit, heres how close they would end up being to the combustion chamber.
then matchport the block to that size
the second thing I think would benifit circulation would be this.. Look at the headgasket outer gallery holes.. The jackets are huge, however the headgasket is somewhat limit in water feed.. 8mm on the exhaust and barely 3mm on the intake side I asume this acts as a restricter to keep the water in the cylinder head, Or feeds more to the exhaust side because of the extra heat through the ports.
intake side of headgasket water gallerys
exhaust side
as you can see when corosion sets in it eats up a larger hole
My idea is to largen up the intake side of the gasket to 5/6mm also. However the hole would need to be elongated as the hole in the gasket is as far away from the combustion chamber as possible in the gasket. Opening it straight up would mean contact with the surface of the block/head.
Personally I think the reason number 5/6 suffer so much is because the water circulation is quite poor at the back of the block already because water does not pass between the cylinders in the block, it has to work its way around the back of the block to get back around to the intake side. So more heat is created in that cylinder.. having the smaller holes in the head gasket on the intake side reduces the cooling efficency in that corner.. hense why 5/6 go. Thats my diagnosis anyway.. see what you think.
I have taken the liberty to cut an 885 head in half.. dont worry it was cracked. Straight down the middle of the tunnel/combustion chamber. It was a pain in the ass, but could be worth it. Plus its interesting.
this is down the inlet side..
here is where they crack on the 5th cyl underneath the tunnel. The aluminium is just as thick here as it is anywhere else.. Why it cracks here could be answered as this thread gets more involved.
Lets start with the small water gallery holes in between the combustion chambers. Because the hole is so small, over time it becomes clogged from corrosion/rust/debris floating around the cooling system. I had one completely blocked. Standard size they are 4.7mm unblocked.
They head up at an ANGLE into the main watergallery that runs under the cam tunnel. The circular upright you see behind it with the brace is what the headbolt runs through.
On the block side it runs down like so.
This is my idea to help improve the water flow. Feel free to add your opinion.
Drill out the hole to 5mm instead of 4.7mm
or even 6mm
Then you would need to drill out the headgasket to suit, heres how close they would end up being to the combustion chamber.
then matchport the block to that size
the second thing I think would benifit circulation would be this.. Look at the headgasket outer gallery holes.. The jackets are huge, however the headgasket is somewhat limit in water feed.. 8mm on the exhaust and barely 3mm on the intake side I asume this acts as a restricter to keep the water in the cylinder head, Or feeds more to the exhaust side because of the extra heat through the ports.
intake side of headgasket water gallerys
exhaust side
as you can see when corosion sets in it eats up a larger hole
My idea is to largen up the intake side of the gasket to 5/6mm also. However the hole would need to be elongated as the hole in the gasket is as far away from the combustion chamber as possible in the gasket. Opening it straight up would mean contact with the surface of the block/head.
Personally I think the reason number 5/6 suffer so much is because the water circulation is quite poor at the back of the block already because water does not pass between the cylinders in the block, it has to work its way around the back of the block to get back around to the intake side. So more heat is created in that cylinder.. having the smaller holes in the head gasket on the intake side reduces the cooling efficency in that corner.. hense why 5/6 go. Thats my diagnosis anyway.. see what you think.
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