This is what the #56 drill hole looks like in the 4mm screw.

The hole can be drilled larger to bypass more oil if the pressure is higher than desirable.

My piston will probably not be back from getting the skirt coated for 3 weeks....I will have plenty of time to put the cylinder and head back on the engine, and work out how this bypass will work.  I wouldn't be surprised if I upgrade to 1/4" hose......the little stuff looks better - but I like the longer nipple and larger passages for the larger fittings and hose.

Ruttly wrote on 01/25/26 at 08:34:42:


I share your concerns - I don't want an unreliable bike.

I looked around at AN style fittings - they are all much bigger than I need.  The oil bleed/bypass rubber line will essentially have zero pressure, as the restriction is prior to the hose nipple.  The only pressure is what is required to move the oil up through the hose to the head cover, and that is likely very small.  It takes a rise of around 2.5 feet of oil to make 1psi of pressure....so with the flow the end result is likely less than 2psi in the line.

There is no doubt I will watch this thing carefully as I get the engine running again - hopefully this time without a head gasket oil leak!  (Or an oil leak from anywhere else).  I am using an official Suzuki head gasket this time, and I am going to put a tiny amount of sealer around the oil port to help make sure the oil doesn't move around in the head gasket.

If the oil bypass hose doesn't work well and I get concerned it is not trustworthy - it can be easily removed and put back to the bypass in the oil filter housing.

The inlet to the head was a tough one to figure out.  The easiest thing to do would be to used one of the valve inspection caps for the place to bring in the oil.  The rear was most convenient - but it is likely a lot of the oil would just go down the cam chain housing and provide no real benefit.  Using the exhaust valve inspection cap would have provided a bit of cooling for the exhaust side of the head, and it would have provided more oil for the left side crank bearing.

I chose this location as it was going to have a better chance of getting oil to the cam and rockers.

This is a tube held in place on my other project bike, I was using it to figure out where there was good access.  It is on the inlet side of the engine between the valve inspection cap and the top engine mount.

This is what it looks like in place.

I need to clean up the shavings off all the parts and then JB weld the hose nipple in place.