Need help with new head gasket

Anonymous

Guest
850, rebuilt head, new rings. Used new graphite appearing head gasket with metal rings around pistons. Also used small amount of Yamahbond on gasket (each side) around each push rod opening (was told this was a common leak area). When engine fired up, after about 3 minutes, oil started to leak out of the front two studs that go up thru head and are held in place with washer and nut. Upon taking apart to investigate found pooled engine oil in left cylinder and other cylinder oil wet also. It appears pistons might have been pumping out oil. I torqued head down in manual suggested sequence and pounds (30 lbs except 20 lbs on the two leaking front studs). Gasket looked ok and no obvious signs of why it leaked so bad. I removed the two studs from the cylinder barrel and short thread was in down position, long threads in up position like it is supposed to be. Also after first leak, I let motor cool down and retorqued and it still leaked same amount. Anybody ever have this head gasket problem or ideas on what is going wrong? The only thing I have discovered is that the 2 studs don't seem to have much thread left when head tightened down. Thanks for your help.
Dennis
 

Anonymous

Guest
Dennis,
Check both the head and the cylinder with a straight edge and feeler gauges to make sure they are both true.

Next, make sure none of the studs have pulled from the head leaving a raised area around the base. If so, you'll need to either drill and tap and make a special stud, or helicoil after machining the head flat.

Also, when you "Yamabond" the pushrod tube holes smear a little around the intake chamber drainback hole at the rear of the cylinder. This would not account for oil inside the cylinder, but often will seep around the cylinder/head mating surface and show up at the left exhaust port.

Ron L
 

Anonymous

Guest
Dennis.
You have got the same problem that has been driving me mad for 20 years, but I feel I am getting close to the answer. Dont worry about the oil on the piston top, that is the a spillage from disasembly. The oil around the studs is our real problem cos it makes such a mess during riding. the problem is the aluminium thickness from machined area near the stud to the push rod tunnel is very thin-probably only 3/4 mm. The standard of casting is very poor and the result is a very fine crack, or porosity between the push rod tunnel to the machinedsurface 3 fins up. I have observed the oil coming through the aluminum after I coated it with flaw finder developer. I only wish I knew an answer. What I shall try is to replace the 5/16 BSC nuts with sleeve nuts like those under the cylinder at the front of the engine and building the area of leaking aluminium up with a titanium metal filled putty that is avaiable from Radio Spares. I have tried with a previous head that I had to have it welded, but aluminium is so thin and poor quality that It could not be done
 

Anonymous

Guest
Follow up on new head gasket oil leak

Well, I qualify for dummy of the year award! After the bike was started and ran for about 2 minutes, the oil started to run down from the head fin level that the two front head stud nuts were located. So I naturally figured the two studs somehow were leaking oil (actually impossible since oil would have to travel up the studs to the top of the nut but is surrounded by the gasket with not oil source). Took the head back off, had it surfaced, case surfaced and several other small things to try to stop the leak. Reassembled and started bike after all of this and oil leaked out again after about 2 minutes. Happened to look the head over closely when running and lo and behold, oil was leaking out of the rear rocker spindle cover, running down to the fin in the center of the head, thru it and then down the fin in front where the 2 head stud nuts were located!!! Since the Norton motor is tilted forward, it took a few minutes for the oil to run to the front of the motor and down. But was I happy, as this was an easy fix, just reseal and tighten down the cover bolts. We couldn't see the trees for the forest! No oil leaks and everything is great. I was told that oil on bike motors can splay every which way and fool you on the source of the leak and boy was that a correct statement. Live and learn!

Dennis
Vancouver, Washington
 
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