Head gasket
- Thread starter Flathead
- Start date
Use an inch pound torque wrench. Many of us recommend 120 to 140 inch pounds.
We also recommend the cylinder head be 'lapped' before assembly and to 'check' the torque after a few heat/cool cycles. By 'check' I mean don't try to get a turn on the wrench just see if they are still at the torque range mentioned above.
Unless you have one of the more recent engines with the tall acorn nuts we tell new builders to discard the chrome acorn nuts that came with the engine in favor of standard or shouldered hex nuts. The earlier acorn nuts were notorious for bottoming out on the studs before they were tight against the head.
Tom
We also recommend the cylinder head be 'lapped' before assembly and to 'check' the torque after a few heat/cool cycles. By 'check' I mean don't try to get a turn on the wrench just see if they are still at the torque range mentioned above.
Unless you have one of the more recent engines with the tall acorn nuts we tell new builders to discard the chrome acorn nuts that came with the engine in favor of standard or shouldered hex nuts. The earlier acorn nuts were notorious for bottoming out on the studs before they were tight against the head.
Tom
+1 to what Tom said.
If you plan on doing most of your own engine work you really should invest in an inch pound torque wrench to get it right. A wrench that ranges from 0 to 200 inch pounds will cover most of what you'll want to measure on the China girl engine, and it goes a long way toward eliminating the pull out of case threads due to over tightening when not using a torque wrench.
Don
If you plan on doing most of your own engine work you really should invest in an inch pound torque wrench to get it right. A wrench that ranges from 0 to 200 inch pounds will cover most of what you'll want to measure on the China girl engine, and it goes a long way toward eliminating the pull out of case threads due to over tightening when not using a torque wrench.
Don
My first hint that I had a blown headgasket was a slightly louder exhaust note on a tough hillclimb. I had heard a bit of rattle or a "popcorn popping" sound just before this and the cylinderhead was smoking hot. When I stopped I could see oil and soot between the head and cylinder. The bike drove home merrily with no further signs of head gasket leakage. When I tore the head off, this is what I saw:
So why did it blow? Was it warped from the factory? Will lapping solve this?
I doubt it. The rattle I heard is detonation, a spike in combustion pressure that shocks and drives heat into the metal and bearings. There are many causes, poor fuel, too much compression, oil, hotspots, too hot a plug, ignition advance. One of the ways to get rid of it is to keep the air/fuel mixture moving with squish induced turbulence.
Lapping it involves putting a new flat sheet of 100 grit (80 to 250 would probably work too) paper on a flat surface like a glass sheet, and sanding it in an orbital pattern. This is my head more than half done. You can still see the dark hollows at top and bottom from where it was warped:
I ran into a problem with this. I tested the gap between head and piston with a small piece of 0.060" (1.5mm) lead solder and found the gap now too small. Plus, that gap was a terrible shape, trapping combustion gasses out near the edge of the cylinder instead of in the center bowl. That close contact area is called the "squish" or "quench" area and should match the piston shape, so how to machine it 10 or 20 thou? Here is how I did it:
I wrapped a thin piece of sandpaper (waterpaper because it is thin and tough) over a piston's done and ground it into the center of the head's chamber. When the sanded pattern matched the headgasket bore, I stopped. Here is how the head looks compared to a new head:
Notice the squish area is about 3 times larger? The gap now is about 1mm (should be between 0.5mm and 1.5mm) There is no detonation rattle when climbing hills and no more blown headgaskets.
Steve
So why did it blow? Was it warped from the factory? Will lapping solve this?
I doubt it. The rattle I heard is detonation, a spike in combustion pressure that shocks and drives heat into the metal and bearings. There are many causes, poor fuel, too much compression, oil, hotspots, too hot a plug, ignition advance. One of the ways to get rid of it is to keep the air/fuel mixture moving with squish induced turbulence.
Lapping it involves putting a new flat sheet of 100 grit (80 to 250 would probably work too) paper on a flat surface like a glass sheet, and sanding it in an orbital pattern. This is my head more than half done. You can still see the dark hollows at top and bottom from where it was warped:
I ran into a problem with this. I tested the gap between head and piston with a small piece of 0.060" (1.5mm) lead solder and found the gap now too small. Plus, that gap was a terrible shape, trapping combustion gasses out near the edge of the cylinder instead of in the center bowl. That close contact area is called the "squish" or "quench" area and should match the piston shape, so how to machine it 10 or 20 thou? Here is how I did it:
I wrapped a thin piece of sandpaper (waterpaper because it is thin and tough) over a piston's done and ground it into the center of the head's chamber. When the sanded pattern matched the headgasket bore, I stopped. Here is how the head looks compared to a new head:
Notice the squish area is about 3 times larger? The gap now is about 1mm (should be between 0.5mm and 1.5mm) There is no detonation rattle when climbing hills and no more blown headgaskets.
Steve
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Thanks Steve,
Now for a sure fire fix not helicoil for the stud/s that strip when the head goes???
Now for a sure fire fix not helicoil for the stud/s that strip when the head goes???