Weird head gasket issue

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fischer550

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Mar 24, 2014
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So I put on a fred head, and when I look very closely, the head is not very tightly squeezing the gasket, even though the head bolts are very tight. I can see a little gap from the top of the gasket to the bottom of the head.

Is this normal? What can be a cause? New gasket by the way.
 
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Agreen

Agreen

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Feb 10, 2013
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Southeastern GA
Either a warped head or cylinder. Take them off, rub a marker on the mating surfaces, and lap each one on some 300 grit sandpaper taped to a smooth surface like glass or a mirror. After a couple strokes, you'll see the high and low spots.
 
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langolier

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Jul 6, 2015
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Wisconsin
What type of head bolts are you using ? If they are of the Acorn nut variety get rid of them and use a good quality standard nut. Acorn nuts have a bad habit of bottoming out before head is tight.
 
crassius

crassius

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Sep 30, 2012
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never seen a fred head, but standard heads have a compression ring at bottom to apply greater force to the gasket - these heads always leave what appears to be a gap at edges
 
MotorBicycleRacing

MotorBicycleRacing

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Jul 28, 2010
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fischer550 said:
So I put on a fred head, and when I look very closely, the head is not very tightly squeezing the gasket, even though the head bolts are very tight. I can see a little gap from the top of the gasket to the bottom of the head.

Is this normal? What can be a cause? New gasket by the way.
Click to expand...
Yes, it is normal.
The Fred head has a slightly raised sealing lip so that is the gap you are seeing.

Take a look at the stock head you replaced and you will see it.

I hope you didn't take the advice of sanding your head.
There is no chance a Fred head would not be dead flat and removing material would change the squish band. Also the head comes with custom made deep nuts.
 
Last edited:
Agreen

Agreen

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Feb 10, 2013
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Southeastern GA
Missed the "Fred" part.

CR machine would definitely not let one out that was warped. I have seen warped jugs though.

A couple passes on the sandpaper wouldn't have hurt anything. All you'd have done is verified that the head and jug were true. It's not like a couple rubs of sandpaper will ruin the cylinder. It would take a while on 300 grit to mess with the squish band.

It's always a good idea to use a feeler gauge between the head and cylinder before tightening it together. If you can pass the thinnest one through in some areas but not others, chances are some lapping is called for.
 
MotorBicycleRacing

MotorBicycleRacing

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Agreen said:
Missed the "Fred" part.

CR machine would definitely not let one out that was warped. I have seen warped jugs though.

A couple passes on the sandpaper wouldn't have hurt anything. All you'd have done is verified that the head and jug were true. It's not like a couple rubs of sandpaper will ruin the cylinder. It would take a while on 300 grit to mess with the squish band.

It's always a good idea to use a feeler gauge between the head and cylinder before tightening it together. If you can pass the thinnest one through in some areas but not others, chances are some lapping is called for.
Click to expand...
Actually sand paper will never get a truly flat surface. It will be rounded over.
Only a fly cutter on a mill or a lathe will make a flat surface.

Sanding the cylinder will not ruin the squish band. Only sanding the head would ruin the squish band.

Actually he probably needs to deck the cylinder to set the squish band height correctly.

Give it a rest, the slight gap he is seeing is due to the raised sealing ring on the head.
 
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