Topic: Head Gasket HELP!

[81cb650]

Hey SOHC/4 owners,

Struggling through a top end rebuild on my 81 CB650.  I tore it apart and rebuilt everything after my head and cylinder base gaskets sprang leaks.  I went with the cheapest gasket kit I could find on ebay (I think it was vesrah), tore apart and put everything back together.  Surprise-- 40 miles later, the head gasket leaks again.

Tore it apart for a second time last night.  Put in the most expensive head gasket I could find- Cometic, looks a whole lot beefier than my first replacement. Cleaned the gasket surfaces thoroughly with brake cleaner and scotch brite. Torqued the head bolts to spec in the specified pattern laid out in the manual. I even went through the trouble to tap and die all my threads to get them nice and clean.  Went for a quick ride around the block to test it out...a single mile later and the gasket is weeping. 

What the heck? Needless to say, it's driving me crazy.  Anybody experience this?  Am I missing something obvious?  I put hondabond down on my cylinder base gasket when I installed initially, but not on the head gasket, I've heard not to do this since the gasket is metal and is supposed to crush in evenly.

Running 10w40 honda brand mineral oil.

[millla03]

It sounds like you're using a Cometic MLS gasket? Cometic says they require a specific surface roughness (Ra) to seal properly. Though I've gotten away with no leaks on freshly decked head/cylinders of unknown surface roughness, but both surfaces were darn flat.

Gouges and surface imperfections, or a warped head/cylinder gasket surface might also cause head gasket leaks. If you take it apart again, use a straight edge to verify the flatness of the gasket surfaces.

The Cometic MLS gaskets I've used come coated, so no sealant needed.

[pjlogue]

Check your head and cylinder deck for flatness and have them resurfaced if out of spec.  Use a good quality gasket and torque it down to spec.  Wait 24 hrs and re torque the head bolts again.  Gaskets compress and waiting and re torquing will make sure the head bolts are tight.

-P.

[scunny]

it could also be the pucks on top of the head bolts. there were some that were a bit thin.

[81cb650]

Check your head and cylinder deck for flatness and have them resurfaced if out of spec.  Use a good quality gasket and torque it down to spec.  Wait 24 hrs and re torque the head bolts again.  Gaskets compress and waiting and re torquing will make sure the head bolts are tight.

-P.

Thanks everyone,

I think I'll try and re torque.  My first thought is to tear down past the valve cover and simply tighten to torque again without actually removing the cylinder head.  I'm leary of removing the new gasket since the test ride may have already started to burn it into the mating surfaces and it will more than likely become damaged if I try. 

Do you think this stands a chance of working or is this gasket toast now that oil has wept through?

[CBGhia]

This ^^^^
Guaranteed that both the block and head need milling to achieve true flatness.

On a budget, you can get a nice thick flat piece of glass and then tape a long sheet of 220 or maybe 400 grit sandpaper to it.

Clean the head and then mark the surface with a sharpie or something.  Start working the head over the sandpaper in a figure 8 pattern. 
No need to push, just let the weight of the head do that work.  When the sharpie doesn't show up on any part of the head, then you have it flat. 
Do the same with the cylinder. 
Clean them both and reinstall. 

[Little_Phil]

On a car a head gasket is usually replaced because of a blow between the cylinder and water jacket. Most talk of gasket failure here is about an oil leaks from the cam chain tunnel area and the O rings at the feeds to the cams. Check these O rings are new and being compressed if you pull it apart again.