Fresh oil on top of cylinder head

Joast

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I have a secondhand bike with a 66 80 Chinese engine of some sort. It has been difficult to get the idle adjusted with the screw for a few days.
I think the engine seems to be running rough for the last few days, but don't know for sure how these should sound when riding it.
I previously had an exhaust flange leak, and I thought it was sealed with a new thick gasket as recommended here. Now I found some fresh oil on the TOP,
front, corner of the head near the cooling fins. See pic. Plug seems tight and the head/exhaust bolts are tight, but I didn't torque the head bolts (they were installed by the builder). Does this seem like a blown head gasket? I can't find much sign of oil on the front of the engine or around the exhaust manifold. I have some spare gaskets on hand if needed, but thought I would see if anyone could think of other possibilities to consider first. Thanks for any thoughts and help on this. John
 

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ImpulseRocket89

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It could possibly be the head gasket not sealing and the oil seeping through somewhere. Looking at it myself I would assume the spark plug crush washer may just be spent and not sealing and oil is seeping past it.

If you have new head gaskets I would say to pull the head clean everything up really good, level the head mating surface with a piece of glass and some sand paper, install a new head gasket and spark plug, and go from there. This will give you a good chance to inspect the jug and piston top and clean up any possible carbon buildup as well.
 

Joast

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The plug and washers were installed new last week--NGK. I can't see any fresh oil around the plug itself.
I can see the edge of the head gasket and it looks intact just looking at the silver edge if that matters.
Thanks, John
 

mony0_3

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I have a secondhand bike with a 66 80 Chinese engine of some sort. It has been difficult to get the idle adjusted with the screw for a few days.
I think the engine seems to be running rough for the last few days, but don't know for sure how these should sound when riding it.
I previously had an exhaust flange leak, and I thought it was sealed with a new thick gasket as recommended here. Now I found some fresh oil on the TOP,
front, corner of the head near the cooling fins. See pic. Plug seems tight and the head/exhaust bolts are tight, but I didn't torque the head bolts (they were installed by the builder). Does this seem like a blown head gasket? I can't find much sign of oil on the front of the engine or around the exhaust manifold. I have some spare gaskets on hand if needed, but thought I would see if anyone could think of other possibilities to consider first. Thanks for any thoughts and help on this. John
Replace the exhaust gasket.
 

Joast

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Here are some pics of the head and gasket. Looks like oil is seeping around between the head and gasket.
Once the bolts broke loose, they did not seem overly tight. Under torqued possibly? I don't have a torque wrench here with the bike. Is proper torque about 10-12 ft /lbs for the head bolts? Any other thoughts from the pics? I don't think there is much leakage coming from the exhaust gasket now, but I have another muffler ordered because of the prior bent muffler flange I tried to straighten. Thanks John
 

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Chainlube

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Here are some pics of the head and gasket. Looks like oil is seeping around between the head and gasket.
Once the bolts broke loose, they did not seem overly tight. Under torqued possibly? I don't have a torque wrench here with the bike. Is proper torque about 10-12 ft /lbs for the head bolts? Any other thoughts from the pics? I don't think there is much leakage coming from the exhaust gasket now, but I have another muffler ordered because of the prior bent muffler flange I tried to straighten. Thanks John
That head gasket had uneven tension on it, the front right portion is crushed more than the intake side. If you have or access to a wire wheel, then clean the head off with that. Get a sheet of sandpaper 150grit?? something like that and a known flat surface and sand the head mating surface so it seals even. Give it a few good swipes and then check it for straightness, easy to see some areas not sanded at all.

Use a new gasket putting it back together.
 

Joast

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Thanks, I don't have access to a wire wheel but can sand it. Are you talking about the surface of the gasket- or the head -or the cylinder top or all of them? Here is the new gasket I have --will it be ok just to get it back together? I only have a 1/2 in drive torque wrench and will need to get the smaller 1/4" referred to by Damien above. Thanks for the help. John
 

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Chainlube

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Thanks, I don't have access to a wire wheel but can sand it. Are you talking about the surface of the gasket- or the head -or the cylinder top or all of them? Here is the new gasket I have --will it be ok just to get it back together? I only have a 1/2 in drive torque wrench and will need to get the smaller 1/4" referred to by Damien above. Thanks for the help. John
Just the part of the head that touches the gasket, we usually sand them on a flat surface so we can tell they're flat and not cast poorly.

Doesn't take much a few swipes and you'll be able to tell if it's flat, I've had one that rocked on the sand paper before I sanded. That's a bad casting.
 
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