New update. Riding around yesterday and pulled back into the garage and noticed small black spots of dark colored oil on the front of the engine. Looked like a gasket might have blown or something but I couldn’t tell. I wiped it down and rode down the street one more time to see if they re-appeared. Once I got to the end of my street all the sudden the engine rpms skyrocketed suddenly and then the engine died and now I can’t even get it started. I believe the piston is moving freely but I can’t get the bike started at all. The head gasket doesn’t seem to be blown/leaking at all but maybe the gasket the seals the cylinder to the crank case? Is there anyway to diagnose which gasket blew if this is the case? Right before all this happened I was just starting to realize the bike would always work really well before the engine got hot. Once the engine was hot I started to have all the issues I’ve been listing above... would a blown gasket cause this?
Finally got the Mack Mag built!
- Thread starter Kpi890
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FurryOnTheInside
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If the oil is blackened then it has to be the head gasket or exhaust gasket. Why would there be enough pressure to blow the exhaust gasket if you're running the exhaust muffler capless? You might try taking the muffler off and blowing through it to see if it is blocked up with something. Idk why it would be. You're not over oiling the premix. Still, it sped up when the leak happened? So that is the one I would check first.
Head gasket failure normally just causes low power I believe.
Same with crank seals, low power, but there should be no burnt and blackened oil.
Base gasket, same as crank seals.
Sudden high revs is typically an intake vacuum leak, but there should be no burnt blackened oil there! :/
I'm guessing your muffler has been blocked the whole time and that's why you noticed little difference when running it with the cap vs slightly better running it capless.
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So the only gasket that would cause the black oil spatter is the head gasket or exhaust gasket?
I wonder if this high compression head I have on here is not helping anything on this build. May just be running it too hot with too much compression that’s not needed, but I’m not sure. I guess when I get home I’ll pull the head off and see what’s going on if I can tell the head gasket was blown I’ll fix it if not I’ll pull the cylinder off and see if I can find anything there causing any issues. And after all that if I don’t see anything I’m on the verge of replacing the motor flat out. I have a brand new Zeda80 in a box waiting for another build but this one has me so frustrated I want this bike to work out for me.
FurryOnTheInside
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That is my understanding.
I thought you have a new exhaust coming? Have you had the muffler off to check for blockage/ restriction?
Yea I took the exhaust off yesterday to put the expansion chamber on there and it was not blocked. I’m starting to believe that my head has too much compression for this engine because when I saw the dark oil spots I wiped a clean paper towel all around the exhaust manifold and there wasn’t anything on it. When I get off work I’ll pull the head off and see what’s going on but as of now the engine won’t start so I’m hoping to find some problem so I can fix it.
FurryOnTheInside
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How much cranking pressure does it have? And where is the dark oil coming from? :/
I never checked the pressure on it but once I get home I’ll pull the head and see what’s going on. I know it had a whole lot of pressure though because it was always difficult to get started compared to engines in the past I’ve had with stock heads
FurryOnTheInside
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Picture 1 is that pitting, that speckled appearance? If so that could be from running lean or high compression I think.. The scratches on the crush ring could be a source of a leak or maybe they're not enough to cause a leak.. Can you feel them when you run your fingernail over them? If so you can spin the head on very fine wet n dry paper on glass to make concentric rings of scratches instead.
Picture 2 is the wet left side from a leak or did the oil just run over there after you loosened/ removed it? It's the stock aluminium gasket so I already hate it (prejudice lol) what is the squish gap measurement with this 0.7mm gasket? Do you have a spare, or any of the copper head gaskets?
Picture 3 are the rings in good order and correctly positioned with the gap over the locating pun in the piston? Are there any of those suspicious speckles on the piston?
Picture 4 is there any trace of the blackened oil in the crankcase or is that just a bit of scorching on the base gaskets.
I would like to see the top of the cylinder too. Also you could check inside the mag cover and the clutch cover to see if any fuel is present (from a crank seal leak) just in case.
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