Supercharged bike blowing oil cap off

TURBO200R4 said:

a bit like holding your nose and blowing...your ears pop...

i have an image in my head can u post a picture

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Tal said:

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why does that look just like me when the dog farts

Crankcase pressurisation could also be leaking head gasket under pressure from high throttle openings. Is it blowing coolant as well???

How much boost are you running?

Ruzz and Warp know.... A comp test may not be conclusive. If your rings are cracked up you may still get near stock compression readings, but have massive blowby when you have boost. If your comp test is ok, rig up a container which can both breath and catch fluid to your rear engine breather, tape the oil cap in place, and go for a short ride, give it the berries and check results. Assuming it is a TTS kit you may have up to 18psi boost. Much more than advertised. I have recorded this on several occasions. If you need pistons etc Jvheli has made an offer. If you have got it apart an want to make it go properly, you can add at least 50hp JUST by fitting cams with timing to suit forced induction and a re tune obviously. I also have some forged turbo/s/charged pistons here still. Going covid-19 cheap. Our $ is worth SFA.... Good luck.

R-III-R Turbo said:

As above, possibly blocked breather but more likely blow-by past your pistons. Do comp test and go from there...

re claviger iirc he was trying to make a slight vacuum in his NA motor crankcase by using the exhaust for a venturi, like exhaust scavenging only this would be crankcase scavenging, to lower wind resistance on the pistons coming down.
I wouldn't try it in this case.

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Could take an old plug, solder or braze air chuck and hose and pressure cyls. with air and listen for leakage. Try and get piston on top and valves closed.

I am not even drinking and I am seeing double

Not any more.

ruzzle said:

Not any more.

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Thank you, my screw up.

warp9.9 said:

You are suffering from the detorats!!!! Check your rear crank case vent your probably blowing oil out it too.
Easily fixed by changing out the bad piston or pistons. That's where your boost is going by and pressurizing the lower crank case!!!! You can scope the pistons to verify or run a compression test. In the picture below the almost white section on the pison edge is the top compression ring.


The only other thing it could be is your rear crank case vent is soaked with oil to the pressure blows the oil cap off. I suggest you try the scope or at least a compression check when you do the compression test make surre all the plugs in the other two cylinders are out.

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I sure hope it isn't the piston.. It only has a few hundred miles on it.

Justin Lakes said:

I sure hope it isn't the piston.. It only has a few hundred miles on it.

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Well we all hope that its something minor. Have you had ther air intake modifications that included a rear crank case filter? If so it just might be extra dirty or you might have puked some oil up in it clogging the filter (soaked with oil) who tuned it? You might want to invest in a cylinder leak down detector. If you haven't had problems before. You might have popped the head gasket. When I did it would blow water out the overflow bottle under high boost. It wouldn't over heat. I could ride it 1000 miles and not blow any water but give her the beans and it would. Usually 10 psi and more. Of course the pistins were damaged at least two of them were. When I blew oil it was definetly pistons. One time it pinched the top ring so it wouldn't float as needed. So it carved up a couple of the liners. I'm not going to say it was a easy fix as that was the time frame when I had never tore a motorcycle engine down before. If you did the blower installation I'm sure you can do the pistons and head gasket. While the engine is still in the bike. First check the rear crank case vent or vent filter if one was installed. Then compression and leak down test. Harbor freight will be your cheapest leak down test kit. They work fine without pissing a lot money away. I even used one to set and test the BOV.