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Discussion Starter · #1 ·
bike is 2007 suzuki m50, with 18K miles, show room condition.

it had a knocking noise matching with the rpm. we (with my mechanical engineer wife, our first big job) took it apart and figured that piston clearance was too big. piston and the cylinder had scratches. we replaced and the piston with a new one. we tried to do everything by the book as we otherwise did not know what to do. an automechanic friend of mine honed the cylinder just a bit to smooth out the scratch.

we put it together. bike started, though it took a while, it did not want to idle itself, so i kept the throttle just enough so it runs comfortably. then i noticed oil dripping from where the muffler is connected to the front cylinders' exhaust. i had not applied any permatex gasket or whatsoever. also before i took apart the engine, th muffler was a cobra and now i put the original one. would this cause the leak? i dont think so.

Now it has been more than a year we started this and we deeply regret to even start, my wife is giving up among so many other responsibilities, we just are desperate and angry now. we dont know what to do with the bike.

any ideas or speculations about the potential cause of oil leak?
 

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Hmmm..first, make sure it is really oil. It would not uncommon for black liquid to drip out of the exhaust that is really just condensation mixed with the black sooty carbon built up on the inside of the exhaust. It could also be engine coolant mixed with the carbon residue- see item three below.

If it is really oil, there are three probable causes. The first is that new piston you put in. I assume you replaced the rings also. Did you use OEM? Are they properly gapped? Did you install them with the gaps not lined up with each other? Are they the type that needs to warm up and run a bit before they seal? Was the cylinder honed to the proper level, i.e not too smooth and not too rough? Was the cylinder honed to the point where you should have put in a larger set of rings? Damaged/ improperly sized/ improperly seated rings will allow engine oil to get from the crankcase to the combustion chamber, and then get pushed out the exhaust pipe.

The second is the valve train. If a valve seal is not seated or was damaged, it will allow oil to get down into the combustion chamber from the head.

The third is the head gasket. If it was damaged or is not sealing correctly then oil and or water cold be entering the combustion chamber and then go out the exhaust.

Do you have an air compressor or access to one? If so, rent or borrow a leak down tester. Hook it up, and put in the appropriate air pressure into the combustion chamber. If you hear air leaking out the exhaust, it is the head gasket (check for oil in the radiator or a drop in coolant level). If you hear air coming out the engine breather, it is the rings. If you don't hear air leaking but do show a significant drop in the leakdown test, it is most likely the valve seals. My money is on the rings.
 

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Discussion Starter · #3 ·
Hi DrBob,

Sorry it took a lobg while till we finally got back to work on the bike.

As we were about to take the engine off of the frame the second time, we noticed that the bolts around the valve covers were not tightened, almost not even hand tight. thus your theories were proven right: "The second is the valve train. If a valve seal is not seated or was damaged, it will allow oil to get down into the combustion chamber from the head. The third is the head gasket. If it was damaged or is not sealing correctly then oil and or water cold be entering the combustion chamber and then go out the exhaust."

Now with the new battery it starts right up and no knocking noise and no oil coming out of exhaust.

We have one problem however: the gears are not shifting. neutral light never lights up. I start by squezing the clutch i let the clutch go and it idles well in neutral but N light is not on. I push the gear down to one, nothing happens, does not engage. I push it up, it goes to second gear I think.

I suspect we might have over torqued the clutch plates. I remember we broke two bolts and replaced them while installing the clutch plates.

Any opinions?
 

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Discussion Starter · #4 ·
with the bolts around the valve covers, I dont mean valve cover bolts, the other larger and deeper bolts that connects the top of the engine to the rest.
 

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Glad you got it running- failing to torque the head bolts would certainly have mimicked a blown head gasket.

The clutch plate torque spec is usually given in inch/feet and not pounds/feet, so it is easy to overtorque them. It is also possible that you did not get the shifter put back together and adjusted correctly. Also make sure the neutral switch is hooked up and positioned correctly. And also make sure the clutch is adjusted correctly- not just the cable, but the actual clutch.
 
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