Went to Loundon yesterday for the USCRA races. We had a Formula 160 bike (#305) that we were sure was ready to go. There had been a few problems with the bike but we were sure that we had eliminated each one.
Unfortunately this wasn't the case. There had been a persistent oil leak into the area of the front sprocket. We had first suspected a leaky oil seal and replaced them all. However that didn't solve the problem. We then suspected a pumping problem that was causing pressure in the crankcase to push oil out. The Honda 160 engine has a 360° crankshaft where the pistons rise and fall at the same time. This causes a high pressure when they descend and a low pressure when they rise. At sustained race speeds this can cause problems. To counter this we put in a second, larger breather that vented directly into the crankcase.
This seemed to work in our limited testing and we left for the track. The first practice laps revealed that the problem was not fixed. Oil covered the left rear of the bike, most dangerously, the left side of the rear tire. All the work and money for race entry seemed wasted.
One of the other racers told us that it was common for the rubber seal that passed the alternator wires through the left cover to harden and shrink. This could allow the oil to pass through. While not a problem when riding on the street, sustained red line running down the front straight would push the oil past in large quantities. So off to Concord (the nearest town of size) in search of an auto parts store. $50 later I was armed with red and blue RTV, extra oil, and everything else I could think of needing.
Back at the track I tore off the left cover, wrapped the seal with rubber tape and then coated everything with Hi-Temp RTV. Hurrying, I got it all back together in time for the first call for our first race. We felt confident and the bike got a good start off the line. However, it was last around on the first lap and came into the pits on the third lap. The rear tire was again coated in oil. We were devastated! There was nothing to do except load it on the trailer and head home. It was a long, quiet trip.
At home it was very strange. I pulled the drain plug to let the oil drain overnight so I could look at the engine today. By now I'm wondering if the case is cracked or has a porous section. When the drain plug was removed instead of a rush of oil I only got a small, slow stream. Then there was a burp and some more oil came out. Sort of like when you hold a bottle of oil upside down and oil drains until it needs air, then it burps, and then more oil comes out. This was really strange! I blew into the breather tube and there was free space through the tube and out the drain hole. No reason for the air burping.
Now for strange part #2. Only about half a cup of oil came out. Could that much oil have been lost in 3 laps? The normal capacity is 1 liter and I had checked it just before the last race. Now I checked it again and it showed FULL with bright clean oil!!! With the drain plug out and the oil drained. And, yes, I wiped the dip stick before I inserted it to check. In fact, I checked it twice to make sure.
I am totally baffled! My plan is to pull the right (clutch) cover first to see what clues may be there. Then I'll pull the left (alternator cover) to look for the leak. If you have any suggestions, please leave them in the comments section. I need all the help I can get on this one. I'll follow up with pictures and reports of progress in the next few days.
J: I think your "ketchup bottle" analogy could be nailing it. I'm guessing the oil is going up into case/head, and it's blocked coming out of there, and can't come down; the vacuum produced would hold the oil up in the top of the engine, AND above the oil pan. Of course, the dipstick showing full kind-of contradicts that ... but if I'm correct, look for leaks higher up, like around the head and head cover gaskets, and oil trails along the frame and subframe on the left . Twilight Zone for sure. Good luck.
ReplyDeleteDCT
When you said that you replaced the oil seals I expect that you were referring to the countershaft, clutch rod and gearshift shaft all under the sprocket cover.
ReplyDeleteCould one of the replacements been 1mm oversize on the ID?
How about the crankcase halves mating surface in the area around the sprocket.
ScottK
St. Louis
Running an engine at racing speeds and loads creates an enormous amount of blow-by compared to normal street running. While at the track did you eyeball the breather system of other bikes? I've always been amazed at the size of breathers on race bikes, huge 1" diameter tubes and the like. Perhaps you just need a much bigger breather.
ReplyDeletereally clean the engine, run it fast briefly then blow some talcum powder around the suspected leaking area. The talcum powder will stick and turn brown where the oil is. I am also leaning towards the breather, try a catch bottle.
ReplyDeleteHow are the breathers routed? Do they have a PCV valve? Do they both go to a catch can and if so what is in that can after a hot run?
ReplyDeleteThe right side cover should drain into the sump and yet it sounds as if your is not.
I'd pull the right engine cover first to see what was happening in there.
Then I'd connect an air supply to the dip stick hose, blank off the top breather hose and listen for leaks on the left side. Or blank off teh dip stick hole and pressurize the top cover breather hose.
Last question: 4 speeds or 5?
When doing a 5 speed conversion, the crankcase halves usually distort and leak.
J, I had a slightly bent clutch push rod once in the area of the seal. Another time the crankcase vent at the top of the engine was full of clay but still managed to pass air. Discovered during engine assembly.
ReplyDeleteI purchased a new shift shaft once labeled for a 160 that was either smaller or larger in diameter than a 160. I think it may have been for the CL-175 sloper 5 speed.
Good luck !!