Hey guys,
I'm currently rebuilding a CA95 from the ground up. I had the engine rebuilt at a shop in Michigan. I've since put 200 miles on the bike. At about 100 miles the right cylinder started burning oil.
At the 200 mile mark I did the following:
- Valve clearances
- Ignition timing
- Points clearances
- New spark plugs
- Carburetor re-tune
- Cylinder head re-torque
- Oil change
The bike is still burning a considerable amount of oil out of the right cylinder. With the bike warmed up I ran both a compression and leak down test. Here are the results:
Compression Test
Right Cylinder
Dry 80psi
Wet 95psi
Left Cylinder
Dry 75psi
Wet 80psi
Leak Down Test @100psi
Right Cylinder: 2% leak
- Heavy airflow from cylinder head breather tube and oil fill cap.
Left Cylinder: 5% leak
- Heavy airflow from cylinder head breather tube and oil fill cap.
- Light airflow from exhaust & opposite side spark plug hole
The manual says compression should be 130psi, so obviously there's an issue here. The airflow out the cylinder head breather and oil fill cap makes me think the rings are leaking pretty bad.
Again the bike only has 200 miles on it since the rebuild. Should the rings have seated and be sealing better by now or is this normal until about the 500 mile mark? I've been finding conflicting opinions on this. Some say burning a oil up until 500 miles is normal. Some say the rings should be seated within the first 20 miles.
Thanks for any help,
Dave
Rebuilt Engine Cylinder Smoking - w/ compression results
There shouldn't be any smoking at 100 miles. Once any oil used on assembly burns off there should be no smoke.
What kind of shop rebuilt it? Did they re-bore it or just hone it? If they bored it, where did they get the specs for the clearances? Rings not staggered correctly could contribute to the problem. In any case it sounds like a redo by the shop is in order. 63 CA78
Ok, so today I realized I made a big mistake when running the compression test. I completely forgot to hold the throttle open. I'm used to doing it in cars where there's a bypass valve feeding air in.
I of course remembered this after we already pulled the engine out and took it all apart. What we did find was that the ring gaps were not spaced correctly. Some had the gaps aligned. We also found that there wasn't an o-ring around the oil journal which was letting oil in passed the headgasket on the right cylinder. My question is how much would not having the throttle open hinder the compression results? In both cases I ran the test until the cylinder stopped increasing compression, which were the numbers above. So now I need some opinions. We found the obvious leak causing the burning oil via the missing o-ring, and we found that the ring gaps were not set properly. We also heard through leak down that there was a considerable amount of air coming from the crankcase and cylinder head breather. Would you still pay to send the engine out to a shop to re-hone, put in new rings and check measurements of the cylinders? Or would you put it all back together with the fixes to the o-ring and ring gaps and retest the compression correctly? We're already way over budget on this bike so I'd like to not spend even more money if it isn't needed. Thanks!
My background is as an aircraft engine mechanic. I have rebuilt several of these engines, bored oversized and honed. Each time I got no smoke at all, and compression was around 125-130 using the pump up compression test. (Denver, Co altitude) Each time I got a bit of air out the breather and oil cap using the leakdown test... more on that later, but in each case I personally knew the cylinder dimensions and bore job quality, as well as the hone pattern and roughness.
If I were you I would put it back together because it seems you found the source of the oil getting into the cylinder and causing it to smoke. Was there another indication of poor compression like being sluggish or running poorly? Chances are the smoke caused a great deal of concern, and that's why you took it apart. Also I would apply a little (a little goes a long way here) sealant around the o-rings and use a new head gasket, torque it very gently, wipe up anything that squeezes out (hopefully you didn't use too much and nothing comes out) and let it sit overnight. This way the sealant can firm up a bit, then when you final spec torque, you will have a great seal here and wont squeeze sealant anywhere you don't want it. I'm not the best typist, and I don't want to drone on forever, but some things to think about on compression tests on an engine this small: 1) When using the pump up gage, does it have a check valve? (it should if you want any results you can trust) Is it a sensitive check valve that opens at very low differential pressures? Is the check valve in the spark plug boss, or is it halfway up the tube to the gage? Is the throttle open? Now imagine how small the volume in the combustion chamber of this engine is when the piston is at TDC. If the check valve is 1 foot up a tube between the spark plug boss, and the gage, (as many cheap ones are) then you have effectively doubled the volume of the combustion chamber, and the reading will never be very high. This is so because each time the cylinder exhausts, and then comes to compression again it must compress the air in the combustion chamber AND the air in the hose (prior to the check valve) from scratch. This effect is considerably lower on engines with LARGE combustion chambers, because the hose volume is proportionally low compared to the combustion chamber. The CA95 combustion chamber is tiny. 2) Now imagine that it takes 10psi differential pressure to open the check valve. The reading on the gage might be 10 psi lower than actual because near the end of the test, the higher pressure in the combustion chamber may not be enough to open the check valve, and read on the gage. I personally only use this type of gage if the check valve is very good condition and located IN the spark plug boss. Its harder to find these but they are out there. Don't use a tire Schrader because the spring is too stiff. 3) **The following is opinion** Leakdown tests are great for locating faulty valves, (because there should be NO leakage here during this test, which you can hear) but be careful on taking too much away from how much leakage there is or how much air sounds like is escaping. This test should be performed while at TDC, with the engine hot ( that's when the piston is biggest, and roundest...Aluminum expands a lot more than the cylinder casting) and sometimes tiny movements make a great deal of difference on the amount of leakage. This is easy to do with an airplane, because you have a 7 foot lever on the crankshaft called a propeller that you can move a bit to get the best test. This is really hard to do on a motorcycle engine. The leakdown tester I use is designed for aviation engines and is calibrated for a piston approximately 6-7 inches in diameter. A lot of leakage is pretty normal over a circumference that large. The CA95 piston is tiny! Not sure how much leakage would be normal or what your gage is calibrated for, chances are its a big engine. 4) I would torque the head and leave the carb off... with the engine not even installed in the bike yet, you can use the electric starter to turn it and get a pretty good idea of the compression. Especially now that you know you did the test wrong before. Hope this helps.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
