Crankcase Pressure Test Fail

[Idratherbehunting]

I removed the powerhead from a 1988 Classic 50. I am trying to figure out the problem with this motor. I have gotten to the point of pressure testing the engine and it will not hold any pressure. The first time I pressure tested it air was leaking by the lower oil seals. I removed the seals and installed new seals and bearings since I was in there. I went ahead and did the same on the top end.

I have the intake ports closed off and the exhaust port sealed off. I am using a bicycle air pump to pump air into the #1 cylinder at Bottom dead center. After a few pumps I begin to hear/feel air coming out of the "water inlet tube" port. To my knowledge at no time should air be able to cross from the combustion air (both intake and exhaust air) and into the water jacket.

I removed the cylinder block cover, removed the old gasket and used gasket maker to make another one. Next I removed the exhaust manifold and did the same thing. I am using the high temp gasket maker to try and find the problem while waiting on the actual gaskets to arrive. The air is still coming out the "water inlet tube". Am i missing something? The gasket between the powerhead and the exhaust plate is a brand new gasket as well.

 

[schematic]

inlet, exhaust and water all congregate through several passages. Tricky to do a pressure test.

 

[racerone]

Judging by the information posted I would say everything is normal.------What is your engine doing / not doing that led you to doing this testing ?

 

[Idratherbehunting]

The original problem is that it will not make full power. The engine bogs down at half throttle, at the point that the throttle begins to open in the carb. I have rebuilt both carbs, rebuilt the fuel pump, one mechanic said stator another reed valves, changed those out. The entire engine was taken apart and put back together and it still runs the same as before.

I don't think pressuring a cylinder, thus air exiting into the exhaust manifold should be able to work its way into the water jacket? I also noticed there was a clean spot inside the exhaust manifold whereas everywhere else was black. Starting to think water is be forced into the engine at higher RPMs causing the engine to bog down. As the water pressure increases this could be forming a mist into the engine? It will rev high RPM without a load. I did notice the spark plugs had drops of liquid, at the time I thought it was just oil/fuel, that could have been water droplets.

 

[GA_Boater]

The exhaust is water cooled. The water from the water jacket exits the motor through the exhaust. I would expect the water tube to hiss by pressurizing a cylinder, especially one at BDC with both ports wide open.

Have you checked compression? And for a strong spark.

Are both the exhaust cover and plate flat?

 

[Texasmark]

If you are getting water into a cylinder it will be spotless (piston crown and spark plug) as compared to the other 3.

The exhaust gasses go into the exhaust manifold which has a cover plate. On the other side of that cover plate is cooling water independent of the engine cooling water and obviously a cover over that. Both exhaust and exhaust cooling water exit into the mid section.

 

[Chris1956]

Remember, the individual cylinder crankcases are mostly sealed from each other. Cylinders 1 and 2; 3 and 4 share carbs, but the reedblocks and bearings seal them from each other. In other words, I do not think your crankcase pressure test is valid.

Your issue could simply be one of lack of available power, which is not usually associated with crankcase compression. First test is compression. If that is good, are all cylinders firing?

 

[Idratherbehunting]

Spark and cylinder compression test both are good. Those were the first things checked. I also hooked up a timing light, found TDC and marked the flywheel with numbers. Then tested to make sure each cylinder was firing correctly.

The leak is somewhere on the exhaust side because if it were before the compression stroke then the pistons would be clean as mentioned (and the motor still runs).

Here is a link as to what I am trying to do http://www.klemmvintage.com/airleaks.htm

I'm starting to wonder if this engine was overheated and I possibly have a lot bigger issue on my hands. Motor was bought but I was only able to see it run with muffs and conduct a compression test. I have never been able to get it past half throttle without it completely dropping RPM.

 

[GA_Boater]

The test linked above is invalid. Air-cooled bikes and water-cooled outboards are 2 different animals.

Not to be picky, but what are the compression and spark test results? And the condition of the exhaust cover and plate?

 

[racerone]

This pressure testing is a good idea.-------But it is only an idea.-----You are aware that this motor has 4 seperate crankcases !.-------How are you testing the 4 crankcases ?------Is exhaust tuner clear of any blockage ?---------Have you removed intake / bypass covers for inspection of pistons and rings ?---------Posted results of a compression test ?-------Does spark jump a gap of 3/8" on all 4 leads ?-----------Is spark properly timed ?--------Have you checked the flywheel key ?

 

[Idratherbehunting]

When I pressure tested I have 1 cylinder at bottom dead center, therefore air will pass into both the exhaust and intake manifolds and then into the crankcase and exhaust tube. I have the two intake ports (carburetors) blocked off with a rubber gasket. I took off the carbs then fitted a piece of rubber between the intake and the carbs. I then have to motor upside down and have plugged the exhaust tube. So by forcing air through the spark plug hole, the air should not be able to leave. What concerns me is how this air is getting into the cooling jacket? I understand I am not check combustion chamber pressure

Spark was tested using a actual spark tool, from what I remember it was able to jump about an inch, so no problem there. The power head has been removed and the exhaust is completely free of obstructions.

When I replaced the reed valves, I ended up removing the whole crankshaft with the pistons. Rings and pistons look OK. The engine is properly timed using a timing light and the manual. The flywheel key is installed.

The compression test had all cylinder between 125-128PSI.

The exhaust cover and plate look in good condition. The inner cover is all black with the exception of 1 area about 2 inches by 1 inch, that area looks cleaner (not an area where a gasket covers it). The water side of the exhaust manifold looks normal, light tan discoloration from the muddy water.

Could that cleaner spot be where water is going through a bad gasket into the exhaust manifold?

Thanks for all the help, I can post a few pictures if that helps.

 

[Chris1956]

Well, the cooling water is allowed to mix with the exhaust, above the exhaust tube. Also, the idle relief ports are connected to the exhaust tube and water jacket. I therefore do not think you can seal the exhaust ports easily.

You should not need the rubber gaskets under the carbs, as the reed valves are the only seal that matters.

I doubt your problem is in the crankcase sealing. Have you checked and set max timing advance? Have you checked the main jets in the carbs to see if they are clean? Have you checked the float, inlet needles and float height? Have you pumped the primer bulb when the motor bogs, to see if you have a fuel delivery issue?

 

[clanton]

You have to block the exhaust port on the block not at the exhaust plate and cover for testing, cover and plate should be removed.. Each cylinder is not sealed from the other cylinder 100%, so you will have some leakage between cylinders.

 

[clanton]

You said throttle plates opened at half throttle, I think plates should open sooner, link&sync.

 

[clanton]

Was the stator tested with the engine running at idle and 3000 rpms with a peak reading meter?