火箭三R中气缸压缩为零。有人知道原因吗？

[JAPANユーザー]

This may sound obvious but did you ensure both intake and exhaust valves were closed (piston on the power stroke)? We don't want to assume anything here... Is it possible the exhaust valves for that cylinder were on the exhaust stroke when you forced air in the spark plug hole???

Yes, I have confirmed that the cylinder is in compression. From the photo, you can see that the left exhaust valve on the exhaust side is leaking, but the right one is not.

 

[JAPANユーザー]

See my earlier comment about decompressors. They always hold the exhaust valves open until started.

You’ve been committed to a compression problem from the start of this thread. I think the solution is going to be something else much much simpler, but we still need some basic questions answered (see above).

But what I don't understand is why only the middle cylinder has low compression when not starting? There are two valves on each side of the intake and exhaust, but only one valve on the exhaust side has a leak.

 

[Journeyman]

The exhaust valves will never ever close if the bike is not running. I explained that on page 2 of this thread. I have first hand knowledge about this. You have a bike that runs, but idles poorly. I suggest you pursue another theory

 

[JAPANユーザー]

I'm concerned with the color of the exhaust port.....Looks very lean.....NO carbon present.....was or is the valves stuck(from running lean?)
I would spray a light oil WD-40 on the valve shafts and with a spark plug per cylinder removed crank the motor over while watching for smooth valve operation......

I observed the valve moving up and down during startup. However, the exhaust valve has a leak and cannot close completely.

 

[JAPANユーザー]

The exhaust valves will never ever close if the bike is not running. I explained that on page 2 of this thread. I have first hand knowledge about this. You have a bike that runs, but idles poorly. I suggest you pursue another theory

The motorcycle can be started but the middle cylinder is not working, so the pressure value of the middle cylinder is very low.

 

[Journeyman]

Or, perhaps for just one example, the plug is not getting a spark so that cylinder isn’t running and the exhaust pipe would therefore not be hot.

 

[JAPANユーザー]

Or, perhaps for just one example, the plug is not getting a spark so that cylinder isn’t running and the exhaust pipe would therefore not be hot.

I have checked the spark plugs and there is no problem. I even swapped the spark plugs of the three cylinders and the middle cylinder still did not work.

 

[Journeyman]

The compression is reduced by momentarily opening an exhaust valve on the compression stroke of the piston to partially vent the combustion chamber. Reducing the engine compression reduces the force required to kick start or pull start the engine, and allows the use of smaller less powerful electric starting components.

Engine Decompression Systems - Motorcycle & Powersports News

A poorly maintained decompression system can result in poor starting and excessive strain on starting components.

www.motorcyclepowersportsnews.com

 

[JAPANユーザー]

The compression is reduced by momentarily opening an exhaust valve on the compression stroke of the piston to partially vent the combustion chamber. Reducing the engine compression reduces the force required to kick start or pull start the engine, and allows the use of smaller less powerful electric starting components.

Engine Decompression Systems - Motorcycle & Powersports News

A poorly maintained decompression system can result in poor starting and excessive strain on starting components.

www.motorcyclepowersportsnews.com

Thank you. Next, I'll open the cover and check the reducer. Can you tell me the valve clearance data?