How do I test my compression?

[Renegade88]

How do I test my compression? without a compression tester? I have a pulstart.

 

[mcvickj]

If you have had the engine since it was new you should be able to judge the compression just by pulling the engine. I have heard of a few tips but I don't remember em off the top of my head. I am sure someone else will chime in. You could also take it to your LHS and they should be able to tell you.

 

[Renegade88]

Compression test

I have had my engine since new. Now that its run in the compression is not the same as it was. I can pull the pullstart and all the engine does is make a plopping sound. But it starts fine!

 

[Candyman]

One thing that's a dead giveaway for low compression is whether you can turn the flywheel past top dead center by hand. Just take your finger and rotate the flywheel counterclockwise. When you reach top dead center, you shouldn't be able to easily turn it past that peak compression by hand. If it pops over easily, compression is too low.

 

[Renegade88]

Not another engine gone!

F#$% I have just taken a day to run this engine in properly and now it seems like its toast. Should have gone for the OS.

 

[Akina'sMtx-2]

Originally posted by Candyman
One thing that's a dead giveaway for low compression is whether you can turn the flywheel past top dead center by hand. Just take your finger and rotate the flywheel counterclockwise. When you reach top dead center, you shouldn't be able to easily turn it past that peak compression by hand. If it pops over easily, compression is too low.

I 2nd this. If your able to use your finger to turn the flywheel over easily over top dead center, then your engine pretty much needs a rebuilt. This is with the glow plug and head in place.

 

[chrisexv6]

Hate to resurrect an old thread, but I was wondering if anyone could give some idea of how much force should be required to turn an engine over TDC by hand with the plug and head installed.

Right now, I can turn my engine over TDC, but there is at least some resistance as it gets there and goes over TDC. Should I not be able to do it by hand AT ALL? If so, I guess my engine is in trouble.

Thanks, and again I apologize for the old thread resurrection.

-Chris

 

[mcvickj]

You should be able to turn the engine over by hand. When the piston comes to TDC it should almost feel rather stiff but if you use your thumb you will be able to turn it over. I hope that gives you some kind of idea. Someone else will likely stop by and they might have a better description of what it should feel like.

 

[Akina'sMtx-2]

If you feel some sort of resistance, then your engine still have compression. If your able to turn the engine over with out trying, like turning a CD on a discman, then the engine needs a new piston and sleeve.

 

[Kuma]

The flywheel turning method is the best way, but sometimes with a pull starter you can test by slowing pulling the cord to TDC and see if it picks up the rear of your RC vehicle. This won't work on a warm engine though, my GS 21B01 after 2 gallons and OS 21RG-X after a gallon and half still picks up the rear of the MBX when I pull the pull start cord.

 

[RobH]

Originally posted by chrisexv6


Thanks, and again I apologize for the old thread resurrection.

-Chris

there is nothing to appologive for. you found this thread via searching obviously and that's more than most new members do. in the mean time, we found out the lifting the car via the pullstart method.

welcome to RCNT

-Rob