Nytro Compression Issue

tjc · Apr 18, 2013

So I have a turbo nytro and I am afraid I may have damaged the engine. I tested the compression on the stock motor today to end the season. I warmed it up to about 140 to 150 degrees on the digital temp gauge and shut it down then tested it. I have about 2200 miles on the engine with about 600 boosted (hard miles and a little lean a couple times about 13:1 on AFR so I would not be surprised although I didn't really run it long at those levels).

I got around 135-145 PSI plus or minus a couple on all three cylinders. Then we added a little oil to the cylinders and it jumped to about 230 PSI across the board. Does this sound like rings?

It is weird to me that all three are low and all are the same. Maybe this is not out of the ordinary but with my experiences on two strokes it would be one cylinder or the other.

Im going to try another compression gauge to be sure its not my gauge. Any other thoughts? I dont get smoke or anything when it is running.

BOOSTD · Apr 18, 2013

What headshim do you have and what's your elevation. At sea level with a .080 shim we get 150psi on a brand new motor. No headshim is 200+.

tjc · Apr 18, 2013

stock engine - no headshim. I was running low boost.

up-high · Apr 18, 2013

What elevation?

tjc · Apr 19, 2013

sea level - about 1,000 ft.

Just seems odd that they are all about the same?

zebiraross · Apr 19, 2013

Did something precipitate you to check the compression, or were you just checking for no particular reason?

tjc · Apr 19, 2013

not really, I have been running it a bit lean for short bursts (13:1 at wide open with a torco/pump blend at 7 pounds of boost) so I wanted to check. I knew I was pushing it so I wanted to check it.

And before the wolves are set on me I know this is not a good idea. It was just too fun.

up-high · Apr 19, 2013

If its not smoking and runs good, you didn't hurt the motor. But, if your going to keep pushing the envelope, get some low comp pistons( and run 10#) or better fuel. Any 4 cycle motor will show increased compression(especially one with some wear) if you put oil in the cylinders. Better seal better compression. If all cylinders are the same comp, you didn't hurt it. For peace of mind, pull the plugs and take a look. They'll show if you have deto.

julio · Apr 22, 2013

oil

if they are the same and it doesnt smoke or burn oil i would think it fine. the oil will help seal the rings but if you put much in it will also take up some compression chamber volume increasing compression as well. julio

another thing to ponder - when i ran race i pulled the head off my sled thinking i had lost a valve to find carbon build up the on the valve the problem, all the valves had it just one was bad enuff to stumble, after cleaning all cylinders compression came up. yammy makes an additive to clean the carbon out..

tjc · Apr 22, 2013

yeah I did the check per the manuals recommendations from Yamaha. They suggested if it is low you add a couple drops of oil. If the compression goes up it will likely be rings.
I just thought it was weird they were all the same.

tjc · Apr 30, 2013

well my gauge is bad, 205 across the board on a good gauge. Thanks to all who provided input.

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Nytro Compression Issue

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