120 compression after new top end

[Ladle58]

I'm sure this has been discussed many times over here.  Not finding what I'm looking for though after rummaging through the forums. (I'm also a newbie) 

.020 over bore by reputable company and fitted to new weisco pistons and rings. Installed very carefully myself and proper break in.  Leak down test performed.  Still getting between 115 and 120 on both sides. Seems to run fine but wanting to know what I'm missing. If I had to question anything I did it would maybe be the leak down test as I made my own tester. Wondering also if a leak somewhere on the bottom would cause lower compression? 

Any help as to where to go from here would be greatly appreciated! 

[Canadianshee]

How long did the leakdown test hold 6psi for. Do you have stock head or coolhead with domes.

Sent from my LG-H873 using Tapatalk

[registered user]

if it runs good then just ride the dam thing. personally i find a compession gauge mostly useless for any relevant info. u can use it to see if both sides r the same but beyond that i wouldnt lose sleep over it

[Canadianshee]

Should still repeat leakdown to be sure since you not confident, then plug chop it

Sent from my LG-H873 using Tapatalk

[Ladle58]

Thanks for the input guys.  That is the exact path I was heading down.  Originally, was just going to ride as is. That being said, I'm not the type of person that can relax and enjoy the ride if I feel something isn't right. Plan was to perform a better leak down test and do a plug chop. So glad to hear someone conquers.  Any other input on this topic will be appreciated. 

[Canadianshee]

When you repeat leakdown just make sure it hold 6psi for about 6 min if not spray around with soapy water to find leak.
When i did mine I could not find the leak, but ended up being a leak on pressure gauge. So check your equipment too.


Sent from my LG-H873 using Tapatalk

[Ladle58]

I need to find a gauge with a smaller range like a 0 - 10 if there is such a thing.  

 

Plug chop won't have anything to do with compression correct?  And would a small leak effect compression?

Edited December 17, 2018 by Ladle58

[Canadianshee]

Correct plug chop is seeing how your jetting is lean, rich ect.
A smaller increment gauge would be a good idea.
How long did it hold pressue with your current set up.

Sent from my LG-H873 using Tapatalk

[Ladle58]

I gave up at 5 min....  it was really hard to tell with that gauge. All I can say is it looked like it may have dropped a tiny bit. Which, if accurate, maybe .25 at the most if I had to guess.

[Canadianshee]

Well if you want to make sure.
Build a better tester for pressue testing. And retest. 6 psi for 6 min. If it dosen't, check all your fittings and spay motor with soapy water to find leak.
Make sure you are using the correct end for your compression tester, must be same length as the spark plug goes in. Hold throttle wide open and kick till neddles does not move
Did retourqe everything after heat cycle.


Sent from my LG-H873 using Tapatalk

[Ladle58]

Yep

[97Screamer]

With a stock head at sea level your compression should be 120psi. What head/domes are you using and what is your elevation? Most of the flex hose compression testers have shorter threads than your plug and in my experience read 5-7psi low. You'll need to get an adapter that threads in as far as the plug for an accurate reading but I usually don't bother to even get mine out of the drawer. No, an air leak will not impact on your compression unless its huge. 

[Ladle58]

Stock head. I am 750 feet above sea level.

So leak down test is good to do for peace of mind but not for compression since if I have a leak, its small.

[sheerider11]

Stock head. I am 750 feet above sea level.
So leak down test is good to do for peace of mind but not for compression since if I have a leak, its small.

Really good chance you are fine. 120 is a good stock number for 750'
Do a leak down, it wont hurt.
But I think you are okay.

Sent from my SAMSUNG-SM-G891A using Tapatalk

[Ladle58]

Cool and thanks.

I plan on picking up 2nd compression tester for back up and troubleshooting. 

Perform better leak down.

Plug chop.

Good to know 120 probably ok. Funny that Yamaha didn't really note compression number for the Banshee.