Compression and break in on 900 rmk?
- Thread starter Gmiller
- Start date
C
ckspeed
Member
What are you getting for compression?
I was about to ask this too as I'm chasing a weird problem, I tested mine with a SLP head and I'm getting 128/123 at about 1200 ft, checked a friends with stock head and got about 120/115.
Also need to remember, these little gauges come in a wide variety of qualities and accuracy can vary somewhat wildly.
I dunno what it should be though, I'm curious too
I was about to ask this too as I'm chasing a weird problem, I tested mine with a SLP head and I'm getting 128/123 at about 1200 ft, checked a friends with stock head and got about 120/115.
Also need to remember, these little gauges come in a wide variety of qualities and accuracy can vary somewhat wildly.
I dunno what it should be though, I'm curious too
Last edited:
C
ckspeed
Member
I guess i should say im at 9500 feet, i know i should premix my first tank of gas with the new pistons, but what else should i do? Does anyone know what the compression should be? i haven't tested it yet but will soon! I do have the SLP head as well!
Thanks
Grant
Thanks
Grant
Increased Altitude decreases compression.
Changes in temperature influence compression.
Oil concentration on the cylinder/pistons walls influence compression.
The most important parameter to consider is the pressure difference between each cylinder. A variance greater than 15% my lead to problems.
As a general rule of thumb minimum compression above 100 is okay (remember the influences) Most will rebuild below 115.
Above 115 is normal for a big cc
Above 125 is great
Above 160 and something is wrong.
Changes in temperature influence compression.
Oil concentration on the cylinder/pistons walls influence compression.
The most important parameter to consider is the pressure difference between each cylinder. A variance greater than 15% my lead to problems.
As a general rule of thumb minimum compression above 100 is okay (remember the influences) Most will rebuild below 115.
Above 115 is normal for a big cc
Above 125 is great
Above 160 and something is wrong.
C
ckspeed
Member
Hmmm, no I don't that's right. At 1200 feet my atmospheric pressure is about 14.0 psi, and my compression is approximately 13:1, so that would give me 182
DonBrown, what altitude are you using for your info?
Finally got it completely together! Started on third pull with the new pistons! I bled the coolant system, do i have to bleed the oil or will that do its own thing? How much oil would you recommend i mix with my fuel? Obviously i have not obtained an owners/service manual yet or i would be not be asking but THANKS FOR YOUR HELP
Grant
Grant
Hmmm, no I don't that's right. At 1200 feet my atmospheric pressure is about 14.0 psi, and my compression is approximately 13:1, so that would give me 182
DonBrown, what altitude are you using for your info?
I usually ride around 8000 so when I check it is between 7000-9000 feet.
Remember the most important is the difference between cylinders.
Also, the influences can make a BIG difference.
C
ckspeed
Member
Yeah, these are all cold checks and about 50 degrees ambient air temp.
Anyone know how to translate psi (as it relates to compression) for any given altitude. Pilots??
Maybe this will help?
http://www.dragtimes.com/da-density-altitude-calculator.php
GreenSkyAdventures.com has something similar somewhere on their web site, or can search for Density Air Calculator.
H
^^^^^^^^^^^x2
