Compression readings?

DAVE BOOS · 11/25/14, 12:04 PM

I've got a 08 R-1 that just started smoking last time we raced it, my son got it to 280 degrees in Dodge City over the 4th of July, melted the stator, I replaced it has run good since then.So I decided to do a compression test on it last weekend before I put it away for winter #1 cyl 165, #2 cyl 155 #3 cyl 162 #4 162, I shot a little bit of oil in lower cylinder next test it shot up to 180, obviously ive got a ring problem. Two guys that we race with that I trust there opinions said to rering it or get another motor, which I am planning on doing. My question is how much variance should there be between cylinders before I become concerned? And also keep in mind that we are at 5600 feet elevation were it was tested at and raced not much lower than that, is there any kind of corrected formula for figuring out what this motor should pump up to (if it was healthy) here at this altitude vs. sea level? I know a lot of guys say they should hit somewhere between 180-200psi? Is it because of altitude that my readings are so low or is this thing just a sick pig? Thank You In Advance! Dave

DAVE BOOS · 11/25/14, 12:07 PM

Sorry didn't mean to put it in the classified section.

BikerTrash · 11/25/14, 12:48 PM

Could it be a valve issue causing the lower compression readings and inconsistant accross them and possibly not a ring issue at all ?

Tom23 · 11/25/14, 2:22 PM

Personally, I would run a leak down on it before I did anything. Compression test can be very misleading.

Bradleyracing86 · 11/25/14, 6:29 PM

What he said ^

jcspringer28 · 11/27/14, 2:54 PM

How much should it leak down in how much time?

TQ29m · 11/27/14, 3:06 PM

It isn't like leaking a 2-smoke, where you're looking for crankcase, seal leaks, on a 4 stroke, it will be steady, either past the rings, or the valves, which you can hear and tell which it is, or even a head gasket, or something worse! I've talked to racers who say they'll be happy at 20%, if it's consistent, and they have decided which it is, so a leak down setup is a good investment, I have one with 2 gauges, which I prefer, Speedy Bill, TAVIA I think is the brand name, has a nice one. Bob

Bradleyracing86 · 11/27/14, 5:12 PM

3-8...

bobby01 · 11/27/14, 5:58 PM

I like to start my motor up and let it slightly warm up. then do a leak down test. Anything more than 15% really needs to be looked at.

11/27/14, 3:06 PM	#7 Re: Compression readings?
TQ29m Senior Member Join Date: Aug 2008 Posts: 6,558	It isn't like leaking a 2-smoke, where you're looking for crankcase, seal leaks, on a 4 stroke, it will be steady, either past the rings, or the valves, which you can hear and tell which it is, or even a head gasket, or something worse! I've talked to racers who say they'll be happy at 20%, if it's consistent, and they have decided which it is, so a leak down setup is a good investment, I have one with 2 gauges, which I prefer, Speedy Bill, TAVIA I think is the brand name, has a nice one. Bob __________________ "Being old, isn't half as much fun, as getting there"! Ole Robert I!

11/25/14, 12:04 PM	#1 Compression readings?
DAVE BOOS Member Join Date: Mar 2014 Posts: 53	I've got a 08 R-1 that just started smoking last time we raced it, my son got it to 280 degrees in Dodge City over the 4th of July, melted the stator, I replaced it has run good since then.So I decided to do a compression test on it last weekend before I put it away for winter #1 cyl 165, #2 cyl 155 #3 cyl 162 #4 162, I shot a little bit of oil in lower cylinder next test it shot up to 180, obviously ive got a ring problem. Two guys that we race with that I trust there opinions said to rering it or get another motor, which I am planning on doing. My question is how much variance should there be between cylinders before I become concerned? And also keep in mind that we are at 5600 feet elevation were it was tested at and raced not much lower than that, is there any kind of corrected formula for figuring out what this motor should pump up to (if it was healthy) here at this altitude vs. sea level? I know a lot of guys say they should hit somewhere between 180-200psi? Is it because of altitude that my readings are so low or is this thing just a sick pig? Thank You In Advance! Dave

11/25/14, 12:07 PM	#2 Re: Compression readings?
DAVE BOOS Member Join Date: Mar 2014 Posts: 53	Sorry didn't mean to put it in the classified section.

11/25/14, 12:48 PM	#3 Re: Compression readings?
BikerTrash Member Join Date: Dec 2013 Posts: 84	Could it be a valve issue causing the lower compression readings and inconsistant accross them and possibly not a ring issue at all ?

11/25/14, 2:22 PM	#4
Tom23 Senior Member Join Date: Dec 2007 Posts: 500	Personally, I would run a leak down on it before I did anything. Compression test can be very misleading.

11/25/14, 6:29 PM	#5
Bradleyracing86 Senior Member Join Date: Nov 2007 Posts: 1,621	What he said ^

11/27/14, 2:54 PM	#6
jcspringer28 Member Join Date: Sep 2010 Posts: 149	How much should it leak down in how much time?

11/27/14, 5:12 PM	#8
Bradleyracing86 Senior Member Join Date: Nov 2007 Posts: 1,621	3-8...

11/27/14, 5:58 PM	#9 Re: Compression readings?
bobby01 Member Join Date: Nov 2011 Posts: 128	I like to start my motor up and let it slightly warm up. then do a leak down test. Anything more than 15% really needs to be looked at.