Compression Tests/KACR and KACR-less - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

 
LinkBack Thread Tools Display Modes
post #1 of 7 Old 08-27-2015, 11:22 PM Thread Starter
OverDrive
 
Join Date: Nov 2009
Location: Lander, Wyoming
Posts: 6,490
Compression Tests/KACR and KACR-less

Quote:
Originally Posted by Tom Schmitz View Post
Based upon the number of reports of KACR failure (it's uncommon, but I attract disaster) and folks saying that they removed their KACR and had no problems, I removed mine.

I have had problems with occasional kickback while starting. Also, if the piston stops on the verge of a compression stroke (don't it always?) I will have to bump the starter to get things going, as there's not enough ooomph for the starter motor to push it through. The battery is new, in good shape, and charged. It always starts on the second bump. This is when cold. Hot is no problem.

Sometime this week I'll be pulling the tank off to install a different banjo bolt at the head. When I do that I'll be putting an exhaust cam with a KACR back on it.

Tom
Tom,
Can you do a before and after 'COLD Compression Test'?

I'd really like to know the limits of the 'starter limiter gear'. If I remember correctly, my buddy Keith C's. bike, was about 154 PSI. Too Much, for the limiter gear!

pdwestman
Modify at "YOUR OWN RISK"!

Still riding my 1987 KL650-A1. 85,000+ miles & counting
pdwestman is offline  
Sponsored Links
Advertisement
 
post #2 of 7 Old 09-02-2015, 10:04 AM Thread Starter
OverDrive
 
Join Date: Nov 2009
Location: Lander, Wyoming
Posts: 6,490
Quote:
Originally Posted by Tom Schmitz View Post
It was bad data, Paul. Defective equipment; found the problem.

I deleted the post.

I have to do it all over tomorrow!

Tom
Tom,
I would not bother going back over it. Not that important.

It was almost convenient, now it is not!

pdwestman
Modify at "YOUR OWN RISK"!

Still riding my 1987 KL650-A1. 85,000+ miles & counting
pdwestman is offline  
post #3 of 7 Old 09-02-2015, 02:14 PM
Pretty in Pink, dunno why
 
Tom Schmitz's Avatar
 
Join Date: Feb 2009
Location: Redondo Beach
Posts: 8,087
Garage
Quote:
Originally Posted by pdwestman View Post
Tom,
I would not bother going back over it. Not that important.

It was almost convenient, now it is not!
Nah! I wanted to know, too.

Here are the numbers, now that the defective 12mm adapter is repaired:

Stock Timing
Without KACR: 177psi
With KACR: 103psi

Timing advanced 1 tooth <Advanced the exhaust cam one tooth, i.e. the "MC Mod"
Without KACR: 175psi
With KACR: 123psi

Each test was repeated three times with no real variation in the numbers. The pressure gauge reached it's reading in four revolutions.

It appears that the MC mod increases starting compression by about 25%, which follows with what I experienced when I did the mod. There was some difficulty in starting from time to time, taking a bump or two to push it through the first compression stroke.

It doesn't seem to affect the true compression, just starting compression due to the change in KACR timing. It's relieving pressure earlier in the compression stroke when there is less pressure available to vent part of the incoming charge. Less stuff goes out the exhaust valve, leaving mores stuff to compress later in the stroke.

The KACR reduces the starting compression by about 40% and, from my experience, is pretty handy. Without it I'd get some nasty noises and kick-back from time to time (usually when hot) and the starter doesn't have enough grunt to spin it up quick. It usually took a bump or two, when cold, to get it going. That seems to follow what you saw with Keith's bike.

One of my plans was to install a Wossner domed piston to bump up the compression ratio. I wonder if I'd run onto the same "too high a starting pressure" issues.

Tom

Tom [email protected]

“On the way downtown I stopped at a bar and had a couple of double Scotches. They didn't do me any good. All they did was make me think of Silver-Wig, and I never saw her again.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

Sting like a butterfly.
Noli Timere Messorem

Last edited by Tom Schmitz; 09-02-2015 at 08:42 PM. Reason: edited for Clarity, whoever she is...
Tom Schmitz is offline  
 
post #4 of 7 Old 09-02-2015, 08:36 PM Thread Starter
OverDrive
 
Join Date: Nov 2009
Location: Lander, Wyoming
Posts: 6,490
Better LATE Than NEVER!

Tom S.,
I would like to sincerely THANK YOU!
For taking the time and effort to Go Backwards, and do what Mike Coe (MC Mod) and Eagle Mike should have done, Right UP FRONT!

I could not even get Mike Coe to understand that he WAS affecting the Cold Start Compression, via the KACR. Sent 2 PM's on the 'other forum', way back, when this was Hot News. (Well, he was a Honda Racer. Not a Race Mechanic. As I remember.)

Hopefully, Eagle Mike clarified the issue, to Mike Coe! But, 'Why Not to the rest of the public?'
Full disclosure / documentation, early would have been 'Best' for all of us riders.

I tried to tell all / show all with my oil flow project.

OH, By the way, we have hi-jacked this thread!
Apologies to 'Music Man'. Have you been able to get any pics of the RH Exhaust Camshaft Bearing?

pdwestman
Modify at "YOUR OWN RISK"!

Still riding my 1987 KL650-A1. 85,000+ miles & counting
pdwestman is offline  
post #5 of 7 Old 09-02-2015, 10:11 PM
Pretty in Pink, dunno why
 
Tom Schmitz's Avatar
 
Join Date: Feb 2009
Location: Redondo Beach
Posts: 8,087
Garage
You're welcome, Paul.

I needed to end the 'no-KACR' experiment anyway, so it wasn't much extra work.

The new banjo feeding the cams went in.

I'm going to split this thread-jack off into it's own thread.

Tom

Tom [email protected]

“On the way downtown I stopped at a bar and had a couple of double Scotches. They didn't do me any good. All they did was make me think of Silver-Wig, and I never saw her again.” -Philip Marlowe

“'Why' and 'How' are words so important they cannot be too often used.” -Napoleon Bonaparte

Sting like a butterfly.
Noli Timere Messorem

Last edited by Tom Schmitz; 09-02-2015 at 10:18 PM.
Tom Schmitz is offline  
post #6 of 7 Old 09-02-2015, 11:29 PM
4th Gear
 
Join Date: Oct 2013
Location: Chilliwack, BC, Canada
Posts: 1,481
Tom, your kicking back experience, was that to Gen2 or Gen1?

If Gen1, I'm wondering if you could check to see whether unplugging and replugging the single yellow wire leading to the ignition module changes timing by 3 or so degrees? If that circuit isn't working during cranking, it might cause the symptoms you report.

I think it's Yellow/Red on Gen2 but don't think it can simply be unplugged as goes to Junction #12 in the harness. Perhaps I'll be feeling ambitious some time when time allows to disconnect a Gen2.
Normk is offline  
post #7 of 7 Old 09-03-2015, 09:20 AM
5th Gear
 
Join Date: Jan 2011
Posts: 4,711
Since the MC mod closes the exhaust valves earlier in the cycle, closure of the KACR's exhaust valve lift earlier (and consequent higher cranking combustion chamber pressure with KACR) is no surprise. Thanks for validating an assumption, Tom!

With no increase in non-KACR cranking combustion chamber pressure measured with the MC mod in place, we must look elsewhere for the elusive explanation of how the MC mod produces additional power.

Invoking volumetric efficiency (associated with the pressure in the cylinder at BDC vs. atmospheric), valve overlap generally favors scavenging at higher rpm, consequently increasing combustion efficiency and delivering higher power. The MC mod, reducing valve overlap, somehow operates oppositely. The mystery continues!

Last edited by Damocles; 09-03-2015 at 09:26 AM.
Damocles is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Kawasaki KLR 650 Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Similar Threads
Thread Thread Starter Forum Replies Last Post
Bad News - Missing KACR Pieces! ilmontgo Other KLR's - 250, 600, Tengai, C Models, KLX... 14 10-19-2013 12:37 PM
Compression Release biglar 2008+ KLR650 Wrenching & Mod Questions 6 07-01-2013 12:40 AM
What's the KACR, how does it work, and how can you disable it for a compression test Tom Schmitz How To's & Tech Guides 7 06-26-2013 01:52 PM
How do I deactivate the KACR for compression check? GO_OUTSIDE! 1987 to 2007 Wrenching & Mods 2 07-24-2011 08:06 AM
Normal range for Compression and Leak Down Tests? binsel 1987 to 2007 Wrenching & Mods 2 06-15-2010 11:52 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome