Community
Search
Notices
Engine Conversions Discuss all aspects of engine conversions in this forum

how low is too low for compression?

Thread Tools
 
Search this Thread
 
Old 04-12-2008 | 09:07 PM
  #1  
Thread Starter
Senior Member
My Feedback: (13)
 
Joined: Jul 2005
Posts: 1,686
Likes: 0
Received 0 Likes on 0 Posts
From: Salem, OR
Default how low is too low for compression?

I am just curious as far as what compression figures (PSI) I should be leary of in doing a compression test. I have one engine I got 60psi out of (after many pulls) and it was scored to heck... one that was to 90 and looks new inside (but ring gap is in the exhaust port, can't help anything I'm sure) and one that was at 100 or 110 and ran like new. I've only ran the last one I mentioned, I tried to start a ryobi that I measured to 90psi, but it wouldn't run (could be fuel or spark)

I was just curious and figured I'd ask those that have more experience with various random engines...
Old 04-13-2008 | 01:40 PM
  #2  
Sr-Telemaster's Avatar
Member
 
Joined: Apr 2006
Posts: 40
Likes: 0
Received 0 Likes on 0 Posts
From: Alliance, OH
Default RE: how low is too low for compression?

Homelite blower service book sayes 12 to 15 pulls on starter.
90 psi hot
100 psi cold
Old 04-30-2008 | 09:20 PM
  #3  
Thread Starter
Senior Member
My Feedback: (13)
 
Joined: Jul 2005
Posts: 1,686
Likes: 0
Received 0 Likes on 0 Posts
From: Salem, OR
Default RE: how low is too low for compression?

somehow I missed your reply... just what I wanted to know!

I've been doing like 4 pulls on the starter. I've never bought a two stroke engine other than two glow engines new in my life, so I haven't seen much in the way of manuals for these

Thanks
Old 05-03-2008 | 03:54 PM
  #4  
Senior Member
 
Joined: Mar 2002
Posts: 4,925
Likes: 0
Received 5 Likes on 5 Posts
From: Kingston, ON, CANADA
Default RE: how low is too low for compression?

Anything below 75 psi is pretty well impossible to start.
Old 05-03-2008 | 06:11 PM
  #5  
meridianclocks's Avatar
Senior Member
 
Joined: Mar 2008
Posts: 135
Likes: 0
Received 0 Likes on 0 Posts
From: Northeast, PA
Default RE: how low is too low for compression?

Over 100 good, Under 100 not so good, Under 80 the only way it will fly is if you throw it in the trash!

Rich
Old 05-05-2008 | 07:09 AM
  #6  
Member
 
Joined: Feb 2007
Posts: 30
Likes: 0
Received 0 Likes on 0 Posts
Default RE: how low is too low for compression?

My FeatherLite 18cc would eventually start by hand flipping, but would only turn a 16-6 Top Flight Super M 5700rpm. Compression was 35 to 40 lbs, ring gap .012". This was using gas glow. Does anyone have the service limits for the ring gap on these. Its possible the motor was run hot and removed the ring temper? Or maybe the ring bevel is gone or worn...glazed cylinder etc. We found the weedeater in the dumpster, but they also get pitched when the string won't feed right. The bore looks like chrome and I assume it is, is it advisable to polish with a fine hone?
Old 05-05-2008 | 01:57 PM
  #7  
av8tor1977's Avatar
My Feedback: (6)
 
Joined: May 2003
Posts: 7,245
Likes: 0
Received 6 Likes on 5 Posts
From: Tucson, AZ
Default RE: how low is too low for compression?

Specified ring gap in these size engines is usually 0 to .003". Your ring gap is four times wider than it should be. Contact Frank Bowman for the best rings made...

AV8TOR

Posting Rules
You may not post new threads
You may not 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 Off
Pingbacks are Off
Refbacks are On



Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.