Jump to content

Nominations for Tractor of the Month
Garden Tractors and Parts on eBay



Photo
- - - - -

Fb23 Compression


  • Please log in to reply
7 replies to this topic

#1 Ryan313 OFFLINE  

Ryan313

    PK Fanatic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 7087
  • 3,239 Thanks
  • 5,159 posts
  • Location: Wallkill, NY

Posted April 04, 2012 - 11:16 AM

Does anybody know what the compression on a B&S FB23 is supposed to be? I got 35psi, I dont know what any engine is normally at but I dont think thats quite right.

#2 JDBrian OFFLINE  

JDBrian

    Super Moderator

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2507
  • 9,574 Thanks
  • 14,136 posts
  • Location: Hubley, Nova Scotia - Canada

Posted April 05, 2012 - 10:43 AM

Sounds pretty low. If you put some oil in the plug hole and measure again you can get an indication if it's the rings that are bad. A stuck valve can also cause low or no compression as well. I bought an mf8 with no compression and it was only a stuck valve that was keeping it from running.

#3 Ryan313 OFFLINE  

Ryan313

    PK Fanatic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 7087
  • 3,239 Thanks
  • 5,159 posts
  • Location: Wallkill, NY

Posted April 05, 2012 - 01:02 PM

I pulled the covers and head off and the valve seats were pretty bad. I dont have a spring compressor so I couldn't take them out but I tried to clean them the best I could with them still in and I got it up to 50psi.

#4 Bruce Dorsi ONLINE  

Bruce Dorsi

    Old, but not dead -- yet!

  • Senior Member
  • -GTt Supporter-
  • Contributor
  • Member No: 1525
  • 3,177 Thanks
  • 2,148 posts
  • Location: New Jersey

Posted April 05, 2012 - 05:33 PM

Ryan:

I am not familiar with the Fb23 engine designation as you posted.

Is this a Model FB with the overhead valves, or a Model 23FB with the valves in the block (flathead)?

B&S never published compression pressures for their older engines (I doubt they do it now either).

Many of their engines had "compression relief" ground into the camshaft profile, so that when cranking the engine, cylinder pressure would bleed off to make starting easier. ....Once the engine was running, the loss of compression at speed was insignificant.

The method recommended by B&S to check for adequate compression is to spin the engine counterclockwise (flywheel side) against the compression stroke. ....If compression is adequate, the flywheel should "bounce back" in a clockwise direction. ....Slight or no "bounce back" indicates low compression.

#5 Ryan313 OFFLINE  

Ryan313

    PK Fanatic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 7087
  • 3,239 Thanks
  • 5,159 posts
  • Location: Wallkill, NY

Posted April 05, 2012 - 06:44 PM

I mentioned 23 db, my fault. I will. Try the bounce back method and see what happens.

#6 Ryan313 OFFLINE  

Ryan313

    PK Fanatic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 7087
  • 3,239 Thanks
  • 5,159 posts
  • Location: Wallkill, NY

Posted April 05, 2012 - 07:00 PM

In the last post mentioned is supposed to be meant and 23 db is supposed to be 23fb, my phone auto corrects spelling errors. I trued the bounce back and it did nothing. I could feel more resistance on the compression stroke but it wasn't a big difference.

#7 DougT ONLINE  

DougT

    Dog Approved

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 584
  • 5,731 Thanks
  • 4,287 posts
  • Location: north central Ohio

Posted April 06, 2012 - 06:09 PM

Ryan, When you cleaned the valves, did you rotate them? Did you check the valve clearance? You could get some lapping compound and lift them up and put some compound around the seat. Make sure the valve is closed and rotate the valve back and forth. Since you can't get the valve out, make sure you get it cleaned real good especially on the intake side. Sometimes if you give it a shot of carb or brake cleaner in the plug hole it will fire and knock the rust off the valves. Engines that have sat a while sometimes regain their compression after they are run.

#8 Ryan313 OFFLINE  

Ryan313

    PK Fanatic

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 7087
  • 3,239 Thanks
  • 5,159 posts
  • Location: Wallkill, NY

Posted April 06, 2012 - 09:13 PM

I didn't rotate them, or check the clearance. After I cleaned them I only pulled it about 3 times and the rope broke and I couldn't find another so I haunt really done much since cleaning them. The only rope I could find was either too small or too big.




Top