« previous next »
Pages: [1]   Go Down

Author Topic: Engine Compression question  (Read 1158 times)

0 Members and 1 Guest are viewing this topic.

Offline lhemrick

  • Enthusiast
  • **
  • Posts: 113
Engine Compression question
« on: October 20, 2007, 04:04:47 PM »
I have a used 72 350f engine that I know nothing about but all the cylinders but one have great compression. It only has about 80 lbs; is there anything I can do or check short of ripping it apart to replace the rings?

Lynn Hemrick
Logged
Don't give up; Rust is only Temporary!
77 Honda CB750
70 Honda CB350 twin
71 Honda CB350 twin
72 Honda CB350 Four
72 Honda CB175
81 KZ550C2
81 KZ750H2
82 KZ750M1 CSR
84 ZN700 Shaft

Offline 333

  • Time for change
  • Really Old Timer ...
  • *******
  • Posts: 7,559
  • Mail List Member #162 - Call me Stan
Re: Engine Compression question
« Reply #1 on: October 20, 2007, 04:34:47 PM »
Try adjusting the valves and check again. 
Logged
Go metric, every inch of the way!

CB350F0  "Scrouching Tiger"
CT70K0    "Sneezing Poodle"

www.alexandriaseaport.org

Offline scunny

  • Old Timer
  • ******
  • Posts: 4,613
  • don't call me expert
Re: Engine Compression question
« Reply #2 on: October 20, 2007, 04:42:47 PM »
what 333 said
after that, if there is no improvement put a teaspoon of oil down the spark plug hole, repeat compression test. if no change it is valves, if the compression improves it's rings
Logged
past-cb100,ts250,cb500,cb500,gs1000,gs650g.phillips traveller
present-CB 650 retro
            VTR1000F3
           XL250S riverbed rocket
           TS250[sold]
           TS185[sold]
           XL125S[sold]
           MT50 (white)
           MT50 (red)[sold]
           KN250/XS400 project
           XR/XL250 bitsa under construction
           SL100[sold]
           XL250R
           pedal(pub bike) leaks oil
my gallery http://gallery.sohc4.net/members/personal/scunny

Online MRieck

  • Really Old Timer ...
  • *******
  • Posts: 10,815
  • Big ideas....
Re: Engine Compression question
« Reply #3 on: October 20, 2007, 04:46:54 PM »
 A leakdown test will show you where you are losing pressure.
Logged
Owner of the "Million Dollar CB"

Offline TwoTired

  • Really Old Timer ...
  • *******
  • Posts: 21,802
Re: Engine Compression question
« Reply #4 on: October 20, 2007, 04:48:25 PM »
In addition to what has been said, periods of inactivity can deteriorate the ring seal.  If it isn't too bad, they will re-seat in about 100 miles.  If the compression is still wonky after that, it's time to open it up.

Cheers,
Logged
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline lhemrick

  • Enthusiast
  • **
  • Posts: 113
Re: Engine Compression question
« Reply #5 on: October 20, 2007, 05:06:14 PM »
Thanks for the fast response guys! I have already put a couple of tablespoons of oil in that cylinder and the compression came right up to normal. I was wondering if it would or might get better if I just got it running and got it hot a time or two and I think I might try that first. Actually I have two engines and the other has a couple of weak cylinders also but the man I bought them from promised me that they both run and they are nice clean engines and are well worth what I paid for them. I would just really rather not open them up if I don't have to. Any other ideas?

Lynn Hemrick
Logged
Don't give up; Rust is only Temporary!
77 Honda CB750
70 Honda CB350 twin
71 Honda CB350 twin
72 Honda CB350 Four
72 Honda CB175
81 KZ550C2
81 KZ750H2
82 KZ750M1 CSR
84 ZN700 Shaft

Offline ofreen

  • Old Timer
  • ******
  • Posts: 4,215
Re: Engine Compression question
« Reply #6 on: October 20, 2007, 08:11:30 PM »
As Lloyd said, just run it and see what happens.  Odds are good it will heal itself.
Logged
Greg
'75 CB750F

"I would rather have questions I cannot answer than answers I cannot question." - Dr. Wei-Hock Soon
Pages: [1]   Go Up
« previous next »