Welcome, Guest
Username: Password: Remember me
  • Page:
  • 1
  • 2

TOPIC:

Low Compression Question 27 Mar 2020 15:31 #821941

  • gordone
  • gordone's Avatar
  • Offline
  • Sustaining Member
  • Posts: 1373
  • Thank you received: 67

Daftrusty wrote:

zed1015 wrote: He has put oil down the bore which increased compression and that is a strong indicator of ring or bore issues.
If it was bent or sticking valves there would not be an improvement.


This is very good point, but pouring oil into a cylinder with a perfectly good piston/bore and rings will also lead to an increase in compression as it plugs the ring gaps.
So in theory he may have boosted that cylinders pressure making ability by plugging the ring gaps with oil (raising compression) all the while compression was escaping through a leaking valve. Even with oil he still was 20 psi away from the other cylinders. Hence the leak down test will confirm if he has a broken ring or a melted piston. Or maybe it’s just carbon baked onto a valve seat.

Food for thought....

**Edit**
650ed and I made the exact same point, but he must have posted it while I typing this post. Great minds think alike.


What if you have 100% control over how much oil you adding, adding the same amount and then test all cylinders and then can you compare the increase in compression.

Will the cylinder with bad rings increase more then they others? :)
1981 KZ650-D4, with 1981 z750L engine (Wiensco 810 big bore).

Project:
www.kzrider.com/forum/11-projects/607213...sr-1981-z750l-engine

Please Log in or Create an account to join the conversation.

Low Compression Question 27 Mar 2020 15:57 #821943

  • Mikaw
  • Mikaw's Avatar
  • Offline
  • Sustaining Member
  • Posts: 4879
  • Thank you received: 1843
I must have gone to the same “shade tree” school Rick H did. I’ve done the exact same procedures. I pulled all the plugs that way you can listen to the other cylinders. If you pressurized #1 and hear it out of #2 might be an indication of a bad head gasket. Heed Rick H direction, very low pressure is needed, I was amazed how fast you can slam a piston to BDC,with minimum air pressure. If you do hear air track it down as to where your best guess is your hearing it. That will help in diagnosis.
1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

Please Log in or Create an account to join the conversation.

Low Compression Question 27 Mar 2020 16:07 #821944

  • Mr. E
  • Mr. E's Avatar
  • Offline
  • User
  • Posts: 85
  • Thank you received: 14

Daftrusty wrote: So if the spare motor is in good running condition.....why not just swap the whole motor in rather than taking two motors apart??


My thoughts too, why not just swap engines then...
1981 KZ750 Chopper, 1975 KZ400 , 1984 GPZ750 track build , Res 1977 kz1000a ,1977 kz1000a ...ect.

Please Log in or Create an account to join the conversation.

Last edit: by Mr. E.

Low Compression Question 27 Mar 2020 16:39 #821946

  • zed1015
  • zed1015's Avatar
  • Offline
  • User
  • Posts: 2885
  • Thank you received: 1441

650ed wrote: The issue I have with just putting oil in the cylinder is that even if the rings and cylinder are perfect it will still raise the compression. The images below, which assume a perfect seal between the rings and cylinder wall, show what I mean. Even with perfect rings and cylinder walls the compression will rise if oil is added. Please don't misunderstand - his problem may very well be with rings or cylinder wall condition, but a leak down test will show if there are other issues that should be addressed. Ed

Correct but he isn't putting oil down a good cylinder and one that doesn't respond to the oil.
If it was the valves he wouldn't see an 50 psi improvement of pressure no matter the cylinder condition.
The compression increase strongly indicates piston/bore seal regardless of whether there is any additional valve leakage.
AIR CORRECTOR JETS FOR VM CARBS AND ETHANOL RESISTANT VITON CHOKE PLUNGER SEAL REPLACMENT FOR ALL CLASSIC AND MODERN MOTORCYCLE CARBURETTORS
kzrider.com/forum/23-for-sale/611992-air-corrector-jets-





Please Log in or Create an account to join the conversation.

Last edit: by zed1015.

Low Compression Question 27 Mar 2020 19:36 #821963

  • 650ed
  • 650ed's Avatar
  • Offline
  • User
  • Posts: 15344
  • Thank you received: 2828

zed1015 wrote: Correct but he isn't putting oil down a good cylinder and one that doesn't respond to the oil.
If it was the valves he wouldn't see an 50 psi improvement of pressure no matter the cylinder condition.
The compression increase strongly indicates piston/bore seal regardless of whether there is any additional valve leakage.


That's true. Also, he needs to put the same amount of oil into each cylinder so the tests are apples to apples. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

Please Log in or Create an account to join the conversation.

Last edit: by 650ed.

Low Compression Question 27 Mar 2020 20:03 #821966

  • Your_Boy_Yuriy
  • Your_Boy_Yuriy's Avatar Topic Author
  • Offline
  • User
  • Posts: 57
  • Thank you received: 3
Okay, The results are in! :)

The rings for cylinder 3 are in specs. I also measured the rings for cylinder 2 and they are also the same measurement as cylinder 3.

I flipped the head over and added some water on the valves and you guess it. The exhaust valve of cylinder 3 is leaking water after about 10 mins. I physically see water in the port and on the lip of the valve. However, I also see water on the lip in cylinder 2 for the exhaust valve but no water in the port. I am planning on sending in the head for repair, should I? Or try to fix it myself? What Can I do, just check the springs?

Anyways, I am doing this because the forecast calls for rain all weekend. I aren't riding in the rain in 40 degree F. My waterproof suit isn't going to keep me warm in that. Plus i enjoy it. I also could of swapped the good engine however, I wanted to know what was causing the low compression.
1982 KZ550C (First love)
1979 KZ650 (project Bike)
2007 Ninja (Project bike)
2020 Tracer GT (current love)

Chicago Western Suburbs

Please Log in or Create an account to join the conversation.

Low Compression Question 27 Mar 2020 20:16 #821969

  • Your_Boy_Yuriy
  • Your_Boy_Yuriy's Avatar Topic Author
  • Offline
  • User
  • Posts: 57
  • Thank you received: 3
1982 KZ550C (First love)
1979 KZ650 (project Bike)
2007 Ninja (Project bike)
2020 Tracer GT (current love)

Chicago Western Suburbs
Attachments:

Please Log in or Create an account to join the conversation.

  • Page:
  • 1
  • 2
Powered by Kunena Forum