Page 2 of 7 FirstFirst 123456 ... LastLast
Results 11 to 20 of 70

Thread: Worrisome compression test results on my MGB 18GK

  1. #11

    Re: Worrisome compression test results on my MGB 18GK

    Is it possible that I've burned a valve due to not always having the mixture right? That had a steep learning curve for me, and I feel like there's still alot to learn.

    Also, was the 190deg thermostat a bad idea, or was it just the weak state of my radiator?

    The company that rebuilt the engine should be able to fix the valve seats. They're supposed to be hardened for lead-free gas.

    Thanks,
    -Bill
    William Killeffer
    East Ridge, TN
    1974 MGB

  2. #12
    Great Pumpkin jlaird's Avatar
    Join Date
    Nov 2005
    Location
    Niceville FL
    Posts
    19,505
    Chats
    0
    Items for Sale

    Re: Worrisome compression test results on my MGB 18GK

    Intakes hardened for no lead gas. But then most of us do not bother.

    190 degree thermostat is fine in my opinion.

    Could have a burnt valve but your wet compression check has already proven that something is wrong with 3 and 4 it seems to me. Pull the head and check it out.
    Jack Laird
    Retired USAF

    Miss Agatha. On the road again and smiling.
    Fourteen shows, Eleven firsts and counting.

  3. #13

    Re: Worrisome compression test results on my MGB 18GK

    The car hasn't been run since 2:30 or 3:00, so I asked SWMBO to come out and watch the tailpipe. It required the choke to start, and she said the smoke was grayish white. This wasn't ideal, cause it was under artificial light and it's not like the car sat all night. But it might be something else to think about.
    William Killeffer
    East Ridge, TN
    1974 MGB

  4. #14
    Great Pumpkin tony barnhill's Avatar
    Join Date
    Nov 2002
    Location
    Gurley, Alabama, USA
    Posts
    21,750
    Chats
    0

    Re: Worrisome compression test results on my MGB 18GK

    I was thinknig possible valve seal problems - but, you could have a valve not seating properly

    Would like to know what that smoke looks like in daylight.
    <span style="font-weight: bold"><span style="font-style: italic"><span style="font-size: 14pt"><span style="font-family: 'Comic Sans MS'"><span style="color: #006600"> Tony &quot;theAutoist&quot; Barnhill</span></span></span></span></span>


  5. #15
    Great Pumpkin jlaird's Avatar
    Join Date
    Nov 2005
    Location
    Niceville FL
    Posts
    19,505
    Chats
    0
    Items for Sale

    Re: Worrisome compression test results on my MGB 18GK

    Surely could be Tony. IMHO it is in the valves area for sure.

    Wonder if all the oil he used for the compression check was burnt out when he started it last.

    I think I would pull head, what do you think? Haveing it shop checked is cheep enough.
    Jack Laird
    Retired USAF

    Miss Agatha. On the road again and smiling.
    Fourteen shows, Eleven firsts and counting.

  6. #16
    Great Pumpkin tony barnhill's Avatar
    Join Date
    Nov 2002
    Location
    Gurley, Alabama, USA
    Posts
    21,750
    Chats
    0

    Re: Worrisome compression test results on my MGB 18GK

    I still want to see what happens when he starts it tomorrow morning - smoke-wise - & the dry compression while engine is cold.
    <span style="font-weight: bold"><span style="font-style: italic"><span style="font-size: 14pt"><span style="font-family: 'Comic Sans MS'"><span style="color: #006600"> Tony &quot;theAutoist&quot; Barnhill</span></span></span></span></span>


  7. #17
    Jedi Hopeful Adam58's Avatar
    Join Date
    May 2005
    Location
    San Fernando Valley, California
    Posts
    152
    Chats
    0

    Re: Worrisome compression test results on my MGB 18GK

    Hi there. I don't have any answers for you but maybe some things to think about that may help.

    1. LOOSE valve lash will keep valves from OPENING and will alert you by clattering. TIGHT (too small a gap) will hold the valves OPEN and eventually burn. This could show up as low compression since the combusion chamber won't be sealed. (From your post, it doesn't sound that that's the case here.)

    2. Try propping your carbs open a bit while taking your compression readings. If the throttle butterfly is closed and the bushings are so good they don't allow any air in, what will you compress to take your readings? This is really true with Weber carbs! If your 1/2 carb is set at a different point than your 3/4 carb, it could explain some of the pattern you are seeing. (If the compression evens out, re-tune the carbs!)

    3. I like the idea of taking it for a good long drive with lots of accelleration and decelleration. It'll be a blast and, if a couple of rings had not seated properly, you could get lucky!

    4. All else fails, do a leak down to see where to look next.

    Good luck! Adam
    Baffled but still confused!

    Adam

  8. #18
    Jedi Knight LarryK's Avatar
    Join Date
    Mar 2007
    Location
    Millstadt, IL
    Posts
    897
    Chats
    0

    Re: Worrisome compression test results on my MGB 18GK

    A 20% difference in compression is not a real worry. The engine has been rebuilt and you accidently found this. Was the engine running decent before the testing of the cylinders. Tony is in the mark with #3. Have someone start it for you while watching tailpipe and see what comes out. Also, check tailpipe (cold) and see what color inside is, black (rich fuel), gray ( on the mark), white (coolant), sooty grease ( oil).
    Larry K, ASE Certified
    58 Jag 3.4 MK 1, under restoration,03 Cooper S, SMF Solo, Time trials,
    2011 Cooper S Countryman, Road Rally, 2011 Land Rover LR4 HSE LUX
    Also had , Cortina 1600E, Spit 4 & 1500, GT6 3, Range Rover Classic, P38, Discovery 1
    71 XJ6, 79 XJ6, 86 XJS V-12, 53 XK120 OTS.

  9. #19

    Re: Worrisome compression test results on my MGB 18GK

    The instructions that came with the compression tester said to open the throttle all the way during the test, so I figured out a way to keep it open the whole time.

    The engine seems to chatter like a sewing machine. I'd worry about it if it didn't make any noise.

    With what I've found so far, would driving it at all be a bad idea? I know of a potential good drive area on one of the old highways, but don't want to do it if it might make things worse.

    As far as the tailpipe goes, it's black inside. Seems odd considering all but one of the plug made the mixture look a little lean. But it's not a greasy black.

    How do I do a leak-down test?

    Due to school, it may be a couple of days before I can come back to this other than reading responses to the post. I'll check things and keep everyone posted.

    Thanks to everyone for their help so far.

    -Bill
    William Killeffer
    East Ridge, TN
    1974 MGB

  10. #20

    Re: Worrisome compression test results on my MGB 18GK

    Forgot to answer: the engine wasn't running terribly, but seemed like it could do better. Idle seemed to be the worse problem, as getting it to idle consistently seems to be beyond me. In a way, I'm glad I found this because it gives me a reason to be having trouble instead of the problem stemming from my amateur skills.
    William Killeffer
    East Ridge, TN
    1974 MGB

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •