Results 1 to 8 of 8
  1. #1
    CB750 New Member RowWel's Avatar
    Join Date
    Jun 2020
    Location
    Calgary
    Posts
    4

    Question Can Oil stop light be triggered with bad lights?

    I recently bought a 79 cb750 DOHC, guy converted it in to a cafe racer and put on these shitty after market tail lights and indicators. He blamed the oil stop lamp being on because they were cheap LED lights, uppon inspection of the wiring there are some relatively unreliable connections and the brake lights don't actually engage. More importantly though, I want to know if I was miss informed and that the light is only for oil related issues, it starts with it off but pretty much once I start riding and it warms up the light comes on.

    Oil level is good
    Is there anything I can check to see why the lights actually on? Any known issues with the oil pressure switch? Was he telling me the truth?

    Just trying to make sure I don't kill the engine on the bike

  2. #2
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    3,008
    Engine likely worn out. The light can flicker barely at idle in 90+ degree heat and be fine but anything over idle with light on is a dead engine. No, the rest of the system has nothing to do with the light, it is only for oil pressure. It trips on around 5-7 psi. The oil pressure switches are dependable as hell.

  3. #3
    CB750 Addict Medyo Bastos's Avatar
    Join Date
    Oct 2012
    Location
    Mid South
    Posts
    191


    Not sure if something like this would help! I agree with amc that idling with the light on would be bad.


    Sent from my iPhone using Tapatalk

  4. #4
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    3,008
    A standard good running DOHC has more internal leaks (double the cams and attendant oil restrictions) than a SOHC and can flicker the light a little bit at idle due to it at over 90 degrees. So long as you never get any light at all past 2000 rpm ever you are fine. Oil weight may figure in too, a lot of guys run 20W-50 during the summer in them. A car weight like 30 can cause issue.

  5. #5
    CB750 New Member RowWel's Avatar
    Join Date
    Jun 2020
    Location
    Calgary
    Posts
    4
    It's definitely consistently on, I thought it was strange him saying it was oil or brake light related... Thanks for the insight I just ran a compression test and 3cyls were around 110psi and the other was 90psi.
    Worth a rebuild or should I find a donor motor in your opinion?

  6. #6
    CB750 New Member RowWel's Avatar
    Join Date
    Jun 2020
    Location
    Calgary
    Posts
    4
    Thank you, I know im a bit fucking stupid lol

  7. #7
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    3,008
    He was just poking fun..........nothing intentional or personal.

    You might be better off with new engine, they are harder to get parts for than the SOHC and very expensive to build from the ground up. Low pressure often means the head has dead cam journals and you have to get a new head for that anyway.

    FYI, OEM compression is 170 psi and anything under 100 is absolutely pretty much a dead cylinder. The valves never get set either and tend to burn the exhausts because of it.

  8. #8
    CB750 New Member RowWel's Avatar
    Join Date
    Jun 2020
    Location
    Calgary
    Posts
    4
    Quote Originally Posted by amc49 View Post
    He was just poking fun..........nothing intentional or personal.

    You might be better off with new engine, they are harder to get parts for than the SOHC and very expensive to build from the ground up. Low pressure often means the head has dead cam journals and you have to get a new head for that anyway.

    FYI, OEM compression is 170 psi and anything under 100 is absolutely pretty much a dead cylinder. The valves never get set either and tend to burn the exhausts because of it.
    thank you

Similar Threads

  1. Replies: 2
    Last Post: 12-29-2019, 07:24 PM
  2. K8 running lights and meter lights
    By Hunter1919 in forum Electrical
    Replies: 2
    Last Post: 08-17-2019, 06:43 AM
  3. Throttle stop screw
    By forgiven in forum Carburetors / Fuel
    Replies: 14
    Last Post: 07-20-2019, 04:32 AM
  4. Oil light sensor modification
    By Wez_ in forum Engine / Exhaust
    Replies: 0
    Last Post: 09-18-2018, 12:54 PM
  5. oil pressure stop light. help!
    By Staubig in forum The DOHC Garage (1979-1983)
    Replies: 2
    Last Post: 05-26-2016, 10:36 PM

Tags for this Thread

Posting Permissions

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