Results 1 to 6 of 6
  1. #1
    CB750 Enthusiast John Luke's Avatar
    Join Date
    Aug 2019
    Location
    Ashville
    Posts
    55

    Top end rebuild on a 81 CB750C

    Iím rebuilding the top end on my 1981 CB750C it had a very small head gasket leak so while Iím already in the engine I decided to hone the cylinders and get new rings seeing as itís low on compression. Iím gonna get the head and cylinders resurfaced to make sure the mating surfaces are flat. But the crankcase base gasket I canít get resurfaced because the rods are sticking out and I donít want to tear into it more than I have to. How would yíall best prep the base gasket surface? I used razor blades and a 120 roloc bristle disc. Then finished off with a free 600 grit Scotch-Brite. Any other ideas? To the touch itís very smooth but I just wanted to ask to see if anyone had any ideas.

    Thanks!


    Sent from my iPhone using Tapatalk

  2. #2
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,695
    DON'T surface the head and top of block; you have too little room for that and the valves may hit pistons as well as the cam chain will run looser. Honda made no real allowance for that. I've never done it in a lot of engines too simply no need for it.

    The leaks are from valves not the rings, they do it WAY before the rings ever leak.

  3. #3
    CB750 Enthusiast John Luke's Avatar
    Join Date
    Aug 2019
    Location
    Ashville
    Posts
    55
    Okay. Well currently when I put the head on the cylinder no gasket and I put a light on the other side I can see a little light. Iím not sure if the head flexes after you torque it down but I was worried that that could cause some problems.

    Thanks!


    Sent from my iPhone using Tapatalk

  4. #4
    CB750 Enthusiast John Luke's Avatar
    Join Date
    Aug 2019
    Location
    Ashville
    Posts
    55
    With no gasket


    Sent from my iPhone using Tapatalk

  5. #5
    CB750 Guru amc49's Avatar
    Join Date
    Sep 2015
    Location
    Fort Worth TX.
    Posts
    2,695
    That is NOT a flatness test, almost every engine on earth will do that. If they were that flat you wouldn't need a gasket at all ever.

  6. #6
    CB750 Enthusiast John Luke's Avatar
    Join Date
    Aug 2019
    Location
    Ashville
    Posts
    55
    Alrighty then. Iíll degrease the mating surfaces and start assembling.


    Sent from my iPhone using Tapatalk

Similar Threads

  1. 1972 Engine Seized Post Top End Rebuild
    By gatorforge in forum Engine / Exhaust
    Replies: 3
    Last Post: 07-18-2018, 09:06 AM
  2. No top end power
    By Chuck Hahn in forum Engine / Exhaust
    Replies: 11
    Last Post: 02-06-2018, 01:45 AM
  3. top end rebuild! need some parts and knowledge ..
    By Curtis87 in forum Engine / Exhaust
    Replies: 16
    Last Post: 03-25-2017, 09:12 PM
  4. Top End Rebuild Question
    By kakashi1578 in forum Engine / Exhaust
    Replies: 4
    Last Post: 09-02-2016, 12:17 PM
  5. Top end rebuild question
    By jimminy in forum The SOHC Garage (1969-1978)
    Replies: 16
    Last Post: 11-25-2012, 08:55 PM

Posting Permissions

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