« previous next »
Pages: [1]   Go Down

Author Topic: 750 pressurizing the oil tank  (Read 1720 times)

0 Members and 1 Guest are viewing this topic.

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 21,326
  • Saver of unloved motorcycles.
750 pressurizing the oil tank
« on: July 12, 2015, 06:49:37 PM »
 A friend did an engine rebuild a 750 and now it seems to be pressurizing the oil tank. When you remove the cap it blows out. It's a newer one with the oil separator under the battery box. He can remove the top crankcase vent hose with no relief. I haven't seen it yet. It is pumping oil to the top of the engine, maybe too much.

 Sorry for the lack of info, I got it second hand.
Logged
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 15,166
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: 750 pressurizing the oil tank
« Reply #1 on: July 12, 2015, 07:45:53 PM »
Quote from: Don R on July 12, 2015, 06:49:37 PM
A friend did an engine rebuild a 750 and now it seems to be pressurizing the oil tank. When you remove the cap it blows out. It's a newer one with the oil separator under the battery box. He can remove the top crankcase vent hose with no relief. I haven't seen it yet. It is pumping oil to the top of the engine, maybe too much.

 Sorry for the lack of info, I got it second hand.

Hmmm?
It's not possible to pump too much oil to the top end: it has limiting oil jets in the head: that is, if he installed them (and the 4 O-rings with them) when he put the head back on? If not, it will very soon eat the crank bearings and maybe the cam.
:(
Logged
See SOHC4shop.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book
Link to My CB500/CB550 Book: https://www.lulu.com/search?sortBy=RELEVANCE&page=1&q=my+cb550+book&pageSize=10&adult_audience_rating=00
Link to website: https://sohc4shop.com/  (Note: no longer at www.SOHC4shop.com, moved off WWW. in 2024).

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 21,326
  • Saver of unloved motorcycles.
Re: 750 pressurizing the oil tank
« Reply #2 on: July 12, 2015, 08:22:21 PM »
He says oil is coming up along the outside studs too.
Logged
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 15,166
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: 750 pressurizing the oil tank
« Reply #3 on: July 13, 2015, 03:38:49 PM »
Quote from: Don R on July 12, 2015, 08:22:21 PM
He says oil is coming up along the outside studs too.

Uh-oh...this sounds like very high crankcase pressures, which means the rings are not seated (or worse) or the valve guides are VERY loose, exhaust side.
:(
The oil only rises to the top via the 2 studs alongside the cam chain tunnel, at the back of the cylinders. It then drains back to the crankcase via the other studs, except for the 2 outside front ones, and on some models, the back two outside studs.

I have also seen it happen when the rings are broken, when someone did not gap the new rings to match their new bore and they were too big: it broke the rings on the center 2 cylinders in several places.

None of those scenarios are good news?
Logged
See SOHC4shop.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book
Link to My CB500/CB550 Book: https://www.lulu.com/search?sortBy=RELEVANCE&page=1&q=my+cb550+book&pageSize=10&adult_audience_rating=00
Link to website: https://sohc4shop.com/  (Note: no longer at www.SOHC4shop.com, moved off WWW. in 2024).

Offline Bodi

  • Really Old Timer ...
  • *******
  • Posts: 5,743
Re: 750 pressurizing the oil tank
« Reply #4 on: July 13, 2015, 03:45:54 PM »
WIth a problem like broken rings or such, you should see a lot of blowby coming from the top vent tube as well. Possibly that's blocked somehow? If so even normal "rebuilt engine" blowby with unseated rings would pressurize the cases rather badly.
Logged

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 21,326
  • Saver of unloved motorcycles.
Re: 750 pressurizing the oil tank
« Reply #5 on: July 13, 2015, 03:55:03 PM »
 That's what's weird, my brother said there isn't much coming out of the top hose. I'll have to go look myself and see if I can figure it out. The guy's been working on them since they were new. Should have gotten it on one try.
Logged
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline chewbacca5000

  • I polish covers!
  • Old Timer
  • ******
  • Posts: 3,532
Re: 750 pressurizing the oil tank
« Reply #6 on: July 13, 2015, 08:34:39 PM »
Hey Don,

Make sure top vent hose is not blocked, or vent on oil cap.  Think that is also vented?
Logged

Offline MoMo

  • Really Old Timer ...
  • *******
  • Posts: 8,271
  • Ride like you're invisible
Re: 750 pressurizing the oil tank
« Reply #7 on: July 13, 2015, 08:36:38 PM »
Don, make sure the crankcase breather is not hooked up to the oil reservoir,  ask me how I know
Logged

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 21,326
  • Saver of unloved motorcycles.
Re: 750 pressurizing the oil tank
« Reply #8 on: July 13, 2015, 09:33:17 PM »
Quote from: MoMo on July 13, 2015, 08:36:38 PM
Don, make sure the crankcase breather is not hooked up to the oil reservoir,  ask me how I know
Really I can't imagine doing that. Well, except for that one time. I realized what I did and put a tee in the hose to vent them both. L0L.
Logged
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 21,326
  • Saver of unloved motorcycles.
Re: 750 pressurizing the oil tank
« Reply #9 on: July 24, 2015, 05:28:16 PM »
 The vent nipples were filled with silicone. Another stupid PO trick. He didn't think to look in them while it was apart.
Logged
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline MoMo

  • Really Old Timer ...
  • *******
  • Posts: 8,271
  • Ride like you're invisible
Re: 750 pressurizing the oil tank
« Reply #10 on: July 24, 2015, 06:14:29 PM »
Quote from: Don R on July 24, 2015, 05:28:16 PM
The vent nipples were filled with silicone. Another stupid PO trick. He didn't think to look in them while it was apart.


to keep the oil from blowing out  ::)


and I like your solution to the crankcase/oil tank vent :P
Logged
Pages: [1]   Go Up
« previous next »