Author Topic: '78 CB750K big o-ring pushes out of housing after a few minutes running (Read 1474 times)

RezaM · « **on:** January 27, 2021, 07:28:52 AM »

Hi all,
I'm new to this forum and new to bike building. Long history on this bike but it was thrown in the bushes for 30 years before I got it. I disassembled and rebuilt everything, I mean everything. Finally it's back together and runs great. There were allot of trials and learning that are not relevant to the current issue, so I won't bore you with all that.

There are a few issues with the oil filter/housing:
1) Somehow it or I crack the Aluminum housing around the hole where the bolt goes through. After one oil change, there are 4-5 small cracks that start about 1/2 inch in the housing and go into the hole, sort of like rays of the sun. It has done it to 3 good housings so something systemic is going on.
2) Small leak at the bolt, where it rotates inside the housing. I attribute this to the cracks mentioned above and I have stopped it by putting a backing o-rin between the flange of the bolt and the filter housing.
3) The biggest problem that has me baffled: It keeps pushing the big o-ring out between the oil filter housing and the case. I don't tighter the bolt is the fear of cracking the housing as I mentioned, so I tighten it like a car: Contact plus about 1 turn. This is strange. I'm not talking a leak there. I'm talking a piece of the o-ring sticking out between the case and the housing. It is not broken, just stretched out.

I did a couple of oil pressure test before I put the motor in the frame. It was using the battery to crank and I got 30-40psi that way. I am using AMSOIL 20-50 oill.

It's done it 3 times now, twice with o-ring and filter kits from 4into1 (Emgo), and the last time with OEM Honda parts from Partzilla.

Thank you in advance for any help and advice.

Alan F. · « **Reply #1 on:** January 27, 2021, 07:48:36 AM »

Have a look at this thread: http://forums.sohc4.net/index.php/topic,185265.0.html

RezaM · « **Reply #2 on:** January 27, 2021, 08:46:30 AM »

Thanks for sharing that thread. Seems similar to the issues I am having, particularly about the cracks around the center hole.
The bolt I am using does have a 17mm head and it was already in the bike when I got. I do have another one with 12mm head, so I will try that. It seems almost impossible for this failure to happen, because when I put the filter/housing on, I can see the housing and the case meet tightly, with maybe a hair gap between two. Yet, after idling for a few minutes, somehow almost the entire width of the 4.5mm o-ring comes out. I'll try to post some pix.

Alan F. · « **Reply #3 on:** January 27, 2021, 09:11:17 AM »

There was some mention that the big o-ring is not the correct size for Hondas. I think the Honda part number is supplied. Your big o-ring may be oversized causing the issue you're seeing.

754 · « **Reply #4 on:** January 27, 2021, 09:55:08 AM »

It's supposed to be lightly torqued, like maybe 12 or 14 ft lbs.
With your cracks the side of the cover, is maybe lifting on the side and allowing o ring to push out.
1 turn past tight may be 2 or 3 x times the needed torque..

maxheadflow · « **Reply #5 on:** January 27, 2021, 02:57:07 PM »

?

If the O ring or filter housing is blowing out, chances are that the pressure relief valve in the oil pump is sticking.

Getting 30-40 psi on cranking tells you nothing about the relief valve working.

A lot to housing will have casting lines that look like cracks. Best place to look for cracks is at the machined surfaces. If you see cracks replace the housing.

Stuffing an extra O ring on the bolt between the outside of the housing and the bolt is asking for trouble. You might get a good pinch on the O ring but chances are the there is still some gap between the head of the bolt and the housing. If that is the case, the O ring can blow out.

Yeah, Go to the stock Honda bolt for sure. The 17mm bolt may not have the O ring grove machined correctly.

bryanj · « **Reply #6 on:** January 27, 2021, 03:16:58 PM »

If you are cracking the casing you are tightening the bolt too much!!

754 · « **Reply #7 on:** January 27, 2021, 03:59:52 PM »

Yeah he said one turn past contact... no wonder they crack..

RezaM · « **Reply #8 on:** January 28, 2021, 05:31:04 PM »

Well, put another case on and ran it for seconds. Big pop and oil shooting out of the filter housing. It had split the filter housing pretty well in half.
Installed yet another ones that I had, but this time hooked up an oil gauge and fired it up. Pressure went past 100psi in seconds, actually wrapped the needle around past 100psi max and destroyed the gauge, haha. So at this point, I think my next move is take out the oil pump and investigate. But, it's going to take a while.

Btw, the last few times that I had replace the filter housing, I had only tightened the bolt something like 1/4 turn or less past the o-ring touching the case.....Thanks for all the advice thus far.

754 · « **Reply #9 on:** January 28, 2021, 05:33:20 PM »

Like has been mentioned the bypass spring in your bolt , may be part of it , what bolt did you use this last time ?

RezaM · « **Reply #10 on:** January 29, 2021, 06:34:21 AM »

The bolt and the housing were from a '75 GL1000. Everything was super clean before install. The bolt has the 12mm hex head and I checked the spring action of relief spring, it was nice and smooth. At the moment, I'm having a hard time wrapping my head around the bike making 120+ PSI oil pressure.

bryanj · « **Reply #11 on:** January 29, 2021, 07:11:17 AM »

Pressure relief valve is stuck closed

RezaM · « **Reply #12 on:** January 29, 2021, 08:15:19 AM »

Yeah, I'm afraid so. Is there a good bench test of it's functionality with the pump out of the bike? I disassembled and cleaned the pump, and measured the impeller gap, new o-rings and inspected for signs of defects. But, didn't test the pressure relief valve. Thanks for all the inputs.

bryanj · « **Reply #13 on:** January 29, 2021, 11:12:37 AM »

Just if its free in the housing

maxheadflow · « **Reply #14 on:** January 29, 2021, 07:57:07 PM »

One thing to note is that it's not the relief valve in the filter bolt. That is only there to allow oil to bypass the filter should it become plugged. The bypass/relief is somewhere near the oil pump. I don't really know as I've never had to fix one. It's typically close to the oil pump. On CB750s, it's mounted on the pump housing.

Don R · « **Reply #15 on:** January 29, 2021, 08:05:37 PM »

I remember a spring and a disc on the pump, behind a hex cap. I had one break off in my hand from a perfectly good running engine. I was happy for it to have broken then rather than when it was in use.
If you made enough pressure to push an oil filter cover off, check that casting carefully.

RezaM · « **Reply #16 on:** January 30, 2021, 10:06:05 AM »

OK, so I tore the bike down yesterday and removed the oil pump. Upon removing the pressure relief valve, the problem became quite obvious. Remember I had to basically take every nut and bolt off this bike, clean, repair or replace it. Apparently when I rebuilt the oil pump, I relied on my memory of how it came apart and put in the pressure relief plunger backwards. Relying on memory to put little parts together is not a good idea for and old dude. While I was there I also checked the leak stop valve and that looked correct.

Anyway, dumb rookie mistake. Now doubt it'll provide some choice commentary and a few laughs here. I've attached pics of before (Incorrect} and after (correct) here. So the pump is now put back together but ran out of daylight to install. Hopefully over the weekend and will report back.

RezaM · « **Reply #17 on:** January 30, 2021, 10:08:16 AM »

Incorrect assembly

bryanj · « **Reply #18 on:** January 30, 2021, 01:06:47 PM »

It should have cleared out the restrictor jets for you

754 · « **Reply #19 on:** January 30, 2021, 01:12:39 PM »

I gotta ask his far does the oil squirt after blowing out the O ring ?

ekpent · « **Reply #20 on:** January 30, 2021, 03:09:22 PM »

I'm sure you will hopefully be happy not having to clean up a mess each time and a little break on the oil budget also. No teasing here because that's how we all learn.

Don R · « **Reply #21 on:** January 30, 2021, 03:26:34 PM »

Thanks for the report, we all learn from it when we find out what happened.

seanbarney41 · « **Reply #22 on:** January 30, 2021, 04:47:28 PM »

For sure, we have all made similar mistakes. When you tell us what fixed the problem, everyone gets an extra chance to not make that same mistake. Thank you!

RezaM · « **Reply #23 on:** February 03, 2021, 07:00:54 AM »

Problem solved after installing the pressure relief valve correctly. No leaks from anywhere thus far. Oil pressure (20-50oil) when cold (50deg outside temp) at idle is a steady 60psi. When bike is warmed up and at 3000rpm, pressure goes to about 65ish. I think it's a few pounds more than the specs, but could also be the cheep gauge I bought from the auto parts store. I'm happy.

Thanks to everyone for the help. I have yet another issue with clutch/transmission rattle and jumping out of gear that for some reason has developed and gotten worse now after running the bike for a few miles that I will share in a different post.

ps. To answer 754's question above, oil was shooting out about 5 feet when it was blowing out o-rings and cracking filter cases. Haha.

ekpent · « **Reply #24 on:** February 04, 2021, 05:49:07 AM »

Is it falling out of second gear into a false neutral ?

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Author Topic: '78 CB750K big o-ring pushes out of housing after a few minutes running (Read 1474 times)