Author Topic: 73 CB750 Oil Tank breather spews oil when throttling (Read 21434 times)

Vincent P · « **Reply #50 on:** May 25, 2013, 03:44:10 PM »

Well I pulled the motor this morning and started to pull it apart. Once I had the rocker cover off I cranked the motor with the kick start on the stand while I plugging the spark plug hole with my finger. I had compression (air) coming out of the bolt near the intake valve on #2 cylinder; this bolt was actually very loose. Once the head was pulled off and I looked at the head gasket, here is what I found. Blown head gasket.

Picked up a new gasket kit from a local shop.

I pulled off the jugs and inspected the cylinders and rings; no issues found, so cleaned the cylinders with WD40 and Wet/Dry cloth then gave each one a nice coating of clean WD for the first start when it happens.

I torqued the head and have left it, and will recheck this after is settles for 24 hours.

At least I know what was causing the no compression and my crankcase pressure to build up.

Will let you all know what happens on the first start and setup.

ekpent · « **Reply #51 on:** May 25, 2013, 03:49:33 PM »

So does it have a big bore kit in it like you were told ? If it did you would want a head gasket specific to it,especially if it was an 836 or bigger.

Vincent P · « **Reply #52 on:** May 25, 2013, 03:55:22 PM »

Does not look like a big bore kit was put in.

I am a little concerned about that bolt coming loose again though.

ekpent · « **Reply #53 on:** May 25, 2013, 04:36:15 PM »

Is that one of the bolts under the rubber pucks ? If so inspect the threads in the hole carefully or look for bits of thread on the bolt incase it got partially stripped out from tightening to hard. Maybe it just never got tightened well,if I remember a socket does not fit well on them.

Vincent P · « **Reply #54 on:** May 25, 2013, 04:39:21 PM »

Not one under the rubber puck, it is near the valve spring. I see no signs of stripping on it.

scottly · « **Reply #55 on:** May 25, 2013, 06:38:30 PM »

Quote from: Vincent P on May 25, 2013, 03:44:10 PM

I pulled off the jugs and inspected the cylinders and rings; no issues found, so cleaned the cylinders with WD40 and Wet/Dry cloth then gave each one a nice coating of clean WD for the first start when it happens.

Did you replace the rings with new ones? Your dry/wet compression test showed worn rings on #1 and 4.

crazypj · « **Reply #56 on:** May 25, 2013, 06:46:09 PM »

Looks like someone forgot to torque it?
I use an ordinary deep socket with a 1-1/4" extension

Vincent P · « **Reply #57 on:** May 25, 2013, 07:29:00 PM »

I've been scratching my head on that too, and for the life of me I could swear on a stack of manuals that this was torqued down following the pattern in my shop manual.

Scotty, not I did not replace the rings, will give this a complete overhaul come the winter.

scottly · « **Reply #58 on:** May 25, 2013, 07:40:13 PM »

You were already there!?? Why do all the same work again in a few months to replace parts you already knew were worn out??

Henning · « **Reply #59 on:** May 26, 2013, 02:00:51 AM »

Well, that is interesting! Good job you pulled the head; torquing it down wouldn't have fixed that!

Vincent P · « **Reply #60 on:** May 26, 2013, 03:25:47 AM »

Not at all. I'll re-torque it tonight, and hopefully put the motor back in the frame tomorrow.

Vincent P · « **Reply #61 on:** May 26, 2013, 06:30:33 AM »

So as I sit hear and sip my coffee, I'm thinking that I really don't trust that stud where the head bolt was loose. I have not run the motor at this point, but could I extract the bolt and pull it through and install a fresh one without having to pull the complete motor???

I'd rather be safe than sorry.

crazypj · « **Reply #62 on:** May 26, 2013, 07:50:18 AM »

If it torqued down OK I wouldn't worry about it.
If you want to 'test' give it an extra 5ft/lbs, if it doesn't 'go loose' back off and re-torque to spec
Check the nut isn't damaged or worn s well

joehardy · « **Reply #63 on:** May 26, 2013, 11:44:46 AM »

Okay- I know this is not technically the correct answer, however I had a similar issue of oil spitting from my oil tank vent hose on a freshly built motor, bored 1mm over with new pistons and rings. I have an oil tank with a single breather tube exiting the bottom of the tank next to one of the oil lines. I routed it vent hose into the back of the crank case, via the existing vent pipe, and I routed the breather from the valve cover to exit behind the oil tank. The theory being any pressure in the oil tank simply goes back into the crank case and out through the valve cover along with any pressure in the crankcase. Again, I know it's not technically the correct answer, but I have had zero issues so far with only get a little bit of vapor from the vent hose.

Vincent P · « **Reply #64 on:** May 28, 2013, 04:42:27 AM »

Lately this bike has tested my ability to stay clam. I have the head gasket all torqued down and began installing the camshaft cradles and rocker arms. I get to the last one and go to tighten down the bolt which goes through the cradle holding the rocker arm pin in place, and as the bolt mates with the cradle no real pressure applied to tighten it, the threads pull out.

AAAAARRRRRGGGGGHHHHH!!!

Went to a local auto parts store and purchase a healy-coil kit and installed this. I gave it a rest after the coil install, and will get back at her tonight.

Talk about a lesson in keeping calm these day!!!

crazypj · « **Reply #65 on:** May 28, 2013, 09:45:24 AM »

Patience is the thing you need more than all the rest of the tools.
It's an inanimate object (although it usually feels different

)
If something goes wrong, it's usually your own fault
I learned a LOOOOONG time ago that if you get frustrated and stat bashing things you only have more to fix when you calm down

Vinhead1957 · « **Reply #66 on:** May 28, 2013, 10:10:08 AM »

Beer helps

Vincent P · « **Reply #67 on:** May 28, 2013, 02:12:20 PM »

Acutally so doe Jack Daniels

Vinhead1957 · « **Reply #68 on:** May 28, 2013, 03:34:20 PM »

Jack has betrayed me! Or was it Jim B

Vincent P · « **Reply #69 on:** July 09, 2013, 06:41:30 PM »

So now that work has allowed me sometime to work on the bike, here is an update.

The second head gasket failed 2 days after installation, except this time I was spewing so much smoke out the left side exhaust not to mention raw oil I could cloud an entire block. My decision at this point was to purchase a good running motor to get me riding for the summer, and I could work on this one during the winter, the purchased runner would then go into a bobber project I've been thinking of doing. There has to be something much deeper happening with the old motor???

I managed to find a motor which had just been rebuilt to be used in a cafe project which is now installed.

Once the swap was done; curiosity got the best of me so I had to pull the original motor apart. With the head off like the previous picture posted there was signs of not only one channel being cut through the gasket to a head bolt at cylinder 2 but to all 4, and visible signs of oil seeping through.

At this point I made an interesting discovery on the jugs. The sleeve in number 2 cylinder has dropped 1.5 to 2mm, no longer siting flush at the top of the jug like the other sleeves. It must have been down a bit during the first installation, but I think it slipped down further the second round enough for me to notice this time around. Not to hard to understand now why I was blowing head gaskets. Mystery solved.

So my decision at this time is to strip and clean the old engine and sell it off in parts.

Thanks for all the help all.

crazypj · « **Reply #70 on:** July 10, 2013, 10:23:55 AM »

I've seen that happen before
Block wasn't decked properly after boring or wasn't bored properly.
Some Honda liners only have 0.001" or less interference fit instead of more common 0.003"~0.004"
If too much cut was taken out (highly likely with a 1mm overbore) plus bored from bottom to top the liner would slide 'up'
It would be possible to fix it by fitting a new liner but a replacement cylinder would be easier

Vincent P · « **Reply #71 on:** July 10, 2013, 10:31:17 AM »

Thanks PJ,

Nice to hear I'm not the first person this has ever happened too.

Cheers,
Vince P

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Author Topic: 73 CB750 Oil Tank breather spews oil when throttling (Read 21434 times)