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Discussion Starter · #1 · (Edited)
Hi all,

This is my first post here, but I've been reading the threads on this forum for quite some time. In May of this year, I acquired a 1969 CB350 in parts (well, most of one and half of another). By July, I had it registered and riding. I did everything myself, except for rebuilding the engine, which a mechanic acquaintance did for a fee.

After riding it for a while, it developed a number of oil leaks at various seals on the head and was dripping plenty of oil out of the breather hose. Compression was 120 on the left cylinder - turns out he didn't replace the piston rings and there was a significant amount of blow-by. So I dismantled the engine, replaced the pistons rings and replaced the gaskets myself. I did notice that there was some pitting on some of the mating surfaces, but my machinist (who is a mechanical sage and I wholeheartedly trust) said that I should be able to get away with it if I apply a very thin layer of threebond 1211 to the all gaskets, excluding the head. Once all back together I reassembled the bike and it ran as good as new.

After a week of riding, I noticed the head gasket start to seep a miniscule amount of oil. Oh well, it's an old bike and the mating surfaces weren't perfect. I then took it for a 100 km ride on the highway, taking it easy averaging 95 km/h. On the return trip, it leaked about two teaspoons of oil from the seal above the valve housing every 30 km of highway. It also still drips oil out of the breather tube.

What is going on? Is the crankcase being over-pressurised for some reason? Why?

At this point I am going to take the engine out again, get the mating surfaces lightly machined, make sure all the gaskets have the right holes in the right places and put them in dry. Hopefully the breather overflow is due to the engine trying to vent excess after a fresh oil change.

Ps. Everything I described above was done following the Honda shop manual to the letter. And no, the breather tube is not pinched...
 

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Sensei
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I hate to, but HAVE to ask.....Do you immediately turn the petcock off EVERY time you turn off the engine?.....The oil on the drive looks thin.....
 

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Discussion Starter · #3 · (Edited)
I sure do and I've checked to make sure the petcock is not leaking. The oil leaked in the photo was still hot. Took the photo as soon as I stopped (hence the odd angle). I'm using castrol 10w40 4T.
 

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This is frustrating. How many miles are on the engine, before and after three rebuild? It is very important the piston, bore and rings are in spec. If the piston ring groves are too large you can get ring flutter. This will result in reduced compression at spèed (blowby). It may not show up in a static compression check. The ring must seal to the piston along with the cylinder. Skimming the cylinder and head is a good idea, if you can check it for flatness.

Keep us posted.
 

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rebuilding the engine, which a mechanic acquaintance did for a fee.
If I do something for someone for free and my shoddy workmanship (okay, with me it'd be more like ignorance than malice aforethought, but still...) causes damage, I've got to come up with the money to make things right. And that's if I did it as a favor. For free. (I'm just sayin', lol.)

After riding it for a while, it developed a number of oil leaks at various seals on the head and was dripping plenty of oil out of the breather hose.
I suppose that could have been caused by you overfilling the engine with oil. Or failing to check the oil level after Bubba the Wrench attacked it for you (which would make it the mechanic's fault, but you'd sort of share in the liability due to partial negligence, as they say in courtrooms).

turns out he didn't replace the piston rings
Wait... What, lol? I'm assuming that the cylinder bore and pistons were round and well within Honda's specification and they were reused, too (otherwise the reuse of the old rings goes from "many people would recommend against that" to "unthinkable," lol).

and there was a significant amount of blow-by.
Uh huh.

So I dismantled the engine
One hopes you first... dismantled the mechanic ;) .

replaced the pistons rings and replaced the gaskets myself. I did notice that
Did you notice ANY evidence that your, ah, mechanic had used RTV silicone on/in the engine? If so, some of the bits and blobs that seem to end up inside the engine when people do that might have plugged some oil passages, restricting the oil flow, and causing it to seek the path of least resistance.

After a week of riding, I noticed the head gasket start to seep a miniscule amount of oil. Oh well, it's an old bike and the mating surfaces weren't perfect.
I know you stated that there was some pitting, but were they at least flat?

What is going on? Is the crankcase being over-pressurised for some reason? Why?
I would think it unlikely unless you or he installed some sort of aftermarket "high-performance" oil pump. And, since you didn't mention it - and he didn't even use new rings - I'm guessing that would be negative. Instinct (I have very little actual knowledge, lol, so this post is mostly instinct - and 66Sprint might end up telling me that I didn't have a clue) tells me you have either a flow restriction, an overfilling situation, or both.

As 66Sprint alluded to, the engine could be "self-overfilling" with gasoline (do you call it petrol there?). He/you covered failing to shut off the fuel petcock valve. Some will close it before the arrive at their destination so that the engine stalls as/when they arrive, leaving none (well... a minuscule amount) in the lines/carbs, while others probably don't bother. I figure you can't go wrong by doing the former. If your floats are adjustable (IDK?) and are set incorrectly... Hey Steve, could that cause fuel to enter the cylinders in such quantities that an appreciable amount got into the oil supply?

EDIT: This is, of course, a dumb question if you have ever been around motorcycles before, but in the interest of completeness: You do know that "OFF" on the fuel petcock valve is the middle setting, right?

How do your spark plugs look? Does your oil have even a hint of the scent of gasoline to it?

At this point I am going to take the engine out again, get the mating surfaces lightly machined, make sure all the gaskets have the right holes in the right places and put them in dry.
I chuckled when I read that. But then... I might be wrong, but I'm thinking I saw a thread a while back in which someone confused their head gasket with... "that other one." What's it called, a base gasket? Anyway, is it possible to do that on these engines? If so, I would guess that the hole pattern would be different - possibly meaning that oil passages are blocked.

Is there any way to determine whether or not the oil is reaching the top of the engine and all those bits that are important to lubricate? If it's a case of (either a partial or full) blockage, then I would be surprised if whatever is after that point on the oil's (proper) journey is getting properly lubricated - which could mean that things are being damaged. (Again, IDK, and am just speculating - and hoping to learn.)

Hopefully the breather overflow is due to the engine trying to vent excess after a fresh oil change.
Yeah... No. I mean, that's entirely possible - IF you overfilled the engine in the first place. How are you checking the oil level after doing an oil change? Motorcycle on the center-stand, unscrew the dipstick, wipe it off, place it back in the hole without screwing it back in and then pulling it out and reading it? Your motorcycle looks normal (lol), so I don't guess there's any chance that the engine is tilted way forwards or backwards due to extreme suspension changes (etc.).

Your engine doesn't have an oil filter, but it has one of those centrifugal setups that "spin" the oil and, at least at high RPM, will chuck debris onto a screen, IIRC. What have you seen there, anything?

Everything I described above was done following the Honda shop manual to the letter.
That excludes screwball errors in a 3rd-party publication from the list of possibilities.

And no, the breather tube is not pinched...
No, if oil is successfully leaking out it, I would assume not.

Oiling issues are scary, because the easiest way to ensure engine damage is by oil failing to reach all the surfaces that must be lubricated - or by contamination of the oil supply (things such as gasoline will thin it, significantly harming its ability to do its job, and debris can clog the oil passages).

Another question for the Sensei, lol: Is this engine set up so that there are any banjo bolts - or the like - which are part of the oil system and, if so, is it possible that the person who was first entrusted to rebuild the engine might have managed to use a bolt that didn't have the passages in it - and that such a mistake could have gone unnoticed?

BtW: It could, I suppose, just be a trick of the light or something - but it looks like there's some kind of grayish substance floating on top of the oil that has leaked onto your driveway (img_0127.jpg).

Regards,
 

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Discussion Starter · #8 ·
Haha, sure is frustrating. Thanks for all the responses so far.

- About 200 miles between the initial rebuild and me rebuilding the head.
- I took all parts to my machinist to make sure everything was within spec. Cylinder was honed before measuring.
- I checked for warpage with a steel rule and went over all the pitted mating surfaces with a speedfile, although I didn't take off enough to get it perfect. (You can see the speedfile with wet and dry attached to it in the back of the cylinder pitting photo)

I have found the origin of the leak: a little gap in the threebond to the left of the points housing :( Sorry about the low resolution, the photo was cropped. It's the little darker patch near the centre.

FullSizeRender.jpg
 

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Discussion Starter · #9 ·
Hi MDM,

Thanks for the detailed response. I'll try to go through and address each point/question in order. I'd already responded to another reply before reading this one, so I may be double-answering here.

1. Yeah... I'm not getting into the whole mechanic fiasco, haha. When I approached him, he expected me to pay more to fix it. He is a very nice guy, though. He's just a bit old school (assuming the cylinder/piston/ring condition and "honing" the cylinder with sandpaper).

2. No evidence of RTV silicone on/in the engine. And when I applied the threebond I was very cautious to not over-apply.

3. Surfaces were flat.

4. The dipstick doesn't smell like fuel and since my rebuild, the overflow has still occurred - I am certain the petcock has been turned off every time I park it. I'm sure I adjusted the float height correctly, but I'll check again.

5. Haha, I may have worded that poorly. I don't mean incorrectly installing the gaskets ie. wrong orientation. When I installed the gaskets, of which I am positive are for my model CB350, I noticed some holes (not the engine stud ones) were covered. I saw someone on this forum reference stock gaskets not having a large enough holes for the pin sized oil feeds at the base outermost rear (exhaust side) engine studs.

6. I took off the tappet covers and the rockers, valves, etc are all wet with oil.

7. I put 1.9L of oil in the engine.

8. The greyish looking substance is a reflection, I believe.

Thanks again.
 

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Discussion Starter · #11 ·
I know quick fixes are named for how long they stay fixed, but I'm a PhD student and have little free time at the moment. I slathered on a bit of Threebond 1104. Hopefully it holds until I get a chance to install new clean, dry gaskets.

...yeah, that fin has seen better days.

IMG_0139.JPG
 

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Discussion Starter · #12 ·
Just for anyone who may have this problem in the future - the breather issue was the result of the plate that sits between the the cam case and top cover not being installed upon rebuild.
 
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