Forum life: for better or worse right. I'm typing this as information and a 'warning' to other 350/400 owners:
As I mentioned in my other topic (
http://www.sohc.co.uk/index.php/topic,21101.0.html), I did a frame-swap on my 350f.
Just a couple of evenings worth of tinkering, everything went smooth apart from getting the oil filter off, which required excessive force and destroying the oilfilter housing pipe-bolt. Luckily I had one in my pile of parts.
With almost everything back together, I thought it would be a good moment to finally take care of the small oil leak that my bike has had for the last years. There was always a drop, hanging from the oil drain plug. So I bought a new original drain plug seal, did the oil pump O-rings, new oil filter with O-rings, and gave everything a good clean, put oil back in.. Still a drop next day...
.
While researching in more detail, I spotted something that made my heart stop for a slight moment
... A tiny hairline crack, just at the left front side of the engine, in the lower half of the block. Just behind the front left engine mount to be precise.
Well.. turns out I found the actual oil leak... Seems the bolt used in this engine mount, is slightly too long, and pushed the engine away from the mount, causing pressure in the aluminium and finally cracking the engine lower casing. Correct and too long bolt compared:
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Damnit! Thoughts like 'why didn't I feel this while tightening' and 'why didn't I check fitment before tightening' and 'why did I use that old bolt anyways' etc. But... that doesn't help, so I moved into problem solving mode. Like I said, the oil drip has been part of my CB since as long as I can remember having this 400 engine, so maybe it's good I finally find the cause.
With the bolt out (and pressure gone, the crack isn't visible anymore, not with the naked eye at least.
I wire brushed everything spotless, used a lot of degreaser and towels, went under with a good light source, put the bike nose-up high so the oil in the pan is in the back, and the leak stops.
As welding this is going to:
- require a full dismantle of the just assembled big-bore engine
- heat introduction may warp the casing.
- be a messy job, oil contaminated, old unknown alloy mix, no guarantee of actual solving it long term
- be costly as I certainly can't do that myself with my auto-mig spatter machine...
I made the choice to patch the leak with "Quiksteel 16402" epoxy aluminium. Seems to get extremely good results according to internet reviews, especially for events like this oil leak.
Job scheduled for this weekend...
Does anyone have advice or experience to share with regards to this sort of repair?
Will keep you updated.