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I got home this evening and noticed oil on the fins of the left hand cylinder, it looks like it's the head gasket blowing (photo below). It happened on a 3 mile ride, nothing before and a mess when I got home.

Funny thing is, I noticed a couple of weeks ago that the end cone on the left hand silencer was much cooler after a ride than the right. I could put my hand on the left one and keep it there, but the right was hot and I could only touch it briefly. Another thing, holding my hand behind the silencers, the exhaust gas was noticeably cooler out of the left silencer. I was concerned, but couldn't think what could be causing this. Tuesday I did a dyno run (chart below) and the figures were very good, so I thought I was being paranoid and dismissed it as a problem and then this evening, oil!

I'm trying to work this through in my mind, this engine has covered 4,500 miles and never been apart. There was no evidence of any head gasket trouble until this evening, but there has been the cooler exhaust gas on the left pot for at least the last couple of weeks and yet no reduction in power. I'm a little baffled (excuse the pun).

Anybody any ideas? However bizarre.

I had planned to remove the baffle from the air box tomorrow for the next stage of development, but now it looks like I'll be having the cam cover off to check the head bolt torque.
 

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If it still runs as good as that dyno its not the head gasket .Oil leaks will fool the hell out of ya because the oil blows around so much.Check compression or better yet put a leak down tester on it .It could be as simple as the clutch cover leaking at the front blowing oil back on the jug.Or it could be as bad as a bad cast in the jug leaking out of the oil passage in the jug.If its a head gasket blown you should hear it unless its just leaking to the oil passage.Only thing you can do is clean it off good and try and find the oil leak.
 

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I had a similar problem last year when a header bolt sheared off. The leak drove me nuts. After doing a leak test it seemed to be coming from the head gasket which is impossible since any oil would go out the exhaust and blow smoke. After pulling out the shop manual and going over the exploded view I discovered an oil passage right behind the header stud. I was stunned when I extracted the stud and there sat the 1/8" oil passage. I'd like to kick the engineer that designed that an oil passage next to an exhaust outlet. Bottom line, the oil was blowing by the threads and soaking the right side of my bike and pants. "Manly", that's the name of the two stage epoxy that I got from my machinist, fixed the problem.
 

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Oil leak

Man thats a new one on me!! Wierd F-in place for an oil leak? I could see it MAYBE from short rides & not heating the whole engine completely over a preiod of time? Different metals heat @ different speeds. Had a Pontiac Fiero that had that problem. 3 diff metals in the engine. All heat & expand @ different times, & not heating the engine (whole thing) up fully did it there. Maybe here? Kinda scares me a bit since I broke my ankle 2 weeks ago & have been running the Bonne just to keep the battery up & the fluids movin. Hope to be back up & riding soon? If its the head bolt area, maybe a bit of torque might do the trick?? A thought. Good luck!
 

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I have seen a few of the jugs crack in that area and leak epoxy fixed them to. its piss pore castings that are the problem.But for what our bikes cost i guess thats what we get.Bikes are cheap parts are high as hell.
 

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Your picture is not that good for long distance diagnosis. We need to see more of the side of the motor. My guess for what it is worth is it is simply the cam cover gasket leaking badly just above the spark plug--the oil will run out all over the left side (side-stand lean when parked) and look a lot like what I see in your partial picture.

I wouldn't worry about your temperature differences of the exiting exhaust at idle speeds if you still have stock headers with the crossover pipe in place. Many have reported noticing this temperature difference on their Bonnies. This kind of temperature difference only matters when you have Header pipes WITHOUT a crossover pipe, IMHO.

There is an oil additive you can purchase at an auto parts store that will show exactly where an oil leak is located when viewed with a black light. There was a thread on this forum about six months ago about this--can't remember the name of the product.

Good luck,
 

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The real problem is metallurgy. I luv my bike BUT the quality of the metal on our bikes SUX ROCKS! To date I've had: a peg snap off, a cam screw, at the cam, snap off, a cam cover screw, and both bottom header studs snap off. All these items have been removed more than once for mod work, and before you say anything, all were properly torqued to the proper NM. It just seems like, if a bolt is taken off more than once its subject to break. I've also seen a crankshaft posted on RatNet that snapped in half and if you look closely you can see bubbles due to poor casting, or as we say in the biz...pot metal. Its like things are reversed from the '50's and '60's when Japan was making copies of British Iron and their products were shoddy. Now its the other way around. They're making world class bikes and ours are shoddy! The metal is way too soft. I've been in the process of replacing bolts as I take them off with grade 8. But with all the beeatchin' I'm still in Luv with my baby and will continue to fine tune and ride her.
 

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Hi Pieman,
Look carefully at the valve cover gasket. There are openings in the cooling fins straight out from the spark plug. My valve cover screws were dead loose and enough oil leaked from the valve cover that it flooded (OK flooded is an overstatement) out through those openings and leaked to the outside in a place similar to yours. I tightened the screws at first but then ran a bead of RTV silicone when I did the valve shim check.
Redbirds post seems to describe the same thing.
If your screws are loose do like a lot of other posts have mentioned and don't over-torque.

I hope its not the head gasket, I guess it would not be the end of the world but look for simpler things first... good luck!
 

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Thanks for all your ideas, I think it was the head gasket.


I had the cams out and re-torqued the head today, wiped the engine down and went for a blast. I did two 4th gear to the rev limiter runs and a bit of riding in between, went home and checked the engine, no oil anywhere. On the face of it, it looks like job done, but I'm not convinced. I didn't really identify the source, just took a chance as after checking the oil seepage, the head gasket looked like the only likely culprit. I'll feel better about it after a couple of weeks of no oil seepage.
 

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Leak

You should be OK! Did it take some torque on that bolt?? I bet it did!

As for the busted crank- if you look close @ the pic, you can see "crystalized Metal"!! Had that in a Z-28 once. The factory replaced the motor then & then the whole car stARTED COMMING APART! It was gone in 30 days! Hope all turns out well! Good luck
 

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Hello Mike,

Hope the business is going well. About the cool exhaust, I have to ask the question; are your carbs balanced? I've seen quite a difference in temps with a thermal gun when they are not.
 

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Hello Mike,

Hope the business is going well. About the cool exhaust, I have to ask the question; are your carbs balanced? I've seen quite a difference in temps with a thermal gun when they are not.
It's going fine thanks Greg. I checked the balance about a month ago, it was perfect.

I'm wondering if it's something to do with external air flow, off the rear disk or something like that. I had another feel today and further down the silencers it not far off the same temperature.... bloody hot.
 
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