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Old 10-19-2004, 11:32 PM   #1
Malindi OP
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Why did my airhead die?

What went wrong?

I’m baffled by a failure of my R80G/S engine with about 30K miles on a totally rebuilt engine. And I mean everything rebuilt except removing the crank and cam. I did the timing chain. All new pieces, heads, rods, small and big shells, rings, etc., bar none. This is my fifth airhead engine rebuild. Today, I was doing about 60 mph and suddenly it feels like I’m running out of fuel. But this stumble was different. It was a real knock, in synch with the engine revs. I could hear it and feel it through the foot pegs. Prior to that, the bike worked fine, lots of power etc. I did think the valves were a bit loud, but I was riding in the city without earplugs, but I still made a mental note of it.

So the knock appears and I drop speed, open the second tap. No change. I coast to the shoulder (I’m in a tunnel) and kill the engine. As there was no real shoulder, I rolled to the end of the tunnel and start the engine again to cross a lane and get to the shoulder outside of the tunnel. Definitely a loud knock. Kill the engine and coast. When I stop, there’s a cup of oil dripping from the engine. It’s dark and I can’t see from where. Call a towing company and wait. The left side of the engine is covered, from the bottom of the starter cover down, with oil. From the edge of the timing cover backwards and from the bottom of the starter cover all the way to the tranny and down. It’s not a head gasket, as the head gasket is dry. The right side of the engine is bone dry.

When I got home, I removed the plugs. No soot and good looking color. I turn the engine over by hand in 5th gear. Usual friction, as if you’re setting valves. Start the engine with the plugs removed. It turns over fine. Oil light goes out. Sparks light up as should be (grounded) and lots of air from the spark plug holes. Oil level is fine, nothing measurable lost, about 40 % full after about 3,500 miles, which is “standard” for this engine. I try to start with the plugs in and there’s the knock again. Some other observations: the oil light did not go on, I lost about 80% power, the drive train is fine. I can’t make heads or tails out of this one. I went for dinner and a beer.

So now I’m wondering what it could be. Collapsed oil filter? I used BMW stock bendy filters (OX37) and I don’t have an oil cooler. Oil color is fine. Broken breather? If so, why the knock? Blocked oil galley? I have a magnetic plug and never had an issue with finding anything in the engine oil.

I am going to pull the front cover, starter cover and try and figure out where the oil is coming from. I don’t think I threw a rod, as I think I would feel that when turning over by hand (I’ve done LOTS of valve settings, so I know the friction when in fifth and turning the rear wheel by hand). Pulled stud? The cylinder and head are on firmly. The pushrods look fine and don’t explain the oil at the top. The little breather hole on the left above the carb is dry inside.


So I’m baffled … any ideas?


Thanks,

Kevin
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Old 10-20-2004, 07:03 AM   #2
norton73
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Ahh, I see you've got it over here too. I'll repeat my self

sounds like the oil is coming out the breather. Throwing a rod (Big end) usually is only heard at idle, goes away at speed.
I would bet you got the valve timing off, or it slipped, and a valve hit the piston, cracked it, or the valve bent and cracked a guide, and now the the bottom end is getting pressurized, and pushing oil out the breather. Pull the heads first, then check valve timing. Still just a guess at best, Good luck
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Old 10-20-2004, 08:19 AM   #3
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without seeing it i'm thinking a rod knock.

norton: if it were a valve thumping a piston he would see a bad pug. assuming he removed both, no?

kevin: does it run smoothly? (besides the knock) firing nicely on both sides?
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Old 10-20-2004, 09:02 AM   #4
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Loaded, you'd only see a bad plug if the valve head broke off, or there was something really wrong. I've seen cars and bikes jump timing and all the vavles were bent, but the plugs looked just fine. Now I have seen a piston come apart and whack the plug, but that's not the issue here.
Usually, a rod knock is only heard at idle, once the revs rise, the pressure holds the rod tight against the crank.
Another form of rod knock is at the small (wrist pin) end. That you can hear at all rpms.
But with oil coming out the breather, I'd say what ever is causing the problem is related to the bottom end becoming pressurized.

I rebuilt the engine on my wife's cast iron sporty many years ago. As part of the rebuild, I replaced the cam followers They are two piece jobs, an upper and a lower. After it was together, she complained about an intermitent miss, then it would run fine. I rode it, and experianced no problem. Checked ignition, valve timing, went through every thing I could think of.
At about 500 miles, it quit running on the front cylinder. I was ahead of her when it happened, and by the time I got turned around, she was swapping plugs from the front to the back. She said the front plug was oily, so she thought she'd see if by swapping plugs, she'd see if the problem moved along with the plug.
She fired it up, and oil immediatly started to come out the breather. I told her to shut it down, get on the back of my bbike, and we'd go get the pickup.
Got it home, the two piece cam follower had seperated (must have been doing it intermitantly, and then going back together, hence the earlier miss), caused the valve to whack the piston, broke the ring landing, and was pressurizing the top end, pumping oil out the breather.
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Old 10-20-2004, 09:11 AM   #5
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Quote:
Originally Posted by norton73
Loaded, you'd only see a bad plug if the valve head broke off, or there was something really wrong. I've seen cars and bikes jump timing and all the vavles were bent, but the plugs looked just fine. Now I have seen a piston come apart and whack the plug, but that's not the issue here.
Usually, a rod knock is only heard at idle, once the revs rise, the pressure holds the rod tight against the crank.
Another form of rod knock is at the small (wrist pin) end. That you can hear at all rpms.
But with oil coming out the breather, I'd say what ever is causing the problem is related to the bottom end becoming pressurized.
you'd see a wet plug if there was no or low compression and it was firing wierd or not at all.

when i was talking rod knock i was talking at the gudgeon pin. thats still the way i'm leaning.... based on no inspection.... the oil out the breather.... well... hmmmmm.... my theory has holes in it... as does something else.
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Old 10-20-2004, 10:39 AM   #6
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maybe...

I had a friend with a Guzzi Ambo, he left the fuel tap open for a few weeks and when he started the bike it threw out a ton of gas/oil mix out of the breather. The fuel had gone directly passed the floats into the sump and filled it completely......did you check your oil level? was the gas tank mysteriously empty prior to your ride?
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Old 10-20-2004, 01:38 PM   #7
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Spun the main bearing, chocked oil supply. Dead engine. Problem solved.... fuck. Anyone want a perfectly good G/S with a dead engine?
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Old 10-20-2004, 01:42 PM   #8
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Quote:
Originally Posted by Malindi
Spun the main bearing, chocked oil supply. Dead engine. Problem solved.... fuck. Anyone want a perfectly good G/S with a dead engine?
Where are you?
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Old 10-20-2004, 02:56 PM   #9
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Quote:
Originally Posted by Malindi
Spun the main bearing, chocked oil supply. Dead engine. Problem solved.... fuck. Anyone want a perfectly good G/S with a dead engine?
What a bummer!! At least you have all winter to find another engine.

P
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Old 10-20-2004, 05:08 PM   #10
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Quote:
Originally Posted by Malindi
Spun the main bearing, chocked oil supply. Dead engine. Problem solved.... fuck. Anyone want a perfectly good G/S with a dead engine?

Hmm, I just wrecked my wife's ST. I need a frame, you need an engine.....hmmm
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Old 10-20-2004, 07:10 PM   #11
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Quote:
Originally Posted by Malindi
Anyone want a perfectly good G/S with a dead engine?
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Old 10-20-2004, 08:36 PM   #12
Malindi OP
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Annie, I'm in Vancouver. And sure, Loaded, you can have it ... just leave a stash of cash under my pillow next to you leave here ...
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Old 10-20-2004, 08:38 PM   #13
Malindi OP
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Quote:
Originally Posted by norton73
Hmm, I just wrecked my wife's ST. I need a frame, you need an engine.....hmmm
How badly do you want a completly kitted out bike to go around the world with? Minus engine ---
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Old 10-20-2004, 08:54 PM   #14
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Quote:
Originally Posted by Malindi
How badly do you want a completly kitted out bike to go around the world with? Minus engine ---
it aint exactly "kitted out" if it has no engine
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Old 10-20-2004, 08:56 PM   #15
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Quote:
Originally Posted by Malindi
And sure, Loaded, you can have it ... just leave a stash of cash under my pillow next to you leave here ...
how much? keep in mind how much ruskie sold his gs, less than a year ago with similar kit in top running condition.
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