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2001 Triumph Bonneville 34000 miles

So I went out for a 100 mile ride this weekend. I would call the riding expeditious with a fair amount of revs for a long period of time (fast freeway + fast twisties).
Upon arrival home, oil started dripping (a lot) out of coming out of the air box (crank case breather into the air box) .

I've had done an oil change before the ride and was pretty certain on the amount of oil I added.

so ... the excessive oil blowing out from the crank case breather / air box, did I overfill the oil level or am I getting blow by at the rings ? Other ideas?

And, polling the audience, where should the oil level be relative to the sight glass ? I've read 1/2 way up the sight glass? Mine was clearly above the sight glass.


Ideas ?

Thanks
 

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My nickname at this point is Mr. Blowby as I've run the gamut of blow-by troubleshooting on my '04 Thruxton. I won't bore you with the details, but will instead offer a prioritized (by ease and price) list of things to check.

1. You mentioned it. Oil level. No more than half, maybe even a bit less. Try that first. I run right around 1/4 up the sight glass now with no issues. It took me a long time to get to the "no issues" point.

2. Breather tube seal. This is pressed in to the clutch cover and is around $32 for just the seal. You have to remove the clutch (aka primary) cover to get to it. You will also likely need a new clutch cover gasket unless you have a nice Cometic one. Unless someone has removed the clutch cover lately, this is unlikely to be the cause as they usually don't just go bad. They get buggered up when removing and reinstalling the clutch cover.

3. Centrifugal breather. This is held on by two Torx screws to the primary oil pump gear and is around $60. Dead simple to replace once you have the clutch cover off. In fact I will submit it is easier to replace than the breather tube seal. This is what was faulty on my bike. It took me a year and well over $1,000 to figure this out. There are no moving parts to this piece, but somehow they do fail. If the oil level doesn't fix your problem, my advice is to replace both this and the breather seal at the same time. Because if none of these solutions fix your problem you on are to:

4. Piston rings. Right. I tried this before doing item 3. Went with a 904 kit. New pistons, rings, punched out barrels recoated with Nikasil. Cost me just over $1200 when it was all said and done and I did the install. Boy was I pissed when I still had a ridiculous amount of blowby. Yes, worn rings can cause your crankcase to overpressurize which will result in more blowby and subsequently more oil out the breather into the airbox, but this is unlikely and can be identified by a compression test.

In summary:

1. Check and adjust oil level to somewhere between 1/4 and a little below half. Clean airbox and breather tube, ride and whomp on bike, to include 10 or so minutes at highway speeds. Evaluate blowby. Be aware there will be some residual oil left in the tube. If problem persists, move on to:

2. Get clutch cover gasket, oil breather seal and centrifugal breather. Drain oil, remove clutch cover, replace seal, centrifugal breather and cover gasket, button back up. Replace oil, repeat riding procedure. If problem persists, evaluate discretionary bank account and dedication to bike. Then:

3. Either bump up to 904 kit, or get next size up OEM pistons, rings, have cylinders bored to match pistons and relined with Nikasil and go from there. A stock rebore is almost the same price as getting the 904 kit because of the Nikasil. Or:

4. Sell Bonnie, by new bike.
 

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Getting oil level correct on these bikes is a bit of a fiddle. The sight glass indicated level seems to be very sensitive to bike being dead level to the ground both front to back and side to side. Not sure how folks get this right with just a sidestand to hold the bike up. Even using a centerstand can be misleading as the rear is then higher than normal riding position. Correct way to check is to hold bike level on ground then check the sight glass...but this is very tricky to do without a helper to hold bike or do the looking....

Have you ever emptied the oil drain tube under the airbox? This accumulates blowby and needs regular emptying. Triumph made this tube hard to remove and most folks ignore it. Needs an extended hose with a stopper cap at low end to more easily reach.
 

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I think the clue here is that you changed the oil before the ride. This suggests to me that you overfilled it, unless you don't normally give it a good thrashing and doing so has highlighted an issue. Over the years there have been loads of threads on many forums about checking the oil level in bikes that have a sight glass and that require the oil level to be checked with the engine warm. Over-filling is by far the most common issue, leading to oil leaks and/or excess oil being chucked out through the breather. My approach to this, having over-filled in the past, is to try to drain the oil completely when doing an oil and filter change. Then I add exactly the amount of fresh oil specified by the manufacturer, according to whether I've changed the filter or not (I sometimes don't if the mileage since the last change is too low to warrant this), using a measuring jug and being careful to keep count of how many lots of 500ml I've added. Having filled the engine I then start it, run it for the time specified in the manual, stop the engine and wait for the specified time, then look to see where on the sight glass the oil level is. After that, when checking the oil level after a ride, I assess it against the known mark, taken with the bike on its main stand (I always fit these if the bike doesn't come with one). Pretty well all the bikes I've owned hardly ever need oil adding, though none does the specified mileage anyway, oil changes being done on an annual basis rather than on mileage. I find this systematic approach eliminates other variables, so that should one of my bikes start blowing oil into a breather I'd know that there was a fault.
 

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You answered your own question.

My method is bike on the center stand, pre-fill the filter, add oil until there's 0.4 quart or 0.5 liter left (of four quarts or liters), button it up and walk away. At that point, pay no attention to the level in the sight glass, it means nothing. Check the level next day, should be no higher than middle of the sight glass.

If you want to ride it in the meantime, no problem, but check the level after it sits all day or overnight. It doesn't have to be any more complicated than this, the bike doesn't care exactly how much oil is in there, but too much is not good.

As mentioned, if you don't have a center stand, it's trickier.
 

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Save some time and mess, dont bother filling the filter.

I just add the correct amount of oil and I’m done.
 

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Save some time and mess, dont bother filling the filter.

I just add the correct amount of oil and I’m done.
The OP added "the correct amount of oil" and it didn't work for him. That's why he's here asking about it.
 

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Most likely overfilled it. My "leak free" Thruxton would drip after an oil change. Now I fill so that I can just see oil in sight glass, start & run motor until oil is hot, shutoff, put on centerstand & walk until motor cools completely. I then carefully add oil until it reads half way up the glass.
 
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