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Old 03-21-2013, 09:42 AM   #1
Asianrider OP
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F800GS: rebuild top end

Well, bad luck I guess.. after just over 80'000 km my engine's started to belch a big white smoke, and eats oil like there's no tomorrow. Turns out compression on one cylinder is dead. The ever helpful (sarcasm included) BMW rep tell me I should repair the whole top end, replace pistons, rods, all valves, etc.. Sure, easy for them. But: Big job = big $ - a no go for me right now.

So I'm willing to open up the beast and have a look at the internals, and rebuild what needs to be rebuilt. E.g., if it's just the rings that broke but the pistons are clean, than why replace them, right ? so I've got a few questions for you:

- who's done this before, any major issue ? special tooling ? reports ? I'm not a great wrench but I can get help.
- isn't 80k a bit early for that kind of issue ? it's just less than 3 years old (a 2010 model). Granted I've brought it all around Africa, but that was a lot of long stretches at moderate speed.. Ok, I guess it could happen at any time. I should be happy it's happened at home and not in the middle of Congo
- what parts would you repair anyway once the engine's open, knowing the mileage ?

Thanks,
Laurent

PS: can somebody share a copy of the factory repair DVD to get me a head start ?
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Old 03-22-2013, 09:28 AM   #2
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Big Can o Worms

Well, sorry bout yer luck. At least you had a good time with it first.

Where are you located? This will help with getting help. If you were my neighbour I'd work for beer.

Of course the Dealer will recommend everything. Lets not call 911 when you may just have a boo boo. The way to troubleshoot the problem is to pressurize the bad cylinder at top centre of it's compression stroke with shop air pressure. Bike in first gear with rear brake full on. Now where is the air going? Out the exhaust? Bad exh valve. Into the airbox? Bad int valve. Into the crankcase? Bad rings. Into the radiator? Bad head gasket. Etc.

Sounds like a head gasket to me. There was another guy here with the same problem but under warranty. He was in SA travelling I believe. Got a new head gasket.

There's no point removing the engine until you properly diagnose it first. Then, evaluate the damage step by step as you remove parts. Stop disassembling when you find the smoking gun. Look in the valve adjustment threads for detailed information on disassembly. Paying for the Repair CD would be worthwhile for a mechanic friend to browse the night before.

There was also a near new engine for sale in the Flea Market I think went unsold. It was a 650 twin but over 90% of the parts are the same. You could throw it in "as is" or swap the cams over. A detailed look in the parts fiche would tell you the differences. http://www.ascycles.com/Illustrated_...catname=Engine
It would be cheaper and faster this way. Then sell or repair the blown engine.

You have options. Troubleshoot further before shooting the horse.
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Old 03-24-2013, 08:14 AM   #3
Motorfiets
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I've rebuilt mine...

PM sent
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Old 03-30-2013, 03:00 AM   #4
Asianrider OP
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Thanks for the tips. I'm based in Southern France so yeah, any help is welcome. Beer is aplenty..

I've 'found' the factory repair manual, it helps. Gee, taking apart all these connectors is a chore. On my '84 Tenere there were just a couple of those to undo and that was it

Now I need to find an anchor point to lift the frame, and a way to hold the engine in place once it's off.

I'll keep you posted on how it goes.

Laurent
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Old 03-30-2013, 03:47 AM   #5
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Asianrider, my cam chain thread will get you through engine removal.

http://www.advrider.com/forums/showthread.php?t=727687

The top end will need someone else to assist but but once you can get the engine on a bench you will be 80% there. Granted the last 20% is significant, but the labor should be straight forward.

Good luck!
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Old 03-31-2013, 02:53 PM   #6
JoelWisman
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Looks like you have plenty if help with disassembly, so instead I will posit a guess at what's wrong. Eating oil and lots of smoke. Piston LAN fracture, with likely subsequent bore scoring.

Hope not but its what I've most commonly seen
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Old 04-01-2013, 05:27 AM   #7
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Just my .02, but if I have an engine torn down, I'm going to put all new stuff in. If you're doing it yourself, then the cost difference shouldn't be too great just freshen it all up.
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Old 05-23-2013, 07:52 AM   #8
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Damage assessment

Hi all,
eventually I got it all in pieces. To cut a long story short here's the culprit :



No surprise here. Unfortunately the broken ring pieces have slightly scratched the cylinder surface



I have no idea how bad it is, really. To the touch it doesn't feel like much but I'd need a specialist to know more. I've called BMW to know what they would do but over here they're clueless (or they don't like people doing their own mechanics, whichever. Maybe both). For sure they don't carry oversize pistons so I guess the cylinders aren't supposed to be rebored ?

So has anybody direct experience with this, how does one fix the cylinder surface ?

cheers
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Old 05-23-2013, 07:59 AM   #9
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Hi Laurent,

You should be able to get the cylinder replated with Nikasil or a similar coating to get a uniform surface in the bore again.

If anything else is damaged beyond repair I have lots of used parts in very good condition from a F650GS twin - everything except the camshafts is exactly the same as the F800GS.

Cheers,
Lukas
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Old 05-26-2013, 04:38 PM   #10
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Lukas,
thanks for the tip. I'm looking for some information on who could do that over here in France. But I'm not sure I understand, is the nickasil plating going to "fill" the scratches ?

One thing for sure, BMW isn't selling any oversize piston. How would they fix it ? throw the whole engine away ? (sorry but as usual the BMW retailers here are extremely unsupportive).

Laurent
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Old 05-28-2013, 12:05 AM   #11
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I would imagine that in Europe, you will be able to procure replacement cylinder barrels (from a used or crashed bike) more cheaply than you will be able to repair your damaged part.
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