BMW R1200GS. Piston met valves - new piston needed?

[c_dug]

Boy am I having a bad week! I was literally waiting for the next sunny day to get some nice pictures and list the bike on eBay, but apparently life has a different plan.

Last Monday on what was likely to be my final outing on the GS it fired it's spark plug like a bloody cannon, fortunately it missed the nearby cars and pedestrians. A quick inspection showed the threads had shot out all the way down to the base, I'm guessing there was some damager there, could have caused it myself I suppose, who knows.

Anyway, recovered to my sister's place nearby where they fortunately have a well equipped garage. Tuesday I took the head off and dropped it to a nearby well-regarded workshop to have an insert fitted.

Today I picked it up again and refitted. Clearly made a giant cock of things because very long story short I've managed to break two exhaust valves on the side I was working on. Not entirely sure how this hapoened as I am certain I followed the book to the letter, but obviously I dun-goofed somewhere along the way. Very angry at myself, no need to rub it in (please!).

Tempted as I am to never touch a set of spanners again as it now seems I've fucked both the spark plug thread and the valves, I do need to reverse this mess and can't afford the workshop bill to pay somebody to do it for me, so I'll be fixing it myself one way or another.

Question is, how much do I need to replace?

Cylinder head is a write off for certain, the broken valve stem stabbed a nice hole right beside the valve seat.

The piston has some very minor dents in the centre which I'd imagine would be fine, but there is a slightly deeper dent near the edge which I'm less sure about, I'd like opinions please.

The bike neve fully fired up, it turned over once before stalling. Do I need to worry about crank bearings?

I checked the cylinder bore and that at least looks fine, so no worries there.

Anything else I should be checking?

I still plan on selling the bike so I'd like to repair it as cheaply as possible whilst still doing everything that needs doing, I wouldn't want a dodgy repair job playing on my conscience.

Pictures to follow very shortly, just uploading to Imgur.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[c_dug]

Hopefully this works!

First picture shows the cam sprocket slipped around the camshaft, you can see the locating key and keyway on the camshaft are 20-30° apart. I'm certain they were aligned when I put the cam sprocket on so not sure how this occurred.

https://i.imgur.com/uR1wjeG.jpg

Next picture shows the piston damage, I'm not sure it's shown well in the photograph but at the lower edge in the picture you can see the deepest ding.

https://i.imgur.com/fuRqv8i.jpg

Last picture shows the head.

https://i.imgur.com/tVJeut3.jpg
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Riejufixing]

[Riejufixing]

[c_dug]

The key is still in place and looks undamaged. As per the Haynes book of lies I cable tied the chain and sprocket together when I popped them off of the camshaft, I don't really get how they've ended up so far apart!

Anyway, that's all in the past now.

Can't easily take more pictures, the bike is over an hour away.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Robby]

If you shear a woodruff key then the bolt holding the bits together wasn't tight enough. The key is just for locating, not for taking much torque.

I assume that to do the job right requires buying or making a special tool to lock the camshaft.

(laughs in pushrod)

You can't really gauge the state of the piston until you clean it up. To work out if you damaged crank, rod or bearings you can measure the barrel deck to piston top height using feeling gauges under a straight edge, or a micrometer. Compare measurement against workshop manual (if it has it) or the other side (if you can to dismantle more stuff).

Or just leave it, it's probably fine. The alloy piston is barely marked.

[stinkwheel]

Might want to check the width of the ring lands with some feeler guages to make sure it hasn't collapsed them.

Head is probably salvageable. May be cheaper to just replace with a used one though and definitely easier..
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Riejufixing]

[Pete.]

Nowt wrong with the piston. Main that can hold up to the huge pre-ignition forces you can get on these will be fine too.

If it was my cylinder head I would weld it up, or at least attempt to.

Otherwise, call Motorworks or James Sherlock. My choice (by experience) would be Motorworks as unlike Sherlock they have always given me 100% competent and satisfactory service.

Bloody shame that the 2 engines on ebay both are damaged RHS
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[c_dug]

[Pete.]

Whole engine and box £250 or offer. Dropped a valve on the other pot. Box is worth a couple of hundred probably.

https://www.ebay.co.uk/itm/bmw-R-1200-GS-engine-assembly-for-spares-or-repair/223839051326?hash=item341dd8de3e:g:licAAOSwcABeFK1G
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[buddy]

Id leave that piston, itl go again👍
Ive left much worse on shit cars ect

Edit: yeah if the damage is near the edge of the piston its probably worth checking the land isnt pinching the ring.
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When this baby hits 88 miles per hour... you're gonna see some serious shit.

[c_dug]

[Polarbear]

One of my friends BMW did exactly the same, valves hit piston, and I've heard of others doing it as well. Is there a flaw in the engine they don't want to admit to?

It can't be just down to bad maintenance cause my mates was pretty new at the time and had been religiously maintained.
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Triumph Trophy Launch Edition

[c_dug]

Funnily enough the donor engine I bought apparently dropped a valve with no notice.

I'd love to blame mine on the same, but I'm certain it was my own mistake and not a random mechanical failure.
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[A100man]

[Polarbear]

[MCN]

[c_dug]

Well, it was a loooong day yesterday, but in the end I rode my own bike home 40 odd miles on the motorway and a few miles of country lanes, and it worked flawlessly, actually felt the best it has in a while.

Once I removed the old cam gear the damage was obvious when compared with the replacement.

https://i.imgur.com/Y6DchoF.jpg

I'm still not entirely sure how this happened but my best guess is I hadn't located the key properly into the keyway on the camshaft before torquing it down.

I gave the piston a real good clean up too and the damage at the outside was much less severe than I thought:

https://i.imgur.com/PEyFpr9.jpg

It catches the light in pictures but in reality it's probably .5mm deep at the very most and also a mm or two further in from the edge than I thought which made me much less worried about the rings.

I carefully scraped the burr off of the top then turned the engine over a few times by hand and inspected the cylinder wall. No sign at all of anything untoward going on below the crown of the piston so have gambled on it being fine rather than removing the cylinder and measuring it all up - perhaps I'll regret that, but it was the difference between riding home yesterday or leaving it at my sister's for a about three more weeks.

Home sweet home:

https://i.imgur.com/d6geFww.jpg

Plan now is to do an oil change, run it for a few weeks to make sure it's all hunky dory, then crack on with changing it for something a bit sportier. Borrowed my dad's K1300GT whilst the GS was off the road, and I think it's swung the decision in favour of a VFR1200 rather than K1300S.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[c_dug]

Oh, also, the second engine I picked up must have been run on coal or something. Honestly I've never seen so much carbon buildup in an engine. It was very impressive! I reckon a good tablespoon of loose deposits came off of the piston without even scrubbing.
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Riejufixing]

[Polarbear]

Nicely sorted.
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Triumph Trophy Launch Edition

[c_dug]

[Robby]

I don't think you are. It looks like someone who is not an engineer is trying to get picky about a minor thing with someone who is also not an engineer, but does manage a load of them.

I would call it a key, because it locates something but should be subjected to no torque when in operation. The interference fit or locating bolt does that job.

Not that it matters. It's fixed, you learnt how to avoid that sort of thing in future. I assume it's one of those jobs where really need 3+ hands - one to hold the cam hard onto the shaft when you go it up, and two more to operate the torque wrench. It looks like the bolt moved the sprocket during the last bit of tightening, so it slipped off the key.

Was there a washer between the bolt and sprocket? Seems like the ideal place to use one.

[Riejufixing]