Timing chain stretched?

[DaveH]

Well the fun of the F800ST was brought to an untimely hiatus at the weekend. Loss of power and development of loud rattle/archetypal bag of spanners led to the bike making the test of the journey courtesy of the AA.

Started looking at it yesterday, plugs look OK, I think, other than a huge gap. The valve clearances are within the limits, if at extremes across a the cylinder. Noticed that the timing chain sometimes went slack between the cams though, that shouldn't happen, should it? The timing marks still seem to line up.
Video here, apologies for the sniffing. Bike is in to gear, no plugs and dipstick out, but still required quite an effort to move.
https://youtu.be/7-7ZVWnOU0c

Next move will be head off, PITA that the rear swing arm attaches to the engine case!
Photos:

[Green_Ninja]

could ba that the timing chain tensioner has snapped/broken, that would be my next thing to check.

[DaveH]

Sorry, forgot to post those pictures. Tensioner looked ok, no damage and cleaned up ok.

[Green_Ninja]

yes but does it still tension the chain when in place? For it to happen suddenly it could point to the tension going, or if the chain is stretched it could have 'jumped' a tooth.

[DaveH]

Ah , sorry; still a lot of force in spring and it keeps the chain tensioned, other than the places where it drops between the cam gears and the timing marks still line up, the chain is pulled tight at other points.
Can only think that the chain has stretched at these points as thought that even though it pulls the chain round, the 'push side' should still be taut?

[7550]

Does it happen at the same part of the chain or is it random ?

[DaveH]

Not sure, thought it was a couple of places, but the timing marks still show up in the right place.
Was tough to rotate engine, the later engines have better nickel plating on the bores, apparently and the early engines suffered from piston slap?
Suspecting piston/bore issue and maybe that could stretch chain as it would be dragging during travel but not at tdc, but am just a glorified typist to trade, so...

[Alzo]

I think the camchain Tensioners rely on oil pressure too...the spring is just to keep an initial contact going.
Was it a complete loss of power...from your description it sounds like it has valve issues.

[DaveH]

It seemed to pause, briefly, during acceleration, started to clear, then started rattling - sounded like the exhaust had blown at the headers, but nothing obviously amiss - did cross my mind that it may have thrown a plug as had that happen on my old CB750

Took the decision to try make it the mile or so to Claunie Hotel, despite the additional damage that it would do, as didn't have mobile on me and wasn't sure at what point mates would realise that I had stopped and double back.

Made it there ok, losing power as it went and called the AA.

These early engines had a reputation for going bang, unless they had been recalled and retro fitted with longer pistons that don't wear the bores.

Such is life. Have now got a replacement engine on the way - newer variant, so no such issues, only 1500 miles and comes with a 6 month warranty. Considered breaking the bike for spares, but rest of bike in good enough condition to keep it.

Will be taking the head off the old engine, maybe even the cylinders, to see what the damage is.

[Alzo]

All the best with that Dave.

[DaveH]

Cheers.

Regardless of what was wrong originally, a repair would not be much less than the replacement engine, take more time and there'd always be an element of doubt - assuming I could fix it.

[Manic636]

Shame Dave, went well on memorial and sounded fruity on the throttle. Good luck with the transplant

[DaveH]

Set about the final stage of the engine swap this morning, as in wheel off, swing arm off and starting to undo bolts. The left hand front swing arm /engine bolt was turning but not easing up.
Left it for a bit to settle down and tried later but it went pop.
There was a tiny bit protruding so heated the area up and tried tapping it round, but protruding piece deformed and sheared off.
Drilled it out to see if that eased it before trying an extractor. One drill snapped, one deformed so decided to go risk the extractor snapping.

Anyone had issues like this or have an idea what to try next?

Cheers

Dave

[Alzo]

A quality set of drill bits...start small 4mm for example...then work up in increments.

[DaveH]

Set of cobalt ccw bits on order