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Post by amster on Aug 30, 2010 11:24:09 GMT
Hi,
I've had my divvy S for a couple of months and have just snapped the cam chain.
Is there any easy way of replacing without an engine rebuild?
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Post by m40man on Aug 30, 2010 11:34:28 GMT
... Is there any easy way of replacing without an engine rebuild? That's some bad luck you've had. I guess you might be able to retrieve the chain (wire coat-hanger, try to hook the chain if you can see it?) so that you can use a split replacement & feed it round. But I would have thought you would likely have bent a valve or two if the chain snapped whilst riding. So to be honest, in my opinion, you'd be best finding a replacement engine - could be cheaper. Also, you won't be forever wondering what bits are knocking about in the bottom of your engine, debris from the snap. Prob not what you want to hear - & maybe someone will paint a rosier picture for you - but that's what I'd do. |
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Post by Deleted on Aug 30, 2010 11:41:22 GMT
You'd have to remove the head at least to check the valves and pistons for damage if it snapped during running, can't imagine it snapping when not running. I agree, it's probably cheaper and easier to get a second hand engine.
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Post by amorti on Aug 30, 2010 14:21:20 GMT
... Is there any easy way of replacing without an engine rebuild? That's some bad luck you've had. I guess you might be able to retrieve the chain (wire coat-hanger, try to hook the chain if you can see it?) so that you can use a split replacement & feed it round. But I would have thought you would likely have bent a valve or two if the chain snapped whilst riding. So to be honest, in my opinion, you'd be best finding a replacement engine - could be cheaper. Also, you won't be forever wondering what bits are knocking about in the bottom of your engine, debris from the snap. Prob not what you want to hear - & maybe someone will paint a rosier picture for you - but that's what I'd do.  What they said, you can't just replace the camchain. What happens is, the chain snaps, the engine keeps spinning but the valves stop, and the piston(s) hits the valve(s) and that's where your expensive damage comes from. How many miles does it have? How do you end up with a snapped camchain? It's run full-time in an oil bath, so that's worrying  |
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Post by bobh on Aug 30, 2010 15:47:52 GMT
Bad luck.
As said above, if you can find an engine at a fair price that's probably the best option. But if not, proceed as follows:
1. There will be some damage inside the cylinder head, so it will need to come off to find out what. If you're lucky, it will just be one or two bent valves. If not, it could be a damaged piston or two and possibly scored bores, in which case you have to decide whether you want to carry on at considerable expense, or wait until another engine turns up. There may also be damage to the crank, rods and/or bearings if contact has been very heavy.
2. If it appears to be just valves, retrieve the old chain, plus any bits that might be lurking in the bottom of the engine (tell me. someone - I don't have a Divvy now so can't check for myself - does this engine have a detachable sump base? If it does, then cleaning the engine out, and threading a new chain, would be a lot simpler). Turn the crank over by hand to make sure all is free and as it should be. If you have a depth gauge, check that the piston(s) in the bore(s) where contact has taken place are not sitting measurably lower than the others, which would indicate damage down below. Also make absolutely certain that any apparently undamaged valves do return properly onto their seats. It's probably worth taking them all out and checking the stems for straightness, and lapping them in lightly (i.e. do a good old-fashioned decoke).
3. Once you're satisfied that all is OK and it's worth spending money, replace the bent valves and thread a new chain round the crankshaft (I've not done this when there hasn't been an old chain to pull it round with, but I imagine at is possible, if a bit fiddly, by threading some flexible wire in there first) and rivet it.
4. Check and reset the valve clearances while the head is off the engine (that way you don't need the special tool), then remove the camshafts (again). Set the crankshaft so the pistons are half-way up their travel so the valves don't clash (wouldn't that be dumb?) and fit the head (torques as in Haynes). Thread the camshafts in and set the timing, again as in Haynes.
5. Put everything else back on, fill the engine with some cheap and cheerful oil, cross your fingers and give it a whirl.
6. Change the oil and filter as soon as you think that any residual rubbish in the engine will have had time to get caught in the filter - maybe 50 gentle miles? That should be enough to confirm whether the bike's running sweetly or not.
7. Flog it quick (but not on this site, thank you very much).
Good luck - Bob
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Post by pilgrim on Aug 31, 2010 22:39:54 GMT
Doom and Gloom merchants! Unfortunately they're probably right. Have a look at the top end to evaluate the damage then decide. Trouble with seeking out another engine is just that, possible trouble with the replacement, you just don't know.  The bit that I don't understand is there is no definitive rule on when to change the cam chain and when you do can you simply pull an open chain through and join it? Haynes describes a new continuous chain threaded over the crank shaft, hence the expense in replacing it.  |
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Post by bobh on Sept 1, 2010 8:08:20 GMT
Pilgrim - yes, you sould be able to get an open chain which can be pulled through with the old one, then rivetted (same tool as a drive chain, but smaller anvils).
Life-wise, at least 100K miles should be OK provided the adjuster hasn't stuck at some point and allowed it to flap about.
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