QuestionTiming chain had come off dirtbike, I put back on but, the bike won't start. Someone told me there is a way to "line" up the chain. Any advice would be appreciated.
AnswerPeter..... a "85 Honda dirtbike" isn't very informative, but I will assume that it is a single cylinder 50cc-250cc something....
It is called a "timing chain" for a reason.... it coordinates the crankshaft/piston position with the timing of the intake and exhaust valves. Once the timing has skipped or come off, as you mention, probably the valves have hit the piston and are bent, resulting in NO compression.
Timing chains rarely "come off" without a very good reason... usually they have never been adjusted properly and after they slap around inside for a long time, they break the tensioners and/or wear out a big groove in the cylinder.
The basic setup for cam timing is that you put the crankshaft flywheel in a position where the piston is at the top of the stroke. You will find a T mark on the flywheel and a matching index mark on the crankcase or stator depending on your machine.
Next, the camshaft lobes have to be positioned DOWNWARDS like an upside down V (^), so that both valves are closed and have some clearance at the rocker arms/valve stem interface. Most Hondas only need about .002" at intake and exhausts when the valves are closed and the camshaft is in the correct position. When the cam is positioned correctly, there will be a round punch mark (or sometimes a horizontal line across the cam sprocket which is placed even with the top of the valve cover surface). If it is a punch mark (o) then put it at the 12 o'clock position. In order to install the chain and sprocket on the camshaft, the camchain tensioner has to be backed off to give the chain plenty of slack. Once the cam timing is set correctly, release/adjust the camchain tensioner so there is firm tension on the camchain, when you turn the engine backwards or forwards, using the flywheel to turn the motor over.
Once that is done, you can gently turn the engine over TWO turns. The camsprocket should wind up exactly where you started. If not, then the chain could be off one tooth. Remove, reset and reinstall and recheck.
As I mentioned, if you just stuck the chain without regard to the camsprocket/crankshaft positions, then the valves are bent and the head will have to come off for damage inspection and repair. It is likely that the chain is extremely stretched, as well, and needs replacing along with related tensioner parts. Manuals can be found at most motorcycle shops, once you give them the correct model info. Or check Ebay auctions for various vendors.
Bill Silver
