Timing questions on rebuild

[awoz87]

ok so i finally got all the parts and everything back from the machine shop and have the engine mostly back together, but i hit a snag.

when i was putting the cam in i had the timing mark on the cam straight up and the pistons at TDC, lined everything lined up on the TCI mark on the stator so i put the head on. now today i was getting in to set valve clearance and noticed when i had cylinder #1 (stator side) at TDC on its compression stroke (piston comes up with exhaust valve not opening) the mark on the cam is pointing down. now im wondering if i put the cam in upside down? can the came go in upside down? i have the timing mark facing the stator side of the engine and the threaded end of the cam is facing the clutch cover side.

from what i am making of it the cylinders will be firing at the top of their exhaust strokes. unless both fire at the same time (i dont THINK that is correct) then i am just an idiot


thanks in advance for any help.

 

[5twins]

I think you're OK. The pistons rise and fall together but at TDC, only one cylinder is on the compression stroke and ready for valve adjusting. The other is just finishing it's exhaust stroke. The crank is at a 2-1 ratio to the cam - the cam spins half as much as the crank. Rotate the motor another 360° from where you are now to put the motor at TDC again and that cam mark should be pointing back up.

 

[awoz87]

correct, the cam mark will be up, however it will be at the top of its exhaust stoke. the coils fire individually correct?

 

[CDNTX650]

Plugs fire at the same time if you have a TCI ignition model.

pistons rise and fall together. 80+ use a wasted spark set-up. one just fires on the exhaust stroke.

 

[grizld1]

Remember, the valve events are controlled by the camshaft. As far as crank and pistons are concerned, TDC is TDC. If you installed the camshaft at TDC with the punch marks leveled to the head and the notch down instead of up, it would make no difference.

 

[awoz87]

Plugs fire at the same time if you have a TCI ignition model.

pistons rise and fall together. 80+ use a wasted spark set-up. one just fires on the exhaust stroke.

its an 83. but this answers my question i believe, both will fire at the same time always, one at the top of the compression stroke one at the top of the exhaust stroke. correct?

Remember, the valve events are controlled by the camshaft. As far as crank and pistons are concerned, TDC is TDC. If you installed the camshaft at TDC with the punch marks leveled to the head and the notch down instead of up, it would make no difference.

i understand that but it could still be put in backwards right? as in one side of the cam over the wrong cylinder

 

[CDNTX650]

correct. and correct, the cam can be installed backwards. There should be a threaded end on the cam shaft on one side...that side should be on the RIGHT if you are sitting on the bike. That is where the advance mechanism would go if you had a points equipped bike. Other side is the points. Thats what would be under the covers up on the head.

 

[awoz87]

Awesome. Thank you for the help guys, looks like I have no problem after all.