Really odd...

[panzershreck]

ok... while in the process of replacing all the belts & water pump on my M20 engine, i've really run into something totally unexpected... when putting the new timing belt on, i've discovered that the camshaft sprocket is 180 degress off, exactly 180 degrees... the sprocket has never been tampered with as far as i know, nor was it mis-aligned so tremendously in the process of taking off the original belt... so essentially, the engine has been running with a camshaft sprocket completely wrong... is this possible? did somebody just take of the sprocket off once and put it back on incorrectly? do you think i should risk it when i restart my engine with a possible mis-aligned camshaft?

[Bill R.]

ok... while in the process of replacing all the belts & water pump on my M20 engine, i've really run into something totally unexpected... when putting the new timing belt on, i've discovered that the camshaft sprocket is 180 degress off, exactly 180 degrees... the sprocket has never been tampered with as far as i know, nor was it mis-aligned so tremendously in the process of taking off the original belt... so essentially, the engine has been running with a camshaft sprocket completely wrong... is this possible? did somebody just take of the sprocket off once and put it back on incorrectly? do you think i should risk it when i restart my engine with a possible mis-aligned camshaft?

[George M]

ditto...if the cam sprocket is 180 out and you aren't bending any valves...hehe then no.6 was set up to your sprocket being 180 out as Bill stated. Pistons #1 and #6 achieve TDC on a BMW straight sixes at the same time. Valve timing is opposite of course....no.1 and no.6 do not fire at the same time :-) When no. 1 piston is on the beginning of its power stroke, no. 6 is at the beginning of its intake stroke and visa versa. If you change the sprocket location, be sure to set up your cam to the forward most cylinder which is no.1.
HTH,
George

[Bill R.]

rotating things he could bend a valve
Of course this is assuming he already has the belt off, if not then he can rotate the crank until the cam and crank line up correctly.





ditto...if the cam sprocket is 180 out and you aren't bending any valves...hehe then no.6 was set up to your sprocket being 180 out as Bill stated. Pistons #1 and #6 achieve TDC on a BMW straight sixes at the same time. Valve timing is opposite of course....no.1 and no.6 do not fire at the same time :-) When no. 1 piston is on the beginning of its power stroke, no. 6 is at the beginning of its intake stroke and visa versa. If you change the sprocket location, be sure to set up your cam to the forward most cylinder which is no.1.
HTH,
George

[George M]

my thought is...even if he has the belt off...rotate nothing if the motor is set on no.6 TDC at the beginning of the intake stroke which I presume it is with the timing sprocket out by 180 to no.1 being on TDC to the power stroke. Simply remove the sprocket and replace it to where it should be leaving the crank and cam where they are. Then put the fresh belt on. Either way. Safe route is put it back together with the cam sprocket 180 out...but who likes the safe route? :-)
George

[Bill R.]

tdc #6 and the cam is where it should be for that point...




my thought is...even if he has the belt off...rotate nothing if the motor is set on no.6 TDC at the beginning of the intake stroke which I presume it is with the timing sprocket out by 180 to no.1 being on TDC to the power stroke. Simply remove the sprocket and replace it to where it should be leaving the crank and cam where they are. Then put the fresh belt on. Either way. Safe route is put it back together with the cam sprocket 180 out...but who likes the safe route? :-)
George

[winfred]

the alignment pin won't allow that, my solution is throw a belt on and spin the crank over one more time and get it on the right stroke, then adjust if needed, it'll handle being a tooth or two off for a rotation, it's on exhaust stroke it needs to be on intake. what happined he didn't look at the cam mark when he set the crank at tdc it's a 50/50 chance of being right, the cam runs at half the speed of the crank, so you have two rotations of the crank for one rotation of the cam


Simply remove the sprocket and replace it to where it should be leaving the crank and cam where they are

[Bill R.]

Otay.






the alignment pin won't allow that, my solution is throw a belt on and spin the crank over one more time and get it on the right stroke, then adjust if needed, it'll handle being a tooth or two off for a rotation, it's on exhaust stroke it needs to be on intake. what happined he didn't look at the cam mark when he set the crank at tdc it's a 50/50 chance of being right, the cam runs at half the speed of the crank, so you have two rotations of the crank for one rotation of the cam