For Timing/camshaft/ignition experts?

I red already some old 3D on similar subjects. We all know about tearing down top-end for valve reshim:

:eek:

Align marks on crank (clutch side), align marks on camshaft gear, piston on TDC.

Now the manual at valve check page tells about searching for TDC compression stroke.

Same manual, further pages ahead, in topend tear down section, tells about searching for TDC on exhaust stroke. Why? :thumbsup:

We know that TDC on compression is with the cam lobes looking backward while TDC on ex. is 180 degrees opposite.

Now, looking at how the CDI module, flywheel and pickup coil are designed the spark is signaled and fired every crankshaft rotation. So there is always a useless spark (the one with piston at TDC on exhaust).

The question is: having all the marks aligned, it shouldn't matter if I mount the camshaft as dismounted or rotated by 180 degrees (very easy to happen on CRF). If it was dismounted at TDC compression, rotating the camshaft by 180, convert the "mechanic" phase to be a TDC on exhaust.

The bike should fire up when kicked right as everything is aligned from a mechanical perspective and CDI send spark at every rotation. Right or wrong?

:thumbsup:

Possible reasons the engine shouldn't fire with camshaft rotated by 180? I cannot think about any? :bonk:

Than, if above true, why the manual is so complex making all those differences? They should have told: align all the marks as indicated no matter either how the camshaft lobes are positioned or if piston is TDC compression or exhaust (TDC is enough).

Am I missing something? :p

I red already some old 3D on similar subjects. We all know about tearing down top-end for valve reshim:

:cool:

Align marks on crank (clutch side), align marks on camshaft gear, piston on TDC.

Now the manual at valve check page tells about searching for TDC compression stroke.

Same manual, further pages ahead, in topend tear down section, tells about searching for TDC on exhaust stroke. Why? :thumbsup:

We know that TDC on compression is with the cam lobes looking backward while TDC on ex. is 180 degrees opposite.

Now, looking at how the CDI module, flywheel and pickup coil are designed the spark is signaled and fired every crankshaft rotation. So there is always a useless spark (the one with piston at TDC on exhaust).

The question is: having all the marks aligned, it shouldn't matter if I mount the camshaft as dismounted or rotated by 180 degrees (very easy to happen on CRF). If it was dismounted at TDC compression, rotating the camshaft by 180, convert the "mechanic" phase to be a TDC on exhaust.

The bike should fire up when kicked right as everything is aligned from a mechanical perspective and CDI send spark at every rotation. Right or wrong?

:p

Possible reasons the engine shouldn't fire with camshaft rotated by 180? I cannot think about any? :bonk:

Than, if above true, why the manual is so complex making all those differences? They should have told: align all the marks as indicated no matter either how the camshaft lobes are positioned or if piston is TDC compression or exhaust (TDC is enough).

Am I missing something? :prof:

i am so very tired now so i hope that came out kinda understandable ,

i will check it in the morning when i get up and see how bad i butched it :worthy:

ok, i deleted my ramblings because i was wrong and this misinformation can ruin a motor , sorry guys i really was tired ----i can't believe i did that :thumbsup::eek:

i will not do that again :lol:

they tighten the cam down and it opens the valves and pushes the exhaust valves into the piston

At TDC exhaust piston is ending exhaust and going to start intake. That is the overlap area where exhaust valves are almost closed and intake are just starting to open, therefore there is no interference with piston travel.

so if you wanted to install the cam with the lobes facing foward you can only go 90 degreese , not 180 :thumbsup:

if you wanted to install the cam in lobes foward at 180 degreese off you would have to have the piston at bdc in order to get it in time and not hit valves into the piston

No, if you put in BDC your engine is out of timing. From TDC compression to TDC exhaust there is a complete crankshaft turn 360 (half 4S cycle that is 720 dgs.) that is equivalent to 180 turn of the camshaft that as you said is rotating half of crank speed.

You can mount the cam 180 rotated as on exhaust TDC both valves trains are opened very little so not much spring force to overcome.

At TDC exhaust piston is ending exhaust and going to start intake. That is the overlap area where exhaust valves are almost closed and intake are just starting to open, therefore there is no interference with piston travel.

No, if you put in BDC your engine is out of timing. From TDC compression to TDC exhaust there is a complete crankshaft turn 360 (half 4S cycle that is 720 dgs.) that is equivalent to 180 turn of the camshaft that as you said is rotating half of crank speed.

You can mount the cam 180 rotated as on exhaust TDC both valves trains are opened very little so not much spring force to overcome.

Kelstr is correct. Your reasoning sounds good, but you have to consider the cam duration.

Kelstr is correct. Your reasoning sounds good, but you have to consider the cam duration.

maurpra has got us on this one biz, :thumbsup:

i knew i should not have written that so late , i am wrong ,dead wrong.

i got up early this morning and relized what i had done the second i opened my eyes :thumbsup: ( i can't believe i screwed up a 7th grade auto class question --i feel so ashamed )

anyway i am going to re-read the orignal question and see if i can't see what maurpra was seeing in the manuel that i totally overlooked :bonk:

i will add a line in my orignal post warning others to not install their cam or cams like this , ---infact my info was so dangerous i may deleat it because it will ruin a motor .

i just re-did a 06 yz250f that the kid and dad installed their cams like this at bdc and ruined the valves

I red already some old 3D on similar subjects. We all know about tearing down top-end for valve reshim:

:worthy:

Align marks on crank (clutch side), align marks on camshaft gear, piston on TDC.

Now the manual at valve check page tells about searching for TDC compression stroke.

Same manual, further pages ahead, in topend tear down section, tells about searching for TDC on exhaust stroke. Why? :thumbsup:

We know that TDC on compression is with the cam lobes looking backward while TDC on ex. is 180 degrees opposite.

Now, looking at how the CDI module, flywheel and pickup coil are designed the spark is signaled and fired every crankshaft rotation. So there is always a useless spark (the one with piston at TDC on exhaust).

The question is: having all the marks aligned, it shouldn't matter if I mount the camshaft as dismounted or rotated by 180 degrees (very easy to happen on CRF). If it was dismounted at TDC compression, rotating the camshaft by 180, convert the "mechanic" phase to be a TDC on exhaust.

The bike should fire up when kicked right as everything is aligned from a mechanical perspective and CDI send spark at every rotation. Right or wrong?

:eek:

Possible reasons the engine shouldn't fire with camshaft rotated by 180? I cannot think about any? :bonk:

Than, if above true, why the manual is so complex making all those differences? They should have told: align all the marks as indicated no matter either how the camshaft lobes are positioned or if piston is TDC compression or exhaust (TDC is enough).

Am I missing something? :cool:

i can't see where you are missing anything ,( i believe you are correct )the only thing i would kinda consider is that what i noticed doing this is that there is some spring tension when tightening the cam like this because you are finnishing exhaust and it would be easy for the cam carrier to tweak and jam a dowell pin and possable not get the cam and carrier installed flush onto the head :thumbsup:

i am not at the shop so when i get in this morning i will re-read the manuel and see if i can find where they want us to look for tdc on exhaust stroke, i don't remember reading this in the american or canadian manuel :p

i can't see where you are missing anything ,( i believe you are correct )the only thing i would kinda consider is that what i noticed doing this is that there is some spring tension when tightening the cam like this because you are finnishing exhaust and it would be easy for the cam carrier to tweak and jam a dowell pin and possable not get the cam and carrier installed flush onto the head :thumbsup:

/QUOTE]

I agree with you, more difficult but not that much.

i am not at the shop so when i get in this morning i will re-read the manuel and see if i can find where they want us to look for tdc on exhaust stroke, i don't remember reading this in the american or canadian manuel :bonk:

I have a US 2003 manual: Pages 3-10 and 3-13 speaks about compression TDC.

Page 8-5 says TDC on exhaust.

Page 8-25 says TDC on compression again.

May only explanation is that, on 8-5 your are going to dismount the camshaft. To do so, you'll be obliged to unscrew first gear bolt and than to access second gear bolt you'll have to rotate the camshaft exactly by 180. That will bring you back at TDC compression ready for remount (ie page 8-25).

Anyhow assuming the engine will fire anyhow it sound to me un-useful complexity.

I have a US 2003 manual: Pages 3-10 and 3-13 speaks about compression TDC.

Page 8-5 says TDC on exhaust.

Page 8-25 says TDC on compression again.

May only explanation is that, on 8-5 your are going to dismount the camshaft. To do so, you'll be obliged to unscrew first gear bolt and than to access second gear bolt you'll have to rotate the camshaft exactly by 180. That will bring you back at TDC compression ready for remount (ie page 8-25).

Anyhow assuming the engine will fire anyhow it sound to me un-useful complexity.

you got a good point there, i have that same 03 manuel and after reading it several times ,--the dam thing is goofy ,

i can only think they are talking about rotating the engine to remove the second allen head to remove the gear --same as the conclusion you cam too :thumbsup:

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