View Full Version : top dead center question


mikedabike64
December 20th, 2013, 12:19 PM
I'm getting a little nervous because, I have my cams out, waiting on my shims,
and my timing mark for top dead center keeps floating away
it keeps falling to the left counter clockwise, lol and I keep putting it back,
but it does not seem to be moving the piston away from top dead center,
my question is worst case scenario

# of revolutions to get it back to TDC.
because I know one is for the end of the compression stroke and the other top dead center is completely opposite,

worst case would I rotate it 2 revolutions ,



I took measurements of the number one piston as it related to #2 TDC
to rotate the crank as I might be reading into it too much.
ideally I would like to have the confidence to rotate it as many times as I want before I put the cans back in

alex.s
December 20th, 2013, 12:51 PM
1 revolution. the crank is directly mounted to the pistons.

if you are having a hard time visualizing it maybe take the spark plugs out and poke a stick down there? the mark on the crank lines up with tdc. with plugs out and cams off you can rotate the crank freely (try to only rotate the correct direction, make sure the cam chain doesn't get crunched down at the crank pinion)

the cams are what are rotating at a different rate. so if you set it to tdc, then use the marks on the cams to determine a correct alignment of tdc to cam timing, then it "doesn't matter" if the crank was on the intake or the exhaust stroke because you are setting which stroke it is on by setting the cams position.

all that matters is that it's at tdc correctly and the cam lines are lined up with the head case

bruce71198
December 20th, 2013, 03:15 PM
then it "doesn't matter" if the crank was on the intake or the exhaust stroke

At TDC the crank would be on the exhaust stroke or the compression stroke.;)

alex.s
December 20th, 2013, 03:56 PM
notice the word "was" making your attempt at pedantry irrelevant

mikedabike64
December 20th, 2013, 04:50 PM
Thanks guys Alex & everyone,
I really appreciate the help & dare I say I didn't get razzed too bad :) I know it comes with the territory,
but now that I think about it Alex, yes I am setting the intake and all
I feel stupid yet enlightened thanks guys :) cool. I just learned something.

bruce71198
December 20th, 2013, 06:09 PM
notice the word "was" making your attempt at pedantry irrelevant

+1 Just keeping the info accurate.

mikedabike64
December 24th, 2013, 12:23 PM
I just wanted to thank you guys for helping me with that top dead center question
I had fourteen thousand miles on the motorcycle when I got it
and they were never done before
but I could not have done it without the help from you guys and I appreciate that
it's expensive to have somebody do it,

and I really wanted to try to do it myself,
because the last time I tried to do that 17 years ago
on a ZX 6
I put the shim under the bucket instead of the keeper
an $800 later I got my bike back. the bike spit the shim dropped the valve
and bent some more of the other valves.
anyway with the 250
I took the carbs out and clean , & shimmed, new fork seals and heavier oil, chain and sprockets spark plugs , coolant, brake pads brake fluid,
I mean this thing was busted when I got it and it's running really good,
but I would not have been able to do it without your help so I give credit where credit is due thanks

alex.s
December 24th, 2013, 12:27 PM
:thumbup: no pics?? you can't tease like that then not provide the pics.