Dadddio

Getting ready to remove my crank bolt.
When my engine is at TDC do I turn the
til the 45TDC comes around the first time,
or the second?



***Drive it like you stole it***

aaddpp

Earlier thread on topic with a good explanation - Dave

https://rennlist.com/forums/928-foru...ar-offset.html

James Bailey

It can be useful to paint some 45 degree marks on the cam pulleys before removing the belt so you can get it close to right. Reduces the pucker factor when you start rotating the crank with the new belt in place to confirm timing at TDC.

WallyP

Putting the 45-degree marks on the cam sprockets before removing the belt should be standard procedure for everyone. If you check the cam timing, recheck the added markings and get them as close as you can. Makes it much easier and safer when putting the belt on.

And James is right on (as usual) about the pucker factor when checking.

fraggle

... and get a bunch of cheap spring clips from office max, you'll thank me when you're looking for three or four hands when restringing the belt.

dr bob

To the original question--

On the crank, it doesn't matter whether the crank is at 45 degrees before top dead center on compression stroke or the exhaust stroke. For timing the cams, it's important to have the 45 degree mark before top dead center on number 1 on the compression stroke. Once the crankshaft is locked at 45 degrees before top dead center, the cams can be moved to any position you like.

SeanR

Why don't you just put everything at TDC (Crank, both cams) and then lock the crank in place and do it that way? The only time I ever use the 45 degree mark is if I'm removing the cams or heads from a car.

Dadddio

Thank you Dr. Bob.
That's what I needed to know.

Keep ya's posted.


***Drive it like you stole it.***

James Bailey

If the cams roll on valve spring pressure it is thought that you MIGHT bend a valve as the cam rolls .......also if you lack the flywheel tool you MIGHT rotate the crank by accident. 45 degrees and you KNOW the valves are safe.....

Dadddio

So, 45BTDC is the same whether its the first time around
or the second? Is that correct?

James Bailey

the cams are in different positions as the rotate at 1/2 crank speed BUT with the pistons 1/2 way down or up you can move the cams anywhere you like.

WallyP

The point is - there is no TDC-Firing or TDC-Exhaust unless the cams move.

You need the cams at the proper position to put the belt on with the crank at the 45 deg BTDC position. The best way to do that is to turn the crank to TDC, then look at the cams.

If the cam marks are not at the TDC alignment marks, then turn the crank 3/4 of a turn clockwise (tightening) to the 45 deg BTDC position. If the cam marks are at the TDC alignment marks, then turn the crank 1 3/4 turns clockwise (tightening) to the 45 deg BTDC mark.

The cams should now be 22.5 deg BTDC, and the crank 45 deg BTDC. Now is the time to carefully check for marks on the cam sprockets that align with the notches in the backing plate. If there are no marks there, carefully make some. The original timing marks on the cams should be 22.5 deg counterclockwise from the new marks.

The pistons are now all down in the bores, so the valves cannot hit no matter how you turn the cams. (If turning the cams becomes necessary.) You can now remove and replace the timing belt, keeping the cams at the new marks, and the crank at the 45 deg mark. After the belt is installed and tightened to approximately the proper tension, you can turn the crank 45 deg to TDC, and the original timing marks on the cam sprockets should align with the backing plate notches.