When assembling my engine I, of coarse ,established piston TDC w/ a dial indicator in # 1 cylinder. I decided to check the next cylinder in the firing order by rotating the crank 90 degrees. Well the piston was several degrees from TDC. This tells me that my timing( both valve timing and ignition timing )aren't the same on all cylinders w/ this crank. Is this something to worry about w/ a 500 hp engine?? The engine is still on the engine stand and all but buttoned up! Thanks for your replys! Larry

 

If the crank was turned and done right it should have been indexed.
If it's an aftermarket,same thing. It won't kill things but ya are leaving a little on the table.
If ya had what ya thought was a "0" deck ya now have pistons at all differant heights.

 

Not necessarily, Larry. The crank index can be off, without the stroke varying from cylinder to cylinder. It can be a combination of the two, but it isn't automatic.

 

If the index is not at 90* on each throw then that throw is going to bring the piston to a different height than the others and if it's the only throw that's not 90* then 6 will be at 90* height and those two will be whatever half it's measurement is off of 90*.If it's 84* when checked then each piston will be 3* off and however much that is in thousand's for height (ain't worth figuring right now). I have had them as much as 12*off and that's a bunch when trying to run a "0" deck height.

If the key is off then ya got to grind the shaft to get all throws in line at 90* apart.

The way they get that far off is the crank is twisted from load or metal fatigue and the same for the key and the snout.The snout generally doesn't get hurt unless it's a belt drive blower motor. I have had a couple that had to be thrown away because I figured from the amount they were out the metal was like rubber and wouldn't last long.

 

If you are stating the piston will be at a different height when the crank is rotated in 90º increments, because the journal itself would not be at a true 90º, then yes, I agree, the piston height will be different. I stating, if rotating to the most stroke, the stroke could/would be there, but journal would not be at an accurate 90º.

 

Amazing!!!!!!

Aren't the journals suppose to be at 90*?????
That's the way I've always tried run them.Turns out they seem to run better like that.

 

I don't think he was questioning anything other than your point that you have "pistons at all different heights". If the stroke is the same on all throws, and only the angle is wrong, eventually during the rotation, there will be a straight line through the center of the crank, the center of the throw and the center of the wrist pin, and the piston height will be equalfor all cylinders when that happens. It will just reach that height at a different point in the crank rotation than you would figure with true 90deg between throws.

I'm sure he's aware that the intent is to have 90deg between throws.

 

Thanks, Fred. Obviously, we are/were not on same page, Larry.
Different wording, on my part, with same goal in mind, may have made a diff.
The above quote was what compelled me to respond. A twist in crank (journal(s) out of 90º index) has little to do with theoretical deck, as Fred explained. I'm confident you knew what you were attempting to convey though. So it is not you (or your mechanical knowledge) I was questioning, but your wording. Maybe I should have stated the index (crank timing) will be off, but not the actual deck height.

 

Yea, if the index is different between throws,then when it comes time for the valve and ignition event the piston won't be in the right place at the right time.Hence not all are making or doing the same thing,which makes a difference in HP.
If it's different to the key(but at 90* on all throws) all events will be off between crank and cam.
Thats OK I have never been one of those people that can spell it out without showing.I can explain what,when,why&where while I am doing it but ya gotta read between the lines for me to explain at the blackboard.

I knew what I was saying anyway,maybe other folks didn't.