Graduation! My cam has been degreed!

[DrEntropy]

OH! And once you HAVE TDC on the #1 piston, you can use the same gizmo to check the other piston for 120* with a similar method, just that "halving" the points on the degree wheel where it stops SHOULD be 120*. My guess is you were seeing it "look like" TDC on 2&5, but actually it was at 120*... kinda hard to bend one-a them crankshafts. :smirk:

 

[DrEntropy]

Maybe I'm missing something, but how do yo know the kebabpointer is pointing where it needs to be relative to the crank/degree wheel? Seems like a bend would introduce error.

Determine TDC ~then~ align the pointer/degree wheel TO it.

 

[BryanC]

For instance, I could move all the way to 120 AFTDC
and there would be little change in the movement of the
pistons. They could be very close to the top of the
block and actually move very little between, say 112 and
120, but be very close to the top of the block nonetheless.

That's right. The method you used to find TDC on your degree wheel is not nearly accurate enough to do this job. You could be off by 8 deg. or more with this technique. It doesn't look like much movement of the piston but the engine isn't going to run the way it should if you're off by that much. Find out about the stop method and make sure you've got TDC located correctly. Then set the cam to the spec's. Setting based on crank angle at 0.050" open is OK (note that is usually 0.050 valve open with zero lash - not cam lift). If you are going to set it by peak opening, you can't just look at the dial indicator and try to guess where the peak is - you'll get the same inaccurate answer that you are getting with the piston. You'll have to look at lift on both sides of the peak (where it is moving enough to measure on the dial indicator) and then do the math to see where it was at the peak.

Bryan

 

[SilentUnicorn]

down and dirty sketch of a piston stop.


mark

 

[DrEntropy]

Geez, Mark! I'd do mine on paper an' scan it. :smirk:


Perfect, BTW. :thumbsup:

 

[PeterK]

Geez, Mark! I'd do mine on paper an' scan it. :smirk:


Perfect, BTW. :thumbsup:

If we could just get him to put this much effort into his schoolwork ...

 

[Scott_Hower]

Ok, I get it now.

I think I like the positive stop method and splitting the diff between strokes to find 0/TDC.

For future reference, how does one determine how far down to lock the nose of the bolt and how many degrees to split? Seems like it doesnt matter, but there must be some guideline. Or did I miss that yoo?

 

[SilentUnicorn]

Ok, I get it now.

I think I like the positive stop method and splitting the diff between strokes to find 0/TDC.

For future reference, how does one determine how far down to lock the nose of the bolt and how many degrees to split? Seems like it doesnt matter, but there must be some guideline. Or did I miss that yoo?

It doesnt really matter how far down the bolt is locked. About a half inch or so is usually sufficient. Too high and you take the chance of rolling it thu, and damaging the piston when you gently bring it into contact. this method beats a dial indicator for accuracy.

mark

 

[Roger]

. this method beats a dial indicator for accuracy.

No way. If the bolt is screwed down too far, you get a positive stop before TDC. Getting it so it just touches and no more is the way to find TDC, and that's not easy with a bolt - a dial gauge is way more accurate!

 

[swift6]

If I remember the stop bolt technique correctly, the stop isn't at TDC, which is why the height of the nut/bolt isn't critical. You set the bolt, rotate the piston until it stops and mark it on the degree wheel. Rotate the opposite direction until it stops and mark it on the degree wheel. The point directly in the middle of these two points is TDC. Without going back and reading it, I think that is also how it was described earlier in this thread.

As far as being better than a DI... I found it to be easier, quicker and at least as accurate as the most meticulous DI set up.

BTW, here is my bolt stop...

 

[BryanC]

Getting it so it just touches and no more is the way to find TDC,

I disagree. I believe the most accurate way is to find a spot on either side of TDC and mark the degree wheel there. TDC is then half-way in between. You can use a stop as Swift6 and others have described or you can use a dial indicator. The way to use the dial indicator is to pick a depth such as 0.100" below TDC (the exact value isn't critical). Mark the degree wheel at 0.100" as the piston is on the way up and mark it again at 0.100" on the way back down. TDC is half-way in between. There is so little movement of the piston near TDC that trying to tell when it reaches the peak is really just guessing - or at least this has been my experience. YMMV

Bryan