Engine assembly - #1 cyl at TDC how accurate? Important?

[turbogrill]

Hi,

 

I am about to put on my head onto the block. (N47 head, flattop pistont, nothing crazy).  According to all the manuals the cam should be aligned to the mark and #1 cylinder should be at TDC.

 

How accurate at TDC does it have to be? I have turned the crank a few times and I think it is at its top location, but I haven't done any accurate measurements.

 

What happens if it's 2-3 degrees off? Will the cam be out of phase by this amount or will it fix it self once I put the chain on?

 

Thanks

[Gollum]

Is the front timing cover off I assume? Then it doesn't matter to be "exact", it just gets you in the ballpark for the marked links on the chain. One mark will go on the crank sprocket and the other on one of the three marks on the cam (which allows for stretch adjustment).

 

Usually once I get the crank side on and the cam sprocket in the chain properly I use a wrench on the block section in the middle of the cam to adjust the cam a degree or two as needed so the sprocket slips on. Then you can put the tensioner on and reassemble the front cover.

[turbogrill]

Ok thanks!

 

Yes front cover is off, it's just the block. So all I have to do is to make sure that #1 piston is at it's top position?

 

 

[Gollum]

Correct, make sure the piston is visually at the top (it actually pokes OUT just a touch if you look closely, but don't worry if you're not that exact) which make the marks easy enough to align. Make sure the camshaft lobes on the #1 piston are both "up" and you'll be in the ballpark on the head. Then use the lighter color links on the chain to be "sure" timing is right.

[turbogrill]

On 1/10/2018 at 10:00 AM, Gollum said:

Correct, make sure the piston is visually at the top (it actually pokes OUT just a touch if you look closely, but don't worry if you're not that exact) which make the marks easy enough to align. Make sure the camshaft lobes on the #1 piston are both "up" and you'll be in the ballpark on the head. Then use the lighter color links on the chain to be "sure" timing is right.

 

Hi,

 

I had to slightly rotate the camshaft to get the chain on into the correct position, I think it's the same as moving the cam a little like you did.

 

As long as the following is correct I should be good right?

- Cam marker aligned to the "notch"

- Chain bright link at the cam sprocket mark

- Chain bright link at the crank sprocket mark

 

Obviously the cam might be needing some advance/retard but that is a different story I guess.

 

 

So, before (painted a red dot at the marker):

Almost almost

 

Only way it goes on is on the link above, but this is obvously wrong (and doesn't align to mark):

 

After rotating the crank CCW just a tiny bit I managed to get it on right:

 

My cam is almost exactly in the middle of the notch, some say it should be a little to left. So maybe mine is a little advance. Not sure...

 

 

The rebuild book recommend that you should find the exact TDC. But why? This method seems much easier?

 

[TimZ]

Of course this method is easier - it doesn't tell you anything useful.  If you don't know where the crank is with any accuracy then the position of the cam timing mark is meaningless.

 

FFS you have the engine apart - go buy a $40 magnetic base dial indicator and a timing wheel and learn do degree the cam and do it right.  It isn't that hard,to learn how to do and when you're done you will understand the answers to all the questions you are asking.

Edited January 17, 2018 by TimZ

[Gollum]

Tim is right in that there's a lot you can learn by doing it "right" and you can document with certainty what your cam spec is as well as advanced/retarded nature.

 

That said, I hate degreeing a cam while the engine is in the bay. If that's the case, then odds are I'm just going to assemble and run, especially if I'm using all OEM parts. Now, if I bought an aftermarket cam or was using adjustable cam gears, that's another matter entirely. There's a reason people use the tensioner lockup tool in order to avoid pulling the front cover...

 

I think more to Tim's point though, is that doing this once you'll teach yourself a lot and that's worth it. It's like the first time you do anything. Spend the time to learn so that when you do it quickly down the road you have a clear picture in your head as to what's going on.

 

Edit: For feedback sake, those pics look fine. Being a touch advanced is fine as long as you check it semi often for stretch. Also, be sure to check again once you have the crank back to TDC according to the OEM indicator. This is also why I said move the CAM once you assemble, knowing your bottom is close to TDC (when I don't want to pull out my dial indicator I just feel for the "popping" out of the deck that only happens for a very narrow window. You'll see that with anything useful as a rough straight edge.

Edited January 17, 2018 by Gollum
More info

[turbogrill]

2 hours ago, TimZ said:

Of course this method is easier - it doesn't tell you anything useful.  If you don't know where the crank is with any accuracy then the position of the cam timing mark is meaningless.

 

FFS you have the engine apart - go buy a $40 magnetic base dial indicator and a timing wheel and learn do degree the cam and do it right.  It isn't that hard,to learn how to do and when you're done you will understand the answers to all the questions you are asking.

 

1 hour ago, Gollum said:

Tim is right in that there's a lot you can learn by doing it "right" and you can document with certainty what your cam spec is as well as advanced/retarded nature.

 

That said, I hate degreeing a cam while the engine is in the bay. If that's the case, then odds are I'm just going to assemble and run, especially if I'm using all OEM parts. Now, if I bought an aftermarket cam or was using adjustable cam gears, that's another matter entirely. There's a reason people use the tensioner lockup tool in order to avoid pulling the front cover...

 

I think more to Tim's point though, is that doing this once you'll teach yourself a lot and that's worth it. It's like the first time you do anything. Spend the time to learn so that when you do it quickly down the road you have a clear picture in your head as to what's going on.

 

Edit: For feedback sake, those pics look fine. Being a touch advanced is fine as long as you check it semi often for stretch. Also, be sure to check again once you have the crank back to TDC according to the OEM indicator. This is also why I said move the CAM once you assemble, knowing your bottom is close to TDC (when I don't want to pull out my dial indicator I just feel for the "popping" out of the deck that only happens for a very narrow window. You'll see that with anything useful as a rough straight edge.

 

Thanks for the input. I also just realized that I need to know exact TDC for ignition purpose. I am running Megasquirt with a nice timing system, I guess the OEM indicator can't be trusted.

 

BRAAP has a different method from the Rebuild Book, he don't know the exact TDC until the cam is degreed,  http://www.classiczcars.com/forums/topic/20414-how-to-degree-your-l-series-cam/

 

I am having issues getting trust worthy camspecs for my cam as well, I bought it used.

 

Edit:

If this would be a stock cam and a stock head then there would be no need to find exact TDC right? Since the cam would need degreeing.

If the "oblong groove" of the locating plate is in line with the camshaft sprocket then the cam is at TDC, then with marked links it's impossible for the crank not to be at TDC.  

 

Edited January 17, 2018 by turbogrill

[Gollum]

Well for ignition timing your crank pulley and timing mark NEEDS to be God, because it's the one absolute reference you'll have when tuning. The megamanual goes over this, that you configure your settings then with the engine running you use a timing light to see how "off" you are and adjust the trim until what you see on the light is matching what you see in the logs. Now your crank and megasquirt are in sync and unless your mark on the front moves you can trust your tune to be accurate to the mark.