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8.1 re-power update and question on camshaft timing before start

bobct

Advanced Contributor
I can't believe I've been doing this for almost four months, I could have built another house by now :)

I got engine #1 back from the machine shop and doing the reassembly now. This is the one that had the horrible oil analysis and I have to say they pretty much nailed it. I wound up going .30 over because of the cylinder scoring, new pistons/rings, cam bearings. Camshaft and crank were fine, 7 connecting rods were fine (but new bearings) but one was bent. I also did the oil pump and timing chain which leads to my question. The shop installed a single row chain and I swapped that out for a new double row setup like it originally had. The 8.1's have had a few different updates to the cam sensor/timing over the years and that related directly to the type of cam sprocket. So the single row chain wouldn't have worked anyway because the new cam sprocket wouldn't have been read the cam sensor.

I am 100% certain that I had the dots on the cam sprocket and timing gear correctly aligned when I did the swap. What I am starting to doubt is whether I was at TDC vs being 180 degrees off. Is that even possible? I've rotated the engine a couple of times so I know there is no piston/valve interference. If I can do that would you call it good?

Is there a visual check I can do while the valve covers are off to double-check myself? I wish these 8.1's had some type of timing marks anywhere front or rear but I haven't found any.

thanks
Bob
 
Bob:

Glad to hear you are making progress...

If the timing marks on both sprockets were aligned, you should be good to go....because there's only one mark on the cam's sprocket, you can't be "180 off".

If you want to 'double check' the assembly, I'd suggest rotating #1 to TDC (compression stroke) and make sure both valves are closed. If so, you should be fine.

With the computer sensors and controls, GM decided it wasn't 'cost effective' to keep any timing marks....welcome to the age of electronic controls...
 
Thanks, I should be good but will double check tmrw. I’m hoping to get the intake manifold on next and then maybe a day away from doing the first start/break in.
 
I got engine #1 back from the machine shop and doing the reassembly now. This is the one that had the horrible oil analysis and I have to say they pretty much nailed it. I wound up going .30 over because of the cylinder scoring,
That would hopefully be .030" over, not .300" over! :D


I am 100% certain that I had the dots on the cam sprocket and timing gear correctly aligned when I did the swap. What I am starting to doubt is whether I was at TDC vs being 180 degrees off. Is that even possible? I've rotated the engine a couple of times so I know there is no piston/valve interference. If I can do that would you call it good?
As the crankshaft is being rotated, and when the crankshaft's sprocket "dot" is at 12:00 O'clock, the #1 crank throw can't help but place the #1 piston at/near TDC.
(keep in mind that until the camshaft sprocket is also indexed, it does not yet know if this would be on the Compression stroke or on the Exhaust stroke)


Is there a visual check I can do while the valve covers are off to double-check myself? I wish these 8.1's had some type of timing marks anywhere front or rear but I haven't found any.
In order to create true TDC markings, you would want to perform a PPS procedure. (PPS = Positive Piston Stop)
Once true TDC has been established, you would then make your markings.

thanks
Bob

Bob:

Glad to hear you are making progress...

If the timing marks on both sprockets were aligned, you should be good to go....because there's only one mark on the cam's sprocket, you can't be "180 off".

If you want to 'double check' the assembly, I'd suggest rotating #1 to TDC (compression stroke) and make sure both valves are closed. If so, you should be fine.

With the computer sensors and controls, GM decided it wasn't 'cost effective' to keep any timing marks....welcome to the age of electronic controls...
Mark is dead on!

Thanks, I should be good but will double check tmrw. I’m hoping to get the intake manifold on next and then maybe a day away from doing the first start/break in.
Bob, just prior to installing the intake manifold is the perfect time to adjust your cam follower plunger depths .... also known (in a misnomer fashion) as adjusting the valves.

(with the intake manifold not yet installed, you'll have a great visual on the plunger movement)

Bring #1 piston to TDC on the C/S. (this does not necessarily need to be a precision TDC)
Adjust the #1 intake and exhaust valve rocker arm nuts as to set the cam follower plunger depth as per OEM.

Next, rotate the crankshaft 90* so that the next cylinder in the firing order will be @ TDC.
Do the same adjustments to both intake and exhaust rocker arm nuts!

Next, rotate the crankshaft another 90* so that the next cylinder in the firing order will be @ TDC.
Do the same adjustments to both intake and exhaust rocker arm nuts!

Continue until you have completed all 8 cylinders.

This is referred to as the 8 stop static procedure.
Do this, and you will not need to go back through them dynamically.

Good luck!





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Mark, why would it be any different from the earlier version?
As you can see here, the tops of all cam followers are visible with the intake manifold not yet installed, making is very easy to see when the plunger begins to move!

s-l640.jpg






s-l640.jpg
 
....................... I’m hoping to get the intake manifold on next and then maybe a day away from doing the first start/break in.

Be sure to load the engine shortly after your initial run.
In other words, you will not want to run it for very long before you begin your actual "under power" run-in or break-in.
(piston rings need pressure behind them in order to properly seat them to the cylinder walls)


As for Mark's comment...... I would still like to hear back from him.

Unless I've missed something, your hydraulic plungers will be visible prior to installing the intake manifold.
This allows you to view the plungers.
Then after you have achieve zero rocker-arm-to-valve-stem lash, the further adjustment begins to move and set the plunger depth, of which is the actual goal.

I've been using the 8 stop static procedure for well over 50 years.
I have yet to see the need to go back through them dynamically.

Your call on that!

Good luck and have fun!
 
because GM went to a non adjustable valve train in the Big Blocks about 25 years ago.....

where did you get those pics?
 
because GM went to a non adjustable valve train in the Big Blocks about 25 years ago.....

where did you get those pics?

Mark, as you may know, my experience is more so with the SBC.
When I read your post;
"not on a 496...", I questioned myself and did a Google search.
My search query was "BBC long block"!
The pictures that I found came up as a 496/8.1L BBC engine.

So, what you are saying is that the BBC valve train geometry has been pre-determined and is no longer manually adjustable ..... correct?



I just did another search (BBC 8.1L) and came up with this picture.
Gen7 BBC Vortec 8.1L / 496MAG



maxresdefault.jpg



Now, if the rocker arm nuts are intended to be bottomed out (as in Non-Adjustable hydraulic cam followers) after any proper or necessary shimming, the cam follower plungers would incorporate additional travel (over that of the earlier versions).
In other words, these would be what we could call "fully self adjusting" once shimmed correctly.

Keep in mind that
the 8 stop procedure can still be used!
In fact, it would benefit this gentleman who is basically doing the same thing, but while using the 2 or 3 stop procedure.
The 8 stop ensures that we are at exact bottom of base circle for each cylinder being adjusted.
https://www.youtube.com/watch?v=03ci0WdLdKk



So Mark, I'll stand corrected and I'll stand in the barrel for 3 days! :D

man-wearing-a-barrel-caraman.jpg






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Ricardo, yes it was .030! So, the engine came back to me with the heads installed and all the adjustments were done. I actually got it back together and did my pre-break in run of about 25 mins at varying RPM's and then an immediate oil/filter change. It ran great, no noises, idle was smooth, oil pressure was around 65-70 PSI which matched what I got on my mechanical gauge during the manual priming. A couple of very minor punch list items (re-torque exh manifolds, H/E drip) but I think it's ready to go.

Would you guys run it again or call it good (enough) to install and do a real break-in under load? I'm hoping that anything really major would have revealed itself in a 25 min run and not 30 :)

The second one should go a lot quicker and that one might not require as much machine work. I'm going to pull the heads on that tonight.

Bob
 
Congrats on the first half!

I would call that one done, once your punch list items are done. there is no 'cam breakin' required with roller lifters....You need to load the engine to do the remaining break-in....unless you have free access to a dyno......
 
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