Advice needed - timing chain

[kev2809]

Long story short, I'm replacing an engine on a 96 2500 silverado. going through gaskets and "easy" stuff now that I have the used replacement engine on the stand. while doing the timing chain and cover..when I put the new chain back on, the dots line up on the gears, but the teeth were ever so slightly off. I'm talking like 1/16" or so. the points of the teeth didn't quite line up. is this going to cause trouble? I haven't pulled the distributor at all and probably don't plan to. I did line up the dots when removing the old chain and gear...damn I had hell pulling the cam gear sprocket. my puller kept rotating the engine, so I had to keep taking it off and rotating til the dots lines up, then try again til I finally got it.

[AussieinNC]

The dots on the timing gears are sometimes off just a tad.

So long as the dots line up through the centerline of the cam and crank you will be good.

Note....and so many people make this mistake...

When the dots are placed with cam gear dot at bottom and crank gear on the top, the engine is set to fire on cylinder #6.

When the dots are placed with cam gear at 12 oclock and crank gear at 12 oclock, the engine is set to fire on cylinder #1.

Your choice to remove the distributor and intake manifold, but the end gaskets especially at the rear are the usual upper area leak locations.

Finally when you are installing the ignition leads, dont mix up cylinders 5 and 7....again a common mistake.

Have fun...

[kev2809]

I put everything back together and it's sitting on the stand ready to go in, I just got the old engine out yesterday. but yes, the dots seemed ok, just the corresponding teeth looked a little off. but while putting the harmonic balancer and pulley back and tightening them down, the timing line from the timing cover was a little off on the balancer timing line too, seemed even more than the dots. now, the balancer COULDVE moved while tightening the bolt...but I don't remember checking before putting the balancer on


so..I guess my question is...what IF it's a little off...will it run poorly? I should've taken a picture to show the fraction I seen!

[AussieinNC]

The balancer is keyed to the crankshaft....if it moved during tightening the crank would have moved as well.

The outer ring of the balancers sometimes rotates around a little.

If you want to ensure the timing tab and balancer marks line up correctly you can do a positive stop procedure to index a new line on the balancer.

Purchase yourself a positive stop tool (amazon has them cheap). https://www.amazon.com/ZFLXH-Univers...s%2C101&sr=8-2

Set your engine to what you believe is TDC on cylinder 1 on compression. Look for the vales on cylinder 6 to have exhaust just closing and intake just opening. This is known as overlap.

The tool goes into the number 1 spark plug hole but first turn the crank backwards about half a turn. Screw in the stop tool and very slowly, manually turn the crank clockwise until the stop tool prevents any further crank movement. Take a white marker and mark a line on the balancer at the 0 degree mark on the tab. Now rotate the crank BACKWARDS slowly until you feel it stop again and mark a white line on the balancer. Remove the stop tool and turn the crank clockwise until you can see the two white lines. Measure the distance around the balancer using a tape and make a mark on the balancer at the mid point of the distance. This mark is now your true TDC mark and should be used for timing purposes. Remove the other marks. Take a small file and scribe a heavy line across the edge of the balancer then fill it with white permanent paint.

[kev2809]

I actually bought one of those piston stops years ago...but if I don't really care that the lines line up for physical appearance, is still necessary?

[AussieinNC]

Maybe its me, but I always run the true TDC check and mark the balancer....that way I know the timing line is accurate....

I prefer to do it right the first time....

But its your engine....

[MySons68C20]

Originally Posted by AussieinNC

Maybe its me, but I always run the true TDC check and mark the balancer....that way I know the timing line is accurate....

I prefer to do it right the first time....

But its your engine....

I agree! There is no way to know your true timing unless you use a piston stop to establish TDC.

[kev2809]

Originally Posted by AussieinNC

Maybe its me, but I always run the true TDC check and mark the balancer....that way I know the timing line is accurate....

I prefer to do it right the first time....

But its your engine....

Originally Posted by MySons68C20

I agree! There is no way to know your true timing unless you use a piston stop to establish TDC.

agree with both of you guys, I'll dig out the tool and make a new mark if its off. I'm just trying to understand the physical appearance of the gears and the timing dots to actual timing. I figured since nothing on the inside was removed, and I never pulled the distributor, then technically you can slap a timing chain and gear in any way and still functions the same? man I feel so dumb asking this type of stuff lol

also, on these 5.7 vortecs, they don't have a traditional timing tab. there is a solid line on the timing chain cover, and a solid line on the balancer. I remember my old 305 had numbers in that area, this one does not

[RustyPile]

The piston stop procedure is not actually a part of "routine" timing chain replacement. Timing marks cannot "relocate" during a timing chain replacement, as the marks are related to crankshaft position, not camshaft position.. Although, it is a procedure of precision for degreeing in a camshaft position for high performance race engines.. When the balancer ring is suspected of rotating out of position, piston stop is a good way to determine this.. One or two degrees off would be considered acceptable, but any more than that and the balancer should be replaced.

[kev2809]

right, the bottom gear is keyed and only goes on one way, and the same with the top gear with that little "4th" hole..it only goes one way. maybe I am just over thinking this whole thing

[AussieinNC]

Just a thought...

Did the replacement bottom gear have more than one keyway in it?

There are some gear kits that permit a small amount of advance or retard depending on which keyway slot you use in assembling.

If the bottom gear only had one keyway slot, you will be fine.

[kev2809]

Originally Posted by AussieinNC

Just a thought...

Did the replacement bottom gear have more than one keyway in it?

There are some gear kits that permit a small amount of advance or retard depending on which keyway slot you use in assembling.

If the bottom gear only had one keyway slot, you will be fine.

yes, it only had one keyway. I went with a stock replacement. while I have you guys here, I'm thinking of yanking the distributor to make it easier to get the motor back in. if I remember right, I set the #1 piston to TDC, pull the cap and make sure it's pointing at #1 piston, then pull it? same procedure to reinstall? I REALLY don't want to pull it, but it made the bellhousing bolts so easy with it out the way

[AussieinNC]

Depends on clearances above the distributor to replace it....
I usually leave the distributor installed but remove the cap and rotor...

That makes getting to the top two bolts easier most of the time.

Just remember to install the distributor before turning the crank...meaning dont install the convertor bolts until after the distributor is back in place.

[kev2809]

Originally Posted by AussieinNC

Depends on clearances above the distributor to replace it....
I usually leave the distributor installed but remove the cap and rotor...

That makes getting to the top two bolts easier most of the time.

Just remember to install the distributor before turning the crank...meaning dont install the convertor bolts until after the distributor is back in place.

ah good call. on this replacement engine I have not pulled the distributor at all...only on the old engine when I pulled it. I think k the cap and rotor will be good enough to make enough room!

[kev2809]

I pulled the cap and rotated until the timing on the balancer lined up with the timing on the cover. looks to me the rotor is pointing straight to #1

[MySons68C20]

Looks right to me you got it!

[AussieinNC]

That looks good to me....

I would paint that groove in the balancer with white permanent marker...makes seeing the timing easier for these old eyes.

[kev2809]

so, I got it in and after replacing the fuel pump and adding gas (that's another story lol) it turns on and runs but idles rough. I bought a live data scan tool off Amazon and it's showing code 1345 which is crankshaft sensor. this little scan tool shows the timing at -18 when it's in park and idle. I never pulled the distributor..how could it be this far off? could it be a bad sensor or do these need to be "relearned"?

edit - I'm thinking it could be a bad distributor. I seen this video on YouTube and I do remember my rotor having play in it like the video. I just checked the rotor out of the original engine and it has the same play. what do yall think?

https://youtu.be/whldyq0kJOo?si=qjluCpRD8R7dHuGQ

[kev2809]

I went ahead and loosened the distributor and turned it counter clockwise and it immediately idled better and steady. what's weird is the scanner showed the spark advance had dropped to -12...I cleared the code and restart it and it showed -22.5 degrees spark advance..but still idled fine. maybe this spark advance on the scanner is not what I am supposed to be using to get in the +2 -2 range?

[AussieinNC]

The scanner is picking up signals form various sensors including the crank sensor.

Did the fault code on the crank sensor clear and not return?

What is the idle speed?

[kev2809]

i turned it on and let it idle for a bit to warm up and the rpms are right around 750-760 i believe...the "spark advance" is at -22. when i drop it in gear the RPMs rise to about 830ish then drops back down to 750 range. the "spark advance" drops to around -16 then goes back up as well. i need to get this thing out on the road and see how it handles under acceleration. from what i have been reading, this "spark advance" on my little scanner is not telling me the +2 -2 range. i guess i need a better scanner..apparently i need one that reads "CMP retard"..which this one does not.

and for the code, i cleared it myself once it started idling better. im hoping to move a little bit of miles on it and see if it returns, and to see how she runs. either way, i think sometime soon i will be getting an aluminum distributor and get away from the plastic stock ones. with the cap off on both rotors, i can turn the rotor a quarter inch in both directions, so i know they both have a little play in them, which cant be a good thing.

[kev2809]

just little update for my own sake, ran it about 35 miles and no engine light, or ugly running conditions like i was having. also rebuilt the ac system and blows nice and cold! now on to other gremlins i need to work out like the weird jerking around 50 mph..lol

thanks for yalls help!