Timing Chain / TDC Question

[Stamos]

Ok, I'm doing a timing chain replacement on my 87 GN. I did not set the engine at TDC before I started pulling it apart. I now have the front cover off and want to set it at TDC before I put the new double roller timing chain on. I was going to pull the plugs to spin the engine to TDC, but am unsure as to how to determine this at the stage I am at.

Is there an easy way to determine TDC with the stock timing gears?

Thanks in advance.

 

[PSID6]

Ok, I'm doing a timing chain replacement on my 87 GN. I did not set the engine at TDC before I started pulling it apart. I now have the front cover off and want to set it at TDC before I put the new double roller timing chain on. I was going to pull the plugs to spin the engine to TDC, but am unsure as to how to determine this at the stage I am at.

Is there an easy way to determine TDC with the stock timing gears?

Thanks in advance.

You could put your cover back on the dowels with a few bolts then slide your balancer back on then rotate to TDC. Or line up your timing marks or dots, upper gear at 6 o'clock lower gear at 12 o'clock.

 

[pacecarta]

if you didnt line the timing set up before you removed it first thing is remove the valve covers and remove the rocker shafts ..this should be in caps ..i should put this in caps because it must be done before the crank is rotated without a timing set inplace ..or dont move a thing.. put the old timing set and chain back on and then rotate to the point where the dot on crank gear is straight up

then with rocker shafts removed rotate the crank until the keway points directly at the centerof the #1 piston (driverside head)
the keyway lines up with the #1 rod journal
from there you can find the true TDC of the piston and install the crank gear to see that the TDC dot is pointing up
line up cam gear to the bolt holes s and spin the cam so gear indicator is pointing straight down lined up with the crank gear dot
now slide cam and crank gears off put them in the timing chain so they line up the dots and then slide the whole timing set onto the motor , once you get the cam bolts in verify the dots are still lined up with tension on the driverside of the chain
if dots are lined up rotate engine twice and make sure they still line up at TDC , remove cam bolts apply locktite and torque the bolts to 30 lb/ft
if its a double roller chain that looks like a bicycle chain on the backside don't run the tensioner if chain gets a tensioner install it ,
if its a double roller and the chain has a lot of slack on passenger side you should surce the correct timing set , linebored engines sometimes need an undersized timing set
if its smooth back multi bar link chain like the OE then you should run a tensioner

 

[pacecarta]

if all you did was remove the cover do as PSID6 posted

 

[Stamos]

if you didnt line the timing set up before you removed it first thing is remove the valve covers and remove the rocker shafts ..this should be in caps ..i should put this in caps because it must be done before the crank is rotated without a timing set inplace ..or dont move a thing.. put the old timing set and chain back on and then rotate to the point where the dot on crank gear is straight up

then with rocker shafts removed rotate the crank until the keway points directly at the centerof the #1 piston (driverside head)
the keyway lines up with the #1 rod journal
from there you can find the true TDC of the piston and install the crank gear to see that the TDC dot is pointing up
line up cam gear to the bolt holes s and spin the cam so gear indicator is pointing straight down lined up with the crank gear dot
now slide cam and crank gears off put them in the timing chain so they line up the dots and then slide the whole timing set onto the motor , once you get the cam bolts in verify the dots are still lined up with tension on the driverside of the chain
if dots are lined up rotate engine twice and make sure they still line up at TDC , remove cam bolts apply locktite and torque the bolts to 30 lb/ft
if its a double roller chain that looks like a bicycle chain on the backside don't run the tensioner if chain gets a tensioner install it ,
if its a double roller and the chain has a lot of slack on passenger side you should surce the correct timing set , linebored engines sometimes need an undersized timing set
if its smooth back multi bar link chain like the OE then you should run a tensioner

Just to clarify, the stock timing chain and gears are still on. I have not removed them yet. I wanted to know the easiest way to determine TDC with the stock timing gears and chain still in place. I'm preparing to install a Comp Cams double roller chain. This is the backside of it.....my understanding is this unit does not need to run a tensioner.

 

[Stamos]

Or line up your timing marks or dots, upper gear at 6 o'clock lower gear at 12 o'clock.

This is my first time doing this job. Is the hole in the cam gear the timing mark? Sorry for the newb question!

 

[pacecarta]

rotate clockwise about 22degrees and line up the arrows on the stock chain set keyway will point to center of the #1 piston , remove old and tensioner and slide the new set on dot to dot
do not reinstall tensioner

 

[PSID6]

This is my first time doing this job. Is the hole in the cam gear the timing mark? Sorry for the newb question!

No, that's not it. I believe the stock set does not a dot per say on the upper gear, but instead it has a small raised bump in the casting part of the gear. The woodruff key on the crank will be roughly be inline with number 1 cylinder, then wipe the timing set clean to find your timing marks.

 

[PSID6]

This is my first time doing this job. Is the hole in the cam gear the timing mark? Sorry for the newb question!

Be careful of timing set interference with the stock cover. I do not have the same brand as you but I had to grind mine back on the highlighted area in the pic.

 

[pacecarta]

on stock theres a indicator line on the aluminum its 90 degrees from the cam bolt

 

[Stamos]

on stock theres a indicator line on the aluminum its 90 degrees from the cam bolt

Ok, I think I have it at TDC according to what I think are the timing marks on the upper cam gear and lower crank gear. Does this appear correct?

 

[pacecarta]

its close .. needs to be rotated clockwise a little more until the indicator on the cam gear and the dot on crank gear are perfectly lined up as if you drew a line straight through the gears

 

[Stamos]

its close .. needs to be rotated clockwise a little more until the indicator on the cam gear and the dot on crank gear are perfectly lined up as if you drew a line straight through the gears

I thought so too, I planned on doing just that before I break loose the cam gear bolts.

Thanks to all for the help!

 

[pacecarta]

its close enough for removal you just need to move it a little on reinstall

 

[earlbrown]

the way our heads are built, you can pop off the #1 spark plug and have a straight shot down to the piston crown.

normally I'd say 'set up a magnetic base and a dial indicator to accurately locate TDC'... but from your question it sounds like you don't have the tools to properly degree the cam....

...which means you're using the 'close enough/ hope for the best' method.

In that case, remove the plug and drop a screwdriver into the hole DON'T let it bind up, make sure it can float at all times!

When your feel that you've found TDC, you'll notice the crank keyway is at a 45* angle pointing right up the #1 bank of cylinders. The lower timing gear dot will be pretty much sorta kinda vertical.

 

[Stamos]

It is back together and running strong! Thanks for everybody's help.