85 timing tab questions?

[Got Smoke?]

Ok a co-worker of mine just recently purchased a very nice 85 K10 on about 8" of lift with some new 37" Irok's. On his first attempt to go through emmissions he failed by a large margine. He asked me if I could check the timing to see if it was set correctly. I figured sure no problem my 79's very easy to read and adjust. Well at first glance I didn't see a timing tab in the normal (to me) spot behind PS pump underneath the water pump. I finally did find one behind the water pump at the top of the timing case. Its got paint or crud built up on it and its such a tight area I can't reach it to wipe it off.

My two questions are 1) is this the normal location for the timing tab on a 85 motor? and 2) does anybody have a picture of one since I can't read this one right now? I've done a quick google search and still can't find one like the one on this truck...average search comes up with a long style tab like it on my 79 this one is about half the length of that I'd guess.

Sorry for the dumb question...just curious if this thing was done half @$$ed by a previous owner.
Thanks

[Got Smoke?]

Hmm....after another quick google search I came across this picture.

Were these timing cover's ONLY used on 305's? Will they fit on a 350 because this looks identical to what's on my co-workers truck.

[mud.man.rj]

Isn't the 0 in the big notch and the #'s go up as you go to the left of the big notch by 2's at a time. I set all my timing with a vacumn gauge by hooking up to full vacumn sorce and andvancing timing to full vacumn on gauge then pullin back by 2.5 lbs on gauge and always works, with big tires may need to go back 3lbs if not geared correctly because it puts more load on motor with big tires and will ping easier. I do this because a lot of GM balancers slip on the rubber ring and don't show correct timing marks. Good luck.

[yellowGT]

yes. 0 is where number 7 is and goes up to the left.

[GreaseMonkey01]

I agree 0 is where # 7 i have an 85 c20 and that is the correct location also behind waterpump and hard to read.There is a picture on this website but im not much of a puter dude so cant link it

[Got Smoke?]

Originally Posted by mud.man.rj

Isn't the 0 in the big notch and the #'s go up as you go to the left of the big notch by 2's at a time..

Originally Posted by yellowGT

yes. 0 is where number 7 is and goes up to the left.

Originally Posted by GreaseMonkey01

I agree 0 is where # 7 i have an 85 c20 and that is the correct location also behind waterpump and hard to read.There is a picture on this website but im not much of a puter dude so cant link it

Thank you for your replies...I didn't label the picture I linked it just came up in a google search on another chevy site. Where is ideal timing for a jacked up mall cruiser truck?

Greasemonkey, is the correct location for both 305's and 350's? The picture I found stated it was for a 305 motor... previous owner claims it was a 350 but I can't tell without running casting #'s.

[raceman6135]

Yes, both 305 cid and 350 cid engines in the 1980s (approximately - don't know the exact year breaks) had the timing tabs located at the 12 o'clock position.

And yes, timing covers will interchange between 305 and 350 engines of that vintage.

In the image the OP linked to:

#7 = 0 degrees, which is TDC (top dead centre)
#6 = 4 degrees BTDC (before top dead centre)
#5 = 6 degrees BTDC
#4 = 8 degrees BTDC
#3 = 10 degrees BTDC
#2 = 12 degrees BTDC
#1 = don't know for sure, but looks like 16 degrees BTDC

[raws67]

heres a picture for you this is off an 84. I just finished cleaning it up today.

[crazeetxn]

So outta curiosity, anyone have a clue what the round tube lookin thing is for?

[1972BackInBlackC10]

i know this is an old thread but my 1980 gmc has the same timing cover with the tab

[Pampas56]

My 84 Silverado has the same timing mark as shown. I believe that it was moved there when the air pump was added for emissions. IIRC the P/S pump was low on the passenger side before and when it was moved to the other side the timng mark would have been behind the pump.


I recently bought a Targetmaster 350 made in the late 70's that had the "old" timing mark location and had to swap the timing cover and vibration dampener from my 305 to the 350.

I would be curious if anyone knows what the tube is for. Maybe some wierd application that required 9degerees ATDC?

[bowtiemanchevyman]

the best way to time a motor is to get a vacum gauge and and use it to get as much vac as you can. like around 15 to 20 anything less it not time right. it will also so you if you have problem any where else in your, a loss chain, a bad valve or rings. get one and use it. i dont even have a timing tab on my motor.

[mud.man.rj]

We went threw this before, when using a vacumn gauge go full advance, so full vacumn then back it off 2.5" on the gauge so if you get 18 back off to 15.5 and it will be very close, if driving under extreme loads or baggin the hell out of it go .5 more retarded, so to 15" and no matter what cam it will work just fine.

[1972BackInBlackC10]

mud man i will be trying your method tomorrow if i can find tdc by myself hopefully fingers crossed it will all go well

[mud.man.rj]

You don't really need top dead center if it already runs, but if it doesn't or hasn't run yet you will kind of have to for the correct plug wire location, but could pull a v. cover if needed and watch the intake valve open and close then put a long screwdriver in the left/drivers side #1 piston hole and slowly turn the engine over with a bar, not the starter and when the piston pushs the srewdriver to the top just before it starts to go back down is top dead center. So turn the engine back slightly and will be around 10 degrees before top dead center, wher it actually would be correct timing on most small blocks and would at least start for you to use the vacumn gauge to time it. Sound good.

[1972BackInBlackC10]

i will do that, i was messig with the timing light and the lie on the balancer was way to left (pass side of motor) with the vac advance pointing in the direction of the heater motor kinda, then when you turn it so its pointing at number 4 cylinder you cant see the line on the balancer anymore, i even turned even further and still couldnt see it, only when its in that one position which its nowhere near the tab on the cover

so i think when i put the dist back in i didnt put it back in the right position

[mud.man.rj]

The problem with the distributor is the gear is helical cut so when you drop it back in it turns and drops in a tooth out each time so it doesn't line up, have to pull it and insert a long screwdriver down hole and turn the oil pump drive shaft slot back a 1/6th to an 1/8th of a turn the the slot will line up in the inside end of shaft and the gear will line up better as it goes into the shaft. See the problem is when you pull the dist. out of the hole it turns on the gear a part turn and also turns the oli pump shaft a part turn then when you try to put the dist. back in the same spot it won't go in but will just a bit further as the slot in shaft lines up with the slot in bottom of distrib/ so the dist is always back just a bit from where it originally was, that is why you have to turn the oil pump shaft. It would still run when turned back a bit but sometimes don't have enough room to turn the vacumn advance before it hits something. I know I think toooo much. tricks hey.

[1972BackInBlackC10]

sheesh lol so what way do i have to turn it and what kind of screwdriver? philips or? and how do i know if iv turned it enough?

list of things to do is find tdc, pull dist out, adjust the oil pump shaft, reinstall dist with rotor pointing to # 1 cylinder, hook up vac gauge, adjust timing till i reach highest point then retard timing to 2.5 - 3 on vac gauge, did i miss anything?

[mud.man.rj]

Originally Posted by 1972BackInBlackC10

sheesh lol so what way do i have to turn it and what kind of screwdriver? philips or? and how do i know if iv turned it enough?

list of things to do is find tdc, pull dist out, adjust the oil pump shaft, reinstall dist with rotor pointing to # 1 cylinder, hook up vac gauge, adjust timing till i reach highest point then retard timing to 2.5 - 3 on vac gauge, did i miss anything?

Sorry man, a straight blade, long one too, it's a ways down there. Turn it counterclockwise about an 1/8 turn then drop distrib back it to the spot you want, which is about half way between firewall and back of carb. If it drops in and is too far back still then pull it out and turn the slot a bit further, you know trail and error, haha.

[1972BackInBlackC10]

not to sound dumb but what part is supposed to be half way between the firewall and carb, and im not sure i know what you mean by half way between the firewall and carb either lol i feel dumb

[mud.man.rj]

All cool, I meant the vacumn advance on the distrib, it sits about midway between the back of carb and the firewall when dropped in the correct place, if it was too far counterclockwise it would hit back of carb or too far the other way would hit firewall.

[1972BackInBlackC10]

oooh ok got ya now, if the oil pump shaft is in the wrong spot when you put the dist in you wouldnt be able to turn it enough to adjust the timing because it would hit the carb or firewall, where as if its in the right spot your have the room

[mud.man.rj]

Yep you have it, like I mentioned you only have to turn the shaft if it doesn't line up with the slot in shaft below, oh will need a light to look down at the same time you are turning it with screwdriver, hard to see in there. later man, going to bed, dreamin of coll rides, mine mostly, just love my big block truck, makes me smile.

[kikkegek]

Originally Posted by crazeetxn

So outta curiosity, anyone have a clue what the round tube lookin thing is for?

I'd like to know that too...anybody know?

[bowtiemanchevyman]

Originally Posted by kikkegek

I'd like to know that too...anybody know?

on the old timing machine u put a light thing in it to read the mark on the dampner. if you can find one they are the size of some the big snap on tool box. like six ft tall and like ten ft long my high school has one they dont reall do alot, like the new ones do but they do work good for timing a old car