"thumper cam"

[oldblue1968chevy]

I built a piston stop out of a old spark plug and a nut welded to it, but attempted to check it and bent the bolt I was using for the stop, im not really sure what im doing..

[oldblue1968chevy]

Im lookin' at my cam card..

It says 981-16 springs required
valve springs specs furnished
with springs

whats that mean? im running the springs that came in the vortec heads, the machine shop didnt tell me I should swap springs..?

[fleetsidelarry]

Originally Posted by oldblue1968chevy

I built a piston stop out of a old spark plug and a nut welded to it, but attempted to check it and bent the bolt I was using for the stop, im not really sure what im doing..

oldblue, here's some excerpts from a thread over on ChevyTalk:

the way the piston stop works is, when you rotate the engine slowly BY HAND in one direction (say clockwise for this example) and the piston is stopped by the tool, you mark the damper. then you rotate the engine in the opposite direction (counterclockwise in this example) and again mark the damper when the piston stops. the halfway point between the two marks is actual TDC. It should match the 0º line on the timing tab within a couple of degrees. Initial timing, set with a timing light, should place the TDC mark 8-10º counterclockwise from the 0º tab line.
if you're still interested, a piston stop looks like:


http://www.summitracing.com/parts/CCA-4795/
59fins Said:

now I need turn the engine over by hand?
it's pretty tight, I will need to take the plugs back out and see if I can turn it over,




get a tool like this:

http://www.summitracing.com/parts/WMR-W80510/

and an assistant is always helpful (but not necessary)


59fins Said:and loosen and remove the rocker arms on #1 cylinder? is this correct also?




yes, as Greg mentioned earlier. resetting is not a big deal, but first: remember that TDC for #1 is also TDC for #6, so you want to know that you're at (or near) #1. before you start the TDC verification with the stop tool, pull the dist cap and rotate the engine to get the rotor in the vicinity of the firing position for #1 (as opposed to #6). this will help when you go to reset the valves.

the entire thread covers other issues as well as what we've been talking about here. if you want to read to whole thing:

http://www.chevytalk.org/fusionbb/sh...d/261075/tp/1/

[oldblue1968chevy]

Thank you fleetside larry

I needed a 'how to do it for stupid people' FAQ

Is there anyway to turn it over via the bolt I really dont wanna spend $ I dont have on tools i'll use 1 time..

So if its off I just make a mark on the balancer (preferbly something more permanent than sharpie?)

[fleetsidelarry]

I thought us guys liked excuses to buy tools.

you might be able to turn it with the damper bolt, if you pull all the plugs and the motor's not too tight. you don't want to strip it or break it. Also, loosen all the belts, in fact, take em off. shouldn't be a problem going clockwise but you might need to grab the damper and help turn counter-clockwise if the bolt wants to loosen.

I made marks on my damper with a sharpie (at the 0°,90°,180°and 270° points to help with setting the valves), a strong solvent will take the marks off

[Captainfab]

If your 279 Thumper has over about .470-.480 lift, you really should have checked for coil bind of the original valve springs and also spring retainer to valve guide/seal clearance. Did the machine shop assemble your engine?

Originally Posted by oldblue1968chevy

Im lookin' at my cam card..

It says 981-16 springs required
valve springs specs furnished
with springs

whats that mean? im running the springs that came in the vortec heads, the machine shop didnt tell me I should swap springs..?

[gonnuts]

You really need to get a gun that will allow you to check the total advance. I was having problems getting my timing set, when I set total(initial& mechanical) to 34-36, my initial was 18-20, and that was with a recurve kit in. I wasn't getting the 20-25 mechanical adv. that I should have been(yes I checked to make sure it was installed right). I ended up putting the stock(I assume) cam & weights back in with lighter springs & now I'm about 12 btdc initial, it's good enough until I get a different dist.

Anyways long story short you need to know how much mechanical & vacuum advance your getting.

[Bennett68C10]

Originally Posted by oldblue1968chevy

Im lookin' at my cam card..

It says 981-16 springs required
valve springs specs furnished
with springs

whats that mean? im running the springs that came in the vortec heads, the machine shop didnt tell me I should swap springs..?

Aren't your heads the Vortech Heads from Summit that are actually made by Dart. The springs in them are good to .520 lift. If you check Dart's website they use the comp 981-16 springs. I was just researching these heads for myself and came across that.

[oldblue1968chevy]

yes, my heads were dart heads, with summit stamped on the front/back.

ok thats good info, the machine shop did the long block minus the heads, he told me what heads I needed and what else to order etc I assembled the rest.

You check mechanical adv by plugging the vac. advance and using the gun? Correct?

And how would you check vacumn advance. Sorry I just cant grasp the concept of the timing etc..

[benoit454]

that right there is why it has plenty of power then, the heads. vortec's are the best flowing stockers and aftermarket are better then them so you get the idea.

We're running stock iron heads, 2.02 intake and 1.60 exh. old school heads.

[fleetsidelarry]

Oldblue, what is it that you don't get about timing? the difference between mechanical and vacuum? why is timing necessary and why does it have to change with RPM? not sure what you're saying when you say you don't grasp the concept..

you have a timing light already, right? otherwise, how would you know you initial was 18° one time and 8° another?

[oldblue1968chevy]

I have a standard timing light, I didnt know that I would need a light with built in advance at the time..

I dunno, I just dont know how to discover my mechanical timing and the vacumm timing.

Ive done alot of reading links and I know more than I knew a week ago, I understand it a little more.

[fleetsidelarry]

Oh, OK. I don't have one of those fancy timing lights either, just a regular one. I guess they're nice but I'm not going to go out and buy a new one.

You do have to have some marks on your damper, you can get a timing tape that goes around the damper or you can make your own marks. what I did was use a sharpie to make marks on the damper.

use the distance on the timing tab corresponding to 10° (for instance) as a reference as to how far apart to place the marks.
put a mark 10° clockwise of the 0° groove in the damper, another 10° past that and so on. 4 marks would get you 40°, also mark the 0° line on the tab

with the vacuum advance plugged off, as you slowly rev the engine
up, the marks start rotating counter-clockwise.

for example,then, at idle, if your initial timing was set a 10° advance the first mark you made (corresponding to 10°) on the damper will be at the tab 0° line. as you slowly bring the rpms up the next mark will approach the tab 0° line. at some point, 3000 rpm or so, the marks will stop moving, let's say at the 4th mark or 40°. the difference between your initial and the final is your total mechanical advance built into the distributor (in this example 30°)

likewise, the amount of vacuum advance is the number of degrees of change, at idle only, when you hook the vacuum advance back up. for instance let's say the damper jumped from the 10° sharpie mark to the 30° mark, you'd know that you have 20° of vacuum advance in the mechanism.

Makes one of those new timing lights look like a good idea

[fleetsidelarry]

Originally Posted by gonnuts

You really need to get a gun that will allow you to check the total advance. I was having problems getting my timing set, when I set total(initial& mechanical) to 34-36, my initial was 18-20, and that was with a recurve kit in. I wasn't getting the 20-25 mechanical adv. that I should have been(yes I checked to make sure it was installed right). I ended up putting the stock(I assume) cam & weights back in with lighter springs & now I'm about 12 btdc initial, it's good enough until I get a different dist.

Anyways long story short you need to know how much mechanical & vacuum advance your getting.

gonuts, what recurve kit were you using?

[wwotr]

All I gotta say is I'm glad my Mechanic is Installing/Tuning my Thumper Cam.

[oldblue1968chevy]

Sorry to hijack your thread wwotr..

Im going to verify my timing mark on my balancer this afternoon (Or attempt it using my homade tool..)

[wwotr]

Originally Posted by oldblue1968chevy

Sorry to hijack your thread wwotr..

Im going to verify my timing mark on my balancer this afternoon (Or attempt it using my homade tool..)

Yes you should be

So everyone here needs to paypal me $1.00 for my Troubles.

[faribran]

i always enjoy CDOWNS' comments... keep em coming..

[oldblue1968chevy]

Ok got the plugs out belts off and going to attempt to turn motor via the bolt, I hope I dont break anything

if I start a lil before TDC and turn the balancer clockwise (looking at the front of the truck) it bottoms out. I should mark that? Then go clockwise (looking at front of truck) until it bottoms out again, then mark that spot then divide by 2? Correct?

HURRY

Thanks guys!

[oldblue1968chevy]

Oh, and after I determine exact TDC I should reset my valves to zero lash plus 3/4 turn and then check timing?

[wwotr]

Originally Posted by oldblue1968chevy

Oh, and after I determine exact TDC I should reset my valves to zero lash plus 3/4 turn and then check timing?

I commend you "Old Blue" for taking this on.
Your a Braver Man than I!

[fleetsidelarry]

Originally Posted by oldblue1968chevy

Oh, and after I determine exact TDC I should reset my valves to zero lash plus 3/4 turn and then check timing?

setting both intake and exhaust for #1 on TDC is the method I've always used but I've recently read that that method works fine for stock "mild" cams but that the new cams have such aggressive ramps that you may not be truly on the base circle. one method for hotter cams is to turn the motor til the exhaust pushrod just starts to move up and adjust the intake rocker. then turn the motor more until the intake pushrod just starts to move down and adjust the exhaust--its called the EOIC (exhaust opening intake closing) method. and 1/2 a turn should be enough after taking out the pushrod slack

please except my apology, wwotr, for being an active participant in the hijacking

[wwotr]

[QUOTE
please except my apology, wwotr, for being an active participant in the hijacking[/QUOTE]


Like I said.....Paypal works WONDERS to heal "Hijacked Threads".

[oldblue1968chevy]

Im pretty sure I did it right, I was about 5-10* off is there a more permanent way to mark it (I have marks all over paint comming off etc..)

[oldblue1968chevy]

You guys are funny

Well, when I said earlier I HAD the engine at around 18* or so thats where I put it back to (with new mark 8* btdc).

So I need to pull dizzy reset that and re set the valves?