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Username Post: finding tdc heads off        (Topic#246870)
mightymouse22 
Forum Newbie
Posts: 26

Loc: Kelso, WA
Reg: 03-17-09
08-04-10 07:01 PM - Post#1955883    

hey guys, getting the bottom end of the 489 buttoned up, so far i have the rotating assembly done and just got the cam in, want to install the timing chain and start degreeing the cam for my first time, how do i know if tdc is on the compression stroke or exhaust stroke, without the heads and chain on. THANKS

 
acardon 
Senior Member
Posts: 9788
acardon
Loc: DFW TEXAS
Reg: 03-25-05
08-04-10 07:29 PM - Post#1955895    
    In response to mightymouse22

Without the chain, it doesn't matter. The cam timing determines which stroke its on.
Don
66 Corvair (driving)
57 2dr HT (driving)
56 2dr HT (waiting to be restored)


 
greg_moreira 
Very Senior Member
Posts: 3264

Reg: 10-06-03
08-04-10 09:28 PM - Post#1955949    
    In response to acardon

correct. The valves determine whats happening(whether its the compresion stroke....or exhaust stroke).

And since the cam isnt in....it hasnt yet been determined.

You can bring #1 to top dead center, and depending on how you put the cam on.....you can make it be so that its on tdc of the exhaust stroke, or tdc of the compression stroke.

Because of the size of the gears....one turn of the crank equals a half turn of the cam. Takes two crank turns to make one cam turn.

When you put it together with number one at TDC, IF you put them dot to dot(crank dot at 12 oclock and cam at 6 oclock), cylinder number one will be at TDC on the exhaust, and number 6 will be at TDC ready to fire.

Its easier to line em up dot do dot.

With one full crank rotation, now both dots will be at 12 oclock, and cylinder #1 will be at TDC on the compression/firing stroke.

My suggestion: Get #1 at top dead center. Instal cam so that cam gear is at 6 oclock(with crank at 1 oclock obviously). It will be easy to see that the cam is dropped in correct with them dot to dot like that.

Then....rotate the crank one full turn leaving both dots at 12 oclock. Now, number 1 is ready to fire and it makes it easier to drop the distributor in and set it for #1 firing.



 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 16114
grumpyvette
Age: 66
Loc: FLORIDA USA
Reg: 03-16-01
08-05-10 10:04 AM - Post#1956131    
    In response to greg_moreira

http://forum.grumpysperformance.com/viewtopic.php?...

http://forum.grumpysperformance.com/viewtopic.php?...

" " IF YOU CAN'T SMOKE THE TIRES FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK !"


 
mightymouse22 
Forum Newbie
Posts: 26

Loc: Kelso, WA
Reg: 03-17-09
08-05-10 06:24 PM - Post#1956350    
    In response to grumpyvette

much appreciated

 
85Camaro 
Senior Member
Posts: 1145

Loc: East TN
Reg: 07-14-01
08-08-10 06:11 AM - Post#1957394    
    In response to mightymouse22


With degree whell on crank install a piston stop across the bore. Turn engine one direction until piston contacts stop and mark degree whell with a grease pencil. Turn the other way and do the same. Split the difference and you have TDC.
I made a stop from 2 pieces of flat stock with a nut welded in the middle. just make the gap wide enough for it to allow the correct bolts to bolt it down. I used a brass bolt with a jam nut behind it. In a pinch I have used a flat bar type puller using the pressure bolt as the stop bolt.

 
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