The Stovebolt Site Forums The Shop Area Engine Shop finding top dead center

A couple of recent post on this forum got me to thinking, the subjects were, timming marks on flywheel & timming marks.
Lots of times the timing marks aren't easily seen for different reasons & this can be a problem when your trying to find top dead center on the compression stroke, in order to install the distributor or to check the valve gap on a specific cylinder. Over the years I have found some information that was especialy usefull in solving this little riddle, I don't remember exactly where I found it I think in an old Allis Chalmers tractor manual. The procedure was called companion cylinder method of adjusting valves. I have used this method on 4 cyl. 6 cvl & V8 engines, and once you get it down its about as useful a piece of knowledge as I ever acquired.

Ok in order to explain i'll start with the general knowledge about cranks,cylinders, and valve timming, The spot marked on your flywheel for 216, 235, 261 chevrolet engines or on the harmonic balancer on , 230, 250, & 292 chevrolet engines is a reference point so that you can tell when the engines #1 cyl is at top dead center, however it doesn't tell you if your piston is up to fire or up at the top of the exhaust stroke. A good way to tell this, and is what you have to use for the companion cyl method, Is to turn the engine in the direction it normaly rotates and watch the valve train work. Watching the valves on #6 cyl when the exhaust valve closes and the intake starts to open, stop right there and you will know that #6 cyl is at top dead center on the end of the exhaust stroke, fixing to go down on the intake stroke, and #1 cyl is up on Top dead center to fire ,or start the power stroke.
#1 and #6 are companion cylinders, thus the name companion cylinder method. Also the other pairs of companion cylinders are (#2 and #5), and (#3 and #4). If you look at your distributor plug wires, companion cylinders are always wired straight across from one another on your distributor cap, and this is a good way for you to distinguish them. If you ever have your 6 cylinder head off and notice (#1 and #6) pistons travel up and down in their respective cylinders at the same time, You will also notice that numbers (2 and 5) also do this, as well as numbers (3 and 4)also. Each cylinder has a companion that is at top dead center at the same time it is. By watching the valve train on any one cylinder you can tell when that cylinders companion is at top dead center and up to fire.

If you use this method and get proficent with it, it will help you adjust valves ,set your distributor right,make it much easier to wire your plug wires in their correct order,and just give you a better understanding of valve timing events and the way your engine works.
In review valve cover off, rotate engine in direction of normal rotation, watch valves on #6, when exhaust closes and intake starts opening, stop there and adjust valves on #1 cylinder, rotate on watch #2 and adjust # 5, rotate on watch #4 and adjust #3, your half way through, watch #1 adjust #6, Watch #5 adjust #2, last watch #3 adjust #4.
Thanks for letting me bore you with this little explination of companion cylinders and how knowledge of them can help you .......Ronnie

to skip lines you can try punching the 'skip line key', usually labeled 'Enter'

like so - to indent you can put the code "& n b s p;" [with no spaces or quotes] 4 or more times
like this

you can also click on the little paper&pencil icon at the top of the original post and add the line feeds, and you can click the same thing on yer 2nd post and check the 'delete post' box

an easier way to find TDC to start yer sequence is to put a finger over the plug hole and when you feel the compression pushing on yer finger yer there

Bill

you can skip a line by hitting the enter button, at least that is one way, one time for each line skip

you can indent by the use of the space bar.. at least one way that I know of.

thanks for the post.

Red58 & Joker thanks for the info on operating this mach.....Ronnie

Ronnie,

Thanks for that tidbit. Sometimes I get brain-freeze trying to follow the firing & valve sequence in my head. I imaging people staring at me, wondering my I'm standing there, looking into space, mumbling to myself and making peculiar gestures with my hands . . .

Ya' know, I'm apt to think a two-cylce motor is a heck of a lot simpler!!! I think I'll go time my grass trimmer . . .

-Michael

Good explanation Ronnie. I never noticed they were across from each other on the dizzy.I have always determined them by taking the firing order of any engine (in this case 1,5,3,6,2,4) and arrange the first half of the numbers over the last half (1 over 6, 5 over 3, and 3 over 4 ) to determine companions. I use companions for cylinder balance testing. If an engine is run at high idle firing only on 2 companion cylinders at a time while hooked to a vacuum gauge the reading of each pair can be compared to determine power balance and narrow down a weak cylinder.
Curt B.

Ronnie, nice explanation, hope you won't be offended by the equipment lesson!! I thought this was the stovebolt page not computer 101.

:confused:

Curt Well thas sopmething else you can figure with that knowledge. thank for the tip. One of the points I really should have made is that the rocking of the valves at the top of the exhaust stroke is the only easily reconized valve timing event & is what the manufactures mark on the timming gear is indexed off of....Ronnie

Oh the computer lesson wasnt ofensive at all i am a real ignoramos when it comes to these computers just learning. Hope this info is a help for someone...Ronnie

thanks for the reply 41 chevy

41Chevy - the "computer lesson" was in response to Ron's 2nd post asking for such direction, which he removed per my suggestion when he edited the original post, per suggestion

I could delete my post now, but think I'll leave it for anyone else who might need some '101' until some more helpful hints get added to the stovebolt IT ShortBus and the FAQ

any ideas on how to get folks to check out those 2 forums when they first join up? we are about ol 'bolts, but we're all filtered thru this infernal technology that's left some bolters bewildered!

Bill

you can do the centerline method as in degreeing a cam... to find top dead center you need a stop for the piston. such as a half inch bolt head. This is whith the head off... for head on, you can devise a screw in spark plug hole or something that will go on top of the piston to stop the piston.
In other words you stop the piston turning the crank by hand hitting something that is a half inch or so from the top... mark the crank pulley..or use a degree wheel... back around the other way so the piston hits the same stop after top dead center...and mark the pulley... then you divide it by two to find true top dead center. its easy with a degree wheel.. you can also do a lifter .050 before and after top lift to find the center line or top dead center of lift.. thats how you degree a cam or...hehehe blueprint it....

I'm still trying to figure out who you are, Ronnie. My first name is Dean, I grew up in HC, and most of my family is still there. Give me a hint, last initial?

The two Ronnies that come to mind there is one with a brother Roy and a last name starting with U.

The other is still mechanicing, and is a Mopar guy. Has three GTXs, one a 440 6-pack, the other a convertible and the other the one he drove in high school.

I'm well acquainted with the two Ronnies you speak of both friends of mine. I only arived in H
C in 1992 so you may have left already.....Ronnie
Oh yea its Ronald F

Thanks! Well, we had a few months of overlap, we moved to Canyon in Jan '94. Don't guess I know you, but I'll keep my eyes open when I'm down that way.

If your buy I live on 14th st Have29 truck on trailer & 54 3100 under carport in back stop by if your in town. we might turn one another to some good deals weve seen. If you see ether of the two Ronnies they'll tell you where I am, and how full of BS,.....Ronnie