oamhmad

iTrader: (1)

I just swapped in a new Goodwrench 350 crate motor (Pre 86 block) to replace the old 305 in my 84 TA.

As you know the 305's timing tab is welded to the center of the timing cover in the 12'o clock position. The new crate motor came with a timing tab mounted on the drivers side of the timing cover at the 2'o clock position.

I'm using the 305 balancer so the timing mark scribed into it needs a 12' o clock mounted timing tab to indicate TDC. (Some one told me that all first gen SBC 305 and 350 parts are interchangeable! They sure are not!)

I need a way to place the #1 piston on TDC and then make a new mark on my balancer that coincides with the 2'o clock mounted timing tab. The problem is that I cannot use the piston stop method by turning the crank till the piston stops, marking the balancer and then turning the crank the other way and making a second mark and splitting the difference.

Because the motor is so new and everything is tight, turning the crank counter clockwise just loosens the center bolt, even with all the plugs out. I've torqued the bolt down to specs, but it still breaks loose if the crank is turned against the normal rotation.

Besides, I don't like the idea of my new pistons getting scratched up against a piston stop.

Is there any other way to determine true TDC without pulling the heads? Like does #2 exhaust valve just start opening when #1 reaches TDC, or something like that?

Does any one know exactly how far off the TDC marks would be between the 2 different balancers?

sofakingdom

iTrader: (1)

Sure they are. Those 2 particular ones, just need to be interchanged as a set.

Don't know exactly how far off the mark is; but it's near about 35°.

An option would be, to get the damper for an older car with a 350, which would have the right mark to match that particular cover. A mid 70s one would be about right. Should be pretty cheeeep at yerbasic parts store, maybe $40, prolly less. Get the Pioneer brand.

#1 TDC occurs twice during a complete 4-stroke engine cycle, and at the same time as #6 TDC (the cyl 4 cyls away from it in the firing order). One instance of course is firing. The other is the end of the exh stroke and beginning of the int stroke. At that point, the exh valve is just closing and the int is just opening. #1 & #6 are exactly opposite each other: when one is firing, the other is "swapping over". While not exactly "precise", catching it as the valves are "swapping over" will get you fairly close.

camaronewbie

What makes you think the piston would get scratched? This has been the method used by everyone for 100 years+.

A pencil certainly won't scratch a piston - stick a pencil in the plug hole.

Remove the spark plugs (all of them) - engine will turn over easy by hand then.

Get a prybar, get it lodged into the flywheel, and tighten that balancer bolt down like it should be, so you can then turn motor by hand without loosening the bolt.

Stick finger in #1 plug hole, turn motor until you feel the outward air pressure - now you know you on the #1 compression stroke. Now, put pencil in the #1 plug hole, and turn engine until the pencil comes up out of the hole as high as it can - now you are TDC #1 compression stroke - now scribe balancer.

It doesn't have to be 100% exact - this isn't Nascar or a 6 second funny car that needs exact tolerances within 1/10,000 of an inch. It's just a mark, on a wheel, that changes position relative to a non-moving tab when the timing is changed - all it really serves for is a visual for the human brain to literally see whether it's getting advanced or retarded, and by what "amount" in order to allow us to think about what changes will have what effects.

five7kid

iTrader: (14)

http://www.summitracing.com/parts/MRG-4600/

oamhmad

iTrader: (1)

Thanks five7Kid! That is certainly a solution to my problem. I don't like the idea of peering over the cooling fan to time the engine. I like the driver side timing tab. It is much easier and safer to read.

I'm going to try poking something in the spark plug hole to find TDC.

five7kid

iTrader: (14)

A spark plug hole piston stop is a pretty good something to poke in there.

gen3guy

Just went through this my self this tool saved me a lot of headaches

http://www.sears.com/shc/s/p_10153_1...u=00999047000P

and then i used
http://www.summitracing.com/parts/PRO-66792/

as long as you take your time and rotate slow you should be ok

ntrider1991

pull the timing cover off and put the bottom timing gear mark at 12 oclock then you got tdc could not hurt to change fluids anyway flush it if its already together clean is better the timing gear on the bottom has a key way that should point ruffly 2 oclock but the gear itself has a timing mark just put it at 12 oclock

oamhmad

iTrader: (1)

I ended up not having to find TDC to make marks on my balancer.

I just mounted the new drivers side tab on my old block and measured how far the new TDC mark is from the old 12'o clock tab TDC mark.

Turns out the TDC mark using the driver's side tab is exactly 1.75" away from the 12 'o clock tab TDC mark on a 6.75" balancer.

88gunmetalgta

iTrader: (1)

What worked for mine was screwing down the stop and first rotating the piston BACKWARDS first, just a little bit til it hits the stop, then you can turn it clockwise with no problem.

Apeiron

The correct way to use a piston stop involves rotating the engine forward and backward.

88gunmetalgta

iTrader: (1)

Yes, I used mixed terms.

rotate the crank backwards first, a short distance, then forwards for the longer duration, that way you don't have to worry about breaking the bolt loose so much.

OR,
rotate the crank counterclockwise first, then clockwise.



EDIT: However, I missed the post about the OP having solved his problem, disregard.....

Apeiron

Or turn it by the crank snout, balancer hub or flywheel like you're supposed to instead of the crank bolt, and you don't have to worry about it at all.

InfernalVortex

iTrader: (4)

Isnt there some superstition about not turning an engine backwards after its broken in?

sofakingdom

iTrader: (1)

Prolly.... and about throwing salt over you shoulder if you spill some, and not crossing the path of a black cat, and using only Delco O2 sensors, and various other things most literate people pay no mind to.