Tripper511

I just got a new engine from Jeg's put in my car (here's all the specs: JEGS High Performance - GM Performance Parts 350ci / 290hp Engine)
The timing cover doesn't match up with my damper so I need to buy a new one since GM threw away my old timing cover All I know is that I need either a 6 3/4" or 8" damper, but I have no idea what the difference is and I'm not sure if my engine is internaly or externaly balanced. Please help I can't stand driving with my car popping all the time because of bad timing. Thanks.

Tripper511

bump

Damon

You're correct, you can use either size as long as you have the right pointer to match up with the dampener diameter (the TDC mark will be in the right place regardless, but you want the tab floating a fraction of an inch from the edge of the dampener to make reading the timing against it possible). I THINK that motor is designed to work with an 8" unit, but don't quote me on that.

A typical 8" unit (neutral balanced, not the counter-balanced unit a 400 uses) would be something like this (clickable link):

Summit OEM Harmonic Dampers: SUM-161358 - summitracing.com

It's like a stock one but it also has 0-60* markings along the outside edge, not just a single TDC line. Handy feature, but not absolutely required. Summit has the same deal but in the smaller 6-3/4" size as well:

Summit OEM Harmonic Dampers: SUM-161350 - summitracing.com

On the cheap, you can just find true TDC of the engine, and scribe a new line on your existing (6-3/4") balancer to match the TDC mark on your new timing tab, assuming you have a timing tab to work with a 6-3/4" balancer. It'll be about 35-40* clockwise on the balancer from the stock mark.

Tripper511

Can I get by just buying timing tape and still using my existing damper?

Sonix

iTrader: (1)

no, I don't think so. Your old balancer won't work with your new timing cover.

I have that first one, the 8" one. It's a nice piece, those marks are really handy. Plus it'll never fall off like tape does.

Damon

Tape is no fun. It will work if you line it up right against your new tab TDC-to-TDC (assuming the engine is actually on TDC when you line them up) but like Sonix says..... it'll fall off. I went as far as clear-coating over top of the tape once installed. It helped a little. Few months of driving later.... it still peeled off.

five7kid

iTrader: (14)

Humm, I must have done something wrong. My timing tape is still stuck on tight after 6+ years. . .

You have to get a piston stop (that screws into the spark plug hole) in order to find TDC and use that tape. Not a bad idea even when using an aftermarket timing tab - the one I got was 2 degrees off.

Tripper511

Yeah i just ended up going with the tape because it was cheap and easy. My car is running great now. O and one thing I came across during my research is that the difference between the 6 3/4 and 8" damper is that the smaller one gives u better revs but the larger one gives better cooling. Just a little food for thought

firebirdjosh

iTrader: (1)

What does a damper have to do with cooling?

Supervisor42

Me 2. I gotta hear this answer. "well, I changed to the 8" damper when I changed my fan clutch and now it runs much cooler"; "I tell ya that 8" damper's a hell of an engine cooler".....

Tripper511

It's has to do with making the fan turn twice per every revolution as opposed to one and a half times with a 6 3/4" damper

chesterfield

You're confusing the damper diameter with the pully diameter.

Tripper511

You might be right. But then what is the reason for using a 6 3/4" or an 8" damper. Is it just the ability to have higher revs?

Sonix

iTrader: (1)

the smaller dampner is used to dampen smaller vibrations basically, so with a lighter rotating assembly it matches better (stock, that would be the 305, with it's lighter pistons and crank bob weights.)
If you were building a 350, you could use either, an 8" might run smoother, and rev down slower, but the 6 3/4" would rev faster, but be a bit shakier i'd guess.

Yea, definately no effect on cooling though.

firebirdjosh

iTrader: (1)

Might want to edit out what you "learned" a few posts back. Hopefully other newbs won't get confused.

Tripper511

Hmm, that makes sense. I think I'll have to go out and get an 8" damper