radiateu2

Ok, disconnected all belts started it up still vibrates. disconnected the TC strated it up still vibrates. Replaced the damper, still vibrates. Do you think I have an engine balance isuue or could my problem be a lean condition at this rpm. It vibrates in park and cruising. I checked the flex plate bolts they are tight and the flexplate was installed new when the engine was installed. I thought I might have a miss but icant feel it or hear it. Engine and tranny mounts are ok too. What do you guys think

ede

i'd suspect a miss of some sort is causeing your vibration problem. do you know that your tune up is good? no coeds set?

Tom91Bird

iTrader: (5)

When you swapped in the new motor (earlier block) did you swap over the original dampner? Cause if the motor you have now is an older block, then it's a 2 piece rear main seal and probably exteranally balanced so if you switched over the original dampner from the 87, it is probably an interanally balanced dampner which could cause a vibration. Just a thought though.

Tom

Vader

The dampers are usually neutrally balanced except on 400s. The flex plate is what changes the engien balance. The '87-up flexplates have a different bolt pattern, so it would be very difficult to install one on an earlier crank.

Was the engine balanced when built?

radiateu2

Vader, No the engine wasnt balanced when built. I was not certain if it needed to be since so many other people never ran into any problems. But I will know better when I start to build the the 350 I am planning.

Ede the tuneup should be good all new plugs wires distributor cap rotor and coil. Choke working fine. No computer, so no codes.

The flexplate from a late 86 on will not fit on this pre 86 motor. The damper for a late 70 to 96 I beleive are the same thing. Bolt patterns are different and the pre 86 motors do not have the counterweight on the flex plate like the one peice rear main seal flexplates do.

I think Vader hit the answer. I beleive I have a balancing issue. Do I correct it can it be corrected without a tear down? Think I will wait till I build up my 350.

Vader

Gamma-Maker,

From what I have been able to determine through some crude average measurements, crude calculations, observation, and limited understanding of harmonics, the stock SBC 350 with average piston and rod mass, 5.7" CD rods, and all other factory equipment seems to generate its worst harmonics at 1,700=1,800 RPM (and, of course, in multiples of that). Allowing for some variation in tachometers, engine components, and my observations/calculations, your problem seems to be the result of perhaps a worst-case mismatch of components from a dynamic balance perspective.

Pardon me if I wasn't paying attention to your previous threads and postings, but what components were used in the rotating assembly, and what work was done to those components? For example, what brand/size/material pistos were installed, what rods, etcetera? Was the crank turned and ground undersize? Did you install different rod bolts?

I'm hoping that by listing the parts you've installed, someone will be able to volunteer some mass data and we can determine if you have a severe imbalance issue.

radiateu2

the block was bored 30 over The pistons were new wolverines all new the connecting rods were stock and yes I replaced the rod bolts with ARP bolts. The crank micd out to stock and didnt need to be reground. Rings are Hasting Moly. I did replace a rod with a GM rod. I was told that it would not make a difference since the part numbers were the same (machine shop) all I know is the vibration drives me crazy especially when it has this droning sound at cruising speed. i was wondering if the 081 heads are causing the problem since they are EGR heads but I have a non EGR intake effectively blocking of the EGR ports. At this point I dont know what is going on

Riley's35089rs+

Check your diveshaft lately...and u-joints?..The Drone sound you describe makes me ask,,,

Vader

Can you get a part number for the pistons, or contact the manufacturer for an average mass on their +30 pistons? I'd also be a little concerend about one factory replacement rod not matched to the rest. Same part number or not, the factory is not well-revered for matching component mass.

radiateu2

Well, thanks for the replies guys. I dont think I am gonna mess with it at this point. I am gonna get a 350 shortblock from GM and put the 416 heads I have ported on it. Atleast if it comes from GM I shouldnt have to worry about it not being balanced. I hope.