Crankshaft Balancer

[72LT-ONE]

Could someone let me know if the harmonic balancer on my 72 LT-1 is a billet piece or one of those two part rubber isolated setups? The reason I am asking is that I cannot properly time it. At idle with the advance plugged the timing
appears to be roughly 15 or so degrees ahead of where it should be. If the HB is a rubber isolated version and it has slipped that may be the cause of the problem. Any ideas???


Thanks,

Mike

 

[motorman]

Could someone let me know if the harmonic balancer on my 72 LT-1 is a billet piece or one of those two part rubber isolated setups? The reason I am asking is that I cannot properly time it. At idle with the advance plugged the timing
appears to be roughly 15 or so degrees ahead of where it should be. If the HB is a rubber isolated version and it has slipped that may be the cause of the problem. Any ideas???


Thanks,

Mike

buy a brass piston stop and check the TDC mark. GM sells one part # 12364087

 

[Jack]

OEM balancer/damper was the type with rubber ... and the outer ring can/will slip causing timing issues. It's normal for them to fail/slip due to rubber degradation from age, heat, oils, engine degreasers, ozone etc. Slipping outer rings can rub a hole into timing cover or get into belts and tear up a bunch of expensive stuff. Simply get a replacement ... no need to get fancy ... a new OE replacement type will last many, many years if you keep oil/solvents/engine degreasers away.
JACK:gap

 

[72LT-ONE]

If it's of rubber construction why is there such a big price difference between a "standard balancer" ($55.00) and one for a "High Performance" LT-1 ($208.00)?

 

[JohnZ]

The standard balancer is much smaller and lighter; the LT-1 uses the large 8" diameter, 1-3/4" thick balancer. If you have the part number, try GMPartsDirect.com for it - much less expensive than at your dealer (it's still available from GM - that's the one the vendors are selling).

It's extremely unusual for the outer ring on a balancer to "slip" - it's designed to take over 1,000 ft-lbs. to shear the elastomeric isolator's bond to the inner hub and outer ring. Easy to check - the timing index line on the outer ring should be EXACTLY in line with the center of the keyway in the hub.

 

[72LT-ONE]

Thank John (and the rest of you guys) thats the 411 I NEEDED.

M

 

[JJS]

Got a question off the subject for you LT-1 guys. Will the exhaust manifolds off a 1971 350/270 be the same for a 1971 LT-1 (350/330)?
Someone's parting out a '71 350/270, and I might be interested in the exhaust manifolds if they're the same. Thanks in advance.

-john

 

[72LT-ONE]

I don't know, maybe someone else does...is there anywhere we could get part numbers? I looked in my assembly manual and couldn't even locate the crankshaft balancer, lot of good that publication is.

Thx,

M

 

[JohnZ]

Got a question off the subject for you LT-1 guys. Will the exhaust manifolds off a 1971 350/270 be the same for a 1971 LT-1 (350/330)?
Someone's parting out a '71 350/270, and I might be interested in the exhaust manifolds if they're the same. Thanks in advance.

-john

No, they're different. The '71 350/270 uses 3846559 (LH) and 3989036 (RH) and the '71 LT-1 uses 3872765 (LH) and 3932461 (RH). Both are 2" outlets - the only difference is that the LT-1 manifolds are drilled/tapped for the A.I.R. injection tubes (A.I.R. wasn't used on the 350/270). ALL Corvette SB exhaust manifolds after 1965 were 2", regardless of the engine.

 

[JohnZ]

I don't know, maybe someone else does...is there anywhere we could get part numbers? I looked in my assembly manual and couldn't even locate the crankshaft balancer, lot of good that publication is.

Thx,

M

That's because the Assembly Manual only shows the parts that were installed at the assembly plant; the balancer was part of the engine assembly as-shipped from Flint Engine and Tonawanda, so it's not called out with a part number in the manual - it was already on the engine as they received it.

 

[JJS]

No, they're different. The '71 350/270 uses 3846559 (LH) and 3989036 (RH) and the '71 LT-1 uses 3872765 (LH) and 3932461 (RH). Both are 2" outlets - the only difference is that the LT-1 manifolds are drilled/tapped for the A.I.R. injection tubes (A.I.R. wasn't used on the 350/270). ALL Corvette SB exhaust manifolds after 1965 were 2", regardless of the engine.

Thanks for the info, guys. I really appreciate it!

-John