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Jay, Chevy Mechanic
Category: Chevy
Satisfied Customers: 596
Experience:  Several yrs experience, GM Trained,
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What size bolt do I need to hold the harmonic Balancer on a

Customer Question

What size bolt do I need to hold the harmonic Balancer on a 1984 GMC C1500 inline6 4.1L. I need the washer size also.
Submitted: 8 years ago.
Category: Chevy
Expert:  Jay replied 8 years ago.
HelloCustomer I have never measured or checked the bolt size and threads on a harmonic balancer bolt. I think it would be best if you went to a parts store and told them what you needed. If a regular parts store cannot help you then check with the chevy dealer parts person, he may be able to get the bolt and washer for you and look into it for you. Please reply if you have any questions.
Customer: replied 8 years ago.
Thanks alot. I have called all the hardware stores and they can't pull it up. The dealers say that there computer does not go back to an 84. I guess I am going to have to guess. lol
Expert:  Jay replied 8 years ago.
HelloCustomer if the dealers can get the parts you need for an 85 and the engine style was not different (check with them if it is different) from that of a 84 get a bolt and washer for an 85.
Customer: replied 8 years ago.

A guy today gave me a size for the bolt and washer this is what he put.


socket size: 1-1/16
Thread size: 7/16-20
UHL: 2.470


I don't know what this means.

Expert:  Jay replied 8 years ago.

Was the guy a parts person or how did he obtain this information because it does not seem normal. First you usually do not classify bolts by socket size and I have never heard of UHL and do not know what that 2.470 means the thread size could make sense if the width of the the threaded bolt part is 7/16 and it has 20 threads per inch. Typically a bolt is labeled as an example 3/8-16 UNF *4 meaning:

3/8 =diameter in inches

16=threads per inch

UNF=united national fine

4=length in inches

Bolts also if standard have marks in them a harmonic balancer bolt would have probably 6 marks or more meaning it is a grade 8 bolt or greater which is its strength rating.

Customer: replied 8 years ago.
I know it is a grade eight bolt but it seems smaller than a 7/16 bolt I have already tried it. I think the thread is 20 I am not for sure on the lenght and the washer.
Expert:  Jay replied 8 years ago.
The only thing smaller than a 7/16 is a 3/8, but like I said try checking with a parts person about one for an 85.