How many bolts on a "61"

[jack alexander]

I have a "61" 315 HP "feulie" I was talking about it with a mechanic friend of mine, and he told me that he thought that the solid lifter "283" for that year was a four bolt main while the lower HP versions are two bolt? Thanks in advance.
Jack Alexander
#35730

[Ed Jennings]

Re: How many bolts on a "61"

All 283's are 2 bolt, steel crank.

[Joe L.]

Re: How many bolts on a "61"

Ed and Jack-----

All Corvette 283s used a steel crank. However, many passenger car 283s from 1965 onward used a cast nodular iron crankshaft.

Also, as far as 4 bolt mains go, there is a pervasive myth out there that some SHP 283s and SHP 327s used 4 bolt mains. GM NEVER built ANY 283s or 327s with 4 bolt mains. All 283s and 327s, regardless of horsepower or application, used 2 bolt mains. They could be converted to 4 bolt utilizing aftermarket 4 bolt intermediate caps (#2,3,4), but they were never built that way.

The first small block PRODUCTION engines to use 4 bolt main caps were certain 1969 350 cid engines and all 1969 302 engines. For 1969, all 350 cid engines with 4 barrel carburetors were manufactured with 4 bolt main bearing caps and this practice continued for 1970. From 1971 onward, 4 bolt caps were usually used only for SHP small blocks and certain truck applications. These caps were used only on the intermediate positions (#2,3,4). NO GM-manufactured Gen I or II small block (1955-2001) EVER used 4 bolt caps on all 5 main bearing positions.

[Tom P.]

Re: How many bolts on a "61"

Not only is Joe 100% on the money, but "experts" who give out info such as described above need to be avoided like the plague!!!!!!!!!!!!!! Today, there is so much misinformation and so many misinformed people out there who JUST CANNOT be convinced otherwise because, "an expert who knows his stuff", told him it was so!

[Mike E.]

Re: How many bolts on a "61"

I'm glad he's your mechanic/friend/expert, not mine.

[Jim T.]

Re: How many bolts on a "61"

Joe if a 70 Corvette received a CE replacement short block for a 350/300 dated July 70, what do you think the engine is, a two bolt or four bolt block?

[Joe L.]

Re: How many bolts on a "61"

Jim------

The liklihood is very great that the replacement block will be a 4 bolt main configuration. If the part number of the replacement short block assembly was GM #3970655, which is likely, then the chances that it is a 4 bolt configuration is 100%.

[jack alexander]

Re: How many bolts on a "61"

Thanks guys for all the informative comments.Just for the record this guy is my friend, but when it comes to my "baby" that is where the friendship ends. You see friends come and go like pets and wives, but your Corvette mechanic is on the level of a diety. I don't even let my real mechanic touch my car until I've searched the archives or talked to you guys on the tech board. One more question. Since the cranks are all 2-bolt, are all the "283' cranks interchangable regardless of HP? The amount of HP determined by other factors such as cam,heads pistons etc?

[Joe L.]

Re: How many bolts on a "61"

Jack-----

All 283 cranks are functionally interchangeable since all 283s were manufactured with the same size main bearing journals. Of course, the nodular cast iron versions might not be the best idea for a really high performance 283, but they'll fit just fine in such an engine. As a matter of fact, though, even the cast iron cranks will likely easily withstand all of the power that anyone's going to be able to make with a 283 cid engine regardless of its performance configuration.

Also, although no 283 ever used 4 bolt mains, the fact that a particular engine has 2 or 4 bolt mains has no effect, whatsoever, on the crankshaft. The same crankshafts can be used in either a 2 bolt or 4 bolt main bearing block.

[John H.]

Re: How many bolts on a "61"

Although it didn't affect production Corvettes (which were all 327's in 1964), a cast nodular iron 283 crank was introduced in 1964; these cast cranks can't be used in 283's prior to that date, as the nodular crank required larger counterweights which wouldn't clear the "straight" bottom of the cylinder bores in pre-1964 283 blocks. The bottom of the bores in mid-1964 and later 283 blocks were cast "scalloped" to clear the larger counterweights on the cast crank.

[Jim T.]

Re: How many bolts on a "61"

Do not know what the part number was for the short block, the casting number is 3970010 and casting date is D 25 or 23 0.

[Joe L.]

Re: How many bolts on a "61"

Jim-----

With that date on the block, if it was originally supplied as a complete short block (partial engine) for a 1970 300/350, it will be of the part number I provided and it will be a 4 bolt main block.

[Tom P.]

Re: How many bolts on a "61"

John is 100% on the money. LATE 283 cranks will not fit into an EARLY block because of the larger counterweights. Guess how I know!!!!!!!!!!!!!!!!!!!

[Joe L.]

Re: How many bolts on a "61"

John and Tom-----

Yes, my "memory banks" failed on this one. It's a case of "not seeing the forest for the trees". My mind was focusing on carnk journal size and I completely forgot about the difference in counterweight size for forged versus cast 283 cranks. I think that the earlier blocks can have the lower cylinder area relieved by machining if a cast crank is to be used in them. However, it's really a moot point since it would be a lot of work. Much easier to just find a forged crank.

[Mike McKown]

Re: How many bolts on a "61"

I believe the nodular iron cranks also used a different harmonic balancer than the steel cranks. In addition, I believe if you use the steel crank pistons in a nodular crank application, the engine seriously needs a balance job.