When I finally got to look at my 400HP block, I found the bosses drilled and tapped indicating 4 bolt main. Block is very early production (J126) for '67 year. My question now is: what are the tapped holes over by the starter that are similar in size to these?
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Re: Back to four-bolt mains
Dave --- There's not much on the starter (passenger) side. Other than the 3 tapped holes for the motor mount, there's another just above and slightly ahead of the forward end of the starter, which is for the starter support brace. Also, above the pan, about the middle of the block, is the lower drain plug for the water jacket (one on each side of the block).
Since this 2/4-bolt thread has started, yours is the first reporting of an L68 with 4-bolt mains (or at least the tapped boss configuration that is believed to be a proxy for 4-bolts). Several persons have responded via the NDB or e-mailed me to state that their 400 hp versions have 2-bolts. -
Re: Back to four-bolt mains
Dave,
Excuse me if I am wrong, but if I understand the earlier discussions of this topic correctly, the presense of drilled and tapped basses does NOT automatically indicate a 4-bolt block. My '69 L68 also has those drilled & tapped bosses, but without a "spare" pipe plug sealing one of those holes. I thought it was the presence of the "spare" square headed pipe plug that indicated the 4-bolt block. The 2-bolt blocks had the drilled and tapped bosses, but the holes did not extend all the way through the wall of the block, and thus did not require the plug to "keep the oil in". From your description, your block sounds like a 2-bolt. Let us know if you have the pipe plug.
Joe Peplinski - '69 L68 Conv.Comment
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Re: Back to four-bolt mains
Gang,
Keep in mind that if the engine plant exhausted their supply of 2 bolt cylinder cases and still needed to produce x engines to meet the order they could substitute 4 bolt case in place of the 2 bolt. Thus some lucky folks could get 390/400 hp engine with 4 bolt or base motor with 4 bolt.
They could upgrade part, but not downgrade - so no 435 hp 2 bolt cases.
Terry
TerryComment
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Re: Back to four-bolt mains
Joe,
If it's still possible for Dave to tell us if he has the square hole plug above the oil filter then I'd like to know also. But I don't want to create a confusion or misunderstanding with some of what Wayne M. or I might have said earlier. Though I questioned it before, Wayne has answered that machining the external oil fitting boss was more than likely done as part of the run that produced the 4 bolt main blocks. And it is still possible that Dave, or anyone else would have that plug as well as 4 bolt mains even though their engine option is the 390 hp L36 or 400 hp L68. TBarr #24014Comment
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How about a borescope?
As a "smallblock guy" maybe I shouldn't butt into your discussion, guys, but I've got a way to settle the issue. Someone, anyone, come up with a borescope and peer through the oil drain hole the next time you change oil. The only issue might be blockage of the view by a windage tray if the 390/400 horsepower engines have them (?). I use a borescope periodically to peer through the oil drain hole of my Cosworth Vega as the second order unbalanced vertical shaking force has disintegrated the oil baffle and pickup tube twice from all the high rev time hot-lapping Willow Springs. A borescope gives a very nice panoramic view of the crankcase.
DukeComment
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Re: Back to four-bolt mains
Well, both the larger square plug and the smaller plug are screwed into the block. I don't know if the fact that the car is in the first 2500 produced for '67 helps explain that, until I drop the pan to know for sure, maybe Chevrolette put the 4 bolt mains into earlier models, and then decided to not do it for cost savings (?).Comment
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Re: Back to four-bolt mains
Dave,
As you previously mentioned, and from all indications I would say your block would / should have 4 bolt mains. TBarr #24014Comment
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Re: Back to four-bolt mains
Dave et al --- Here's another bit of info on the oil galley plugs for FOUR-BOLT MAINS, gleaned from Hot Rodding BBC's: the larger plug is 3/4" NPT (National Pipe Thread). The smaller plug (forward of the big one), or block-to-first-reducer fitting if the oil line is attached there, is 1/2" NPT.Comment
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