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Both Doug Anderson and I have written a number of articles and columnsabout these engines, but for some reason I continue to hear about thedifficulties. So it’s time to go back to the basics, start from thebeginning and review the old and add some new things that have comealong.

The first engine in the Gen III family was introduced in 1997 in theLS1 Corvette. This crankshaft, with casting number 1255216 (or “216” asmost of us call it) is easily identified by the 24.5 mm gun-holedrilled through the middle of all mains except the first one. This holewas drilled all the way through from the rear so there is a soft plugat the rear of the crank that, if not installed, will cause ahorrendous oil leak in the rear (Figure 1).This crank is a standalone due to the hole down the center that isthere to equalize crankcase pressure between the main bearing web bulkheads in this application.

The second crank is the one used for the 4.8L engine that came intwo flavors – automatic and standard transmission.  The standardtransmission crankshaft (c/n 1225312) has a wide rear flange 1.250? andthe automatic transmission crankshaft (c/n 12553482) is a narrow .857?.The wide/narrow crank scenario happened in ’99-’00; after that they allbecame narrow flange (Figure 2).

The early manual crankshaft engines are few and far between and findingcrank cores is a tough nut to crack. Obviously that became an issue forGM as well because there was an adaptor kit designed to convert anautomatic crank to a manual crank (Figure 3).  These kits are available from both GM and aftermarket providers, so trying to find cores becomes a non-issue.

Because the Gen III block says “4.8 and 5.3” on it you may havegathered the 4.8L and 5.3L engines use the same crank. That’s a goodguess – but it’s not correct. The two used different cranks and rodsdue to stroke differences and each had different casting numbers.

How do you tell the difference? When they were installed in a longblock, it might have been challenging, but here’s a visual “new thing”that I’ve recently become aware of. Look at the counterweights of eachcrank. The interior counter weight outer edges are “as cast” on the4.8L, while they are machined on the 5.3L cranks (see Figure 4).

The 5.3L crankshaft has the same casting number (c
12552216) as the5.7L crank but is not gun-drilled so there is very little otheridentification than what you see in Figure 4 with the “as cast” andmachined counterweights. Because it was never a manual transmissionengine, it will always have a narrow flange crank. By the way, you willnot be able to use this crank for a 5.7L engine, especially without thegun drilled hole through the mains.  

The 6.0L crank has the same stroke (92mm) as the 5.3L and 5.7L cranks.In 1999-2000 this crankshaft was identified with c
12552215 and hadonly a wide flange. Then in 2001-’04 the 6.0L went to narrow flangeonly with c
1255216, the same as the 5.3L and 5.7L.

The piston weights are different enough for the 5.3L, 5.7L and 6.0Lthat you would not think that any of them would interchange. Howeverword on the street is that 6.0L and 5.3L cranks will interchange andthat there have been no complaints. So I am surmising that they aresimilar to the 305 and 350 situation: most of the time you will be OKbut there may be those few times that it could bite you. I will leavethe interchange decision purely up to you. I can tell you for a factthat there are “216” cranks that are being rifle drilled and used asthe 5.7L crank. I am making the assumption that they are beingrebalanced but have not been able to verify it.

There is another crank that has come on the scene recently that isknown as a “218.” Reports are that it is the same as the “216” exceptin the reluctor ring area. I have not seen it yet but I do know that ithas the new design reluctor ring on it. You will need to keep an eyeout for this one as well.

Roy Berndt has decades of machine shop experience.He is the EDS Data Acquisition Contractor for the Production EngineRemanufacturers Association (PERA), and Program Manager for PROFormancePowertrain Products, a PER in Springfield, MO. You can reach Roy at [email protected].Figure 1 On the left you can see the rifle-drilled hole through the center of the LS1, 5.7L crankshaft. On the right, the soft plug is installed in the rear of the crankshaft to seal off crankcase oil. This is the only Gen III crankshaft that has these features.Figure 2 Wide and narrow flanges were found in the Gen III cranks in 1999-2000. The narrow one was used with the automatic and the wide with the manual transmissions.Figure 3 Narrow flange automatic transmission Gen III cranks can be made into wide manual transmission by the use of a spacer adaptor and longer bolts.”Figure

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Roy Berndt
Roy Berndt has decades of machine shop experience. He is the Program Manager for PROFormance Powertrain Products, a PER in Springfield, MO. You can reach Roy at [email protected]