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Ok a friend has dropped of a crank to see if i can get him another . it's a welded stroker crank from a motor he bought in a basket . the motor was run with loose flywheel so dowels are toast and cracked. I want to ensure I'm getting him same thing in a crank
the only markings I see on it is a bb and what looks like 82v hand stamped on one counter weight

can anyone help with how to ensure I order the right one

measure it. or have it measured.

Put a straightedge along the counterweights, parallel to the centerline of the crank - measure from it to two adjacent rod journals, the difference is the stroke.

I'm not familiar with anyone building welded strokers with the moniker "bb" but from the stampings you report I would expect it to be an 82mm stroke with VW rod journal diameters (2.165"= STD).

Welded strokers can be built in just about any stroke/journal combination one could imagine, but "production" items typically come in 74, 76, 78 (78.4 was common in years gone by), and 82mm with VW journals. Longer strokes usually have smaller rod journals ("Chev"/Buick V6, Porsche), but those can be found on nearly any stroke.

82mm with a stock-length rod yields a very short rod ratio, suitable only for a "thumper" motor IMO. Fine for a bus or off-road engine built for low-end grunt, but a bad plan if high revs are anticipated.

"bb" is probably Bernie Bergman. He made a lot of 82mm welded stroker cranks back in the day. For a replacement, a new forged crank from CB is the safest way to go. They are forged overseas, but (supposedly) machined here. DPR makes beautiful welded cranks, but they are a bit more money..

An 82mm crank with stock 137mm rods is only 1.67 rod ratio - still towards the high end for hotrodders. The CB forged crank is not a bad choice, but there are some cheaper ones out there to avoid. 82mm on a welded crank with stock journals is pretty unusual, and to be avoided if at all possible, with chev journals not much better.

The above advice of putting a straight edge along the counterweights won't work unless you include subtracting the distance to the rod journal from it, BTW.

Marc wrote:Put a straightedge along the counterweights, parallel to the centerline of the crank - measure from it to two adjacent rod journals, the difference is the stroke. ...82mm with a stock-length rod yields a very short rod ratio, suitable only for a "thumper" motor IMO. Fine for a bus or off-road engine built for low-end grunt, but a bad plan if high revs are anticipated.

The inertial forces are just too high IMO to run stock rods with an 82mm stroke; if you're going to run it past ~4500 RPM you should upgrade to good I-beam or H-beam rods. It takes a good bit of case (and even camshaft) clearancing to stuff an 82 crank w/I-beams into a stock case, but it's doable...H-beams can simplify this aspect of the build some as well as being stronger as a rule.
1.67 is a hair better than the 1.64 of a 350 Chev w/5.7" rods...but it's an accepted fact that those motors benefit greatly by stepping up to 6" (or longer) rods. We aren't limited by the height of the block the way they are, and can more easily use a higher rod ratio - if you need to buy rods anyway, they may as well be longer-than-stock.

I've got a crank stamped H78, was told it was stroker 78mm.

But when I measure depth at TCD to BDC on any of the pistons I come up with 69-70mm
It is an 8 dowel, with massive 1 ⁷/⁸ gland nut.

Any ideas? It's not a forged stock crank, shows areas of welding.