Cost of offset grinding a crank?

[travis]

Just an idea I was kicking around...

Does anyone still offset grind cranks? How much more $$$’s versus a standard crank grind? This is for stock cast iron stuff...

[PackardV8]

duplicate

[PackardV8]

Let's agree on terminology.

Offset grinding is usually defined as moving the rod throw centerline by going to a smaller crankpin diameter with a slight change in stroke. That costs very little more than a standard regrind. The BBF/BBM, et al, using BBC rods often offset grind while going to the smaller diameter.

A welded stroker crankshaft has weld built up on the outside of the rod throws sufficient to provide enough material to offset grind and move the centerline outward for a substantial (1/8"-5/8") increase in stroke.

Yes, a few smaller crank shops will still build a welded stroker if you twist their arm and give them over the winter to do it. No crank shop I know solicits welded strokers any more. Too much work for the $1500=$2500 they can charge. That plus so many Chicom forgings on the market these days.

[modok]

Going down to a smaller rod size should not be a HUGE problem.
Having to re-balance the crank may actually be more work/time than the extra grinding.

[user-23911]

I've done a couple of offset strokers for myself.
Jap stuff where there's no billet one available or rather too expensive (maybe US$3500).

As for cost, that depends on hourly rate, different options take different lengths of time.
The first one takes the longest.
Cutting down the mains at the same time (fit a crank to a different block)takes longer.


I've probably put over 20 hours into one and over 30 into another, that's steel cranks which still require nitriding and balancing afterwards.
Then afterwards, depending on the recipe used, you might end up modding conrods from something else to use on it, that's yet more hours........like narrowing the big ends and making the piston pin holes bigger.
Then using factory pistons and cutting the tops to make them fit.
Doing it for yourself, you don't worry about the hours because you'll end up with something no one else has yet figured out.


As far as comparing cost of an offset grind compared with a normal grind, it's not even close.
A normal grind you might take off 0.25 mm in diameter, 0.125 mm all the way around. An offset grind, you might take off 5 mm diameter but only from the inside.
There's a big difference in cutting time comparing 0.25 to 5.
It also depends on the machine, how old it is, how many adjustments you have to make etc.
Setup time is important, the more time you put into the setup, the more accurate the end result will be.

[pamotorman]

off set grinding a 350 chevy 2.100 crank pins to 2.000 diameter crank pins 283 size and make a 3.562 stroker. TRW even sold pistons to do this and this was the poor man stroker

[fdicrasto]

Call Moldex if no-one near you wants the work. Lunati sold sbc cast cranks with slight offset to take advantage of stroke allowance rules and they were very reasonable. That was MANY years ago. As previously stated,TRW offered an off the shelf piston for the 350 sbc offset deal. It was somewhat common practice offset grinding large journal 302 sbc forged cranks to destroke them back when 277" and 296" modified eliminator engines were killer high winders in the 70's and 80's. So much for that history lesson.

[Walter R. Malik]

Let's agree on terminology.

Offset grinding is usually defined as moving the rod throw centerline by going to a smaller crankpin diameter with a slight change in stroke. That costs very little more than a standard regrind. The BBF/BBM, et al, using BBC rods often offset grind while going to the smaller diameter.

A welded stroker crankshaft has weld built up on the outside of the rod throws sufficient to provide enough material to offset grind and move the centerline outward for a substantial (1/8"-5/8") increase in stroke.

Yes, a few smaller crank shops will still build a welded stroker if you twist their arm and give them over the winter to do it. No crank shop I know solicits welded strokers any more. Too much work for the $1500=$2500 they can charge. That plus so many Chicom forgings on the market these days.

The cost of "Offset grinding" usually depends upon the amount of time THAT particular crankshaft will take to complete.
A small block Chevrolet offsetting .090" is definitely less expensive than a Big Block Ford crank removing .300" from one side of the throw.

[travis]

I’m not looking at anything crazy...just something like .030-.060” offset (I didn’t realize until today that .040-.060 undersized rod bearings was even available for many engines). My thinking being that on one of my low buck 305/350 Chevys or 351w’s, under 350 HP, with cheap cast rebuilder type pistons, this may be a better alternative to getting decent quench without excessive deck milling (and its associated problems). For example, a recent 350 Chevy I did...block decked .008”, .010/.010 cast crank, 4vr cast flat tops 345NP’s...ended up .045” in the hole. With rebuilder type .041” head gaskets it ended up with .086” quench. If it was offset ground .040” instead, pistons would have been .025” DITH, and with a felpro 1094 .015” thick, would have given .040” quench (way better!).

I’ve run .040 under rod journals before on a couple of cheap sub-325 HP 350’s and never had an issue (spun a rod, no money type deals). Would .050 or .060 under even be safe at under 6000 rpm’s on a stock cast crank? Cost-wise it could be a better deal, but would it be strong enough to last in a non-serious performance type application?

[DrillDawg]

I think the CH for a 350 is 1.54" and for a 327 is 1.65, if you use a cheap 327 piston you'll be about .020'" out the hole and the piston can be machined down to whatever you want the clearance to be.

[modok]

Yeah better to do it with pistons.

Extra thick rod bearings are not a great idea. It's not as strong, although it is a small difference. The thicker the bearing the more likely to fatigue from flex. It's like if you painted two pieces of sheetmetal, 1/8 and .030 thick material. Bend them. The paint will stay on the thin piece but chip off the thick piece, and I think you can imagine why.

Another concern would be finding good quality bearings in the far undersizes. Best way would be a thicker steel backing, but many just have a thicker layer of bearing material, which yet again, more likely to fatigue.
One time I took apart an odd chevy 350 that had a real CUSTOM grind.
Most rods were .020 under but one pair were .050
The .050 under bearings were flaking apart but the others were not, same brand, in same engine.
I thought it was a really neat unintentional experiment

I would not worry so much about undersize main bearings, because they flex a lot less, but far as rods there is a reason they all have right around .060 thickness

I figured we;d be going down to the next size, 2.100 down to 2.00, as was done in the beginning and ever-after.

[Walter R. Malik]

Yeah better to do it with pistons.

Extra thick rod bearings are not a great idea. It's not as strong, although it is a small difference. The thicker the bearing the more likely to fatigue from flex.

With today's bearings, that notion is completely wrong. An engine bearing may move a very, very little with whatever the rod flexes but, if it ever was to bend ... you have other issues.

[amc fan]

What would an AMC 401 steel crank cost to upstroke from 3.68 to 3.8? The crank pin is 2.25 taking it to SBC 2.1 . That way I can use standard Chevy bearings and 6 or 6.1 aftermarket connecting rods?. My go to guy retired!

[PackardV8]

What would an AMC 401 steel crank cost to upstroke from 3.68 to 3.8? The crank pin is 2.25 taking it to SBC 2.1 . That way I can use standard Chevy bearings and 6 or 6.1 aftermarket connecting rods?. My go to guy retired!

$1500 - $2500, depending on balance, nitriding, how busy the shop and what kind of mood they're in after dealing with the last weird-ball engine guy.

[LCaverly]

Call Adney Brown ( Performance Crankshaft ). He will tell you whats possible and how much. 1-586-549-7557
Len C