Offset Grinding 351w Issues

[Topsp33d]

I found a local crank grinder who says he’s taken stock 351w cranks pretty far. I asked him if we could turn it down to a Honda rod journal and he responded that it’s fine, albeit the oil hole migration. I’m wondering what else needs to happen for this build to work out correctly.

There’s a good selection of used nascar rods that have the 1.850 journal but have an import wrist pin so I will most likely have to order custom pistons unless it’s easy to hone a small end from .787 or .827 to a regular .927

Anyways I’m just wondering about some math and some finishing processes

2.311 stock rod journal
1.850 Honda journal
~ .46 offset grind
3.50 stock stroke + 0.46 = 3.96 stroke
3.96 /2 = 1.98

9.480 - 1.98 - 6.200 = 1.300 compression height

Is it really that simple?! There are loads of pistons in that size due to 408 strokers but none that have the small wrist pin. Is it better to bore the rod to .927 or order pistons with the small wrist pin?

The grinder says he only grinds and doesn’t offer any nitriding or cryotreat or balancing. Should I cryotreat this before it’s cut? Or nitride after? Both/neither? It just seems like it should have some sort of treatment after taking half an inch out…

Anything else I’m missing please clue me in, it seems to be a relatively simple job. And before someone says why don’t you just buy a new crank: it’s because the offset cut was quoted at $260 and those rods are $100. With custom pistons I am still way under any other option. Thanks

[BillK]

Seems to me that if the reason you are doing this is to gain more stroke you will most likely be much better off just buying a crankshaft. One of the things that you did not mention and need to consider is the counterweight diameters and whether they are going to need to be cut down to clear the pistons with the extra stroke. Etc Etc Etc.

Eagle has a 4" stroke cast steel crank for less that $400. I cannot imagine you doing your stock crank for any less and the Eagle will be much stronger.

[Joe-71]

I have done this stroke increase, and do not recommend going any further than 2.000" journal. The oil hole will elongate and weaken the crankshaft if you go too small. It will live for a short time, but ultimately break. BTDT. Finding 6.200" or longer rods at the 2.000" journal will be an issue, and finding the 2.100" journal rods will be much easier. Narrowing the big end of the rods will cost, balancing, stroking the crankshaft, etc., does not justify the whole process with today's stroker kits available IMO. Just because something CAN be done does not mean it SHOULD be done. Joe-71

[Walter R. Malik]

IF the journals are RE-indexed a few degrees differently, the oil holes won't migrate much however, you will now need to adjust the cam timing and damper markings to align correctly with the woodruff keyway on the snout. And, of course balance for that assembly.

[frnkeore]

Although I'm doing something similar, I would also recommend a after market 2.100, rod journal crank, of your choice.

There are lots of pistons to fit. My custom Ross pistons are costing me almost $1100, with shipping. They were the only company that had a exceptable delivery time and that was late. All the cheap pistons, with the small pin holes, have the wrong valve relief for a Windsor and if you open the pin hole, the pin retainer grooves will have to be machined deeper.

The only reason I'm doing it, is because I get a steel crank (Ford FE truck) when I'm done and I like doing different things. Plus, I have a machine shop that I can use to modify stuff, like the big end of the LS rods I'm using. You haven't said if the 1.850 rods are narrow enough for the narrow Ford crank throw.

It will be a slippery, expensive slope!

[rustbucket79]

Ahh the good old days. I recall seeing a Windsor come in where a local shop had modified a 400 M crankshaft to fit. Counterweights heavily cut, 4 to 6 slugs of mallory per end, plus custom external balancing.

I applaud you for trying to reinvent, but keep in mind this is a cast crankshaft with very large factory lightening holes in the rod pins. Your budget build isn’t a great idea if the crank breaks.

[Topsp33d]

Thank you all very much for your insight, I will take it all into consideration. For the sake of continuing this thought I would like to expand on them.

1: oil hole migration. I’ve read on here that someone and their builder determined a 351w crank could safely go 4.00 stroke, so has anyone tried it specifically with this crank and found otherwise? & What exactly does reindexing mean? Is that a different type of offset?

2: counterweight depth: stock rods are 5.956 and the proposed set are 6.2 which leaves .244 of known clearance. Far cry from .46 of offset which is something I will have to measure, thank you for the heads up.

3: budget and availability: I know there are ready to go kits for this, just trying to use what I have and support local work. Nothing against using a kit, the budget can get as wild as I can get the wife to approve of, haha

[Geoff2]

That is a huge amount of metal to remove; not only will it be close to the oil hole, you are significantly reducing the overlap that gives the crank so much of it's strength.

[1972ho]

I did a 351 cleveland last year for stroker 377 cid I used stock type cleveland pistons and Chevy 2.100x5.700 using the .912 cleveland pin diameter so I had to replace the bushing in the Chevy rods.The balancing was 500.00 because the cleveland counterweights had to be reduced to clear the pistons skirts so heavy metal had to be used to balance the crankshaft.So you more than likely will be in for more than you are expecting with the Honda journal size.

[PackardV8]

Back in the day, a local rebuilder did a big business in marine BBF 514" builds, enough to order custom pistons by the pallet. He'd offset grind BBF cranks to take Chevy rods, have the pistons made with Chevy wrist pins. When the SCAT/Eagle Chicom cranks became available, it was more cost-effective just to buy the kit. When his shop closed, he still had a pallet-and-a-half of the custom pistons.

[Topsp33d]

I called JE pistons today to ask if the wrist pin would be a $5 change and the rep said nope! Too drastic and they would have to get engineering involved. So that is still an issue to solve.

I checked crank overlap and I am doing okay compared to other cranks that eagle/scat/lunati make, like a Cleveland main 4.1 stroke
3.00 main + 1.850 rod - 3.96 = 0.89/2 = 0.445

To compare a shelf 408 crank:
3.00 main + 2.100 rod -4.00 = 1.1/2 =0.55


I don’t think I’ll need to add Mallory to this because the nascar rod + custom piston will be very lightweight. Hopefully the counterweights will clear with a 6.200 rod.

I’m grateful for everyone sharing their expertise, I will pull the crank soon and do some basic numbers to see if it’s worth going farther

[rustbucket79]

Back in the day, a local rebuilder did a big business in marine BBF 514" builds, enough to order custom pistons by the pallet. He'd offset grind BBF cranks to take Chevy rods, have the pistons made with Chevy wrist pins. When the SCAT/Eagle Chicom cranks became available, it was more cost-effective just to buy the kit. When his shop closed, he still had a pallet-and-a-half of the custom pistons.

Ouch!!

We had a Windsor crank with the preliminary journal grinding to fit a 302 block, and the some sort of offset ground Windsor with SBD rod journals that an old employee machined 10 years prior , it stung a bit but in the end much cheaper to toss in the recycling bin than investing the job to the end.

[rustbucket79]

Thank you all very much for your insight, I will take it all into consideration. For the sake of continuing this thought I would like to expand on them.

1: oil hole migration. I’ve read on here that someone and their builder determined a 351w crank could safely go 4.00 stroke, so has anyone tried it specifically with this crank and found otherwise? & What exactly does reindexing mean? Is that a different type of offset?

2: counterweight depth: stock rods are 5.956 and the proposed set are 6.2 which leaves .244 of known clearance. Far cry from .46 of offset which is something I will have to measure, thank you for the heads up.

3: budget and availability: I know there are ready to go kits for this, just trying to use what I have and support local work. Nothing against using a kit, the budget can get as wild as I can get the wife to approve of, haha

The builder hasn’t offset ground a crank before, it is impossible to offset that much stroke. Take your 1.850 journal rod. Assuming your crank is perfect in both stroke, index, and straightness, you have .461” of material to fit the new bearing at standard or 3.500 stroke. You gain stroke by removing from the underside of the rod pin, but as you do this, you move the opposite side of the rod pin AWAY from the grinding stone, so to add .010” stroke you need .020” of journal to remove. (In a perfect world) In a perfect world, you could offset half the available material, or .2305” giving you a final stroke of 3.961”.

Finding a perfect factory crank means finding that 1 in 100 or 1000. Reality and shooting for a standard bearing size means reducing the stroke target, and since there’s no point in doing the job unless you shoot for perfection, so we’ll use the index locks on the crank grinder along with “set and forget” the stroke, so now we need added material since some pins might be advanced, and others might be retarded from the front pin.

We haven’t even addressed the counterweight to piston clearance, nor the impending balance job. Oh, and those nice light Rods might not be that light on the big end, making the bobweight not that much lighter than stock.

[Walter R. Malik]

Thank you all very much for your insight, I will take it all into consideration. For the sake of continuing this thought I would like to expand on them.

1: oil hole migration. What exactly does reindexing mean? Is that a different type of offset?

RE-indexing simply means NOT offset grinding the journal at the same centerline location as it was originally. In other words, advancing or retarding the journal when grinding it, to keep the oil holes in about the same place.

Call Adney Brown at Performance Crankshaft in Michigan ... he has done several "offsets" in that way. (586) 549-7557

[frnkeore]

I called JE pistons today to ask if the wrist pin would be a $5 change and the rep said nope! Too drastic and they would have to get engineering involved. So that is still an issue to solve.

I checked crank overlap and I am doing okay compared to other cranks that eagle/scat/lunati make, like a Cleveland main 4.1 stroke
3.00 main + 1.850 rod - 3.96 = 0.89/2 = 0.445

To compare a shelf 408 crank:
3.00 main + 2.100 rod -4.00 = 1.1/2 =0.55

You do know that you can gain a lot more cubes by getting the after market 4.10, 4.17 or 4.25 cranks?