How do I fix this??

[Tony, NY]

The fact that the piston C/L is offset from the rod C/L would concern me. Seems there would be forces cocking one side. Eventual problems. I could be wrong.

[Brian]

Yes Tony, it is a concern.....and I agree with you. What I've done will enable it to work, but I don't like it!

[cas3]

hot rod model T guys have been putting model A cranks into the T,s for decades. when you do this the result is like brians problem, the holes dont center on the rod journals. so, like brian they run the piston off center. seems to work, however my guess is these are high performance engines that are not trying to set a record for high mileage. best wishes brian, i know you like your 21 studders !

[Brian]

Thank you cas3, didn't know that. Good to know. Should make me feel better, but it don't!! lol

[Lawrie]

Geez Brian ,I was going to get one of those cranks.to use in a 36 block,I think I,m better off using another 99a block.
What piston clearance will you use with the ross pistons( assume they are forged)
Could you measure the centres of the crank pins on the crank and compare those to the bore centres ,just o know where the error is .
Lawrie

[Brian]

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Lawrie, If you want a 4" stroke in your 36 block, trust me, your best bet will be to get a genuine Merc crank, reduce the main journals to 2.399, and widen the front and middle journals to suit the 36 block. You'll need to make a spacer for between the front main and timing gear to locate gear in correct spot. Shorten the snout and turn down to 36 size [not essential- you could probably run the later pulley[s]]
I don't know if 99A/8BA rods will clear block, but if you're boring to 3 3/16, you'd probably be able to run those which would eliminate grinding rod journals down to 2".
Only other thing would be the absence of the slinger for rear oil control, but I think Reds Headers has a seal conversion to fit 36 rear main, so you'd have positive oil seal control.
Ross instructions call for .004" clearance
The centre to centre errors for the three rearmost cylinders was around 0.5 - 1.0 mm [.020" - .040"
The front cyl's centre /centre error was around 2 mm [.080"]

[cas3]

if you have to cut the journals down to 36 size, could'nt the crank grinder grind them to the location you want?

[Lawrie]

Brian ,I think I will stick with a 99a block when I need to get the larger displacement,
But will do an engine change out on the 34 in the next week or so,I,m fitting the nicest smoothest engine I have,the original 33 babbit engine with sts bore and those little skinny rods with flat top pistons.
I have a standard bore 37 block that would be a good exercise though.
You have any hair left,LOL
Lawrie

[Brian]

cas3, The 36-38 221 cranks run 2.399" dia mains, but the front and centre journals are longer than the subsequent 39 on cranks with the 2.499" dia mains. When scat manufactured this piece of scrap iron, they ground to the smaller journal size, BUT used the later bearing widths [too narrow]. So, in order to primarily get the crank to fit a 21 stud block, I had to widen those two journals. If I had have used a genuine 255 crank, I would still have had to have modified those widths [and dia's]. The positioning of the thrust faces determines everything else.
So, not only did Scat bugger up the mains, they also referenced the positions of the conrod journals in regard to the thrust faces incorrectly.

[Kohnke Rebabbitting]

Originally Posted by Brian

You may recall a while back I posted about issues with the main bearings on my Scat 221 4" stroke crankshaft. I fixed that little problem, posted on here, advised Scat; they didn't want to know!
Well, during a mock up assembly yet another problem has surfaced. I honestly don't know how to fix this.....Look at the photos; these are shots of numbers 1 and 5 cylinders. No, the rods are not bent; they are NOS 21A conrods. The crankpins on the crank have been ground on a different centre to the cylinders, consequently, the rods are hard over one side. I cannot run it like this; what to do?
I know what I'd like to do with that crank, and it wouldn't be pretty!!

Take a picture of all 3 mains, at right angles with the crank in the block, with caps, so I can see where the crank has come out, for position.

Then, you said, No, the rods are not bent; they are NOS 21A conrods. " END QUOTE "

Did you check the rods for Alignment, or are you assuming, that they are straight, because they are new in the box. If you are, being new does not mean a thing. Every rod that is put into an engine should be checked for alignment!

Twist ,Bend, and Off Set.

Your pictures clearly show Rod Off Set. That can be caused, By the Rods, Crank set wrong, Crank made wrong, Cylinders Bored Off, Ect.

Have you Checked the Scat crank Measurements, against a Ford crank?

Herm. KohnkeRebabbittingService.com

[Brian]

Herm, you are so right! Of course the rods were checked for alignment. And I can fit any rods on that journal and have the same offset. Block was a virgin unbored block, now bored to 3 3/16 on the exact centres that it came from the factory with. A new head gasket locates nicely around all cylinders.
Comes back to only one scenario you mention doesn't it?

Incidently, surprise ,surprise, Scat don't want to acknowledge this. They don't recognise what sort of rods they are; they don't look like Scat rods! Which is a damn good thing!!