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Using small crank hub smallblock adapter crank spacer on large hub crank and trans
https://www.slantsix.org/forum/viewtopic.php?t=68363		 Page 1 of 2
Author:  Reed [ Sun Sep 21, 2025 3:28 pm ]
Post subject:  Using small crank hub smallblock adapter crank spacer on large hub crank and trans
I am (slowly) moving forward with my plan to install a 1988 A500 transmission behind my 1976 225. One of the issues I have is the smallblock trans adapter package I have is for a small hub (pre-67) slant crank.

I believe I can use the crank spacer in this combination by (a) enlarging the bore on the torque converter side of the spacer and (b) using one of the spacer rings on the crank hub side of the spacer.

Is that right?

Anybody got a crank adapter ring for sale?
Author:  volaredon [ Sun Sep 21, 2025 8:02 pm ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
I remember checking into what would be needed to use this setup on a 68-newer slant and it's been a while but I thought all that needed done was your "step A" but I've slept since then.
My combo would be '74 engine, 64 adapter package and '91 A500
Author:  Charrlie_S [ Mon Sep 22, 2025 4:00 am ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
I haven't done one of these, but I think all you would need to do is get a crank bushing (adapter) to allow the early 904 to be used with a late crank engine. Then use the Factory spacer/adapter . Measure the factory spacer/adapter converter pilot hole. That adapter setup was to use the small block 727 trans behind the slant six. All 727 transmissions had the large converter pilot. If I am correct there is no machineing required.
Author:  Dart270 [ Mon Sep 22, 2025 4:11 am ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
On my factory crank adapter, the hole in the forward (of car) side that mates to the crank fits OVER the OD of the factory crank's small hub. You need to machine that out to fit your big hub crank. The other side worked w/o modification to the late big snout converter. This is what I did. It is trivial for any machine shop with a lathe to do this.

Lou
Author:  Reed [ Mon Sep 22, 2025 9:52 am ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
This is what I have:
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IMG_7650.JPG
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And here are some notes about crank hub sizes I stole from somewhere:
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flywheel-hubsize.jpg
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The pocket on the side of the crank spacer with a raised lip fits snugly over the snout of the A500 torque converter.
Attachment:
CRANK SPACER TO TC.jpg
CRANK SPACER TO TC.jpg [ 138.89 KiB | Viewed 322 times ]
I don't have a loose slant six crank or motor, but the raised flange on the back of a 1999 Magnum 360 crank over which the flex plate fits measures 2.158 inches from outer edge to outer edge. That is exactly the same as the diamter of the raised lip on the crank spacer.

So my question, then, is does the pocket on the flat side of the crank spacer fit over the flange on the slant crank? It must, because the flex plate must bolt directly to the torque converter and the raised lip on the crank spacer fits the hole in the middle of the flex plate. So I think I have the crank spacer orientated correctly in the picture above. If that is true, no spacer ring is needed, just a quick trip to a machine shop with a lathe to open up the pocket on the flat side of the crank spacer to 2.165 inches.

Sounds like I just confirmed what Lou already told me! Does this all sound correct?
Author:  Dart270 [ Mon Sep 22, 2025 10:47 am ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Yes, that is correct. Just lathe it out to lightly slip or tap fit the spacer onto the Slant crank snout. 2.165" sounds too big to me. You want it at 2.159" assuming your caliper is right. BEST would be to carry a late Slant crank to the shop that will do the lathing and tell them to make it a light slip fit. 0.006" in diameter difference will not center it well enough and you'll have a vibration.

Lou
Author:  Reed [ Mon Sep 22, 2025 11:34 am ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Quote:
Yes, that is correct. Just lathe it out to lightly slip or tap fit the spacer onto the Slant crank snout. 2.165" sounds too big to me. You want it at 2.159" assuming your caliper is right. BEST would be to carry a late Slant crank to the shop that will do the lathing and tell them to make it a light slip fit. 0.006" in diameter difference will not center it well enough and you'll have a vibration.

Lou
Thanks, Lou. I might take the slant crank in or at least measure the flange on the slant crank. I certainly don't want to lathe the piece wrong since I would have a heck of a time finding another one and manufacturing a new one would likely be cost prohibitive.
Author:  Charrlie_S [ Mon Sep 22, 2025 2:14 pm ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Thanks LOU, I thought that the crank spacer/adapter, went into the pocket of the crank.
Author:  Dart270 [ Mon Sep 22, 2025 2:45 pm ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Since I did all of this already (24 yrs ago!), it is easy to answer...

Best to take at least some Slant crank to them. There is hardly any variation crank-to-crank, but there might be more error in your digital caliper...

Lou
Author:  Rick Covalt [ Mon Sep 22, 2025 4:58 pm ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Yes, I would say it is best for the guys doing the lathe work to do the measuring themselves.
Author:  Reed [ Mon Sep 22, 2025 7:39 pm ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Hmm. I definitely want to do this right. If that means pulling the crank to take it to the machinist with the spacer, so be it. That will cause this project to go in a different direction, but that is why I have contingency plans. OK, now I know how I will be proceeding.

Lou- you mean you don't trust Harbor Freight to sell accurate calipers? :lol: Me either. Someday I will get a set of real ones, but tis one works for gross measurement.
Author:  Dart270 [ Tue Sep 23, 2025 3:49 am ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Reed,
I would not worry about using the exact crank in the engine, just take another one over. Let me look at my measurements to see if I have a reliable number. Not worth pulling your crank...
Lou
Author:  Reed [ Tue Sep 23, 2025 12:33 pm ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Thanks, Lou!
Author:  volaredon [ Thu Sep 25, 2025 7:44 am ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
I'm guessing that even if had a SB to measure off of that it would be the same
Author:  Dart270 [ Thu Sep 25, 2025 1:47 pm ]
Post subject:  Re: Using small crank hub smallblock adapter crank spacer on large hub crank and trans
Sorry, I cannot find a reliable number for the large crank register OD. It is close to 2.16", but I would not trust that without doing a good measurement with known good tools (caliper, micrometer). I guess you don't have a spare crank to carry to your machine shop? Will contemplate and/or ask someone trustworthy...

Lou
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