Shaft coupling shoulder sizing
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=51256
Printed Date: November-28-2024 at 5:32am
Topic: Shaft coupling shoulder sizing
Posted By: BF_skier
Subject: Shaft coupling shoulder sizing
Date Posted: July-20-2023 at 11:45pm
| Hey CCfans! I have been working on a 1984 BFN that was taken apart by the PO before I purchased it. I am expecting that I will need a new prop and shaft but I want to see how the original gear all lines up before I place the order. One thing I noticed is that the shoulder on the shaft side coupler is very loose inside the transmission coupler. I can move the coupler roughly a 1/4” up and down and side to side between the shoulder and recess in the transmission coupler. The shoulder doesn’t look worn down so I am wondering if this coupler is even right. I thought a 4” flange should be standard but based on this mismatch I want to make sure I have the right information. From the outside, the transmission output looks standard and the shaft coupler looks like a typical 4” shrink fit coupler. |
Replies:
Posted By: KENO
Date Posted: July-21-2023 at 7:09am
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What's this thing got for an engine and transmission? 454's came hooked to a Borg Warner 72C or a 10-18 and they had 5 inch output flanges Small blocks usually had a 71c or 10-17 and had 4 inch output flanges Silly question...............Is it a good assumption that both of your couplers are the same diameter?
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Posted By: BF_skier
Date Posted: July-21-2023 at 8:48am
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Hi Keno! Thanks for your response. My assumption that they are the same diameter is based on the fact that the bolt patterns and outer diameter of the couplers match. I assume that means they are both the same size but I could be wrong. The engine is a 351 and the model tag on the trans reads 10-18-002. I uploaded a video showing how much play there is when the coupling faces are held together. https://youtu.be/lKB8usT1_Gw |
Posted By: GottaSki
Date Posted: July-21-2023 at 9:00am
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Yeah thats jacked up, but i think if you just center it by feel about the OD as you snug it up, should be inconsequential ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: KENO
Date Posted: July-21-2023 at 12:31pm
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I knew it was a silly question but had to ask it. I measured the shoulder on a prop shaft flange for a 71c (4 inch) and it was 2.49 inches The recess on the transmission flange was just a teeny bit bigger.........it slid in, but no free play like you have. Same dimensions for the shoulder and recess for a 5 inch setup So since it seems obvious that one of yours is the wrong size to mate properly, with these measurements you can figure which is the bad one. I wouldn't put it together with what you have now and expect things to stay concentric. If you're planning on a new shaft and coupler, cross your fingers and hope the transmission flange is the good one, so you're not buying one of those also. And hopefully you're thinking about a double taper shaft and coupler, it's worth every penny in saved aggravation
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Posted By: BF_skier
Date Posted: July-21-2023 at 3:09pm
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Thanks again Keno. Based on your measurement it looks like it is the coupler that is out of spec. I measured 2.25” on the coupler shoulder and 2.5” for the recess on the trans output flange. The OD of the flange is 5”. Looks like I will be putting in a order for a double taper shaft and prop while I am at it. Is there a go to prop for an 84 351 BFN? |
Posted By: KENO
Date Posted: July-21-2023 at 3:50pm
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Wherever you're getting the shaft and coupler , make sure you give them all the info they're looking for and measure according to their instructions. A phone call would be a real good idea. As far as the prop, an ACME 540 is probably a good choice assuming you're wanting to maintain a good top speed and all around performance
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