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09-07-2023, 09:54 PM | #1 |
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18-and 21A rods interchange?
I am building my 32 engine. I have NOS 32 connecting rods and also NOS 21A rods. The bearing placement and dimensions look the same. The later rods are much beefier. The engine will be completely stock so I really don't need better rods but I have them. Any comments?
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09-07-2023, 10:56 PM | #2 |
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Re: 18-and 21A rods interchange?
Yes, totally interchangeable. The 21A rods are beefier as you've noticed.
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09-08-2023, 05:49 PM | #3 | |
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Re: 18-and 21A rods interchange?
Quote:
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09-08-2023, 06:12 PM | #4 |
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Re: 18-and 21A rods interchange?
You need to check, I am pretty sure the 18 rods are heavier,,funny enough,
they dont look it, But I have a memory of weighing them and the 21 a year or two back. Lawrie |
09-08-2023, 06:36 PM | #5 |
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Re: 18-and 21A rods interchange?
I though the 18 rods used flanged bearings where the 21A rods do not. I think the rods can be swapped as long as you use matching bearings.
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09-08-2023, 06:55 PM | #6 |
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Re: 18-and 21A rods interchange?
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A weight difference would push me to the 18 rods. The engine will have the low compression heads and the stock cam and carb. I would like it to run smooth. It will not see high rpm. |
09-08-2023, 08:35 PM | #7 |
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Re: 18-and 21A rods interchange?
I've always used 21A rods in my 21 stud builds...however, I always get engine balanced.
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09-09-2023, 08:08 AM | #8 |
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Re: 18-and 21A rods interchange?
At the risk of side tracking Andy's discussion, I have a question. I have not assembled the bottom end of a 21 stud motor with flanged rod bearings.
Question: Is the crank pin for the rod journals wider on the early cranks to fit the flanged bearings? I looked in the Green Book for interchange guidance but didn't find what I was looking for.
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09-09-2023, 09:39 AM | #9 |
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Re: 18-and 21A rods interchange?
The 21A rods with original wrist pin bushings are machined for the center clip wristpins.
The clip can be removed from center lock rods to use end lock pistons The flanged bearings have wider journal. Center to center length is same |
09-09-2023, 02:24 PM | #10 |
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Re: 18-and 21A rods interchange?
>>> am building my 32 engine. I have NOS 32 connecting rods >>>I really don't need better rods>>
Agreed. 8^) |
09-13-2023, 12:20 PM | #11 |
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Re: 18-and 21A rods interchange?
My new concern is the crank. It do not know what year it is. It may be balanced for the later rods. It has three large holes in both large counter weights. Maybe it is a later production replacement crank that was balanced for the earlier rods? Sure looks like a lot of metal was removed.
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09-13-2023, 12:30 PM | #12 |
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Re: 18-and 21A rods interchange?
If you are building and engine, would you not have your machine shop balance the entire rotating assembly? Why worry about if your crank and rods are balanced when you can have all the components balanced as you should do anyway? To not do so is just guessing.
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09-13-2023, 01:13 PM | #13 |
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Re: 18-and 21A rods interchange?
At my age I have to say that I've had very few crank assys balance. For one thing, nobody did it. here was a place in New Jersey that did it for the Offys and other race enginrs. but the cost was out of sight as well as the wait time. Built sllot of engines in the 80's thru thr early 2000. None were balanced. Fortunately, some are still running todayYes balancing is important, but most street engines neve hit 4k and cruise in the 2k reagion. I just had My 258 balanced $300 bucks. When building a flathead the cran and rods are balaced at the factory and the pistond don't need to be balanced. Some people will disagree with me here, BUT! !!
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