48 2a #4 cylinder knocking

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42GPW
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48 2a #4 cylinder knocking

Post by 42GPW » Sat Apr 28, 2018 2:27 pm

I bought a connecting rod New Old Stock from a guy on eBay. My number four connecting rod was spinning on the bearings. So I bought this one on eBay said it was for a number 2 or number 4. New Old Stock made in South Korea. Should fit the to a 2a, 3a, 606 etcetera. It never knocked before. But once I replaced it due to the bearing spinning on the connecting rod it started knocking. At an idle it does not knock but when I rev it up and knocks hard. Did I buy a bad New Old Stock connecting rod?

Should I try and find an original to a standard size connecting rod and replace it? I also posted this on the cj-2a page. Hoping somebody here might be able to give some insight also.


            Matt R
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Re: 48 2a #4 cylinder knocking

Post by Ben Dover » Sat Apr 28, 2018 2:58 pm

What's the condition of the bearing Journal, is it rough and did you "Mike" it to check the diameter against the insert you installed?
Providing the #4 Journal is still within spec for it's size, the insert bearing has to match the diameter of the journal. How did you determine what size bearing insert to install?
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Re: 48 2a #4 cylinder knocking

Post by 42GPW » Sat Apr 28, 2018 7:23 pm

Std came out and went back in. We used a small mic dad had. A professional one is about an hour drive away we did not pull the engine apart just pulled the piston and the rod with the head and the pan off. And replaced it. Kind of an in the garage thing last winter. I'm wondering if the South Korean Rod( New Old Stock) that I bought is different than the ones that were originally put in in the forties and fifties. Thinking maybe it might be just a little bit too long and it's hammering away on the top of the head. It didnt knock before. The reason we pulled it apart with a check the compression on the number for because it was only at 80 lbs when everything else was at 1:20 and above. Then we noticed that the bearings in the #4 were spinning. So we went ahead and pulled all the Pistons and check the Rings and cleaned them up. Put it back together the new rod and it started knocking.
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Re: 48 2a #4 cylinder knocking

Post by Ben Dover » Sun Apr 29, 2018 5:19 am

Regardless of how innocent it all transpired, your engine now needs some serious work and an experienced mechanic. Spun bearings do not heal by themselves and the cause is serious. Best get it to a shop.
2011 MVPA PIONEER AWARD - MVPA #1064
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Re: 48 2a #4 cylinder knocking

Post by 42GPW » Sun Apr 29, 2018 7:16 am

Spoke to a guy locally, He said he could do all the machine work from anywhere to five or six hundred if I tear it down and put it back together. I have a list of things that needs to be done. I just don't have that list with me now.

Matt R
48 cj2a
U.S Army (11C3P2B) 1989-2006
82nd Abn, 1st Gulf War Vet


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Re: 48 2a #4 cylinder knocking

Post by Wolfman » Sun Apr 29, 2018 7:22 am

I am with Joel on this one.
The usual reason rod bearings spin is, they stick to the crankshaft journal, damaging the journal. Not normal to just, replace the bearing.
The crankshaft usually needs re-ground to repair the damage.
So, what condition was the number four rod journal in ??
I will admit, I don't know anything about Korean rods.
No knock at idle but knocks up to speed does sound like a piston slapping the cylinder head.
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Re: 48 2a #4 cylinder knocking

Post by Ben Dover » Sun Apr 29, 2018 8:24 am

Best find a shop that will reassemble your block. Too many details that need experience.
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HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
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Re: 48 2a #4 cylinder knocking

Post by 42GPW » Mon Apr 30, 2018 2:13 pm

Yeah it's kind of where I'm at guys I just got to save up the money to do it.
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Re: 48 2a #4 cylinder knocking

Post by artificer » Tue May 01, 2018 11:39 am

You can check/do this yourself. That is why most come to this forum....advice on checking/fixing things!

Many do not check bearing nip or crush when fitting bearing inserts.
http://www.acl.com.au/web/acl00056.nsf/ ... enDocument
This should be done even if the connecting rod is thought to be new no matter what the source.
Many do not re-size [& check straightness of] used connecting rods.
This also should be done & both could contribute to what went on & is going on.

Also suggest you check the con rod IS located centrally [i.e. with equal space either side] on the piston pin from underneath [very important], the oil squirt is away from the camshaft [toward the major thrust side] & the piston split is on the opposite side toward the camshaft [which is the minor thrust side].
All these things being incorrect could cause a noise not apparent @ unloaded engine idle speed.
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TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: 48 2a #4 cylinder knocking

Post by 42GPW » Fri May 04, 2018 10:14 am

Thanks for your help guys, looks like this fall and then go ahead pull the engine teardown and send it to a machine shop and have them do it all professionally. And a good friend of mine that's a mechanic will help me assemble it properly. Thanks again for the help.

Matt R
48 cj2a
U.S Army (11C3P2B) 1989-2006
82nd Abn, 1st Gulf War Vet

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