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Old 03-27-2016, 08:59 AM   #1
CT Jack
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Default Installing New Connecting Rods

Great running engine with 12K miles started to make random knocking noise at low RPM's. Pulled timing gear cover, gear is tight no tooth issues. Pulled pan and found chunks of babbit in pan. Found 2 connecting rod journals missing side pieces of babbit. Rod ends have excessive lateral movement. Decided to replace all connecting rods with new insert bearing type.
Question: Working from the underside of the engine, can the connecting rods be removed without removing the pistons? It looks like the pistons can be lowered down enough to expose the wrist pin for removal. Am I dreaming?
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Old 03-27-2016, 09:18 AM   #2
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Default Re: Installing New Connecting Rods

You are dreaming, take the head off, check for a ridge, pull the pistons and rods. If it goes smooth your done it a day.
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Old 03-27-2016, 09:19 AM   #3
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Default Re: Installing New Connecting Rods

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Old 03-27-2016, 09:23 AM   #4
Mitch//pa
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Default Re: Installing New Connecting Rods

Pull the engine and do a full rebuild
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Old 03-27-2016, 10:15 AM   #5
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Default Re: Installing New Connecting Rods

You should have gotten more than 12k miles on a rebuild with good babbitt. If the babbitt failed in so short a time, something was not done correctly. If you know who rebuilt the engine, you should go back to him and question him about the rebuild.

If you can't do that, or get no satisfaction from the rebuilder, I would pull the engine and tear it down to find out what else, if anything, is wrong. I would be especially attentive to the condition of the babbitt in the mains.
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Old 03-27-2016, 10:39 AM   #6
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Default Re: Installing New Connecting Rods

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The simple answer to your question is: No.

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Old 03-27-2016, 11:23 AM   #7
Kurt in NJ
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Default Re: Installing New Connecting Rods

I have taken rods out without removing the head-----all I removed was the oil pan,---only on a stock engine, only if it didn't have centerlock pins, can't be done with counterweighted crank, I'm not saying it was easy, and if doing all 4 take the head off
I did#3, pulled the rod off the crank, rotated the crank so the piston could be pulled down as far as it could, rotated about 45 degrees, removed circlip and using right angle snap ring pliers and pushing/moving the rod in unison with the snap ring pliers I moved the wristpin over far enough to replace the rod ----together was easier

Before you order your new bearings you have to measure the crankshaft---for babbitt rods the exact crankshaft size is not that important, the rods can be adjusted some to the crank, but for inserts the crankshaft HAS to match the proper size(and be round,no taper, scoring) to have proper clearance

If some of the babbitt is coming apart you had better look at all the babbitt
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Old 03-27-2016, 11:39 PM   #8
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Default Re: Installing New Connecting Rods

Can you?
Should you?

Well the answer to the first is, most likey.
The answer to the second, NO WAY! As was mentioned by the second generation mechanic Mitch and for the reasons given by 700RPM.

You can do it right, or do it again and again.
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Old 03-28-2016, 02:51 AM   #9
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Default Re: Installing New Connecting Rods

Pull the engine and check it all out you will most likely need to grind the crank if only to get the clearance correct for the new inserts
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Old 03-28-2016, 10:00 AM   #10
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Default Re: Installing New Connecting Rods

And if the rod babbit is bad, likely the mains are bad too
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Old 03-28-2016, 12:54 PM   #11
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Default Re: Installing New Connecting Rods

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Originally Posted by colin1928 View Post
Pull the engine and check it all out you will most likely need to grind the crank if only to get the clearance correct for the new inserts
Replacing the rods in an engine is a lot of work when it is still in the car. When faced with the same task, I always pull the engine. I find I am time ahead removing the engine and working on it when in an engine stand. You will also find it, physically, a much easier task and the resulting quality of work may be better given you are working with the engine oriented correctly for the task you are completing. 12,000 miles...time to check the main bearing clearance and record the results if not adjust them. If your engine builder gave you a sheet with the clearances on the bearings, you will have a means to predict when the next clearance check should be made. Regardless, record the clearances and odometer reading and keep this information with your car records for the next time you check clearances.
Sorry to hear about your failed rods. Carefully measure the rod journal sizes at all four locations and compare the results with the required sizing for the insert rods you plan to use. Snyder's insert rods require a different size than Antique Engine Restoring's rods. You may need to grind the rod journals to use insert rods. If the journals are the wrong size to work with inserts, you may want to consider replacement remanufactured Babbitt rods as they are somewhat adjustable with the included shims.
Final thought: Make sure you are not running your engine with more than 28 degrees advance. To much advance will pound out Babbitt or insert bearings in no time.
This past fall, I replaced the insert mains and rod bearings on a Burlington crankshaft engine I had built a couple years ago for a gentleman who was using a NU-Rex automatic advance and set the timing by mistake so it was over 36 degrees when at road speed. Luckily, the crankshaft had no damage but the main bearings were in pieces about 1/4" square but still contained by the shells. Close call for him but an easy repair for me.
Good Day and Good luck with your project.

Last edited by Dave in MN; 03-29-2016 at 09:16 AM.
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Old 03-28-2016, 08:33 PM   #12
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Default Re: Installing New Connecting Rods

Thanks for all the tips. Yes, I ran the 1st 12K miles with a Nu-Rex auto advance but I am certain I didn't run the engine with a 36 + degree advance. I think the engine would knock something terrible at that setting.
I have decided to pull the engine, go all the way and have the the job done correctly. I talked with a nearby Mass. engine rebuilder today and they said more than likely the babbit was improperely poured due to too low of a part temperature which created poor bonding.
My plan is to have the crank inspected, reground if necessary, rebabbited, and align bored. Install new insert connecting rods, install new rings, hone cyclinders, and rebalance. The valves are SS with hardened seats and single piece bronze guide bushings which appear to be in excellent condition. If the cam is not to spec I will either have it reground to a touring type or replace it.
I like to drive my "A" long distances on mostly secondary roads. This requires maintaining the engine well otherwise serious problems can occur which takes all the fun out of touring in a Model A.
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Old 03-29-2016, 09:24 AM   #13
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Default Re: Installing New Connecting Rods

"Thanks for all the tips. Yes, I ran the 1st 12K miles with a Nu-Rex auto advance but I am certain I didn't run the engine with a 36 + degree advance. I think the engine would knock something terrible at that setting."

The last thing I want to do is offend you but the gent I made repairs for said almost the same: "The engine had great power and did not knock" with the Snyder's 6:1 head he had on it. Sometimes, an engine will not knock when running too much advance. If you continue to use the Nu-Rex advance, check your timing with a timing light at about 2000 rpm and make sure you are not exceeding 28 degrees before driving it. I know the first time I set one up, the directions were not clear and it just did not sound right when starting. Setting your timing with a timing light at 2000 rpm between 26-27 degrees (for a standard head) will give you good performance and likely be much better for your bearings. JMO...formed from repairing these things.
Good Day!

Last edited by Dave in MN; 03-30-2016 at 07:51 AM.
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Old 03-29-2016, 07:46 PM   #14
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Default Re: Installing New Connecting Rods

frankly with a 6.0 head i am finding the sweet spot for max timing is at 23° at 2000

i think 28 is too much and will destroy bearings

these days no two ppl have the same engine goodies: there are various cams, heads, intake sizes, etc and i feel the timing must be dialed in to accomodate the specs of the motor
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Old 03-29-2016, 08:06 PM   #15
CT Jack
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Default Re: Installing New Connecting Rods

I agree with everything you are recommending. How all this recently came about is I was hearing the occasional knocking at different speeds. Since installing the Nu-Rex advance unit the engine always had a slightly clacky noise at idle. I thought maybe the mechanical advance unit had some mechanical slop or backlash because when I increased the RPM's it went away. As part of my spring startup I decided I would remove the Nu-Rex auto advance and replace my distributor with an FS Ignition Zipper distributor. This distibutor has mechanical centrifical advance like the "B" and electronic ignition. I also decided to check valve gaps. After installing the Zipper the engine started on the 1st revolution. The noises I was hearing before were still there and then is when I started digging deeper and found the babbit problem,etc.
Once I fix my problems I plan on setting the timing with a timing light. With the Zipper you can set the timing very precise because the distributor base can be rotated while the engine is running. It isn't pinned to the head like a stock "A" distributor.
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Old 03-29-2016, 08:27 PM   #16
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Default Re: Installing New Connecting Rods

I used the fact that the distributor could be turned to get the timing in one of my cars right. I initially set it as per the book but it was too far advanced and would ping under load. I gradually backed it off till the pinging disappeared. It might be a little retarded at an idle now but that causes no damage, after all, it's only idling for a short time now and then. I think I have the sweet spot because it runs REALLY well. As I type this, I've taken a break from reassembling things after replacing a head gasket (caused by a "leakless" water pump leaking). I have noted where the distributor fires on the timing scale on the front of the block at idle and I'll set it there again in a few minutes. Should be just as good as before but if not, I'll just do the same gradual adjustments as before.
The amount of advance your motor needs changes as you change things like camshaft timing, compression ratio, fuel and carburettor. If you've changed any of these, it may not be good enough to set the timing by the book.
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Old 03-29-2016, 10:47 PM   #17
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Default Re: Installing New Connecting Rods

The Zipper comes with 28-29° advance. I would contact Mel at FSI. They have a shim available that will drop the advance by about 4 degrees; easily installed
That way you can still have a few degrees of advance at idle
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Old 03-30-2016, 08:09 AM   #18
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Default Re: Installing New Connecting Rods

Quote:
Originally Posted by tbirdtbird View Post
frankly with a 6.0 head i am finding the sweet spot for max timing is at 23° at 2000

i think 28 is too much and will destroy bearings

these days no two ppl have the same engine goodies: there are various cams, heads, intake sizes, etc and i feel the timing must be dialed in to accomodate the specs of the motor
tbirdtbird, You are right, I made the assumption CT Jack was using a standard head, since he did not mention a compression ratio in his posts. For a standard compression head 26-27 degrees will be okay. With a higher compression head, your suggestion of 23 degrees is proper. Thanks for commenting.
Good Day!
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