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Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics
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samstrader
Posted 2020-10-28 7:40 PM (#605004)
Subject: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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In my 1955 Plymouth Service Manual on page 171, it says in the right hand column that "Allowable bearing clearance is from .005 to .0015 inches."

I think this is wrong and think they meant to say the allowable clearance is from .0005 to .0015. This would be the same as the rod bearings.

What does everyone think about the spec for the clearance of the main bearings.


Background....

I have a knock low in my engine when the engine is warm and the oil is warm. I am using Mobil 1 15w50 oil. The knock is not there when the engine is first started and the engine is cold.

When the engine is hot, I can make the knock stop by unplugging the Number 5 spark plug wire. This is why I was thinking I had a rod knock, specifically a rod knock on the number 5 cylinder.

I have plasitgaged all of my rod bearings and all are .0015 which is the maximum spec, but it is still within spec. The bearings look smooth and good, not perfect but really pretty good. I thought the knocking noise was a rod but with these clearance measurements, I'm not so sure it is a rod knock anymore.

I checked the thrust clearance on the crankshaft. The spec is .002 to .007 and I measured .007 with a feeler gauge on the number 3 main bearing thrust collar. The number 3 main bearings is also the thrust bearing for the crank. So I am within spec but at the maximum.

I plasitgaged the main bearing number 3 and the clearance is .003, which is too big if the real spec for main bearing clearance is .0005 to .0015, like I suspect it is. This bearing was just replaced less than 500 miles ago and the bearing and the crank looks perfect, so it means that my crank was ground down too small. (I have having some awful luck with machine shop work I think).

I plastigaged the main bearing number 4 and the clearance is .002 which is also too much gap but not as bad and number.

Based on all of this, I think my knock is the number 3 main bearing. Does anyone have thoughts on this?

Is there any way I can fix this without pulling the engine and starting over on the crankshaft? Can I get a .030 main bearing and machine it down to .025 for example? This would give me a clearance of .0005 which is tight but within spec. Just want to make sure I look at options before pulling the engine. Norm saved my from pulling the engine with his cam shaft bearing fix idea before.

Thanks for your thoughts... Sam
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56D500boy
Posted 2020-10-28 8:58 PM (#605005 - in reply to #605004)
Subject: RE: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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From the 1957 Dodge Factory Service Manual:

"0.0005 to 0.0015" ":





(57DodgeCrankshaftClearances.jpg)



Attachments
----------------
Attachments 57DodgeCrankshaftClearances.jpg (102KB - 161 downloads)
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samstrader
Posted 2020-10-28 9:04 PM (#605006 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks!!!

It is good to see the "maximum allowable" section. This does not show in my service manual. I'll do some more plastigage work and try to determine how close I am to maximum allowable on the other bearings. At .003 on number 3 bearing, I am over maximum allowable which is bad.... This makes me feel better about my thrust measurement of .007 since the maximum allowable is .010....
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58coupe
Posted 2020-10-28 9:14 PM (#605007 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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You said you just had new bearings installed. What about the pistons and bore size? It could be piston slap if they are a little loose although piston noise is usually louder when cold. My daughter once had a Ferd van with a 302 with a knock at about 50K miles and I was sure it was a rod knock. I removed the engine (not an easy job) and tore it down. A portion of piston skirt was missing from one of the pistons and causing the knock. Even though your bearing clearances are a little loose, many racers build their engines with this much clearance and it works well.
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samstrader
Posted 2020-10-28 9:14 PM (#605008 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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I just found on the Specifications Table on Page 160 of my service manual that the bearing clearance specifications for Main and Rod bearings is .0005 to .0015. So the spec shown on page 171 of the service manual is a mis-print. I should have looked closer I guess. All bearings are .0005 to .0015 or an average of .001...
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Shep
Posted 2020-10-28 9:15 PM (#605009 - in reply to #605006)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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I've never seen .003 main bearing clearance cause an audible knock. Remember using plastigage with the engine in the car the crank is hanging down in the bearing bore, so the readings are somewhat tighter than the true clearance.

Edited by Shep 2020-10-28 9:16 PM
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samstrader
Posted 2020-10-29 3:32 AM (#605017 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks 58 Coupe. My pistons are new, well 10 years old but less than 1000 miles and they all look good. I still have the honing marks on the cylinders. All of my piston skirts are intact and look good, at least as much as I can tell from looking up from the crank. They all slide tight and smooth. I pushed up each piston to check the condition of the top bearing on each rod. There doesn't seem to be any slack there. I have also heard that racers build in extra clearance, just heard today from a friend actually. It makes sense. I may be safe to drive it like it is because after about 500 miles, the bearing is looking absolutely brand new. That's one of the things I'm trying to figure out.

Thanks Shep... I did not support the crank like you are supposed to do when using plastigage on the crank. I really didn't know a good way to do this. So I think that if the crank is hanging down some that it will make the clearance read a little tighter than actual which means my clearance is actually a little bigger than .003, just like you are saying. I honestly can't imagine the crank causing this kind of knock, especially when the engine is idling and the pistons are not really pushing down on the crankshaft enough to drive it down to the bottom of the bearing. But so far, this is the only measurement I have found that is out of spec. All of this extra clearance sure is not good for the oil pressure and if I run 10w30 oil instead of 15w50, the knock is worse.

It is so frustrating to pay for an engine rebuild and then have to do all of this work to try to fix it and then not even be able to figure out what is the problem.

If you unplug a spark plug and this makes a knock go away, what would be the suspected cause of the knock?
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wizard
Posted 2020-10-29 5:10 AM (#605018 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Remove one cup in the front and one in the rear of the cup that you want to measure - insert a paper shim slightly thicker than the expected clearance and retighten but not to full torque. Now you can measure the cup in between correctly.
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Shep
Posted 2020-10-29 8:23 AM (#605021 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Yes, killing one cylinder at a time at say 1200 rpm, should change sound of the knock, if it is a rod, or excess piston to wall, the cylinder does affect the noise is your suspect..
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Powerflite
Posted 2020-10-29 11:01 AM (#605025 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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What do we know?
1. The knock changes with oil thickness (hot vs. cold, thin vs. thick)
2. The knock is coming from cylinder #5 at hot idle (at least) when firing.
3. At low rpm, your oil pressure is lower (how low?? - give us a reading.)
4. All bearings currently still look good.

I assume you want to avoid regrinding your crank at this point.
You can try getting .001" oversize bearings for the crank & rods if you know that they are too loose. They used to make them, but I don't know if you can find any now. Try a local auto machine shop, they have more sources than we do.
It could be that your rod end is a little mis-shapen causing the loose clearance issue on the rod journal. You can check that to see if replacing it would help. Measure side to side accurately. I'm not sure if you can get the piston & rod out without removing the crank though....probably not.

BUT.....since your bearings all look good, that can mean only one thing....that you don't have a rod knock at higher rpm or under load while driving. If you did, your bearings would definitely be shot. So you could attack it from another angle and get a high volume oil pump to put into it to make up the difference. Before you buy one, get the numbers to compare its volume to what you currently have.
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samstrader
Posted 2020-10-29 4:07 PM (#605033 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks Wizard for the idea of how to hold up the crank. I was thinking of having to put a jack under the crank and guess about how hard to jack it up to hold the crank in the right position so I was afraid to try this. This seems like a pretty easy way to hold up the crank and it is very controllable. I'll try it for measuring the center main bearing.
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samstrader
Posted 2020-10-29 4:20 PM (#605034 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks Nathan... I like your analysis method...

My oil pressure is a little above the lower good mark on the oil pressure gauge when the engine is hot and idling and right on the upper good mark when the engine is hot and running up. I have not put a pressure gauge on it but I'm pretty sure the pressure gauge in the car is good because when the engine is cold and the spring release on the oil pump is working, the oil pressure shows just a little bit above the upper good mark.

My crank is ground down to .020, actually ground more because it is over ground. I'll call HotHeads and see if they know anything about an oversize .020 bearing. That would be the perfect solution. And I'll definitely get a high volume oil pump which might just solve the whole problem. Is there any thing to worry about when putting in a high volume oil pump????

My rod bearings were coated and as they have broken in, some of the coating has worn off so I can sort of see how the bearings are rubbing. It really looks like they are rubbing out pretty round. I have a bunch of pictures I'll post a little later just to get opinions. I have to get them off my phone. I wonder if I should just go ahead and change out all of my rod bearings.

I have a lot of data now but just need to put it all together so I'll do that this evening and post it with pictures.

I very much appreciate everyone's help...
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Powerflite
Posted 2020-10-29 8:34 PM (#605042 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Another thing to check is the side-to-side clearance between the rods. If the gap is too big, it can cause loss of oil pressure there and a knock.
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Shep
Posted 2020-10-29 8:39 PM (#605043 - in reply to #605034)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Why is it "overground", that is the machinists mistake. As far as I know there is no .021 or so bearings.
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samstrader
Posted 2020-10-30 4:42 AM (#605054 - in reply to #605004)
Subject: RE: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks Nathan and Dave. The crank was over ground or the bearings I bought were not really .020. I can't measure the main bearing journals without pulling the crank so I'm having to guess what is wrong. I think it unlikely that the bearings were sized that much wrong so I am assuming the crank was over ground. Not really sure how this mistake could have been made but to fight with the machinist, I'll have to pull the engine and I'm trying to avoid this. I didn't tell the machinist what diameter to grind down to and am wondering if he just took off another .010 from where it was. This could have caused the mistake. A lesson learned from all of this for me is to make sure you tell the machinist what diameter you want on your bearings just so there is not any misunderstanding.

I measured the side clearance of the rods tonight and the measurements are shown on the attachment. The specification is .006 to .014 inches of side clearance. But I don't know if this means for one rod or two. You can only measure the clearance for two rods since two rods are on one journal. Anyway, the side clearance of the rods on my 4 rod journals is .025, .024, .021, and .021. If the side clearance specification is for two rods, I'm too wide but if the side clearance specification is for one rod and you measure two rods, then I'm at .012 or so for each rod and that is within specification. I can see how this could make a knock if they are too loose.

Here is the data sheet I made for my measurements and pictures that show the bearings. I don't think these bearings "look" too bad but not an expert on what good looks like actually so would appreciate comments. the rod bearings are not as good looking as the main bearings. I can change them out if the look bad to you.



(Rod.jpg)



(Rod 3.jpg)



(Rod 8.jpg)



(Main 2.jpg)



(Main 2a.jpg)



(Rear Main Seal.jpg)



Attachments
----------------
Attachments Plymouth Engine Bearing Measurements 10.28.20.xlsx (11KB - 163 downloads)
Attachments Rod.jpg (239KB - 160 downloads)
Attachments Rod 3.jpg (237KB - 165 downloads)
Attachments Rod 8.jpg (239KB - 165 downloads)
Attachments Main 2.jpg (242KB - 160 downloads)
Attachments Main 2a.jpg (244KB - 159 downloads)
Attachments Rear Main Seal.jpg (247KB - 166 downloads)
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samstrader
Posted 2020-10-30 4:50 AM (#605055 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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note that you have to click on "Plymouth Engine Bearing Measurements 10.28.20" to make the excel spreadsheet open
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Shep
Posted 2020-10-30 7:24 PM (#605089 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Rod side clearance is always the actual clearance between 2 rods, yours is excessive, which can lower the oil pressure. Your journals should all be miked to confirm the final size. Or the machinist should have provided this data. Your bearing clearances that you have provided so far, would not cause a knock. Low oil pressure definitely could.
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samstrader
Posted 2020-10-31 4:25 AM (#605105 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks Shep. I understand what you are saying about measuring the clearance between the two rods. I sure don't see any wear on the side of the rods but the crank may have worn down some.

I am looking into a higher volume oil pump. Nathan said that might help and I want to change the oil pump anyway. I'm trying to find a pump that will fit my car and my oil pan now. My oil pressure is always between the two marks on my pressure gauge so I don't think I have real low oil pressure but I think a higher volume pump will make the oil pressure at idle higher and I think this might help lower or stop the knock.

I did mike the rod journals and they are very close to correct (the mike matches what the plastigage says) but I could not mike the main bearing journals with the crank in the car. I'm pretty sure the main bearings got over ground because they have been ground twice now.
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samstrader
Posted 2020-10-31 4:29 AM (#605106 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Just a thought, which way is the bevel on the rod bearing cap supposed to be, pointing toward the crank or pointing toward the other rod? Mine are set up so the flat side of the rod bearings are together in the middle and the angled part is pointing toward the crank.
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Powerflite
Posted 2020-10-31 8:17 AM (#605109 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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There is a fillet on the crank before it transitions from the journal to the crank arm. That bevel in the bearing is there so that the bearing doesn't ride on the crank fillet. So the bevels go toward the outsides of the crank, and the flat parts go towards each rod. If you have excess clearance between your rods, the guy who ground your crank likely cut them out too far, giving you too much clearance. Sounds like you used a lousy crank grinder. I'm not sure if there is a fix for that other than using a higher volume pump. You can get a high volume 340 pump to work on your motor from Hot Heads. But give him a call and find out how much more volume it will provide over your stock one. Once you receive it, measure the inside diameters & depths of your pump rotors to compare the two as a sanity check to ensure that you really will be getting more volume out of it.
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Shep
Posted 2020-10-31 9:48 AM (#605112 - in reply to #605109)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Hmm, I didn't think that engine had full radius fillets, my Maxwedge did not, nor did my 331 Hemi.
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Powerflite
Posted 2020-10-31 12:34 PM (#605116 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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I didn't say "full radius" fillet. There is always a small fillet.
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Shep
Posted 2020-10-31 2:00 PM (#605123 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Sorry, misunderstood.
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wizard
Posted 2020-10-31 3:01 PM (#605124 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Try single grade 30 mineral oil instead of the Mobil 1 15W50.
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samstrader
Posted 2020-10-31 9:48 PM (#605139 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks Nathan,

I saw that fillet in my service manual but didn't look for it when looking at the crank so I'll look again to see if I can see it. It must be pretty small and I should have studied that more. But the good news is that I have my rods in correctly because the tapers are out and the flat sides butt up to each other on each journal. I agree there was a problem with grinding my crank but the engine being frozen up and sitting for 40 years may have compounded the problem for the machinist. Also he is more accustomed to working on Chevrolets. I wonder if that extra clearance between the rods could be making them sort of slap together and this is what is causing the noise?

I think I will get the higher volume pump. I was going to get a new pump anyway and this higher volume one doesn't cost much more. And that is a real good idea to measure out the inside of the new pump and compare to my existing pump to make sure there is more volume so I'll know what I have. Had not thought about doing that but is a real good idea. I also have got to make sure the high volume pump will fit without interfering with my oil pan so I plan to try to get the dimensions from Hot Heads on Monday and measure out my engine compartment to make sure there is enough room. I also have to make sure the relief pressure on the new pump is not set up way too high. I think the Hot Heads guy said they are preset at 70 PSI which is too much pressure.

Thanks Sven,

I was not thinking 30W oil would be more viscous than 15W50 weight oil when at running temperatures. But this is real easy to try and a good way to clean out the engine anyway. I'll try that out and see what happens I know when I put 10W30 in, on the first start of the engine, it that it really knocked loud, a lot worse than now. So I only ran the 10W30 for a couple of minutes and then shut down and changed it out to the 15W50.


Do you guys think my bearing wear looks OK? Especially the rod bearings. Do I need to change the rod bearings out or just keep these.

Thanks again for all of your help.

Sam
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samstrader
Posted 2020-10-31 9:52 PM (#605140 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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What is the purpose of that ground slit on the bolt hole on the rod bearing cap. It's just on one side.
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wizard
Posted 2020-11-01 2:33 AM (#605157 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Cylinder wall oiling.

Forgot to mention that the 30 Oil must be mineral.

I used the singel grade Oil for many years, but when the Oil pressure finally started to drop somewhat I installd a high volume pump.
with the hv pump the sigle 30 gives way to high Oil pressure and the 20W50 too. Now I use 20W40 mineral and the pressure is on the high side but within the normal range.
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samstrader
Posted 2020-11-01 3:25 AM (#605158 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks again Sven. Just to make sure I understand, the mineral oil you are talking about is non detergent oil. Is this correct or is it straight 30 weight Pennzoil or something like this? It sounds like the straight 30W oil might help my situation based on your comments above.

I'm going to double check all of the holes in the rods and make sure they point properly to the cylinder walls. Thanks for this information.

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wizard
Posted 2020-11-01 4:36 AM (#605159 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics



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Exactly, I used Pennzoil straight 30W until it wasn't sold here anymore. Topped up with ZDDP, extra zinc and phosphus.

Engine ran very smooth, lesser oil burn and more silent.

My engine is still not renovated, 1960 383 cui.
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samstrader
Posted 2020-11-01 1:51 PM (#605173 - in reply to #605004)
Subject: Re: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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Thanks Sven. I think I can still get Pennzoil straight 30W here and I have seen the ZDDP. I'll try this for sure. It's very easy to do and I live in a climate where straight 30W is good year around. It never gets below 0C here.
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samstrader
Posted 2020-11-11 1:02 AM (#605525 - in reply to #605004)
Subject: RE: Main Bearing Clearance Specs - 1955 Plymouth 259 V8 - Need Help from Mechanics


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I installed a high volume oil pump, Melling M72HV from Hot Heads and it helped reduce the loudness of the knock I have but it did not eliminate the knock. But the knock is noticeably less. I'm almost certain that my knock is caused by the side clearance on the piston rods. The gap is too big; (.0021 to .0025 and the spec is .006 to .014). The only thing I don't understand is why would just the 5 & 6 journal be knocking and not the others. I believe if I had tighter clearances on the main bearings, I would have more oil pressure going up to the rods and therefore, more oil to dampen the side clearance. My Main Bearing clearances are .003 (plastigage) and they are supposed to be .0005 to .0015. I am going to call Egge and see if they can make me special sized main bearings using the old cores that I have. If I could get .025 bearings, I think my clearance would be right on the money at .001. But just thinking about this for now.

I did a lot of study on the different oil pump options so here is some data that may be interesting. You only have to measure the rotor to compare the volume the pump will pump since all the pumps turn the same speed. These are Gerotor Style Pumps..

*** My Original OEM Pump --- .999 inches tall and the sweep of the rotor is 1.61 inches. Relief pressure spring is 50 PSIG. I measured this with a micrometer.
*** Melling M50 Pump --- .997 inches tall and the sweep of the rotor is 1.5853 Inches. Relief Pressure spring is 70 PSIG. I got this from the Technical Service Rep at Melling. Very helpful people there. I talked to a guy named Eric.
*** Melling M74HV Pump with Hot Heads Conversion --- 1.035 inches tall and the sweep of the rotor is 1.778 inches. Relief pressure spring is 70 PSIG. I measured this with a micrometer.
Some pictures of the OEM vs the Melling M74HV are below. The big one is the Melling.

During all of the checks, I think I can see that the bearings are not getting damaged so I plan to drive it like this for a while until I can't stand the noise anymore.

The help I get from all of the knowledgeable folks on the forum is really valuable. Without the tips and support, I would not be able to work on this stuff. And I don't know where else you could go to find the help. So thank you all very much.

Sam



(1.jpg)



(2.jpg)



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Attachments 1.jpg (124KB - 150 downloads)
Attachments 2.jpg (114KB - 146 downloads)
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