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Rod Bearing Replacement - 1975 MGB

Posted by SSGt Olivero 
SSGt Olivero Avatar
Eric Olivero
Montgomery, TX, USA   usa
1975 MG MGB "Julia"
1975 MG MGB

I have spent a lot of time reading postings in the MGB Forum and haven't found a thread on procedures for replacing rod bearings. I have discovered a lot of reasons why to do replace the bearings, but not so much on how. From what I understand, it is possible to replace the rod bearings and main bearing from under the engine. I have NEVER done this before, so I have a lot of questions and concerns before I start.

What I have done so far:
1) Removed the oil pan. Thanks for the postings on how to remove the front 4 bolts = PITA!
2) Removed the oil pump and cheked the lobe clearance, etc. The pump checks out good.
3) Gotten plenty of oil drips onto my face

Questions:
1) What Rod Bearing Set do I need for a 5 Main? (.010 / .020 / .030 / .040) How do I figure this out?
2) Do I also replace the Main Bearing? Size?
3) Will I need any special tools?
4) Are there any video postings that I can view to give me perspective and guidance?
5) Anything else I need to know?
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balloonfoot Avatar
Lloyd Faust
Southlake, TEXAS, USA   usa
1967 MG MGB "MAX"
1985 Chevrolet Corvette "EASY 1ST"
1986 Chevrolet Corvette "Gas Mileage Special"
1989 Chevrolet Camaro ""I Rock""

take a rod cap off and read the bearing size on the back size. That is the size you need. Only special tool is a torque wrench to do up the nuts when you put the cap back on.



“Better to remain silent and be thought a fool than to speak out and remove all doubt”.
- Abraham Lincoln

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."
SSGt Olivero Avatar
Eric Olivero
Montgomery, TX, USA   usa
1975 MG MGB "Julia"
1975 MG MGB

So I have to take it apart first to figure out the size. So much for doing it all at once. It would be nice to have the parts I need first to be able to do it all in one session.
I'm still confused on how to do it. Every video I watch, the engine is out of the car and the replacement is done from the top.
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balloonfoot Avatar
Lloyd Faust
Southlake, TEXAS, USA   usa
1967 MG MGB "MAX"
1985 Chevrolet Corvette "EASY 1ST"
1986 Chevrolet Corvette "Gas Mileage Special"
1989 Chevrolet Camaro ""I Rock""

Eric...if you already have the pan off....it will take you two minutes to remove a rod cap. Tha's all you do...you don't take the rod/piston assy out of the engine. Just crawl underneath and take on cap off. Slide the bearing shell out of the cap and read the size on the abck size. Report back.



“Better to remain silent and be thought a fool than to speak out and remove all doubt”.
- Abraham Lincoln

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."
chris Avatar
Chris Roop
Pendleton, OR, USA   usa

Adding to what Lloyd said, it is helpful to have the rod that you want to remove the cap from in the down position. Remove the cap. Put rubber hose over the rod bolts. Push the rod up and retrieve the other half of the bearing shell. The reason for the hose is to keep the rod bolt from banging on the crank journal and scarring it. Do this operation one rod at a time. Remove shells, replace shells, retorque rod caps. Move to next rod.
I don't replace some main bearings ie the 3 in the middle, because of a phobia about fluids taking the path of least resistance. By replacing just the 3 inner bearings, that would mean oil is really running out of the front and rear mains. I'm probably being a schmuck on this one as others have done it successfully. Mains don't wear at the same rate as rods though.

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58twincam Avatar
Charlie K
Allentown, USA   usa

Eric, you did not say why you want/think you need to replace the crank bearings. Are you experiencing low oil pressure, knocking noises, or do you just want to replace them. There is more to it than just taking out the old bearing shells and replacing them. There are other things to consider, such as what is the condition of the crankshaft journals ( are they smooth and shiny or do they have lines in them or grooves). The journals should also be checked for concentricity. Then you have to consider how much wear the journal has expierienced and calculate the oil clearance between the journal and the bearing with plastigauge. If you think that the oil pressure has been ok and the bearings are not knocking then I would leave them alone. If you mess something up you will end up with a complete rebuild $$$$.
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SSGt Olivero Avatar
Eric Olivero
Montgomery, TX, USA   usa
1975 MG MGB "Julia"
1975 MG MGB

I will have to start fresh in the morning. Wife just left to the store and I now have a grumpy 3 year old to kep me busy.

Once I take off ONE cap and determine the size, will each rod bearing be the exact same size for every connecting rod?
balloonfoot Avatar
Lloyd Faust
Southlake, TEXAS, USA   usa
1967 MG MGB "MAX"
1985 Chevrolet Corvette "EASY 1ST"
1986 Chevrolet Corvette "Gas Mileage Special"
1989 Chevrolet Camaro ""I Rock""

yup



“Better to remain silent and be thought a fool than to speak out and remove all doubt”.
- Abraham Lincoln

"Anyone with an intense emotional interest in a subject loses the ability to observe it objectively: You selectively perceive events. You ignore data and facts that disagree with your main philosophy. Even your memory works to fool you, as you selectively retain what you believe in, and subtly mask any memories that might conflict."
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chris Avatar
Chris Roop
Pendleton, OR, USA   usa

Yes, but listen to 58twincam below. He makes a couple of exelent points.

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Ken Plumstead Avatar
Smithers, B.C., Canada   can
1965 MG MGB

One quick note; Whether removing one or all bearing caps make sure they go back in the same place and the same orientation. Do not mix them up.

Ken



MGB: Transforming gasoline into Fun!!!
SSGt Olivero Avatar
Eric Olivero
Montgomery, TX, USA   usa
1975 MG MGB "Julia"
1975 MG MGB

Okay - I took of one cap, noted the orientation of the cap. I have the both sides of the bearings on my workbench. I see nothing that indicates size. What now?
dickmoritz Avatar
Dick Moritz
Philly 'burbs, PA, USA   usa

Eric,

Look at the back of the shells. They'll say "STD," ".010," etc., or they'll just have a part number with no size indicated, in which case they're standard...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
SSGt Olivero Avatar
Eric Olivero
Montgomery, TX, USA   usa
1975 MG MGB "Julia"
1975 MG MGB

So what if I don't see anything at all? Does that mean just STANDARD?
SSGt Olivero Avatar
Eric Olivero
Montgomery, TX, USA   usa
1975 MG MGB "Julia"
1975 MG MGB

I took off each cap, one at a time, replaced the caps after removing the bearings. Now I know the caps are in the same position and orientation.
The only markings I could find on the back of the bearings:
A makers stamp - 5116
The other side - 12H2719
I'm assuming these numbers are part numbers for the manufacturer.

Now to order the parts:

Connecting Rod Bearing Set, std. (5 Main)- MOSS = $28.95 / BHive = Tri-Metal = $46.90 / O'Rielly = Beck/Arnley = $47.99
I have a few other parts I need too. I prefer to get them all at once and save on shipping.
I like dealing with Gordan at BHive, but Moss is great too. I use O'Rielly whenever I need basic stuff. Not too sure what product is going to be the better quality.

Overall, for the other parts I need, BHive has the best prices. I will most likely by everything from Gordon. UNLESS someone can tell me why I shouldn't buy the TRI-METAL bearing set.
Since I'm at it - replace the oil filter and pick a new oil. I could read the forums for MONTHS to get advice on oil filters and oil types. I think I will keep this to myself, I wouldn't want to start a controversy.

In the end - replacing the connecting rod bearings hasn't been that hard. I was nervous at first, but thanks for all the help! I will post more results once I get my parts in.



Edited 1 time(s). Last edit at 08/05/2012 10:36AM by SSGt Olivero.
dickmoritz Avatar
Dick Moritz
Philly 'burbs, PA, USA   usa

Eric,

As noted earlier, no size marking means standard size. You'd be remiss if you didn't at least pull down the second and fourth main bearing caps to examine the bearings, and with a little finagling, you can also pull down the center cap, although it will be a bit tighter than the others. Note that the center main cap also houses the thrust washers, that just sit in place.
The only thing you need to remember about the thrust washers is that the grooves for oil face outward, toward the ends of the block, not inward toward each other. Suggest you post photos of your rod bearing shells, as well as photos of the number two and four main bearing shells, since you now have the opportunity to replace three out of the five pairs of main bearings, which is little additional work or cost as long as you're in there...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
chris Avatar
Chris Roop
Pendleton, OR, USA   usa

Tri-metal is good. Moss has been sending King tri-metal bearings, but if you call them, check to be sure. You are correct that the 12h....... # is a part number. Good luck!

Member Services:
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SSGt Olivero Avatar
Eric Olivero
Montgomery, TX, USA   usa
1975 MG MGB "Julia"
1975 MG MGB

UPDATE

Thank you everyone for all the advice and help. My parts arrived on Friday. With some help from a good friend, we managed to get the rod bearings replaced one at a time. It was nice to have someone under the car with me to make sure I didn't put the cap on wrong.
Re-installed the oil pump with new gaskets.
Re-installed the oil pan with a new gasket. The 4 front bolts went back in without much issue or headache.
While I was under the car, I bled the clutch slave cylinder. Finally able to get a little more pressure.
We made some minor adjustments to the accelerator cable to improve the tension.
Installed the new oil filter (NAPA Gold Part# 1068).
Filled up with Gastrol GTX 20W-50.
We replaced the valve cover gasket to help with the leak I was getting with the rubber (re-usable) gasket. I don't reccomend them at all!
Replaced the passenger side door mirror plinth with a new plastic one. My son broke the original plinth while trying to jump inside the car "Duke's of Hazard - style". Not one of his better moments.
Replaced the driver side door mirror with a brand new EVERYTHING. No one ever admitted to breaking the mirror. I guess I'll never know.

Started up the car and at idle my oil pressure gauge read 80 PSI. The weather wasn't cooperating so I will take the madien voyage soon.
In the meantime, we celebrated with a few - MUCH DESERVED - pints.

Thanks again!

the omega man Avatar
phil wilkins
staffordshire, Stafford, United Kingdom   gbr

i have never replaced the bearings,but i was under the impression-true or false- that you have to use plastigauge to ascertain the correct clearances.over the years the journals will wear,all at different rates,so putting in new replacement bearings of the same size may not give you the correct clearances.
You can shoot me down in flames if this is not correct,as i have not done this job myself as i say.
dickmoritz Avatar
Dick Moritz
Philly 'burbs, PA, USA   usa

Phil,

As a general rule, crankshaft rod and main journals are standard size or are machined to incremental undersizes, in increments of 0.010. It may take a cut of .020 or even .030 to cut past damaged areas, and some may go as far as .040 undersize, although I wouldn't want to use a crank cut that far just on general principles.

When a crankshaft is ground, all the rod journals are turned to the same undersize, and all the main journals are turned to the same undersize, although it is common and perfectly acceptable to have, say, rod journals at -0.010 and mains at -0.020.

Likewise rod and main bearings are supplied in standard, .010, .020, etc. So bearings are ordered based on the nominal journal size.

Factory manuals and engine builders' preferences dictate the target clearance between the assembled bearings and their respective journals. Plastigage, invented and manufactured by Perfect Circle, is a reasonable field tool for determining approximate bearing clearances. The preferred method is to mike each journal, then install the bearing shells in the rod or main saddles, torque to spec, and then measure the I.D. of the assembled bearings. Simple subtraction reveals the actual bearing clearance for that journal and that combination of bearing shells. Someone who's really good at reading a micrometer and/or dial bore gauge can sometimes read as closely as one or several ten-thousandths of an inch, although it does take a special feel to read something that closely, and not a lot of people have that feel.

All that being said, Eric noted, IIRC, that the bearing shells he removed were standard, assuring him that the crankshaft had not been ground undersize. So he ordered and installed new standard-size bearing shells. Typically crankshaft journals do not wear much, if at all. Rather they are subject to scoring or, in the case of a more catastrophic failure like a spun bearing, physical damage to the journal. But since this was not the case in Eric's situation, there was a reasonable chance that new standard-size bearing shells would provide clearances within, or not very far out of, recommended specifications.

He could have used Plastigage to verify the approximate bearing clearances. Plastigage is a very thin, thinner than a pencil lead, strip of material that crushes at a known and specific rate. To use it, you break off a piece about an inch long, lay it on a bearing shell or on a crankshaft journal, and install the rod or main cap and torque to spec without rotating the crankshaft. Then you remove the bearing cap and note the width of the now-crushed Plastigage. The tighter the fit, the more "squished" the Plastigage is. The envelope in which Plastigage is sold has a calibrated scale on it, so you simply find the width on the package that matches the width of the squished Plastigage, and that tells you the approximate clearance. It's an OK tool, but nowhere near as accurate as measuring using the procedure described above. So virtually all performance engine builders use the micrometer approach, and some may choose to use Plastigage upon final assembly just as a double-check.

For the record, I use the micrometer method of determining bearing clearances and, during one of several trial assemblies of an engine, I mark the specific journal (i.e., #3 connecting rod) and position (upper or lower) at which I measured bearing clearances. This assures that, even with manufacturing tolerances, I will end up with the clearances I actually measured.

In Eric's case, installing new standard-size bearings was not risky, with the only possible down side being that clearances, if anything, might be a little loose. But, based on the oil pressure he reports, that is likely not the case.

One other tidbit of trivia. For the most popular performance engines, like the venerable small-block Chevy V-8, manufacturers actually offer bearings in increments of half a thousandth, one thousandth, and sometimes two thousandths. This way the engine builder can mix and match bearing shells at a particular journal in order to achieve precisely the clearance he wants at each journal. And sometimes, when the engine builder knows with certainty what size his crankshaft will be, he will purchase bearings, install them and mike their I.D., and then provide those specifications to his crankshaft grinder, who will then custom-grind and polish each journal to achieve the clearance desired by the engine builder.

I know, I know, waaaaaaaaay too much information... cool smiley

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)
the omega man Avatar
phil wilkins
staffordshire, Stafford, United Kingdom   gbr

Thanks for taking the time Dick,very interesting points.
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