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MG MGA - Groove in Cam Bearing

Good Friday to you-

Just curious if you have ever noticed a groove in the front-most cam bearing. There are no other indications of abnormal wear and this groove does not appear to line up with the groove on the camshaft journal. That is there is a wider part and a more narrow part of the front-most cam journal and these two grooves (one on the cam bearing, one on the cam) don't line up.

I have another set of new bearings that don't appear to have this groove.

Obviously, the safest bet is to just have all the bearings replaced and call it good, but as with any real world problem, the problem is logistically a little more tedious than just having them replaced!

Thanks for reading and the help!

-J. DeRienzo
J DeRienzo

Is this a machined groove or a worn groove?
Art Pearse

Great question.

It looks uniform to be machined, but like I said, the replacement ones don't have it.

What's puzzling is that my machinist only power washes the block so I seriously doubt he took the bearings out during his "hot tanking" procedure to clean the block. This would eliminate the idea that the bearings were removed and then installed backwards, but no scenario can be eliminated because I just don't know.

There doesn't appear to be any marring or marks on the camshaft in that area.

So here's the scenarios I've thought of:

A) Machined Groove

i) Bearings Removed before hot tanking
1) Bearings Installed Backwards

ii) Bearings Not Removed before hot tanking
1) This are the original factory bearings and always had this
- As long as tolerances are within spec and no damage to
bearings, okay to continue use

B) Non Machined Groove

i) Bearings Removed before hot tanking & engine was run after
1) Camshaft caused this - This triggers the question, why are
there no marring or marks on the camshaft or bearings?

ii) Bearings Removed before hot tanking & engine not run after
1) Not caused by camshaft and these may need to be removed
and reinstalled correctly or replaced with new bearings

iii) Bearings Not Removed before hot tanking & engine was run after
1) This would mean that the groove could be okay, in my
opinion, because there is no marring or marks on the
camshaft or bearings. The problem is that the motor did have
extraordinarily high oil pressure after the first rebuild. There
was warping as well as discoloration on the crankshaft from,
what I take the high oil pressure to mean, oil starvation.
Could the camshaft have bearings installed incorrectly that
resulted in the crankshaft not getting enough oil pressure,
while the camshaft had enough oil to keep lubricated and

iv) Bearings Not Removed before hot tanking & engine not run after
1) This would mean that this was a factory installed setup and
given that the oil pressures before the first rebuild were great,
this is an acceptable setup.
J DeRienzo

Can you ask your machinist what he did if anything with the bearings? Highly unlikely he took them out IMO, if he does not caustic wash.
Art Pearse

I can.

This was done in 2009 the second time and 2001 the first time.

Expounding on what I've been thinking, I'd like to just assume that the bearings were never removed.

I guess I am being a little wishy-washy on details, but reference the camshaft picture here (not same crankshaft, but the picture illustrates what I'm talking about).

This groove that separates this "thicker" part from the "narrower" part of the cam shaft is what I'm referencing. On the bearing (not picture) the groove is about in the middle of the "thicker" part of this part in the camshaft.

I guess the question now could be, "is this normal" rather than "guess what may or may not have happened in my motor!"

I will ask my machinist, but, full disclosure, is that I'm having to fly back and forth to where this car is located to work on it, and changing cam bearings could cost me a trip and another month or more until the next trip is possible to get this done...

Of course the alternative is, "So, ya wanna rebuild the motor again?!?"

I'd like to get it right, one way or another!

J DeRienzo

First give us a coherent account of events since before the first 2001 rebuild.

"the oil pressures before the first rebuild were great,"
Why was that done and what was done?

Then, "The problem is that the motor did have
extraordinarily high oil pressure after the first rebuild. There was warping as well as discoloration on the crankshaft from, what I take the high oil pressure to mean, oil starvation. "
What distortion and discoloration?
Again, what was found and done? (2001)
What was the basis for the presumed idea that "it is fixed"?

What were the symptoms that led to rebuild #2, 2009?
Again, what was found and done?
And all the same Q's.

Now we are evidently at rebuild #3, 2011.
Other than a groove in the front cam bearing, why are you doing it?
And, if you have not determined the cause of these failures, what makes you think fiddling with cam bearings will help?

First, it is vital to trace the oil passages to see where oil should go, and then to see if something has blocked a passage, or left one open. High oil pressure indicates a blockage rather than an open. Starvation might result from either.

One possibility is that the cam bearing is installed backwards, possibly blocking a hole or two. Another is that it was made for another application, and the groove may not matter, provided there are hole(s) in the right place(s).

I do not know how the oil flows in this engine, and I don't have one to look at; the book is not clear. It is common that oil is fed to the main bearings first, then to the cam bearings, via holes/grooves in the main bearing saddles, bearing shells, etc. Cam bearings are much more lightly loaded than crank bearings, much less likely to fail under marginal lubrication, and cheaper to fix. IF the flow is to the cam bearings then to the mains, an improperly located front cam bearing would cause failure of #1 main and #1 rod.

The very concept of deciding what to do on the basis of perceived immediate convenience, when you have no idea what the problem is, seems upsidedown; only grief can follow.

FR Millmore

Sorry, I thought I was in the TD section!
MGA feeds cam bearings from the mains, so anything wrong with the front cam bearing would at worst starve only that bearing and the chain tensioner.
Still need to know what other damage.signs you have.

FR Millmore

Thanks, FR.

I was trying to analyze the one bearing, but if we can make progress towards finding out what my overall problem is (high oil pressure), that'd be great!

Quick things first, this is only the 2nd rebuild. I tore the motor down because the #11 head stud (all the way next to the firewall) snapped, I couldn't get it out to save my life (or engine pull!) and so I pulled it and had everything cleaned so that any stray shards from the failed e-z-outs and the welding shop that was able to get the broken piece out (without thread damage!) would not be a factor.

While I was in there, I decided to investigate the bottom end because the oil pressure from the only other rebuild (before the on-going, #2, rebuild) was extremely high. I posted pictures maybe several years ago (I only get a few shots at this a year) or maybe just a hair more recently than that that showed the main bearings discolored on one side and normal color on the other (the mains have a symmetrical grove that runs down the center of them; one of these sides was gold colored, the other was the silver-ish "good" bearing color).

The first rebuild was done because the #3 con rod bearing spun on the crankshaft. There was a new crankshaft installed that had the .010" oversized main bearings installed. I didn't put the lower end together.

The reason I was overanalyzing the cam bearing is because I am trying to track down high oil pressure, which, like you said, I believe to be because of a restriction. I'll just go ahead and ask it, are there any references to tracking down oil passages/flow diagrams or anything FAQs or things that might be out there to give me a clue of things to check and look at?

Like you said, I don't want to do this again, and getting it right would mean the world to me!

Thanks again for the help and let me know if I can be even more clear!

J DeRienzo

Horrid story!
Spun bearings are usually the result of oil starvation causing seizure, or bad rods from the last time it happened.
Were rods replaced/resized?
High oil pressure may be the result of heavy spring/shims installed to raise low oil pressure, again possibly from earlier events.
Was the relief spring checked/replaced?
Many stories of out of spec crap springs nowadays.
Failed bearings may result in crap in oil passages, causing restriction. All oil passages need to be cleaned meticulously, which means drilling out gallery plugs to do so. There have even been reports of engines with broken off drill bits in oil galleries from the factory!
Was this done?
"New" crank at .010 means it was not new, but reground.
Size of each journal MUST be measured carefully, as errors are not rare.
Many reports of recent bearings which are not to spec. Must be measured, and checked with Plastigauge.
Good diagram of passages in WSM, MGA or B.

Where are you, or it?
I suggest that you need to find a competent rebuilder, preferably familiar with this engine. When you have this story, it is essential to meticulously measure EVERYTHING!

Might ask on MGExperience>Motorsports.

FR Millmore

Incidentally at no point do you tell us what the pressure is. How about giving us the hot idling pressure at say 750rpm and than again at 3000 rpm and let us judge whether or not the pressure is too high.
Iain MacKintosh


The #3 con rod bearing spun. That was the original motor (my grandmother who just passed away in August has owned the car since off the showroom in '62) from the factory. This was the first rebuild and there were no shims on the oil pressure relief valve. Having not seen any other springs, I don't know if this was a heavy spring or not.

Pressure on the original motor was ~30psi idle and ~60-80psi under load.

I did not replace this "original" spring. I assumed that if it had given us 40 years of good oil pressure, it was good enough for another build. If it would have been bad, it would be low, not high.

We did not drill out gallery plugs, mainly because of the risk and our machinist (who, admittedly has zero experience with MGs) recommended against it as well.

The "new" crank was indeed new. It was from Moss motors and they have a release about the reasons there. Essentially the cranks were made, but were out of original spec so they reground them to .010" over. Obviously, when the factory has to go .010" over to make up for their fabrication mistakes, it doesn't speak too highly.

We had someone with significant experience with MGAs rebuild the lower end, but the long story is that I think that might be one of the broken links in the chain of success, but obviously there are many points that we have discussed here for that.

I am in Ohio and the car is in South Carolina.


The pressure before the rebuild was ~30psi at idle and ~60-80 (been too many years to remember). After the rebuild, no matter if the engine was at idle or under load, it was 80psi; hot or cold.
J DeRienzo

Where in South Carolina?
Don Carlberg

Agreed on the spring. I'd have left it too, and with the quality of replacements would never replace a good one.

Bearings "spin" because of seizure from oil starvation, or due to damage from preceding episodes which are badly repaired, or to bearings that just do not fit correctly.
Only the first applies to your original trouble; an (factory assembled and known good)engine running those pressures should not spin a bearing, unless it is run dry OR something clogs a passage. The second episode may be due to damage from the first, or to the original problem having moved in the interim. As I said, I have seen a two inch piece of drill bit in the main oil gallery, from the factory; oil flows past at a passable rate until it moves.

I've never seen one of these engines run hot oil pressures at 80psi, with correct oil and reasonable idle speeds, so I think it still had a blockage, now responsible for failure #2.

"We did not drill out gallery plugs, mainly because of the risk..."
Only risk is that you might find & fix the problem. (After you find a new "machinist")

Nothing wrong with factory salvaging production errors in a reasonable manner. I think these parts were normally used by BMC in "Gold Seal" or "Silver Seal" factory rebuilt units. Compare to Chrysler, who were known to salvage cranks by grinding journals to various sizes and stamping the size next to each journal; we were most surprised to find ".001", ".002", ".005", and ".010" ALL on the SAME crank(s). These were on virgin factory engines, and a friend who worked at Chrysler's Eastern parts distribution confirmed that these bearing U/S were stock items.

BTW, crankshafts are machined <undersized>; the corresponding bearings are referred to as "undersized", despite the fact that they are physically thicker than "standard sized" ones.

I have successfully cut more corners than I would like in rebuilding engines for one reason of necessity or the other, but this calls for a baseline proper checkout. First and absolute imperative is to unplug and clean and verify ALL oil passages.
There has been far to much done to this poor thing, and far too much memory, error, time etc. involved. You cannot solve this working piecemeal. Take the whole mess to somebody very competent, who knows how to check everything, and has the tools to do so. If the engine is in SC, Hap Waldrop (Acme Speed Shop) in Greenville might be a guy to talk to. I don't know him, but he is on MGExperience > Motorsports all the time, and has a great rep.

Not to niggle, but your sign in says J Rienzo, California, you sign Jamie, or Iain, and are evidently in either Ohio or SC - I'm confused!

FR Millmore

Car is in Florence,SC. I have tried muliple times to change where I'm located at. It says Ohio in the member profile page and lists California when I post. I gave up on that a while back!

FR, I completely agree with everything you have said. I get more nervous and apprehensive about putting things together everyday. I will be discussing where to go from here with the other vested interest soon.

Honestly, the car wasn't driven too much for a good 10-1years before it spun the bearing. At that point it was losing power and almost didn't have enough power to propel the car up hills. It was in poor shape. After the rebuild, minus dieseling on shut dow, the car ran like a dream. I think the carbs were too lean in regards to the dieseling.

I think the saying, "The definition of crazy is repeating the same behaviour and expecting different results," is quite true here. I was thinking this cam bearing or incorrect tolerances on the main and con rod bearings was probably the issue. Like you've pointed out, though, I don't have the oil gallery expertise to verify if that is the or an issue.

The engineer in me wants to solve this problem myself, but as you are pointing out, sometimes engineering is calling on the right expert...
J DeRienzo

This thread was discussed between 21/10/2011 and 03/11/2011

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