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MG MGB Technical - connecting rods installation

Just started my rebuilt engine and ran it for about 30 mins.to bed the cam.Engine ran great with good oil pres.but was leaking oil from lower front engine plate bolt .Removed front plate and found i didnt get a good seal there,also bearing cap seal looked suspect so pulled the oil pan.While tending to my bloody knuckles I was reading a thread about the oil sqirt holes,mine are facing the cam instead of the thrust side.Should I pull the head and turn the rods around ? if so what about the rings and big end bearings? thanks in advance.jim
jab bartol

Jab-
Yes, you should rotate them 180 degrees so that the oil sqirt holes will lubricate the distributor side of the cylinder. However, leave the head on and, with the oil pan off, simply remove the rod caps, individually free the rods from the crankshaft, and rotate them 180 degrees. I doubt if the rings ate seated yet, so ignore them. Check to make sure that the oil holes in the bearings are properly aligned.
Steve S.

Just one quick extra comment... are you sure you got the pistons on the rods the right way round? If you hadn't, and you originally put everything together so that the 'FRONT' marking on the pistons was correctly aligned, it would explain why your rods are backwards.

However, I can't remember whether B series pistons are fully symmetrical or not. Steve?

ttfn,
--
Olly
Oliver Stephenson

Olly-
You're right, I am presuming the the pistons were in fact assembled onto the connecting rods with the "Front" marking on the piston crown properly oriented to the squirt holes of the connecting rod and then the assembly installed backwards.

Jab-
If the above is not the case, you'll have to pull them out and refit them.
Steve S.

Steve, Olly-
The pistons' front marks were definitely aligned correctly -- toward the front of the block. I did not specify to the machine shop when I had the pistons pressed on the connecting rods, as I didn't know about the squirt holes. I assume now that the PO had turned the rods around during the previous rebuild. Found many other strange things in this block.So now I'll pull the head and order some parts.My only concern is the rings and bearings, should I renew or use the current ones? As Steve stated they haven't seated yet. thanks again for the advice.jim.b
jab bartol

jim.b You should have no problems re-using the rings and bearings. I am not even sure that you need to turn the pistons around. The ones I have measured seemed to be round. The "front" markings seem to be an assembly aid to ensure the con rods are pointed correctly--to the distributor, or left, side of the engine. This type of thing is what makes a shop having some background in the MGB, or BMC B series engines, very valuable. They understand the relationship between the "front" side of the pistons and the oil squirt holes on the con rods. Still, if you want to be absolutely correct, I would recommend pulling the pan, removing the piston/con rod assemblies, marking the bearings as to which rod them came off of, and having the pistons turned 180 degrees. Then, reinstall them. My experience suggests you will have no problems if this is done. Les
Les Bengtson

On some pistons there is definately a front due to the location of the split in the piston skirt if it has one. Also some pistons have slightly offset gudgeon pins. Reversing them puts the offset on the wrong side. Make sure that front is front!

With such short running time, the rings and bearing can be reused PROVIDED everything was scrupioulsy clean on assembly the first and again on the second time around.
Blake

Jim, You may be interested in the following two threads about alignment of the oil squirt holes. Roger Parker's post at the end of the second thread is very interesting, read it carefully. BTW, both my engines are assembled with oil squirt holes on the thrust side of the block, distributor side. Regards, Clifton

Thread: Oil Holes in MGB Connecting Rods
Posted 15 October 2000 at 05:21:02 UK time
Mike Brown, Oregon, USA, sevenshop@terragon.com
I happened to notice on another thread some comments respecting the side to which the oil squirt holes on connecting rods should face when installed in the MGB engine.

In the many engines we have disassembled which were clearly assembled only at the factory, we have yet to see one which has the oil holes facing the camshaft side of the engine.

To be very clear about this, the oil holes have ALWAYS faced the distributor or spark plug side of the engine and NEVER faced the camshaft or carburetor side of the engine.

Because of this and other specific references to the matter in factory manuals which we have in our personal library, we have always chosen to reassemble the pistons to the connecting rods so that when the pistons face forward, according to their respective markings, the oil squirt holes face as stated above.

The purpose of these squirt holes is to lubricate the piston pin, the cylinder bores, and bathe the bottom of the piston as an adjunct to cooling. Were the squirt holes aimed towards the camshaft, due to the location of the camshaft in the lower part of the cylinder bank, the stream of oil would be mostly blocked by the cam and prevented from shooting upwards against the piston and piston pin during the critical number of degrees of crankshaft rotation lubrication can possibly occur. This would eventually result in extreme piston pin wear within the piston and the very real likelihood of piston failure, not to mention increased bore wear as well. The cam itself receives abundant lubrication from both the pressure galleries in which it's journals spin and residual oil flowing down the pushrod bores from overflow at the rocker shafts, not to mention oil cast from the main and rod end bearings at the crankshaft.


Best regards,

Mike Brown,
Seven Shop British


Posted 15 October 2000 at 06:48:32 UK time
Barry Parkinson, Petaluma Calif, parki44@hotmail.com
Mike, my machinist very authoritatively advised me the oil holes went to the camshaft side, and assembled the pistons that way. Looking at the tech manuals clearly confirms the oil holes go to the distributor side. So far with only a few thousand miles of right way pistons and wrong way rods my engine seems to be doing fine. The late model rods appear to be symmetrical so that there apparently is no mechanical difference (only lube and cooling). I really don't feel like pulling the head and the pan to reassemble my pistons and rods. I'll have to take it easy until I get the time and motivation to do the job.
Barry


Posted 15 October 2000 at 15:52:28 UK time
Mike Brown, Oregon, USA, sevenshop@terragon.com
Barry:

Can't trust them machinists!!

While a different engine, an "experienced" mechanic once installed the connecting rod wrong in a Continental 0-200 engine in a Cessna 150 we later operated in my flying club at one time. The engine went nearly 800 hours (1800 TBO engine) before failing with one of my instructors and a student aboard...while practicing stalls at 3,000 ft. AGL over then Fremont Sky Sailing airport using airport transfers sevenoaks in the Bay Area. The engine locked up solid as the piston disintegrated and the con rod forged the remains into the top of the cylinder. The instructor (19 yrs. old at the time) spiraled down and landed at the airport neat as could be without a mishap. It was his first student and he had less than 500 hours but a good set of nerves and great hands on the stick. Had the student (female) been on her first solo, which occurred some five hours later, the result might have been different.

(The instructor went on to the Navy and eventually to flying jets from carriers.)

That's what can happen when the oil squirt holes are aimed to the wrong side of an engine.

Maybe your machinist will want to regain his reputation by doing this work for you at his expense and on his own time.

Best regards,

Mike Brown


Posted 15 October 2000 at 16:55:01 UK time
Chris, Essex, UK, chris@octarine-services.fsnet.co.uk; http://www.octarine-services.fsnet.co.uk/octarine.htm
Whilst the engine will run and appear to be OK, it won't be many miles before the pistons wear so much on the thrust side that there is serious danger of putting a rod through the block.

The factory put those oil holes there for a good reason!

Take it back to the mechanic and insist that he corrects the situation.


Posted 16 October 2000 at 02:31:04 UK time
Wade Keene, Oak Park, IL, g_keene@hotmail.com
My machinist also wanted to, and did, put the conrods together with the oil holes pointed at the cam. He told me that all the American engines are put together that way for cam lubrication. I'd guess that anyone who isn't real familiar with A and B series engines would naturally put them together that way.
BTW, I looked at mine before I left the shop and he was happy to re-do them for me at no additional charge.
Safety Fast, Wade


Posted 19 October 2000 at 03:24:10 UK time
Jeffrey Delaney, Texas, USA, missngoo@aol.com
oh god.

I had my block rebuilt close to two years ago with the help of some mechanics that had never worked on MG's. I had done no mechanic work at that time so was obviously in WAY over my head. The machinist asked me which way to put the pistons onto the connecting rods in regards to that oil squirt hole. This was now so long ago, that I don'r remember that we resolved this issue correctly. the block has only been run for brief periods and has never been on the road. It is already installed in the car.
Here are my questions. 1.) Can the piston/rod assembly be put together backwards so that the piston says "front" but the connecting rod is facing the wrong way in regards to the oil squirt, and as long as the oil squirts are facing the right direction, would the piston orientation matter? 2.) Without a major dissassembly can I tell if it is done right. i.e. can I drop the oil pan out and see or feel around to know if the oil squirts are going the right way. Thanks for the help on this. Just as I thought I was getting close to driving it....


Posted 19 October 2000 at 06:00:39 UK time
Barry Parkinson, Petaluma Calif, parki44@hotmail.com
I have read various opinions that wrong way rods will ruin your pistons, but have yet to hear of a specific incident where the dire failure actually occurred. Considering the zillions of these cars repaired over the years by non specialized mechanics there are probably more engines out there with wrong way rods than right way. A hot chevy 350 puts more load on the piston than an mgb by far and it squirts oil at the cam (on one side of the V8 it is towards the thrust side of the piston on the other not. Come on now - how many backward rod, piston failures are documented?
Barry


Thread: Piston & Rod Installation, Help Needed.
Posted 09 November 1997 at 12:16:26 UK time
Andrew in Austin, TX:
Mark Barrington have patience I'm still looking for a
second and third opinion from cyberspace on this.

My first inquiry about, "which side of the piston is
the thrust side?" is still unanswered.

1. Well, which side of the block is the thrust side?
> Could someone with a Leyland/Bentley manual look
> look this up for me? Does Burgess discuss the topic?

2. The connecting rods have an oil squirt hole at the base.
> The Haynes manual show this side of the connecting rod
> facing the distributor/right side of the block.

> My 2nd question is, why don't these oil holes at the
> base of each rod, face the camshaft, where lubrication
> is more important?

> As Haynes shows the connecting rods in the pre 18V engine,
> the squirt holes will be lubricating the walls of the block.

I don't get it. Shouldn't these holes be facing the cam?

3. By the way, I have been referring to the drawings found
> on pages 32, 33 and 37 in Haynes Manual. These are figures
> 1.7,1.8,1.13 and 1.14 respectively.

> I can INFER which side of the piston is the thrust side
> by looking at the figures, but last thing I wish to do
> right now is INFER. Just as I can infer which side the
> of the rod face towards the left.

Also, the 18V connecting rods are different than 1971 and
earlier engines. No big deal, just different. But both
have the lubrication hole at the base of the rod.

Finally, for those of you who will be doing this in the
future. Do not do as I did and mark each rod and end cap
with a magic marker to remember how you removed each part.
I did this in September and the machine shop when they
clean your parts in the vat will clean off your marks as
well. It is nice to have everything clean up to look new.


Posted 09 November 1997 at 22:16:48 UK time
Mark B.. Austin TX
Hi Andrew...

It is my belief that the thrust side is the camshaft
side, opposite the distributor. I also think the squirt
holes go toward the camshaft. But it has been a while since
I did this, so PLEASE get a second opinion. I don't want
the responsibility if anything goes wrong. I can't wait till
you get the thing back together, hopefully before the weather
turns too hot to drive again... Then you can drive to the
MG car club meetings...

Mark B.


Posted 09 November 1997 at 22:58:24 UK time
Andrew in Austin, TX: ayue@mail.utexas.edu
Mark, I sent a ton of e-mail to anyone who
may be an authority on the subject.

What I wish I had is the Bentley/Leyland Manual
for the Rubber Bumper cars.

I also feel that the thrust side is on the camshaft
side of the block and the ring gaps should be set
1 to the rear, then a 2nd 90 degrees toward the
distributor. BUT, this is totally opposite to the
diagrams in Haynes. They even have the oil squirt
holes aligned on the distributor side of the crank.

I found the thread I saw concerning this topic. After
reading it you'll see there can be no confusion on the
topic. I say this with sarcasm.

Read on:
What is the "thrust side"?

From: Leon, lmacdonald@ticz.com on 9/4/1997 23:29

I am putting in new rings. My Haynes says to put the top
rings at 90 degrees to each other away from the "thrust
side". What is thrust side?


From: David Allen ,Me. USA dandr@gwi.net on 10/4/1997 0:01

Hi: The thrust side, if you are looking at the engine and
windshield from the front ,
it's between 12 o'clock and 3 o'clock

Have Fun
Dave



From: Dave in Seattle, WA dkr003@ibm.net on 12/4/1997 5:59

The thrust side of the piston is the side of the piston which is opposite
the connecting rod during the power
stroke. Since the B series engine rotates clockwise from the front, the
thrust side is distributor side of the engine.
I'll double check for you and let you know. I went throught the same
process when I rebuilt my motor, but it has
been a few years, and I have a feeling you have the same desire to do a job
twice as I do. Talk to you soon.

Dave


From: Leon on 14/4/1997 13:36

It appears I am getting two different versions of where the
thrust side is. Dave from Seattle, have you rechecked?

Leon


From: Ed Morse, Ithaca NY on 17/4/1997 18:32

Leon,

I believe both Dave and Dave are correct. The power
stroke of the engine occurs when the _crankshaft_ is
between 12 and 3 (and then 6) o'clock as David from
Maine indicated. The thrust side of the _piston_ is,
as Dave from Seattle nicely describes, on the opposite
(distributor) side of the engine.

I hope this helps (hope I'm not wrong, too! :-)

Ed.


From: David Allen Me. USA dandr@gwi.net on 18/4/1997 0:49

Leon you have a problem, everybody seems to be correct.
The cyl. wall wears on the compression stroke and the
power stroke. The rings also rotate over time. Installing
end gaps over the pin, is often done. A leakdown tester
will tell you what kind of engine you have, Good Luck
Dave


From: Leon on 18/4/1997 14:36

Sorry if I offended anyone. This is the first mechanical
work I've done and do not understand all the termninology.
I did not mean to imply anyone was wrong, but that the
information was not easily understood by this novice.

I now know that the "thrust side" is compression side and
on the side of the distributer.

Thanks,

Leon


Posted 10 November 1997 at 00:14:41 UK time
Roger Parker Tamworth UK roger.parker@virgin.net
As the subject of thrust side was one which has not previously raised it's head quite in the same way
for me in the past, I have taken the opportunity to refer to the Bentley manual, an early Haynes,
a late Haynes and an Intereurope manuals. Of note is the fact that I can only find reference to
assembly with regard to the Thrust Side in the later Haynes.

My considerations when assembling has been to ensure that the con rod is assembled to the piston
the correct way round and then that the piston/rod is fitted to the correct bore with the arrow and
'front' marks on the piston pointing towards the front (water pump) end of the engine. I also
position the ring gaps at the 90 degree (or so) position to each other, including the separate
pieces of the multi piece oil control rings. Coinicidentaly it means I do fit the rings so that
the gaps always fall towards the front or rear faces of the block, and away from what the discussion
refers as the thrust side. Long term heavy use with over 100 bhp at the wheels does seem to indicate
that this isn't a bad practice!!

On the subject of the oil hole in the rod, this is primarily intended to squirt up the bore, to
provide lubrication on the bore wall and on the underside of the piston to remove heat. This does
have a drawback in that it leaves a large amount of oil on the bore walls, not all of which may be swept
by the oil control rings.

The 'O' series engine carried over many features of the 'B' series engine and it is interesting to note
that the latest incarnations of that engine have the oil hole deleted because too much oil was passing
the rings leading to worse emissions. Oil splash is said to provide more than enough lubrication/cooling
for the pistons/rings/bore which seems to be borne out by turbo versions of the engine producing over 250 bhp
reliably and long term.

Not a definitive answer, but I hope it helps.

Rog.




Clifton Gordon

Thanks again guys for your feedback and information. After studying the manuals -- Bentley and Haynes -- it makes sense to me to have the oil squirt holes on the distributor side. Have started to fix the problem. After this, I'm sure I'll be able to work the pit crew for any MG racers out there...
Thanks again for the help. - jim
jab bartol

This thread was discussed between 27/04/2003 and 29/04/2003

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