Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - Knocking horrer

I spent the last two days installing my knew 1500 engine block. It was aquired from a local guy who had set it up for racing.It included just the block, street cam, and really nice cranK, new piston and rods. It appeared beautiful but I just went to start it and I am experiencing a horrible knock. I am completely frustrated and have no idea were to look. I figure it is either the valve hitting something or my worst nightmare, a bad bearing. (which is why I changed out the engine to begin with!) I am almost ready to hang up my MG days and addmit total defeat. Any suggestions welcome
WMR Bill

Pull the oil pan and look for problems with the rods and mains. Don't forget the thrust bearings. Check with the local MG club and you should find somebody who can help you with this. You think it may be a valve hitting the piston? Pull the head and turn over the engine. You should find something out there pretty quickly. Look for marks on the pistons to indicate valve trouble. You also may find something fell into the intake, although it won't quite sound like a knock. Check the valves and seats.
good luck
mike parker

Thanks Mike, I have a suspician it may be the valves. I used my head on this new block. Since it has a sreet cam I assume the valves are opening up further. It is also a possibility that this block may have been shaved as well. Is there any old trick to determine were the knock is coming from berfore I start ripping aapart two weeks worth of work?

WMR Bill


Your local Autozone has a tool loaner program and one of the things they lend is a borescope: essentially a fiber optic viewer and a light. Run it into the spark plug hole and take a look around.

You should see some marks on the top of the piston. Barney has a nice description for how to grind "eyebrows" in the tops of the pistons as necessary.
T McCarthy

T, As I look at some of the pic's of the motor I got (see below) it appears it has the "eyebrows" installed. Does it make a difference that I put an older 1500 head back on that does not require the eyebroe?

WMR Bill

Bill. Use a mechanic's stethoscope to determine where the knock is coming from, then, investigate that area. Inexpensive tool which will be used many times during its long service life.

Les Bengtson

did it ever start or just turn on the starter, did you get oil pressure. Unbolt and lift off the rocker assy and hit the starter again, spark plugs out,and listen again.Crank until oil pressure builds. No knock then valves,....knock then bottom end.

The eyebrow notches don't go on the pisons, they go on the block.

If the block has eyebrow notches already cut in, then you shouldn't be experiencing clearance problems. That is, unless at some point your head has been milled more than than that head that was originally on that engine. That block has eyebrows in it because the head that was installed on it probably had been milled down and/or larger valves installed, along with a higher lift cam. Putting a stock unmodified 1500 head on it should cause you no inherent problems. I'm with Mike, pulling the head off should give you the best look if it's the valves or not.

I had heard about a putty-like material that you can use during a test-fit assembly to check tolerances and clearances. Anyone know of this or what it's called? Might be useful here.

Mark J Michalak

Wyatt, I had this engine on my stand and assembled it myself. I had no problems or any indication of any problems prior to final assembly of the head. I put an extra effot into making sure evry thing was well lubed including filling the oil filter and enjecting oil into the moter with an oil can at the preasure gauge inlet prior to tuning the engin over. The engine preasur went to 70 lb in about 15 seconds without the plugs in. I then instlled the plugs and she started right up and runs great except for the obvious knock. I am not sure were to start the bottom end or the head.
WMR Bill

Waytt, One more comment, I hear nothing while spinning the motor with the starter. It is only after it starts that the knock occurs.
Thanks everyone for your help!
WMR Bill

Whoops that last one is an interesting clue! If you don't hearr that sound while spining under starter I think that takes the valves out of consideration as the problem, and perhaps the bearings.

All of those are mechanical in nature and should happen whether you are spinning with the starter or with the plugs firing!

Is it possible you are simply out of firing order?

I'd go back and pull all the plugs and spin the motor on the starter and make sure the noise isn't there.

Then you have a whole new basis of consideration.
T McCarthy

I had a knock on a rebuilt MG-Td that I had just finished. It was one rod bolt that was just touching the oil pick-up line. That bolt was almost 3/16" longer that the rest. Shortened the bolt and all was well.
conrad sanders

If you have no noise when spinning, I would suspect the lower end. Perhaps a connecting rod. When the engine spins over, there is no real load on the pistons, at least until the cylinders fire under pressure. Tyson is possibly correct with firing order also, something I missed.
mike parker

I will drop the pan this afternoon to inspect. What are the chances that the I just need to change the bearings and rod and crannk are OK?
WMR Bill

You didn't say if the crank was new. If it had been reground there is a slight chance that one of the new bearings was standard size or that one crank surface was ground to the wrong size. Easy to check the rod journals with the pan off
J Heisenfeldt

"I had heard about a putty-like material that you can use during a test-fit assembly to check tolerances and clearances. Anyone know of this or what it's called? Might be useful here."
Jeff Schultz

Plastigauge has been around a long time. You clean all the bearing surfaces, put in a small piece and then bolt the bearing cap on and torque it to rated torque. You then dissasemble it and compare the width of the materail to a gauge that is supplied with it to obtain the bearing clearence. Just don't rotate anything with the plastigauge in or your results will be incorrect.
J Heisenfeldt

....start it up and let it idle, pull the plug wires one at a time to see if the knock goes away, if it does its a rod, if not its mains

Well I droped the pan, What I found were big gouges in both 1 & 4 Rodd bearings. Main were OK but will be replaced. Supriseingly there is no sign of any damage to the crank. All I can say is I hope that this was the problem. I need thiscostly nightmare to end! See pic below of beaing. Please respond if you think this could have caused the knockinh.

WMR Bill

Anothe pic, He did indicate that he raced this engine, obviously a bit longer than he led on which was 2000 miles. Could this be normal ware in a race engine? At this point I feel he really pulled one over on me.

WMR Bill

I wanted to add a pic of the crank in case any of you guy's might notice anything abnormal.
Thank again!

WMR Bill

It could well be your knock, a little hard to see the wear in pictures. Polish the crank with crocus cloth, it should be glass smooth. Get a micrometer and measure the crank bearing surface in several spots too make sure it is round and not tapered end to end. If you have the head off, pull the pistons, bolt the caps on the rods and measure the bearing bore in the rod for roundness. On a race engine it would not be unusual to find the crank slightly undersized giving more bearing clearence, a loose engine runs faster, but not as long.
J Heisenfeldt

I got a better pic of the gouge in the bearing. It does not appear to be normal wear!

WMR Bill

As JH says, put a micrometer on the crank journals first, and they all need to be mirror smooth.

The first bearing picture doesn't look too bad, still has the soft white metal surface, so the crankshaft may not be damaged. The second bearing picture looks worse, has backing metal showing and may have been overheated (discolored). The heat could have distorted the bearing cap making it out of round.

You need to ask why this happened, so you can be sure it doesn't happen again on next startup. Under the circumstances, I think I would leave no stone unturned. I would recommend disassembling the engine to run a wire or compressed air through every oil supply passage in the block and crankshaft to be sure nothing is obstructed.

One possible problem may be that the DPM mixed up the bearing caps on the con rods making the big end bores different diameters (because the split lines are off center). Con rods are right and left handed parts. #1 and #3 rod caps could be switched making #1 too small and #3 too large (or vice versa). #2 and #4 could be switched making #4 too small and #2 too large (or vice versa). Or the whole batch might be an assembly of mismatched parts from different engines.

Most conrods are not marked for mating parts, so the only way to know for sure would be to pull the head to remove the pistons and rods, bolt the caps back on the rods, and measure the big end bores with a dial bore gauge to determine diameter and roundness.

If the big end caps were switched you might figure out how to switch them back to make it right. You might even be able to do that with the engine in place using Plastigage to check bearing clearance (with new bearing shells). If any of the bores are incorrect diameter or out of round you need to have the caps shaved a bit to reduce the bore, then reassemble and rebore the big ends to restore correct bore size and roundness. Main bearing caps are more robust and seldom have this problem.
Barney Gaylord

As you are really going in deeper than you had planned, I think that if you can get somebody who has engine rebuild experience to assist you it would be very beneficial. Measuring the bearing surfaces, as J. Heisenfeldt mentions, does require more than passing knowledge when taking the measurements. You definitely want to measure both sides of the bearing surface (fore and aft) to insure that there is no taper.
Race engines, depending upon the race type, are not always expected to be in "top" condition at the end of a race, and in some cases, the engine is rebuilt between races, or at least after a couple of races.
mike parker

I know its difficult to tell but I've not seen anything in the pictures that equates to 'horrible knocking'. I recently fitted a new cylinder head on my mga and left one tappet unadjusted, it was badly out - when I started the engine there was what I would describe as a 'horrible knocking' and I thought that the engine had run a bearing. In some apprehension I ran the engine again with the rocker cover off and was able to identify the general noise source and also by holding the rocker with the engine running.
J H Cole

Well guy's, I thank all of you for you input! Mike, I have to agree with you that this is know getting out of my relm of expertises. At 50 years of age I am just running out of energy to be crawling in and out from under a MG. My mental state is at wits end and the cash bucket has runnith empty! I have no desire at this point to start purchasing machienest tools. So I think at this point I will just spend the 100 bucks on new bearings and throw them in and hope for the best! I am going to try and get my 1800 engine block back from the guy I traded this motor for and break down and have it professionaly done. I do not want my love and obbsession with this Hobby turn into an Oman of disgust. So I will recognize my limitations and do what I should have done from the begining!
So Cheers and thanks again!

WMR Bill

Rather than throw good money away, I really suggest that you contact somebody. I don't know whether you are close to Titusville, but Fletcher Millmore is in Titusville Pennsylvania and has posted here regularly for some time. If you are near, you may wish to contact him, as he is quite knowledgable and I am sure that he can keep your costs from skyrocketing.
Here is his

Here is his website:
mike parker

Bill, if you are near Bucks County there is supposed to be a good MG shop there too. They did my Brother's TC a while ago.
T McCarthy

This thread was discussed between 03/08/2008 and 05/08/2008

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.