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MG MGB Technical - Engine out...what to examine?

I now have the engine out and mounted on an engine stand. Back plate and also head off. I was told by the PO that the engine had a reground crank with new shells, new pistons and gudgeon pins and a new camshaft (that was in 1994 but has only had 2 years use by him and one year by me since then) Something had been done to the cylinders but he wasn't sure what so maybe just a hone. On examination pistons are marked .030, there is a shallow lip at the top of the cylinder. I'm considering removing the bearing caps to examine the shells. Should I also remove each piston and check the piston ring gaps (as per Haynes)? A bit unchartered territory as I only replaced the camshaft when I did the midget a few years ago. Anything else I should do while I have the engine apart?
Steve Church

Just taken the sump off and taken a piston out. Comments on amount of wear are welcome.

Steve Church

No.1 bearing.

Steve Church

And piston.

Steve Church

Oh, and the shells show .060 undersized.
Steve Church

Almost certainly too much big-end wear, that is the copper that is showing through the white metal and would normally mean new shells at least. Have you Plastigauged?

Crankpin looks a little scored, and there is the scratch in the right-hand shell. I don't have much to compare it with, when I took my V8 caps off the journals were mirror-finished, the clearances at or just inside that for *new* bearings, they were standard sizes, and it is the original engine having done 200k! I did find the right-bank con-rods all facing the wrong way, but that is another story.

Book says +40 is the max for bore so you have a little bit to go, although that is only 5 thou per side and your lip may be more than that. The trouble with a rebore is it is only as good as the clearing out of the oil-ways. What you don't want is metal bits being forced into your bearings the first time you start it up.

But it also says max undersize for journals is 40 thou so you are past that, and the narrower they go the faster they will wear. And if you are intending to put a fast-road head on it may not last too long.

PaulH Solihull

Having taken the piston out I can just feel a lip around part of the circumference at the lower end of the cylinder but only around about 2/3rds of the circumference.

I can feel some scoring on the crank pin but there is no ridge at the edges. I've not taken a bearing apart before so don't know what to look for. Looks like a new set of shells then. Or am I better off sourcing a replacement crank or even a short engine? Not really what I had in mind especially after the PO has said the engine had been looked at. Seems he was not correct. Odd that he would have said so as he is someone I know and part of our church community.

I shall examine all the rest of the bearings. I have heard of Plastigauge but never seen it used. Is it readily available?

I have a suspicion that the oil filter was missing something (a plate at the base of the oil filter housing) which may have negated the effect of the filter. This may explain some of the wear perhaps.

Thanks for the info Paul.
Steve Church

Moss US only lists max. of 0.040" undersized bearings. I don't know where 0.060" under were sourced from. It's possible it is 0.010" but hard to read.

Plastigage will give you an idea of clearances. But you'll want a micrometer check of the journals to determine true diameter, taper and out of round. Compare these to recommended tolerances. The crank should be polished at minimum but you may not have enough metal left.

The MGB bottom end can take quite a bit but if you're truly at 0.060" undersized I'd definitely not use this for performance engine build.

When I bought my 65 MG there was a replacement 18V engine in it. One of the rod bearings was totally mismatched with its cap. You could literally catch your finger nail on the offset between the halfs. The journal was scored and I was down to underlayment on much of the shell. Yet this engine did not knock on the lower end and oil pressure was okay. However, the wristpins were loose and the cam/lifters were totally trash and the rocker bushes/shaft badly worn. The cam bearings were shot..unusual. The machine shop said all this was evidence of dirty oil. The oil looked like tar when I got it and I had to punch the lifters out of varnish.

I replaced the engine with an 18V short block built up in the UK. It was 0.030" over on the bores and 0.010" under on the bearings.

You may be suffering from trash due to the filter problem. You should check the cam bearings also.

If the cylinder just has a ridge lip you can clean that off and see how bad the wear is before you think of a bore. Compare those readings to recommended tolerances. If possible also micrometered the pistons to see what the clearance is. Again compare to recommended tolerances.

If you're just cruising around and not into performance MG engines keep going despite a lot of wear and being out of tolerance. A little oil consumption is not critical and with the 5 main engines the bottom end is robust.

It could be the mechanic mislead the PO. That happens.
Robert McCoy

That's way too much wear for a supposedly low mileage engine. Either the machine shop used whatever parts they had at hand or they simply had to keep machining until the crank and cylinders cleaned up to oversize specifications. If your crank really has been cut to .060" undersize, it is close to the end of its useful life. I would take the engine to a competent machine shop and have them confirm your measurements. That way, they can best advise you on a course of action. RAY
rjm RAY

Steve, sorry be the bringer of bad news mate, but it's stuffed... How many miles do you think it's done in the 3 years? Looks like at least 60k's worth of damage in a badly maintained unit.
If you can feel any ridges/score on the crank with your finger nail it will need a regrind and to put new shells in is only a short term fix to get it through a sale! Moss UK do list .060 under size and therefore your reading could be correct. From the pic's it looks like a new crank is required.
The scoring on the piston skirt is not a real problem (aluminum being softer than cast iron!) but you do need to check the bore with a micrometer and then check the piston size. The difference should be no more than .006 and shoot for .0025 on a new build. If a re-bore is required, I see Moss stock +.60 for the High compression engines. Which engine are (were :o( ) you running? Is the uneven wear you mention on the bore (you suggest 2/3rd's of the diameter) on the Thrust side eg towards the front of the engine? If so you need to take the pistons off the rods and replace the small end bush. If this is an 18V engine that means a set of exchange rods.

A replacement short engine may be the way to go but make sure you know it's pedigree eg bore/crank size, who did the work and how well has it been maintained... There's no point in buying something to rework only to find it's only got one rebuild left in it...

best of luck and a Happy New Year to all.

M McAndrew

Steve, I really should read a bit better!
The missing plate in the bottom (top really as its inverted when fitted!) of the oil filter cover will be the cause of rapid destruction of the engine. The plate (and associated spring) presses the filter against the filter head and ensures the oil actually flows through the filter. If yours has been running without this plate it's almost certain to have sucked in all the grit and crud from three years of running straight into the very parts it shouldn't be allowed to go.

Start from scratch with another engine as the cam bearings and cam will also be U/S.

PS: the guy at church is not lying, the engine has been looked at and worked on by a cowboy :0( Also, he's very trusting but unfortunately isn't an engineer!

M McAndrew

I've just spent the last hour taking the rest of the bearing caps off. Main journals look ok (no copper showing) but the big end shells show varying amounts of copper althought eh one pictured is by far the worst. As far as my digital vernier can tell (reads to 0.5 thou) all big end journals are 1.815 inches.

So starting to look for a reconditionable crankshaft or short engine. I may take all the bits down to the local engine reconditioners to get their opinion.Looks like the respray will have to be put off for another year!
Steve Church

Have just had a block bored plus 60 thou, which Peter Burgess reckons is OK even +80 at a pinch, but the chances of breaking through due to core shift,or hitting slag or casting sand gets quite high, which is presumably one reason why the factory linered their gold seal engines. If the crank has been so over ground it's had it. But has an indication of the engine's life, it's bad news! If the engine has been abused or suffered lubrication problems, then cam follower bores may be oval, check with a new follower. The followers and the cam will also be gone. The oil pump will be scored and it's drive gear damaged, similarly the dizzy drive.The cam bearings shot. I have a block like that in the garden!!!
Allan Reeling

Steve, 1.815 fits with the -.060 shells. New should be 1.8579 to 1.8764. By all means get a second opinion from a reputable workshop as we are only making judgements from pic's and reference documents. Who knows, a polish might get you going again.
As Allan mentions check everything, clean out all the oil ways and replace the cam, followers and bearings. The block may be salvageable for one more rebuild but you must be sure all the important running surfaces are good to go again.
Best of luck..
M McAndrew

Mike, I'm not doubting the advice of fellow members, far from it. By the time I get a rebore, new pistons and rings, new shells etc, I may be better off sourcing a short engine from a reputable source. Not carrying around all that heavy metal has got to be worth something as well.
Steve Church

Steve, I wasn't suggesting you were questioning the advice of the BBS. A good second opinion with eyes on the unit is always a good way to go.
I can understand your position on the short engine ;o) But think of all the fun you'll miss out on and the experience of building your own unit backup is very rewarding.
Isn't that why you bought a MG in the first place :D

M McAndrew

Well I suppose it would add to my skill set. I'll keep all options open for now. There are a couple of crankshafts on ebay at the moment (the Welsh mg centre). I've asked them to measure the journals to see if there's a regrind or two left.
Steve Church

Steve, this might be better value..

Make on offer of around 180 and if you don't want the rocker cover I'll give a tenner for it!

M McAndrew

When I bought my car it was supposed to be a good engine and look what I ended up with. It also had good oil pressure and was quiet. I think that with any secondhand engine I would have to factor in a rebore and regrind. But thanks for looking. I did see a new Zetec engine at the bottom of the page though!
Steve Church

Steve, There is a man who lives in Henstead, which is just south of Lowestoft. He is retired now and used to run an engine shop in lowestoft before he retired.
If you contacted him he could check over your crank etc., tell you if it needed a rebore etc. as he did for me last winter. and was half the price of quotes for doing the work elsewhere. If you need contact details send me an email.
Trevor Harvey

Good advice there
Get someone who knows what they are looking at to look at it. The .060" undersize is a bit of a worry but it's not the end of the world really it doesn't look too bad all up
Shame about the oil filter plate missing, most of the wear/damage has been caused by that and probably previously caused it to get to the 60 under stage as well.
Using plastigauge on old bearings is a waste of time, it's going to have too much clearance and it will be different with new shells anyway.
You need to get the crank miced up and check piston to bore clearances to really know what you've got to work with -- it's the only way
Steve, can I ask, if it was quiet and had good oil pressure, what prompted you to pull it apart (luckily)
William Revit

I was expecting that question. I have had an oil leak from the front and rear of the engine. I took the timing chain cover and sump off and put new gaskets in. This cured the leak from the front of the engine but I was still getting a leak from the clutch housing drain hole so assumed either arear crankshaft seal or front gearbox seal. I also had some oil seapage from the head gasket area and wanted to fit a Peter Burgess fast road head along with a Piper HR270 cam. I thought it would be prudent to pull the engine and gearbox to sort the leaks.

With hindsight this may have proved a blessing in disguise as it has show up a less than perfect engine. I have spoken to a couple of reconditioners locally and will give Trevor's contact a call as well. One of the local shops I contacted specialises in racing engines as well as vintage engines. When I get the rest of the engine apart (camshaft to remove etc) I'll take it for inspection.
Steve Church

Good move
William Revit

On a lateral note, perhaos check that the core plug at the back of the engine is in good shape while you can still get to it is worth doing. There may be some other "usual suspects" to look at at the same time which I have forgotten.
Stan Best

Good point Stan. I was going to change all the core plugs anyway, especially that one as it can't be accessed when the engine is in the car. Any tips on installing the new ones?

I'm taking the metalwork to an engine man tomorrow to see what needs doing. I expect the list to include, rebore, new pistons, refurbished crank and new shells. I also need to get another camshaft followers and pushrods. Could be an expensive week next week.
Steve Church

Depends which type you fit - disc or cup. Disc are fitted in the hole bulge facing outwards, then the bulge is tapped towards flat which spreads the edges of the disc into the hole. Cup should be an interference fit, tapped into place with a large socket or similar drift. Use sealant in the hole with both types.
PaulH Solihull

This thread was discussed between 31/12/2011 and 06/01/2012

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