Moss Motors, Ltd

Hi folks,

 I think I might have cause to revisit last year's engine rebuild project... but would be grateful for advice & discussion.

 Both before, and after the rebuild, the engine is noisy immediately at startup, quieting as soon as oil pressure registers on the gauge. A definite rattling sound, which I was somewhat unhappy with in iteslf, but put down to the obvious lack of oil until the pump refilled the system. However, now that I cured some other noises, discussed elsewhere here (rebuilt gearbox, new clutch etc.) I have also noticed slight tapping/knocking sounds from the engine, notable under two conditions as follows.

1) Steady driving, just at the point where power is maintaining speed and "soft pedaling". Rapid acceleration or lifting "the gas" makes it go away.

2) Revving the engine (car in neutral and stationary) say from 1500 or 2000 rpm, there is just a hint of rattle/knock in one particular range of rpms as the engine speeds up. It can be heard inside the car and from under the bonnet, and I think sounds like it comes from the engine. Under the bonnet, it seemed most noticable from the distributor side of the engine.

The only thing that was not really touched when I rebuilt the engine was the crankshaft. I did have the machine shop check for cracks, measure the journals for size and polish them, but they gave me the thumbs up, specifically saying there was no need to regrind, and to rebuild with stock size bearings, so I took that advice. Obviously, I'm now begining to wonder whether this area really needs some attention. for what it's worth, oil pressure seems to be well behaved, at 65-70 psi according to the gauge during normal running.

Since I have the time at present, It would not be a disaster to have to pull the engine, investigate and make right as necessary. I'd rather do this than ignore something that could result in more serious damage later on, but thought I'd post here before going further along this track

Thanks for listening,

Ed

 

 

 

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I want my MGB

Ed,

Did you replace the pistons and wrist pins? How about the pin bushings in the connecting rods? Were they checked/replaced. Were the rods checked/rebulit in general?

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Hi Bill,

Thanks for the reply.

Pistons & wrist pins were replaced (following +0.040 overbore). When the piston set came back from the shop with the reworked block, the machinist had fitted them to the rods and said I was good to go. I never saw the rods completely dismantled, as the shop said not to bother pulling everything apart possibly to aid them in retaining correct order - so the block was delivered with crank and old pistons still in place.

It is quite possible that something was overlooked, as all is not quite as it should be.

Ed

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I want my MGB

Ed,

Do you mean that the old pistons were still in place on the rods? If so, you can bet the rods were not resized/straightened/checked for pin bush wear. These things really should be done in an overhaul. The machinist, if he's competent and caring, will tell you that. If he knew you weren't going to use the old pistons again (surely he knew) then there would have been no need for him to reinstall them onto the rods, as it was no longer important to keep them in order. Come to think of it, why'd he want them in the first place?  Hmm...

If there's one thing I've learned (the hard way) in all my time in this occupation, it's that there's only one way to do an engine rebuild. Do EVERYTHING, do it thoroughly, do it with the very highest quality components you can find, break it in carefully, and you'll likely only do it once.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Thanks Bill, just to clarify the sequence of events...

Engine was delivered to the machinist with crank & old pistons undisturbed. At his request, the new piston set was also provided so that he could ensure an appropriate fit. These pistons were supplied with new pins (Moss cat. no. 420-415, 2.4" long,  floating pin type AE brand)

When I collected everything from the machinist, he'd fitted the new pistons onto the rods, and gave the impression that things were ready to go. I took that literally and continued rebuilding. Nobody, with the exception of myself, is responsible here, though I would plead inexperience m'lud

This might sound like a stupid question on my part, but would you advise against running the car?

Ed

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I want my MGB

Ed,

As long as the oil pressure holds up I doubt you're causing any further destruction, but I'm not there to hear it...

Did you get an invoice describing the work? If so, what's it say?

Bill

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

not much detail, the relevant lines read:

 "check housing bore on mains - OK",

 "clean housing, bore on rod - OK"

 "R&R pistons"

Nothing obvious regarding the small end bushings, checks for straightness etc. He claimed to have checked everything for balance too, but there's nothing on the invoice slip.

The thing is, part of me wants to go back in and check things out now I know a bit more about it. Of course the rest of me doen't want to tear it all apart again without good cause or a reasonable expectation that I can make a difference. Many times, the perfectionist wins

Ed

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I want my MGB

Ed,

I can't tell from that information if much of anything was done. It doesn't even mention boring and/or honing the block! That was done by the same place, right?

Yeah, I know about that annoying perfectionist voice that just won't go away!

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

... no the boring & honing work was listed, as was a skim of the top of the block. I just skipped a few things that were obviously non rod/crank related.

Ed

 

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I want my MGB

OK, supposing I want to go over the engine again.... The main and rod bearings on the crank can be checked with a Plastigauge or similar kit, but I don't know about the wrist pins & bushings. The tolerance is very fine, according to Haynes, between 0.0001" and 0.00035". How would I go about assessing this and the general condition of the rods, or is it time to call the professionals?

I suppose an outline plan would be to remove the engine, and look critically at the main and big end bearings first, just to see if there is anything obvious lurking there, before the head & pistons are disturbed.

Ed

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I want my MGB

Hmm, don't know if this adds anything to the diagnosis, but the (or a very similar) noise is apparent if the engine is loaded up e.g. conditions of a "hill start" (an infamous part of the UK driving test) where the clutch is allowed to bite before the handbrake is released.

Definite rattling/knocky sounds..... I'm teetering on the edge of buying a tilt lift for an easier time of engine removal, so you can see where this is heading. Any recommendations?

Ed

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I want my MGB

Ed,

Actually, the ones at Harbor Freight (Fright?) don't work so badly if you lubricate the acme screw. Don't forget to position the crank away from the lift boom!, otherwise it becomes quite uncomfortable...

Your previous post comes just as I have been contemplating writing one concerning just what needs to be checked and or machined, cleaned, and balanced during a thorough overhaul. It's a good size list. I'll try to explain each operation and the reasoning behind it if there is enough interest. Any takers?

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Hi Ed,

 New member, old MGB owner here...

I had this very problem many years ago in a Lotus engine.

Just a guess on my part, but I might suspect your crankshaft thrust washers are out of spec. If they weren't replaced at rebuild time, they could be worn thin. The "thin" thrust washers allow a tiny bit of fore-and-aft movement of the crank under just the conditions you describe. The sounds you describe are exactly the same as my old Lotus made before I found the culprit.

 One good thing about this - a new set of thrust washers is about $20. A bit of a pain to change, however, but better than some of the alternatives.

My '69 MGB engine now has almost 200,000 miles on it. Rebuilt about 14 years and 100,000 miles ago. At the time of rebuild, the crankshaft was still virgin, well within stock spec and only received a polish and was put back in with new stock bearings (and properly measured/adjusted thrust washers). Still has over 60psi oil pressure, uses hardly any oil between 5,000 (or so) mile changes. So IMHO your crank is probably A-OK, at least based on my experience.

 

As I said, just a guess & some more food for thought. Good luck!

 

Tim...

To Bill,

Yes please, I'm always interested to learn more, if you have the time to explain.

 To tck,

That's an interesting point. I did replace the thrust washers with new (std) but may have carelessly overlooked an excessive end float contition.

Think I'll be getting hands dirty again pretty soon... I'm just not happy with things as they are, but on the plus side, I do enjoy the learning process - and that is partly what this car is about.

Thanks to everyone for input and patience with this, and my other novice ramblings under the bonnet of my car.

Ed

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I want my MGB

Ed,

My experience is that this is not as critical a thing in B Series engines as many others, and that it's unusual for the thrusts to have serious wear due to the fact that the are well lubricated and quite generous in size. Generally, if the thrusts are in trouble on an MGB engine, the rods and mains are wasted and the crank is in trouble. Of course, the end float is indeed one of the many things which should be checked when building up any engine.

I'll try to find some time to compile a bunch of information on engine machining operations.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon