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MG Midget and Sprite Technical - can belt or chain

Hi,
I have stripped my engine (1275 +.0020) and it will be having the crank, rods and flywheel lightened and balanced next week plus any other machining needed. I hope the bores will just need a hone as the engine has only done a couple of thousand miles since the last rebuild (it is a long story and I will explain if you want me to).
During the rebuild I intend to fit a new can, probably a Kent 276. It will have a Peter Burgess head and 123 dizzy.

I am toying with replacing the timing chain with a belt. They are quite expensive but should be quieter and keep the can timing accurate plus it reduces vibrations being transmitted from the crank to the valve gear.
Has anyone experience of a timing belt on an A series and what are your opinions? Is it worth it?
Thanks
Dave
Dave Brown

I have a timing belt on my 1420cc and haven't had any problem but if I was to do it again I probably wouldn't bother. 25k mile belt change intervals so if you're worried about chain stretch change it then also. I never noticed any noise when I had a duplex chain fitted to the previous engine but then plenty of general noise to drown it out. While I never heard it a few people mentioned a turbo like whine from the car related to engine speed when driven in anger which was put down to the belt drive. You take your choice and pay your money.
David Billington

I agree with David. At least for road use, on a fairly mildly tuned engine, I can't see much point.

I've never broken a timing chain, but I have broken belts on other cars. As for the timing, yep if the chain is old(and they can live for many many many tens of thousands of miles), it drifts a bit. But how much, unless you are measuring your hp or 0-60 speeds, would you really be aware of timing drift -- on the road? Lumpy tickover? You get that from a hotter cam anyway. Noise? I've never had one(duplex) so worn that it slaps against the timing cover. But some might have done.

I'd stick to the chain.

On the other hand. If you have a belt, you'll get to avoid the oil sucking problem altogether. Your engine will be immune to it. :).

Lawrence Slater

"If you have a belt, you'll get to avoid the oil sucking problem altogether" - Why? why does a belt drive eliminate oil sucking?
Guy W

Chain, every time.

The belt will eliminate oil-sucking from the timing cover because there is no oil in there.
Dave O'Neill2

Presactly. ;).

Unless you move the breather to the pump take-off, and it sucks oil from there. But I drift. Slapped wrist. I'll stop. LOL.
Lawrence Slater

The breather is an issue I hadn't thought about. If I go belt, I will have to vent the crank case somehow.
It is looking like a new chain.
Can anyone convince me to get a belt?
Thanks
Dave
Dave Brown

"from the timing cover because there is no oil in there"

Mmmm! I agree, there should not be, but -

I fitted a timing belt, with vernier adjustment, about 6 years ago to our 1380 and did not notice any difference in noise or smoothness.

A couple of years later I fitted a new Piper billet cam, together with a new belt as a precaution, and about 3,000 miles later the belt stripped a number of teeth and ended up bending all 8 pushrods and valves. Also needed a complete repatriation back from France, spoiling the end of our holiday.

Investigation showed that the grub screw in the timing sprocket end of the cam had not be tightened and allowed a small amount of oil into the belt area, which weakened the belt. Fitted a new vernier duplex chain setup and no problems, noise or anything else since!

Current Piper cams come with the grub screw loose and instructions about fitting and tightening it.

Stick with the duplex chain would be my suggestion.
Richard Wale

Picking up on the breather comment, the belt kit I had did have a breather take-off, but it had a very small bore and the oil consumption was very poor. After refitting the duplex chain and timing cover, the consumption went back to around 1,000 per litre, which is OK.

Another reason to stay with the standard chain and breather system.
Richard Wale

Both the post 2005 MX5 and post 2010 Subaru have gone back to timing chains from belts.

In saying that some BMW owners are getting bills of over 1,000 to repair their engines after the timing chain has gone wrong.

eddie
Eddie Cairns

Like anything it is down to the details of the design. A mate works in engine design and we have discussed this issue and it is largely down to maintenance costs, a belt will need to be changed at regular intervals which depend on the design, IIRC my TDI Passat is 60k miles or 6 years, my old Lancias were 25k miles on the dot but quite easy to change. Chain drive can be designed to last the expected life of the engine so sounds like BMW cocked that design up. My mate had a mk3 Escort and that had belt failure at about 29k miles, all valves bent, and the recommended change interval was 30k so he wasn't happy, a relative in the trade mentioned that Ford had originally said belt life was the life of the engine then with experience it kept being reduced to eventually 30k.

BTW a piston expert at Ricardo looked at one of his pistons in a Ford Xflow and noted the valve impact mark from prior to his buying the Caterham and said that piston valve contact can lead to subsequent piston failure. I know many just replace the valves but pistons as well can get expensive, works for most people with just the valves.
David Billington

I have always preferred chains on anything. Interestingly other things can cause cambelt breakage. A workmate had one go on, if I remember correctly his Renault, which when repaired turned out to be caused by waterpump failure. Ironically it had been booked in to have the pump changed the next day.

Trev
T Mason

So this belt kit stops the oil flow from the front cam bearing does it? I suppose it must do, otherwise the belt will be running in oil, Or does the kit involve some arrangement so there is an extra oil seal and front plate of some sort to keep the belt outside the normal oily place?
Guy W

midgethere are various on the market, but all keep the belt dry.

These people(KAD)do a kit too.
Lawrence Slater

Yes Lawrence that is where I was leading. The belt system must have a means of controlling oil flow into the chaincase, which rather points at a solution to your chaincase oil problem. Funny how these things go in circles!
Guy W

Trev,

A number of the VAG engines also use the water pump driven by the cam belt so the issue is a problem with at least a few manufacturers. I was aware of it as a guy I knew changed the cam belt on his Audi but didn't do the pump and it failed shortly after doing a lot of damage so when mine was done recently I said to change the pump if any question of a problem and when I got it back they had changed it and the garage owner ran through the bill and mentioned the water pump change was done as a matter of course as not changing it could be expensive. They also called me to ask about changing the radiator as that was weeping, I knew that, and as the rad has to be removed to change the belt the only cost was a new rad, good after market at 60 + VAT, IIRC the new water pump was about 32 and the belt kit around 100 + VAT plus fitting so the water pump replacement was cheap insurance and I'll likely run this car into the ground like the previous ones.
David Billington

I never understood the belt argument for ...

Even if it makes a quite run sound, have you heard the exhauste sound, what about the tranny noisen, or the road noise thur the tires and suspension...maybe a MX5 is what you need

Duplex with a veiner camshaft gear, in fact id cut a 9 inch hole in the timming chain cover and screw down a plate so you can have easy acess to the camshaft viener gear to easy adjust without the hassle of removing the timming chain cover

I cant hear any noise on my chain even before the rebuid

But thats me

Prop
Prop and the Blackhole Midget

The belt makes less noise when the engine is cold. Never had a belt snap. Currently running with a chain.
Daniel Stapleton

David, yes was aware that it applied to other models too. Cost is another good reason in favour of chains.

Trev
T Mason

David B

If you have the B5 Passat with north-south engine, you don't need to remove the rad to replace the belt. The front panel unbolts and can be slid forward on long bolts or M8 threaded rod into the 'service' position.

There is enough flex in the hoses and electrics to allow for this.

Apparently it is common practice to replace the water pump at the same time, due to the low cost, but high cost of removing everything again to replace it at a later date.

When I did mine, the pump was about 23 IIRC.

Dave O'Neill2

There have been several documented belt failures with all the A-series conversions.
Yes the chance is small but the consequences are big.

So forget about the small advantages and go for the durability of a chain
Onno K

A chain will stretch over time and thus vary the cam timing slightly whereas a belt always remains the same.
Daniel Stapleton

I used a belt on a 1380 mini years ago, it was very quiet compared to the worn out chain it replaced, never had any problems with it and it looked good. The midget has a duplex chain and is quiet enough for me and will not need to be replaced any time soon.
The frequency for belt changes is variable throughout the various automotive manufacturers, I don't know how often the "a" series conversion needs to be replaced but I can tell you my motorcycle has to have it's cam belts changed every 2 years or 6k miles.
I would stick with the chain.
S BREEZE

Wasn't there a gear driven cam kit available, ISTR?

Similar to the Honda VFR.
Dave O'Neill2

I had the gear driven kit in my old frog Dave - originally designed by Slark and then taken up by MED. Nice piece of kit but expensive, and when I snapped the crank....
John Collinson

hi I have had both I will not go back to the belt you will need to replace it at 10.000 miles or 2 years its a pain in ?? a good veiner camshaft gear and chain is the way to go.Ian
ip blain

"A chain will stretch over time and thus vary the cam timing slightly --- "

This is true, and whilst I think it's not sufficient reason to fit a belt, it has set me thinking about the oil sucking issue again. (as it cam up a little way down.)

Quick recap.
Oil gets sucked into inlet tract via the breather on timing chain cover, because there is at a certain point in the warm up of the engine(or indeed cool down), too much oil in cover, and the drain holes can't cope with it.

What actually happens when the timing chain stretches? How does the cam timing vary?

Rather than (as some might suggest it would) spoil this thread, I'll move this theorising to the current oil sucking thread, "Engine Breather and HUUGGGGEEEEE blue clouds !!" Hope to see you there.
Lawrence Slater

Depending on how accurately the cam timing was set when the engine was put together, a little stretch in the chain may improve the performance!
Dave O'Neill2

Hi,
Thanks for all the input and discussion. I think I am going to stick with the chain as there does not seem to be any reason to part with hard earned cash for a belt that gives a quieter engine but introduces the possibility of failure and regular replacement.
Thanks
Dave
Dave Brown

Chain seems perfect to me Dave. Using the KISS principle.

I cannot help but think the a series oil burning issue is ring problems in most cases. This can be caused by poor honing, not enough left to hone after boring, using oil that is too good to let the engines bed in etc etc. This seems to be a fairly modern problem manifesting itself to me. Even the factory had problems from new with poor work on the bores of Metros and subsequent oil burning.

I had a +60 engine do this oil chucking problem. Tried everything we could think of. In the end bored out to +72 with good quality pistons and all else same, problem stopped instantly. I could still see boring tool marks just under the surface of the honing on the +60

Peter
Peter Burgess Tuning

Hi Peter.
"This seems to be a fairly modern problem manifesting itself to me -- ".

Is circa 1979 when I first had the problem, really a modern problem?

Not burning oil in the sense that it bipasses the rings and rises into the bores, where it gets burnt. Instead, oil is sucked up the breather tube and into the inlet, but ceases when the oil is warm enough.
Lawrence Slater

I still think this is excess blow by when cold.

Peter
Peter Burgess Tuning

If it was that bad, wouldn't it show up on a cold compression test?

Given how many people have experienced this, AND rebuilt their engines with new components/bores, and having used different machine shops all over the country, I just don't accept that all these engines are suffering from excess blowby.
Lawrence Slater

Would checking the crankcase pressure with a manometer determine if it was a blowby issue?

Charley
C R Huff

It might well do.

Peter
Peter Burgess Tuning

It might determine how much blowby there is, but how could it determine why too much oil is getting into the timing cover?

P.S. Dave.
I hope you have all you need regarding the chain/belt choice, as this thread seems to be turning into the oil sucking thread again. I did try to divert it to where it belongs. Honest. See my post a little way back. LOL.
Lawrence Slater

Such is life Lawrence and the oil thread is getting laden.
The only way for venting is the front cover, there is no real way for pressure to go up to the head area as with B series engines. That may explain why dipstick lifting common with A series esp race engines where high rpm blowby is much more likely. You could try a plate over the vent to the front cover to try and drain back the oil before it gets to the front cover? Also remember the engines tend to blow past the rear scroll, again a sign of blow by esp when cold.

The A series has been around forever and a day and it does seem to me to be recently folk are talking so much about oil being shoved out. In the past we have only had moaning about oil down guides when worn rockershaft allows too much oil up to head and cannot drain back to sump fast enough. Hence fitting oil seals on ex guides these days just in case. Some A series in high tune nip ex valves in if seals fitted....can't win can we :)

The Metro problem was 70s/80s and a factory balls up whereby thin oil was burnt like no tomorrow (maybe a clue about oil viscocity too)

At what point of engine life did yours start blowing oil out in 79?

Peter

Peter Burgess Tuning

High Peter.
There's the misunderstanding. Not blowing out. Sucking up. Often little or no scroll leak at all, and no oil being blown out of the dipstick hole.

And this is not a recent phenomena. I've found dozens of threads in the archives describing exactly the same thing, going way back. When I first reported this(mine) on here back in 1998, nobody on here had ever even heard of it (at least nobody who responded). But when I dug into the archives last year and found loads more incidents of it, I realised that this was because it was either being poorly described, misinterpreted, or flatly stated by others, as being impossible. It's taken a lot of convincing.

Rather than argue the point about blowby here, and also describe all over again how mine sucks oil, and thereby create another multi hundred post thread, could I direct you to the other threads ? :) :).

Particularly this one, started by Bob beaumont in Feb 2012.
"engine breather" It's in the Midget technical archive.
Last post by me as it happens, Posted 22 August 2013 at 21:40:59 UK time.

Although Bob's has been reslolved, the thread is pretty much chapter and verse on the subject. It spawned several other pretty long threads, in which it became clear that others have the same problem. Hence the most recent lengthy incarnation, "Engine Breather and HUUGGGGEEEEE blue clouds !!". Courtesy of Malc Gilliver. :)

Indulge and enjoy, if you feel so inclined. :).




Lawrence Slater

Lawrence,

You asked: It might determine how much blowby there is, but how could it determine why too much oil is getting into the timing cover?

If you determine that there is excessive blowby (and crankcase pressure), then it may be that the force of the gas flow leaving the crankcase and entering the timing cover is preventing the oil drainback. To determine if that is so, the excessive blowby would have to be eliminated without changing the breathing arrangement. Then, see if the oil sucking problem is resolved or not.

Charley
C R Huff

Hi Charley.

I suggested that crankcase pressure forcing the oil back through the drain holes might be the case, a very long way back, either in this thread or another. However the concencus was that it wouldn't happen.

And if it was crankcase pressure, then given that I had more blowby before I first rebuilt my engines ( -- I had cracked rings and low compression, as a result of the compression being lost to the sump -- ), why didn't I have oil sucking when I had those cracked rings? I had it afterwards, with far better compression, with new pistons/rings fresh bores etc. This is what Tim is experiencing if you read the engine breather thread

I don't doubt that crankcase pressure might play a part, but all these engines have blowby, some far worse than others, and yet only SOME engines have oil sucking. There has to be a prime mover, yet to be identified, without which oil sucking doesn't occur. I don't believe that crankcase pressure is the prime mover.

Lawrence Slater

Does 'oil sucking' occur if the breather is not connected to a lower pressure output such as the filters/carb bodies? IE vent to atmosphere which would negate sucking.

The rings usually snap when the pistons are removed, the rings passing over the wear ridge at the top snaps the rings and the 'stripper' thinks the rings were already broken, hence the low CR. Poor boring and/or honing or even poor or non glazebusting can cause excess oil burning and blow by.

The 1275 seems especially prone to the problem. Lozenging of the bores may play a part, do less folk with thick flange engines have the problem? Assuming the thick flange variant is more rigid (or not).

Peter
Peter Burgess Tuning

Hi Peter.
By definition oil "sucking" can't happen if there is no suction, or suction so low that it can't suck hard enough. The tiny amount of suck, such as there is, by connecting the breather pipe to the rear of the air filters, is insufficient to suck the oil up. And it isn't enough to create sufficient -ve pressure in the sump, to prevent the rear scroll from leaking.

Just leaving the timing cover breather pipe open to the air, doesn't cause the oil to flow out. It needs some suck to bring it up. What does come out of the open pipe is fumes, which make the engine bay stink, as you'd expect. And remember, oil sucking only happens at the point that the oil/engine are at just the right temp.

Both my Sptire engines are thick flange.

On my Midget, I had low compression on a couple of bores, so I suspected a blown hg. However as it didn't look as bad as I expected when I pulled the head, I also dropped the sump, and pulled the pistons on the low reading bores. The pistons came out with the rings unbroken, and went back the same way. I've done this on a few engines. I don't believe I've ever cracked a ring either fitting or removing pistons. I'm careful not to. The ridge has to be pretty bad to stop the piston being pulled.

Not disputing blowby or glazing as a cause for oil consumption and smoky engine. But it is not the cause of oil sucking.

If excess oil can rise up the bores past the rings and into the combustion chamber, then so can can and do gasses blow down into the sump. My experience of these engines is that a smoker smokes hot or cold, and usually worse when hot. But the oil sucking STOPS, when the engine is hot. I'm as certain as I can be that blowby as a cuse to this, is a red herring.
Lawrence Slater

This thread was discussed between 23/03/2014 and 30/03/2014

MG Midget and Sprite Technical index

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