Engine misfire advice

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James k
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Engine misfire advice

Postby James k » Mon Jun 10, 2019 9:00 pm

Hi,
For the last few months my engine has been starting up and initially not running on all cylinders (at least that's what it feels like). After about 10-20 seconds, it sort of 'kicks in' and runs fine. When I drove it on Saturday, it never kicked in and ran badly the whole time. It's running rough, I think on three cylinders, threatening to cut out at idle, especially with the clutch down, and makes a loud rattling sound when going uphill. I can't tell if that's actually from the engine though or just something vibrating in sympathy with the rough running.

Anyway, It's due a service anyway which I'm doing on Saturday. I've ordered all the usual suspects, leads, plugs, rotor arm and cap, plus I'll do an oil change and set the tappets. Is there anything else to look at though? I can't think of why it only did it on startup for a while and now does it permanently.

Thanks in advance,
James

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Re: Engine misfire advice

Postby mowogg » Mon Jun 10, 2019 9:38 pm

Are you able to do a compression test on it? That might give us some clues into what is wrong. Given your description I am suspicious of the head gasket but the compression test will prove or do prove this

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Re: Engine misfire advice

Postby James k » Mon Jun 10, 2019 9:41 pm

I can certainly do a compression test. I can't work out why it would have been doing it on start up though if it was the head gasket.

Bowie69
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Re: Engine misfire advice

Postby Bowie69 » Mon Jun 10, 2019 10:49 pm

Plugs getting oiled up by an oil way leaking into the cylinder.

Been there and done it.... New head gasket cured it.

Can check the plugs for contamination visually, one or more may be black and oily.

oliver90owner
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Re: Engine misfire advice

Postby oliver90owner » Mon Jun 10, 2019 11:06 pm

It may just have needed that service several months ago. A tune-up will show if further diagnosis is required as one cannot always reliably diagnose an engine fault unless the normal clearances are first adjusted to the correct specs.

Spark plugs are a likely culprit - well, one of them.

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Re: Engine misfire advice

Postby Murrayminor » Tue Jun 11, 2019 6:36 am

It could be the timing is out, running on three cylinders, rattling when under load could be pinking.
Before you tear it apart check the distributor is not loose which could cause the issues mentioned.
Worth a try before spending money.
One the timing is set, set the points, gap the plugs check the plug leads are making connection then once all that is done you will have an idea of how she is running.
If there is still an issue you can then probe further, a cylinder compression test looking for equal or close to equal compression across all four cylinders.
good luck.
Proud owner of my first Morris Minor

simmitc
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Re: Engine misfire advice

Postby simmitc » Tue Jun 11, 2019 9:32 am

Like others, been there, seen it, done it. It could be a sticky valve that frees off after running, but the initial description followed by the permanent three cylinder running and noise going up hill makes me verge towards a head gasket. If ony to rule that out, check compression as a matter of urgency and do not run the engine until you are happy that the gasket is OK as running it could damage head and/or block faces.

If compression is OK, then try swapping ignition components one at a time, starting with the dizzy cap. If you swap everything at once then you will never know which bit caused the problem.

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Re: Engine misfire advice

Postby Edward1949 » Tue Jun 11, 2019 2:14 pm

James k wrote:
Mon Jun 10, 2019 9:00 pm
Hi,
For the last few months my engine has been starting up and initially not running on all cylinders (at least that's what it feels like). After about 10-20 seconds, it sort of 'kicks in' and runs fine.
The fact that until recently it "got better" after running briefly suggests either a sticking valve or, more likely, a simple misfire on one cylinder. (Unlike gasket problems which rarely "get better" after first symptoms ) Remove and inspect the plugs and there should be an obvious culprit. Could be caused by worn plug, worn HT lead, hairline crack in distributor cap etc., hopefully a nice simple cheap solution.

Please let us know how you get on !

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Re: Engine misfire advice

Postby James k » Tue Jun 11, 2019 5:24 pm

Thanks for all the replies! I'll begin with a compression test and then try and systematically diagnose it from there. I did wonder about a sticking valve since that would make sense if it was coming free after revving a bit. I hope the head gasket hasn't gone although it's not a huge job to replace. I rebuilt the engine in 2015 and had the head and block skimmed, torqued the head up and then torqued it again after the first heat cycle, everything by the book. I will of course let you know how I get on with it!

Thanks,
James

oliver90owner
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Re: Engine misfire advice

Postby oliver90owner » Wed Jun 12, 2019 9:55 am

There is no point in starting with a compression test if the valve clearances are all too tight. Standard tune up service first, THEN start diagnosing if the fault remains. By all means include a compression test, if felt necessary, at some point but do think about whether it is better to check the compression before setting the valve lash.

I know which way I would do it with the least potential waste of my time. The feeler gauges first!

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Re: Engine misfire advice

Postby James k » Fri Jun 14, 2019 8:17 pm

Hi again,
Thank you for mentally preparing me for the inevitable outcome.

I went through the normal steps of diagnosing an ignition problem. Plugs fine, leads fine, rotor arm and cap fine. I then checked all the valve clearances which were all spot on. I then went ahead with a compression test which revealed virtually no compression on 3 and 4. The head came off and, as expected, the head gasket has blown between those cylinders. I thought at first that it had damaged the head and block where it had blown but this turned out to be copper from the gasket. I've carefully scraped it off both surfaces now and checked it with a straight edge. It appears to be okay.

I'm going to replace it tomorrow. I'll ring around the local parts places in the morning but failing that, I'm only half an hour away from ESM.

I've got several questions now. Firstly, what could have caused the gasket to blow? The engine hasn't been overheated at all and was rebuilt less than 10k miles ago with the head and block skimmed and reassembled by the book. I also don't understand the way that it was only on start up for a while. I can only assume that it was somehow partially blown with a 'flap' of gasket getting back into place once the engine was started. I should emphasise that the engine ran perfectly after the initial misfire on startup and that I took it on several long and hard drives, hence why I assumed it to be something minor.

Secondly, do you have any tips for reassembling the engine, especially with regards to cleaning everything up? Since I was so careful about all the parts being completely clean when I assembled them, I'm a bit worried about the fact that it will be impossible to replicate that same level of cleanliness when reassembling it in the car. Also, should I look for a copper or composite head gasket? This one was copper and I've had a copper one go before on another engine (in reality, I'll probably not get a choice).

Finally, I currently have an 88 degree thermostat in the car. Do you think it would be wise to change it for a lower one to reduce the chances of it blowing again?

On the plus side, the engine looks nice and clean inside. The piston tops and combustion chambers/valves have a small amount of carbon on them but not much at all, the bores are nice and clean and the honing marks are still visible.

Thanks again for all the replies. They are very much appreciated!

Thanks,
James

oliver90owner
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Re: Engine misfire advice

Postby oliver90owner » Sat Jun 15, 2019 9:36 am

I’ve never ever fitted a new thermostat rated below 88 degrees in anything, as far as I know, ever.

Pre-ignition can damage head gaskets (includes ‘pinking’). You might find the rear of the block water passages blocked, causing local overheating? Improper torquing down the head is another. Cheap gaskets (these days) could be another. The list goes on.

simmitc
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Re: Engine misfire advice

Postby simmitc » Sat Jun 15, 2019 10:58 am

Make sure that you get a decent copper gasket by Payen. Last time I ordered from ESM, they were unable to get Payen, but I pointed out that my local motor factor and numerous mini spares specialists had them on the shelf, so there should not be any problem. Cheap gaskets tend to fail.

Although conventional wisdom is to assemble dry, I've fond that a very light smear of grease on the gasket coupled with oiling the threads on the studs tends to prevent (or at least delay) gasket failure.

The startup issue can be that a failing gasket lets a small amount of water into a cylinder (really small amount so that you don't notice the rad level going down) which then makes that cylinder initially unable to fire until the water has been expelled and the plug dried. With modern technology, you can remove the plug abd insert a camera on a flexible wand into the cylinder and then see drolets of water sitting on the piston crown. I think that the water must get drawn in by some form of osmosis as I can;t explain why the colling system does not get (over) preeursied once the engine is running. It's only later that the gasket fails completely.

Every Minor I have ever opwned has blown between 3 and 4 at some point, which is why I (and many others) carry a spare gasket in the boot. One well known MMOC member has told about changing the gasket at the roadside and when the AA turned up, simply asking to borrow their torque wrench - there's a limit to how many tools once can carry in the car "just in case".

It's good to have a positive diagosis, and hopefully the new gaslet will sort it.

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Re: Engine misfire advice

Postby myoldjalopy » Sat Jun 15, 2019 11:25 am

Fit the gasket copper face up - and I lightly greased mine too. Assuming there has been no damage, if you clean the block and head as best you can it will be fine.

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Re: Engine misfire advice

Postby James k » Sat Jun 15, 2019 2:08 pm

All back together and running very nicely now! It took about an hour and a half to get it all back together and there were no nasty surprises. I drove it round the block to get it up to temperature and it's currently sitting with the bonnet open, ready to retorque the head later.

On closer inspection, there was evidence of water having been in cylinders 3 and 4. There were small rust marks and a trail leading back to a water channel. This seems to support the theory that it was leaking a small amount of water causing it to misfire on startup.

Thanks,
James

oliver90owner
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Re: Engine misfire advice

Postby oliver90owner » Sat Jun 15, 2019 5:10 pm

Unless your engine has a special aluminium one :D , it should be torqued hot after first running up to temperature without loading the engine.

Not following the manufacture’s specs can be the start of a failed gasket, sometime in the future.

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Re: Engine misfire advice

Postby James k » Sat Jun 15, 2019 7:45 pm

I've retorqued it now and reset the valve clearances again. I'm sure I've been told in the past to retorque when cold. The workshop manual doesn't mention it but the slip with the gasket said to let it cool fully before retorquing.

oliver90owner
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Re: Engine misfire advice

Postby oliver90owner » Sat Jun 15, 2019 10:54 pm

I can fully understand you might have been told that, but that was wrong - as far as I am concerned

Cast iron heads - re-torqued hot, but aluminium heads must be allowed to completely cool before re-tightening. Presumably you loosened each fixing and re-torqued in the prescribed sequence for fitting the head?

These are all long standing practices when building up an engine. That said, many modern engines use ‘yield point’ head bolts which are tightened down to a specified torque (in stages) then tightened a further specified number of degrees. These bolts must only be used once, but the clamping force provided is more uniform than the old system of re-usable bots or studs.

I suppose you should comply with the gasket instructions, but many instructions are aimed at the more usual alloy heads these days. I don’t have a workshop manual to hand at present, but all my previous cast iron engines have been tightened down when hot. Probably hundreds over the years - the only regular head gasket failure was on the Landrover Sll and Slll diesel engines - a conversion to diesel, of a formerly petrol fuelled design, which was never quite the best engine Landrover ever used.

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Re: Engine misfire advice

Postby James k » Sun Jun 16, 2019 9:51 pm

I did indeed loosen and retorque in the correct sequence. I've been reading up on whether to retorque hot or cold and the explanation seems to be that the steel head studs expand more than the cast iron head so the torque is lower when the engine is hot. Therefore tightening when hot ensures that it doesn't go below the correct torque. Conversely, aluminium expands faster than the steel bolts, hence the need to tighten cold. After some brief research, it seems that the expansion coefficient of cast iron is 12 compared to 13 (fractional expansion per degree centigrade), supporting the `torque when hot' theory. Unless there's some opposing theory someone would like to offer, this seems to make perfect sense.

The question is, is it worth me re torquing again when hot? I have a vague memory of being told that you should only retorque a head once but I can't remember why. Any suggestions?

I have rebuilt a modern engine (Vauxhall Z18XE on a Zafira A) and it did indeed use torque to yield bolts which were torqued and then angle tightened. It did feel like a more reliable method than the method on the A Series.

Thanks,
James

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Re: Engine misfire advice

Postby dalebrignall » Mon Jun 17, 2019 3:52 pm

im glad you are up and running again bga do a composite gasket which might last longer you can order them from bennetts in st albans , ive had a copper payern failafter 3000 miles unfortunatly the quality of the parts is not good thease days
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