head gasket?

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dudload
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head gasket?

Post by dudload »

hi all, been a while!

Over some recent trips, i've become increasingly worried about the rattling sound that my traveller engine makes at certain rpms. When going between 40-50 in 4th, the engine sounds very loud with a noise that can only be described as a mix of knocking/rattling that goes away when over these rpms or opening the throttle fully.

I've played around with timings, and retarding the ignition does help, but only goes away when the ignition is so retarded that performance is poor. Also, recently the engine has had poor performance from cold, and quite often runs rough / 3 cylinders for a bit before it warms up and runs smoothly.

Now, i called a garage to ask if they could have a look and they were certain from the description that it was a head gasket issue between 3 & 4 cyl. I'm not convinced as I did a compression test a few months ago (rattle still present then) and they seemed fine. No 4 plug is normally sootier/a little oily than the rest, but mix looks fine and is a biscuit brown on 1-3. There's no substantial water loss - oil pressure is a little low and goes to about 15-20 on hot idle.

I'm going to do a comp test tonight and will post the results, but was wondering if anyone had thoughts before i go to the hassle of replacing the gasket. I'm wondering if it's bottom end / camshaft related instead?
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Monty-4
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Re: head gasket?

Post by Monty-4 »

A compression test and/or whipping the head off will let you know what's up. I'd personally hope that it's the HG rather than the bottom end!

You seem to know what you're doing but it might also be worth checking the vacuum advance mechanism, given your description of it being sensitive to speed and throttle input.
68' 4-door Saloon, another 'Monty'.
kevin s
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Re: head gasket?

Post by kevin s »

The poor starting and running on 3 when it started was just like ours was when we removed the head the gasket it had sooty marks between the cylinders. We ended up replacing the entire engine so no idea if it was just that but it certainly starts perfectly now.
oliver90owner
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Re: head gasket?

Post by oliver90owner »

I wouldn’t be convinced, either.

Tight valve clearance might be reason for a miss at cold, but also could be plugs or even distributor related.

Most things can be checked without unnecessarily removing the head. A compression test is certainly the better first option! If it is a head gasket, compression would usually be low on two adjacent cylinders and it might start up on two cylinders.

Your problem seems to be on only one pot, so concentrate on No 4. Swapping plugs to see if the fault goes with the plug or stays with the cylinder is a good start with one sooty plug.

Finding the cylinder, which misses on start up, would be good. Removing plug leads until the engine speed does not alter is one way. Measuring temperature with an infrared gun is another.

What would you call a ‘substantial’ water loss? I would not expect any.
dudload
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Re: head gasket?

Post by dudload »

many thanks for the replies - didn't get round to testing compression last night (unexpected post work pub visit), but will do tonight.

on water loss - i probably need to top up a bit every few hundred miles, but i think there may have been a small leak on the bottom hose and tightened that up just recently. the joys of a morris!
dudload
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Re: head gasket?

Post by dudload »

quite a bit later than anticipated, compression readings below:

1 - 175
2 - 165
3 - 180
4 - 180

All seems fine to me, apart from the small (<10%) difference between 2 and the rest. one thing that did strike me is that 3 & 4 plugs were quite oily, so i wonder if top hat seals certainly need replaced? Would explain rough starting, but not the noise.

Looks like the only thing to do is call the garage for them to have a look in person?
oliver90owner
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Re: head gasket?

Post by oliver90owner »

Seems like the garage diagnosis was far less than useful. What about the other suggestions?

I doubt it is a head gasket problem.
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Re: head gasket?

Post by mowogg »

Did the car used to run OK?

It looks like you have a higher than normal compression. Perhaps the head has been skimmed?

Given the compression readings and the description it sounds like pinging at certain revs.

Are you sure you have the right dizzy and advance curve fitted?

Perhaps you could try some higher octane fuel
dudload
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Re: head gasket?

Post by dudload »

It's always been a bit noisy at certain revs, I changed out the dizzy with one from a accuspark for the Morris, so hopefully not timing but you never know!

I only ever use super on the car, so no higher to go unfortunately.

On the readings, they are a little high, but intend to not trust the absolute reading from the import tools. The differential should be comparable however!

Probably needs a trip to the garage to inspect... Mystery continues...
oliver90owner
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Re: head gasket?

Post by oliver90owner »

Starting up from cold is a clear problem but one that can easily be searched out by some simple checks/adjustment. No3, being low might well be a valve issue.
Chipper
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Re: head gasket?

Post by Chipper »

Sounds like maybe a carbon build-up on cyls 3&4, possibly due to valve stem oil seal failure, hence the higher compression readings.

Perhaps try some engine cleaner such as Seafoam and give it a damned good thrashing to clear out the crud...
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Bowie69
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Re: head gasket?

Post by Bowie69 »

dudload wrote: Sun Aug 22, 2021 5:24 pm quite a bit later than anticipated, compression readings below:

1 - 175
2 - 165
3 - 180
4 - 180

All seems fine to me, apart from the small (<10%) difference between 2 and the rest. one thing that did strike me is that 3 & 4 plugs were quite oily, so i wonder if top hat seals certainly need replaced? Would explain rough starting, but not the noise.

Looks like the only thing to do is call the garage for them to have a look in person?
I have had similar, the headgasket had blown allowing oil into 3&4, meaning on startup it would be rough until there was enough of a drying of the plugs to actually make a spark properly, then it smoked for a bit and cleaned up mostly when driving.
New head gasket alone fixed the problem. The blown one was fitted by someone else as a recon drop in engine, and was copper, and failed within a few years and hardly any miles. A composite one went on and have been fine ever since.
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Re: head gasket?

Post by mowogg »

Just reading through the comments again. How sure are you that the spark plugs are good?

It might be worth looking at a cooler temperature?
dudload
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Re: head gasket?

Post by dudload »

hi all,

so, i completely changed the head on the engine (per the other thread on here), and whilst doing discovered that it was a 948 head on a 1098 block.

I've only lightly run the engine round the block and haven't been on a big run, but it appears i can now advance the ignition much further than before before pinking.

which got me thinking.... could the problem (knocking / rattling at certain revs) have been that the 948 head, being on a 1098, was giving too high compression, knocking out the advance curve and causing pinking/detonation at certain revs? Now that the 1098 head is on, hopefully the larger combustion chambers and associated lower/correct compression can accept the advance curve correctly?

could be miles off, but interested what you guys think...
myoldjalopy
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Re: head gasket?

Post by myoldjalopy »

So, presumably, you found the old gasket to be OK when you removed the head?
dudload
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Re: head gasket?

Post by dudload »

yup, old gasket was 100% ok. pistons and head had quite heavy carbon deposits, but aside from that all seemed ok.
jagnut66
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Re: head gasket?

Post by jagnut66 »

New head gasket alone fixed the problem. The blown one was fitted by someone else as a recon drop in engine, and was copper, and failed within a few years and hardly any miles. A composite one went on and have been fine ever since.
And there's a debate that has been raging and will go on forever: copper vs composite.
I have used both, had both types blow but also had good use out of both types.
One of the key things is to make sure that your head and block (the mating surfaces) are flat.
If not you stand no chance.
Best wishes,
Mike.
1954 Series 2: 4 door: "Sally" -- Back on the ground with (slave) wheels and waiting to be resprayed......
1970 Triumph Herald 1200: "Hetty" -- Driven back from Llangollen in Wales (twice.....)
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Re: head gasket?

Post by liammonty »

dudload wrote: Thu Sep 09, 2021 9:26 am

which got me thinking.... could the problem (knocking / rattling at certain revs) have been that the 948 head, being on a 1098, was giving too high compression, knocking out the advance curve and causing pinking/detonation at certain revs? Now that the 1098 head is on, hopefully the larger combustion chambers and associated lower/correct compression can accept the advance curve correctly?

could be miles off, but interested what you guys think...
Yep - you could well be on to something, as the head chamber volume on the 948 head is 24.5cc, vs. 26.1cc on the 1098 (presume 12G202?) head. So with the compression ratio back where it should be, you should be able to have the advance required without experiencing pre-detonation, and therefore performance will be up. The 12G202 head also breaths slightly better than the 948 head.
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