Morris Minor Owners Club

Hi all,

Yesterday I picked up my Traveller from a Workshop that has done a paint job. All was fine, engine running perfectly at normal temperatures. After 15 km on a motorway I realized a loss of power and at slow speed that the engine was running on just 3 cylinders. Additionally there was a a kind of „popping“ out of the air filters sycronous with the ignition in one cylinder whe accelerating from idle. Seemed like a backthrow. Naturally the idle was poor.
Checked the ignition system, all was fine and well, changing spark plugs or cables didn‘t change anything. The 3rd cylinder was missing in action.

To my opinion it could be a burnt inlet valve on the 3rd or the head gasket. But would I have that backtrow in case of a broken head gasket?

What would you think about that? Suggestions welcome.

Chris

A couple of years ago when getting the Midget 1275 back on the road after 20 years in the barn I encountered a similar problem. I tried everything I could think of with the carbs and distributor with no real benefit. Still a royal pain to start and then backfires through the carb. The timing was good!
I borrowed a compression tester from our local garage and got 170, 165, 150, 170. Slightly low on 3 but not too bad I thought.
I then bought a cheap leak down test kit and hooked it up to the compressor. The results were diagnostic. I could hear a clear leak between cylinders 2 and 3. There was also a loud leak from 3 into the exhaust.

When I took the head off the gasket was blown through between 2&3. A new gasket and a new set of valves and springs fixed it. The valves were all a bit corroded and the springs were from several different cars. Some single and some double sprung. It ran better than ever after putting it right.

If you have a compressor or access to one, the leak down test may be a good step.

Cheers

Andrew

Thanks for that idea, Andrew. I‘ll try that. But the head has to come off anyway which I will surely not do myself as the engine in it’s actual state was built by a specialized motor workshop. So it’s a case of guarantee as I expect.

Anyway, I wonder how it can produce a backfire in case of a broken head gasket. Ok, in BMS-A engines the head gasket fails mostly between cylinders 2 and 3 due to the thinner wall between them.

Chris

Could it be when the cylinder fires it leaking into another cylinder via blown head gasket who's inlet valve is open, so that's what you are hearing?

Firing order is 1-3-4-2 and cylinder 3 is not working. It must be a cylinder beneeth no.3 but 4 is rarely involved when the head gasket fails and no. 2 is last in the row. If no 2 is compressing the outlet valve of no 3 is open so the gas would leave thru a damaged gasket into the exaust and not the intake. Or am I mistaken?

Chris

When number 3 is travelling down on it power stroke after firing, number 2 is traveling down on its induction stroke so its inlet valve will be open.
You are guessing head gasket failure, wait until head is removed or do a compression check. If failed gasket between cylinders two compressions will be low.
If you don't have a tester, remove all plugs,ingnition off, turn engine with starting handle thumb over each plug hole in turn and feel for compression differences. If 3 is low and you can hear it firing in intake then possible inlet valve issue
Have you removed valve cover to make sure No3 valves moving ok and valve clearance correct.
With the engine running remove oil filler cap and see if high crankcase pressure ( blow by) suggesting a piston issue.

@Bill,

I‘ll do a compression test tomorrow first. But I will not touch the engine furter more because of a possible gusratee issue. All the rest is left to the engine building workshop.
But anyway the steps to a diagnosis are intresting.

Chris

Good luck, hope your warranty covers the repair.
Please post when you know what the issue was as it will help others in future when searching posts for answers.

As expected: absolutely no compression on cylinders 2 and 3. a test of pressure loss with compressed air showed the same: pressure applied on #2 air comes out on #3. An endoscopic check showed no abnormalities at the valves or pistons. So, we‘ll know more if the head comes off.
Anyway, as it needs a new head gasket I‘ll give it a Metro 1,3 Turbo-gasket. I hope this will stand the load of my high compressed marina engine better than the ones I used before. The engine has had a compression ratio of 10,7:1 which will now rise a bit further. Good for the torque but bad for the temperatures.

Chris

What head have you got?
Mine is a big valve Metro head on a 1275 ex- Marina block - wondering whether a Metro 1.3 turbo gasket would work for me as well?

As I wrote in a different post we had measured a high difference in engine temperatures between the front end and the back end of the engine at an earlier stage of development of this engine. This was 20°C between termostat and heater outlet. That’s why I first made a shunt between the heater outlet pipe and the back flow pipe coming from the heater and inserted a seperated heater valve behind that shunt. This should provide a steady and so improved circulation of coolant even if the heater is not in use. That reduced the difference in temperature seriously but not enough to my opinion. So I installed an electrical booster pump prior to that shunt which reduced the difference to 2-3°C.

As the engine temperature at my gauge never exeeded 85°C I wonder how the head gasket could fail.

The last option is to switch to a completely electric cooling system with electronic temperature control, a bigger electric pump and removed waterpump and termostat.

Chris

@ndevans,

The head was a 1275 head, don’t know what origin. But it is not much left on that head that is original exept the casting. The head was fully ported with bigger valves to the maximum size, strengthened double valve springs an a fast road cam. It’s timed to 107°

As a good friend of mine and former Mini racer told me the Metro Turbo 1300 head gasket will fit any 1275 BMC-A engine that is not overbored and should be the one to use in those high compressed engines that produce a lot more heat than a standard engine.

Chris

Ok thanks, worth knowing. I had a series of head gasket failures a couple of years ago, each lasting 1000-1500 miles. I had the head squared off and that seems to have cured it, I've now gone around 12000 miles without failure *touches wood*. I'll have to check what head gasket I put on.

And: measure the temperature at the head front and backend. I guess you will be surprised.

Chris