Just done compression test

[James k]

Hi,
A couple of months ago I fitted a new electronic distributor and started a thread about a lack of power with it. I've now got back from working in Germany and, as per Roy's advice, have done a compression test (hot engine, throttle down). The results are:

Dry:
1: 130
2: 130
3:135
4:125

Wet:
1: 160
2:160
3: 175
4: 170

I assume this accounts for the lack of power and means that the piston rings need replacing. Is this correct?

I also checked the air filter as I was advised and it turned out to be absolutely filthy. I've ordered a new one.

Thanks
James

[bmcecosse]

Hmmm yes - pretty low figures there 'dry'.

[James k]

Are they low enough to significantly affect power?

[bmcecosse]

It will run - but obviously not best for 'power'. Should really be 160 DRY

[James k]

What I mean is that my car is rather lacking in power and struggles a lot on hills. Would replacing the rings make a noticeable difference?

[simmitc]

It depends upon the condition of the rest of the engine. Checking valve clearances and setting points gap, plugs gap, timing, and the new air filter will all make a difference. Also check that there are no brakes binding. with everything services, you might be pleasantly surprised. Is the engine using much oil?

[bmcecosse]

It's always going to struggle with that low compression - there's no knowing if 'new rings' will be worth doing - or if a full rebore with new over size pistons is required. The engine number doesn't happen to have an ' L' in it ???

[James k]

I set the valve clearances a few months ago but I'll check them again, possibly tomorrow. There are no points but I'll check the plug gaps. I don't think the brakes are binding as it rolls easily. I set the timing when I fitted the new distributor using Roy's method and I think it's the best I can get it. The engine does lose oil but I don't know how much it's actually burning since it's definitely leaking oil (just a slow drip). I did change the dashpot oil today from 3 in 1 to 20w50 and that has made an improvement and got rid of a flat spot that was annoying me.

The other thing is that, as well as struggling uphill, it really struggles to get past 60mph. In fact, that's basically it's top speed and that's with no passengers. At 60, the engine is VERY noisy.

[James k]

I just checked the engine number and it doesn't have an 'L' in it. What would need to be wrong to require a full rebore and new pistons? That sounds rather expensive

[bmcecosse]

The L would have indicated a Low Compression 'Commercial' engine.... If the bores and pistons are worn - then yes a rebore and new pistons is the answer. Of course - since the engine is in bits, it would be unusual to not have the crankshaft reground with new bearing shells - - and of course various other parts will then be begging to be renewed 'while you are in there'.... It is indeed not inexpensive... You could lift the head and inspect the bores -and decide from that whether a new set of rings would be worthwhile. You can of course do the rings without removing the engine.

[James k]

Okay, that sounds like a lot of work and money This lack of power is very irritating though, It slows to a crawl up some hills. When I changed the head gasket I had a look at the bores and they looked alright to me (as a novice). They looked smooth and didn't have any marks on them, though I don't know what to look for.

Out of interest, why were the commercial engines low compression?

[chesney]

They were designed to run on poorer quality fuel (or so I've heard).

[bmcecosse]

If the bores are good you could certainly consider new rings. You have to remember - a Morris Minor is no 'flying machine' unless you increase the engine power with bigger valves and carb, better exhaust and perhaps a camshaft change.....

[James k]

I know that I won't get a high performance car out of it. I just want it to be able to go uphill without complaining. At the moment, on hills, I press the accelerator and basically nothing happens. It's the same for a while after I get off the hill too I suppose one problem is that I've not driven a Minor in top condition so I don't know what to expect.

I set the valve clearances and plug gaps this morning (each needed some adjustment) but I can't really notice any difference in running. It's still got a rough idle and a lack of power. It did seem smoother driving along in top though and it isn't running on any more ( I don't know why that would be). The roughness of the idle and the noise from the engine varies quite a lot. Sometimes it sounds fairly smooth and sometimes it sounds like an old tractor.

[aupickup]

and hastings has got some hills

[simmitc]

If it's stuck at 60, and slows on hills, and is noisy... are you sure that it is firing on all four cylinders - it sounds very much like a 3 cylinder engine to me. Try removing the plugs leads in turn and see if one of them makes no difference. SAFTEY: Switch the engine off, remove a lead, start up and test, then switch off to replace that lead and take off the next one. Repeats as needed.

[James k]

I removed each spark plug in turn and none of them made no difference so I assume its running on all four. However, none of them seemed to make a big difference when removed. In fact, at idle, it was virtually unnoticeable. It was obvious when the engine was revved though.

[bmcecosse]

There could be other reasons (besides low compression) for low power - worn dizzy/poorly adjusted carb/blocked air filter/carb piston sticking/blocked up exhaust - or even a badly worn camshaft. There are no easy answers - they need to be eliminated one by one..... I assume the brakes are not dragging and the car rolls easily?

[James k]

The distributor was recently replaced with a Simonbbc 45d electronic one. The carb piston falls with a clunk as it should and the needle isn't scored. It hasn't been cleaned though. I adjusted the mixture yesterday since it seemed to be running rich. I just leaned it out by one flat. I've just replaced the blocked air filter but it hasn't made any difference. The brakes aren't dragging.

I do know that the timing chain is loose as it rattles a lot, could this contribute to low power.

What I'm thinking though is that, since I know that the compression is low, isn't it likely that that's the cause?

Thanks

[bmcecosse]

Oh yes - the low compression isn't helping. 'one flat' is insignificant mixture variation! What colour are the plugs after a decent run ?