Acceptable engine compression? 86" 2.0l

[cjc_td5]

I am trying to chase down the cause of rough running with my 2.0l petrol in my 86". I have tested the engine compression as 110, 105, 100 & 105psi in cylinders 1-4. Tested "dry", ie plugs out cranking with no oil in cylinders. What would be considered acceptable before taking the off?

[JDNSW]

The 100 is perhaps a little low compared to the others (leaky valve?), and I would have expected pressures about 5-10 higher, but they are not too bad. Have you checked valve clearances?

[cjc_td5]

I checked the tappet clearances today. Inlets were all good and not changed. Exhausts were a little big and were nipped up a little bit each.

[cjc_td5]

My main issue is a persistent miss at idle. I suspect the mixture is all out as it seems way too rich. It blows black smoke on acceleration. I took the compression readings as I suspected a valve or head gasket issue causing the miss??

[1950landy]

You could try a new set of spark plugs, if it is running rich & one of the pluge is week could be causing the miss. Also has it got copper or carbon leads if carbon you could have a faulty lead. Also check the points gap on all 4 lobes if one is worn that could also give a miss

[cjc_td5]

Yes it seems to eat plugs for breakfast. I have gone to one step hotter which has helped plug life a bit.

The leads are new copper leads with new dizzy cap.

[JDNSW]

If you needed to go to hotter plugs, I would suspect the rings are not in real good condition, which fits with the somewhat low compression (been there!). But this should not directly cause rough idling - worn engines often idle very smoothly. Other points to suspect are all the other ignition components, including coil, points and capacitor. But rich running at idle has to be a carburettor issue.

[Bundy]

What carb is on it?
Paul

[cjc_td5]

What carb is on it?
PaulSolex 32PB-2.
I've put a gasket and diaphram kit through it. Also sleeved the spindle which had some free play. No jets appeared blocked.

[cjc_td5]

Mmmmm. On start up cold this morning there is a definate diesel type knock, which does go away when everything warms up. The oil pressure gauge (smiths mechanical gauge fitted) shows oil pressure from startup though....

[cjc_td5]

Mmmm, still chasing a persistent miss. It seems to be in cylinder #1 as it does not change when the lead is removed from this spark plug when idling. Removing all others increases the miss. The miss stays with a new spark plug installed. The spark seems as strong as the others when arcing to the motor. It has near new copper leads. I reset the leads into the dizzy cap last night with no real improvement. The compression on cylinder #1 is still 110 as tested previously.

The motor is a siamese bore 2.0l. I am wondering if I have a leak at the head gasket between cylinders 1 & 2? I don't know why it would affect cylinder #1 more though unless the firing order has something to do with it?

I would like to take it for a blast down the road to clean it out but it is not registered yet. It seems glugged up from slow running all of the time....

[B.S.F.]

When you turn over the engine with the crank handle, does the compression feel and sound the same on all four cylinders ?
.W.

[cjc_td5]

When you turn over the engine with the crank handle, does the compression feel and sound the same on all four cylinders ?
.W.
Hi B.S.F.,
Ha I surprise myself sometimes. I managed to walk out to the shed and locate the crank handle straight away in the spares pile of bits....
No there is no perceptible change in compression between the four compression strokes when turning with the crank handle.

Thanks for your feedback though. It is much appreciated.
Cheers,
Chris

[theelms66]

You mentioned valve clearances are ok .Maybe check valve lift particularly inlet valve.possible cam lobe wear? Bent pushrod etc .

[cjc_td5]

You mentioned valve clearances are ok .Maybe check valve lift particularly inlet valve.possible cam lobe wear? Bent pushrod etc .Re a bent pushrod, wouldn't that be taken up with adjustment to the tappet clearances?

Apart from inspecting the cam lobes, how can you measure valve lift?

[theelms66]

Dial indicator on top of valve or rocker arm . Amount not so critical i guess as long as it is the same as 2 3 and 4

[JDNSW]

If there is even compression, it is difficult to see what could cause a miss in one cylinder at idle other than the suggested cam wear or, possibly more likely, an ignition issue*. Have a close look at the distributor cap and, if using the original spark plug covers, try swapping the one on the suspect cylinder to another cylinder. Another possible issue is wear on the distributor spindle allowing the shaft to wobble, possibly worn so it affects mainly one cylinder.

*Another possibility - a very slight leak on the manifold gasket affecting mainly that cylinder. Put some light oil on the joint between the manifold and the head while idling - it should stop the miss and/or show up in the exhaust.

[B.S.F.]

Have you removed the radiator cap and checked for air bubbles at idle? (after the thermostat opened ,if there is still one fitted). Being a Siamese engine it could still have a sheet metal head gasket fitted, but I don't see how that would make a difference unless it's damaged, but the same could happen with a later gasket. The leak doesn't necessarily have to be from cylinder to cylinder.
.W.

[cjc_td5]

Well I do feel like a bit of a doofus. I realised that the thing I had not changed back to check is the new dizzy cap I had installed a year ago. Transfer the plug connectors back on to the old leads and cap and it fires up beautifully.

A mystery solved. At least I know a bit more about the engine condition. An engine rebuild is on the radar soon but will see how it behaves in the short term...

[B.S.F.]

A great result. I know exactly how you feel. The only time I had a problem with my engine was after I installed a brand new rotor arm that after half an hour developed a short to the shaft. Of course that was the last thing I checked, I never expected a brand new part to fail..W.

[LR1953]

Chris, as you say your S1 isn't registered so the engine only experiences slow running. You'll be surprised how it improves with ordinary work for a day or two, say 2 - 300 km at 60km/hr in hilly conditions. Everything warms up thoroughly. Keep an eye on the engine oil level - it may need a top-up after 3-4 hours. So my point is get it roadworthy and registered, and use it (that's what they were made for!) before considering a rebuild.
Cheers, Rob S