Well my Pinto engine runs well, but only on 3 cylinders.

1 to 3 are fine but I'm getting no bangs in the cylinder on number 4.

I've checked the spark and its good, even tried swapping plugs and leads.

Drawin out the plug, its not wet so I assume its not flooded. Its running off a single carb so its not a faulty bank of carbs.

The seems to be some blow when I turn it over with no plug so its not a stuck exhaust valve (or could be stuck open).

All I can think of is
a) a blockage going into cylinder 4
b) valves really badly adjusted
c) the cam has sheared and isn't acutating cylinder 4
d) Its doing it becuase it hates me.

Any hints/suggestions on trouble shooting?

rocker cover off for a quick look, and a compression test would be my first steps,

but the answer is deffo d)

Ray

The cam could be so worn that it's not lifting the valves, have you looked under the rocker and is it noisy?

quote:

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Originally posted by Peteff
The cam could be so worn that it's not lifting the valves, have you looked under the rocker and is it noisy?

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the pinto has never been good on camshafts, however I had a mini several years ago and had a similar problem I traced that to a sticking valve, took the rocker cover off and gave it a few taps with a bfh well a sfh and voila worked perfectly

Cam follower fallen off?

Leaky inlet manifold gasket

Thanks for the suggestions. I'll try and give it a go tonight.

The engine was bought off one of the guys here. Its had new gaskets and bottom end shells.

There was a slight air squeal on first turn over attempt a few weeks back (quick tighten of head bolts and inlet nuts and all went away).

I've had the rocker box off before to check oil was getting to the top. I noticed about 1mm wear on cylinder 3's cam lobe, but only as a cursory check. I'll look at lobe 4 properly tonight and check valve clearances. I assume its possible that either (or both) valves are not actuating.

Given no horrid bangs or judders, its more likley the inlet valve is at least one of the culprits.

If it is a sticking valve and the engine is running well on three cylinders it's likely to be the exhaust valve sticking as a burnt or sticking inlet would affect the other cylinders . Carry out a compression test, check the valve clearances and inlet manifold for leaks (have you left off a vacuum pipe?)

Check the inlet manifold is not leaking.

If on Twin 40s or motorcylcle carbs check idle jets are clear and tight then and carb synch and mixture.

If on points ignition check the points gap for each cylinder


If nothing obvious check the valve clearance on let and exhaust


If you have compression tester fdo a compression test or better still a cylinder leakdown test

Try plug from offending cylinder in another to rule that out. Not unheard of for them to be faulty out of the box, be cracked when fitting etc.

Check the lead to that plug. (Either swap with another or do a resistance check and wiggle it about while doing so).


Rocker cover off and observe if all valves are moving as they should. Would be nice to know if the oil in spray bar is reaching all of the holes, its a common fault for a hole to get blocked and cause excessive wear on the cam.

Compression test all cylinders. First suspicion is valves not working correctly. Either stuck open / shut, or if the engine has been stood for excessive period with one of the valves open possibly corrosion in the valve seat resulting in the fuel / air charge not staying where it should. If valves are OK could it be a piston ring issue? (im not an expert in those).


Is dizzy cap OK? (should be if you are getting a spark to all plugs).

As said already check no air leak to offending cylinder via inlet manifold.

OK Some progress, I've blagged a compression tester for tomorrow night

The cam looks good and the valve springs actuate fine. One a manual turn over I can here that gentle hiss as the valves move so hopefully the compression test will be a verification.

I drained some oil out the sump, after checking it it was quite a bit over the max mark.

I also loosened off the inlet manifold bolts and re did them.

Disconnected all the plugs except for 4, and it started yay. I'll do tests later in the week just to make sure it was not a one off.

Thanks for the suggestions. I'll see tomorrow what the result is.