The General Engine Issue Thread!

[Twinky]

Hi all,

 

As with the cooling issue thread I started a little while back I would also like to start an engine problem thread.

I will start off.

 

Engine problem: Idle is rough and jumpy

 

I guess I will start off with my main question. Can an exhaust be too small for the engine to run smoothly???

 

The story behind my problem:

 

I initially had a 2" system that I built myself and was running in the car for quite some time. Everything was good.

Eventually I did a 5k + 5 speed conversion + electronic dizzy and everything went well. A couple of months down the track I decided

that I wanted to do a change in the exhaust so I replaced my 2" system back to the original 4k exhaust system. This is where my problems started.

My first issue was that my radiator was being pressurised, that was fixed. Then I had exhaust leaks everywhere and eventually nutted them all out.

The centre two bolts holding the manifolds striped the thread in the head so as that there was no tension there, fixed that this morning by inserting helicoils.

Every single god damn gasket has been replaced, carby is tuned great and there are absolutely no leaks anywhere (oil/air/water).

 

I am now left with an idle issue. I can not get the motor to run smooth like it did with the 2" system in place.

I have done checks all over the engine and have come to no conclusions.

 

Cylinder PSI:

(give or take 2psi as the reading incriments are in 10's

1 90

2 90

3 90

4 90

 

When I was doing the measurements the needle seemed to be jumping up and down between 110 and 80 psi whilst the engine was running, then after turning the engine off it sat at 90.

Is the meter faulty?? Or am I doing it wrong?

Seem a bit low?? These were the same readings back when I got the 5k and had the motor purring like a kitteh.

I had a bent rod and have sorted that issue for the time being untill I can get another set.

One thing that puzzles me is that I can unplug any random cylinder and the engine does not change tempo, rpm, roughness, it even seems to run slightly smoother.

I have gotten tired from beating my head against the wall trying to figure this out myself.

 

Any help would greatly be appreciated.

 

@ altezzaclub: as in the pm convo we had, I feel as though my car want's to cause maximum misery to my life.

I nutt out one problem only to be challenged by the next contender.

 

Cheers!

 

Alex

[altezzaclub]

lol Alex- I'm afriad I think 90psi is more bad news!

 

Either you're doing it wrong or you have knackered rings or burnt valves!

 

They should be well over 130psi uless you have a really low compression motor. Ours were 150-160 and the worn-out donor car were 130.

 

However, a compression test as I do it involves one person disconnecting the coil & jamming the meter in the plug hole, and another person turning the motor over with the throttle held wide open. 4 or5 turns until the meter more or less stops going up and it should hold max pressure on the dial.

 

If you didn't do that do you want to, then we have a good comparison. I don't think you have a problem really, as bad cylinders don't give the same readings like that.

[Twinky]

U unplug the lead and start the motor, should it just be cranking instead of actually running? As is should i disconnect the coil alltogether?

[Trev]

You are better off disconnecting the signal wire from the dizzy to the coil (negative) as you can stuff the coil by energising it and not using the power, I usually wind the engine over for 7 revolutions, this is enough for most engines to get to full operating pressure.

[altezzaclub]

Fair enough Trev-

 

Yes, you crank it over at full throttle without starting it.

[Andy43]

Twinky

Whats the valve clearance like ?

That will cause all issues from rough idle, overheating to low compression.

I'd expect the compression to be 130 to 160 psi, generally the lumper the cam the low compression will read.

 

My idle last week went from good to bad, 3 carbys later discovered PCV valve was stuffed.

 

Cheers

Andy

[B.L.Z.BUB]

General issues?

 

My 4K is too slow. :laff:

[Twinky]

Twinky

Whats the valve clearance like ?

That will cause all issues from rough idle, overheating to low compression.

I'd expect the compression to be 130 to 160 psi, generally the lumper the cam the low compression will read.

 

My idle last week went from good to bad, 3 carbys later discovered PCV valve was stuffed.

 

Cheers

Andy

 

Haven't checked the clearances as it is hydro so I haven't bothered with that. Might see if I can stick a feeler guage in there but I think they are always in contact.

[Andy43]

Ahhh forgot we were talking 5k, There non adjustable.

Correct they should auto adjust to zero clearance.

 

Has the head, or rocker posts been shaved ?

The lifter might be at the bottom of its adjustment which would cause the valve not to shut.

don't know how to check this, I'm interested to see the responses for this.

 

Cheers

Andy

 

 

[Twinky]

Ahhh forgot we were talking 5k, There non adjustable.

Correct they should auto adjust to zero clearance.

 

Has the head, or rocker posts been shaved ?

The lifter might be at the bottom of its adjustment which would cause the valve not to shut.

don't know how to check this, I'm interested to see the responses for this.

 

Cheers

Andy

 

 

It hasn't been shaved since I have owned it, I'll put my vac guage on the manifold and I'll see if it is the valves that are stuffed.

[altezzaclub]

With Armstrong Siddeleys you took a solid screwdriver and levered down on the pushrod end of a rocker slowly, and pushed the little piston down in its cylinder. Eventually you got 75thou valve clearance. It rattled when you started it for 30seconds until they pumped up again, but you never touched them after that.

 

Has anyone leaned on a rocker like that? So long as you get some clearance it means the valve spring is pushing against the hydraulic oil and the lifter has not bottomed out.

 

Back on your original problem Twinky, I though smaller exhausts were good for idle and large exhausts gave a lack of the mysterious backpressure (which doesn't really exist...) that made idles rough & grumpy.

 

How's the idle timing? Not too advanced?

 

Maybe it idled great with the 2" because something else was faulty and now you've fixed that something else! :laff:

Edited March 6, 2011 by altezzaclub

[Twinky]

Well I've done some tests.

Firstly the compression test.

Am I doing it correctly? Dizzy disconnected, turned the motor over untill the highest compression reading was seen. (150psi)

This was the same for each cylinder.

 

Here are two videos of the motor running looking at a vac guage.

 

 

In this one you can see the car idling and having an irratic reading swaying around 4-5 inches on the dial.

Then I give it light throttle, the vaccume increases, I then let go of the throttle and give it a quick stab.

You can see that it looses quite a bit of vaccume when it comes back to trying to idle, almost stalling and then continues on it's irratic idle.

 

NEXT POST CONTINUED

[Twinky]

In this one it almost looks like the engine is operating normally, on light throttle the vac slightly increases then drops at high rpm, then getting max vaccume when the throttle is closed.

I thought maybe worn rings or leaky valves but the compression test seems to be fine...
I'm going to replace the plugs on monday and see if I get any results. Whilst on that topic what gap should I run with electronic dizzy?

Any experts here?

[Evan G]

my 5k with a BHG was getting 90psi. apprently it looked something like this from behind even with gearbox oil in the engine LOL!

 

[altezzaclub]

Sounds like an airleak somewhere, so lean at idle and it won't pick up easily. I'll listen again-

 

Did you change the exhaust manifold when you changed from 2" back to stock??

 

Ah, of course you did, because you helicoiled the two bolts.

 

Are you 100% sure its not leaking in through the inlet manifold gasket?? Broken gasket, flanges different sizes, dirt under a gasket...

 

Atrocious design on that side of the engine, and everything as to be done just right for it to work properly.

Edited March 6, 2011 by altezzaclub