X flow glowing exhaust

[studog]

Ok chaps what do you reckon.

Just tried my crossflow after taking an age to get it back in the car.

Running fine for ten miles smooth from low revs to high despite claims that I couldn't get
a single carb and a 285 cam to pull well. Any way just before I got home it suddenly sounded odd,
like a blow from the exhaust. When I stopped the nos 2 and 3 exhaust manifold pipes are glowing red
and clearly the gasket to the head is blowing.

Has anyone seen this effect from a blown gasket before or is the gasket the effect not the cause?

Don't forget single carb so the mixture should be the same in all cylinders and since I last ran it
the only thing that has changed is the a slight change to the cam timing.

[Sam_68]

When you say 'gasket to the head', do you mean the gasket between the exhaust manifold and the head?

If so, then yes, that might well be the cause of your glowing exhaust headers... drawing in air and unburn fuel in the exhaust gasses continuing to burn in the manifold headers.

eta: I'm surprised you have managed to get the 285 cam to pull well through the rev range; my experience of Crossflows with that cam duration is that they can't pull the skin off a rice pudding before they come on cam!

Have you had the car on a rolling road and an exhaust gas analyser? When I first had my Crossflow set up(254 cam and single Weber, originally, though it's now on twin 40's), when jetted to run best in the lower part of the rev range, it was generating stupid exhaust gas temperatures, too (due to leaning out in the upper part of the rev range, form memory, though it was a long time ago).

Edited by Sam_68 on Monday 23 February 20:57

[Justin S]

ignition timing is out probably.

[studog]

It could be timing but I would be surprised if it would affect. Just the cntre two pipes.

A plug pull looks fine on all four so the mixtures look ok.

The bolts on the manifold were none to tight on these pipes so I guess that could have started the leak. I guess as Sam said once there is extra oxygen then I have apetrol blow torch in the exhaust.

I am well chuffed with with how flexible it is. It will pull from 2000 rpm upwards in top!

[skid-mark]

if tightening the exhaust manifold bolts don't cure it do compression test could be burnt out valves on exhaust side, have the valve seats been hardened is it an early x-flow i only say this as you've said it's only the middle two, if compression is really down could be due to the head gasket failing across the two cylinders which will cause it to run lumpy, would prob be worth while putting it on a emissions machine see what its running at through the rev range first, high hc would indicate a running fault where as high co2 would indicate a set up fault.

Edited by skid-mark on Tuesday 24th February 21:38

[Mr2Mike]

studog said:

Don't forget single carb so the mixture should be the same in all cylinders

That's certainly no guarantee of even mixture distribution!

[fatjon]

Valve clearances too tight on the exhaust valves of the affected cylinders is a good contender. When the valve expands it gets to a point that it never fully closes, this will warm up the affected branches of the manifold very quickly and get the valve even hotter making the problem worse. I would not expect a significant difference in mixture between cylinders in a single carb setup, some but not much. Ignition timing is going to affect all cylinders so thats unlikely, and a blown head gasket, hmmm, I have never seen glowing exhaust manifold branches as a symptom of that and I have blown a few in my time. I would start by opening up the exhaust valve clearances by an extra 5 thou and see what happens, it will cost you nothing but a few minutes of your time.

Jon

[Justin S]

Mr2Mike said:

studog said:

Don't forget single carb so the mixture should be the same in all cylinders

That's certainly no guarantee of even mixture distribution!

True, single twin choke manifold is not the best for balanced flow.

[That Daddy]

Mr2Mike said:

studog said:

Don't forget single carb so the mixture should be the same in all cylinders

That's certainly no guarantee of even mixture distribution!

the stock X flow manifold had poor fuel/air distribution,cylinders 1+4 run leaner from memory(outer inlet runners)where as the Pinto stock manifold was very good