Technical Uno pacer issues..

[Fiat Uno GuY]

Uno 70sx (1372) head issues

Hey all!!

I've got an 1992 Uno pacer (1372), with reprofiled camshaft, ported and polished head,skimmed and oh yes and the valves was made longer to compensate for the reprofiled camshaft..

So my problem with the car is that I change the head gasket more than I service the car!! Just recently, I noticed that when I leave the car idling for a while, the radiator pressure is massive!! So when I took the radiator cap off, the water pushes out of the radiator, and also when I rev the car. Logic tells me that the car is losing compression through the head gasket, on one of the water jackets, but when I take the spark plug leads off one by one, a slight change in engine tone occures, which means all the plugs have compression.. Also what I noticed, after the head has been ported and polished, the exhaust ports in the head was much bigger(about 2 to 3mm) than the exhaust manifold. Could the restriction at the exhaust manifold cause a build-up of pressure in the head, resulting in a blown or damaged head gasket??

There's alot of other problems that I have on the car, but lets handle them one by one...

Thanx for a great forum:worship:
God bless the Fiat Uno, and it's drivers:slayer:

 

[alexGS]

Re: Uno 70sx (1372) head issues

but when I take the spark plug leads off one by one, a slight change in engine tone occures, which means all the plugs have compression..

...and, that compression might be pressurising the cooling system, just as you said. There is a test known as a 'TK test' where a special liquid is placed in a rubber/glass thing like a battery tester - the air above the coolant in the radiator is then 'sampled' and if the liquid turns from blue to green, combustion gases are present. Perhaps ask an engine shop if they can do this test for you?

Otherwise, I think you need to remove the head yet again and resurface, then fit with new gasket and cylinder head bolts (they are a stretch type). Perhaps after the previous engine work, someone skimped on the resurface/new bolts. Perhaps your compression ratio has been increased beyond 10:1 which calls for these ideal fitting conditions. I had 10.5:1 compression on a 1498 Strada engine once, and it blew a head gasket shortly after fitting. After I used new bolts, no more problem.

Also what I noticed, after the head has been ported and polished, the exhaust ports in the head was much bigger(about 2 to 3mm) than the exhaust manifold. Could the restriction at the exhaust manifold cause a build-up of pressure in the head, resulting in a blown or damaged head gasket??

I don't think that is a likely cause/effect... the compression/ignition event generates far more pressure than the back-pressure created on the exhaust stroke.

I have been told that a step-change at the manifold does not actually have a detrimental effect, but personally I think it is worth porting out the manifold as well using a Dremel or similar with tungsten-carbide bit. Though I can't remember for certain (a photo might help), I think the standard 1372cc manifold is the same as the earlier 1301cc manifold and is quite a good design as these things go. It should be good up to 100bhp based on how modified X1/9 engines used to perform. Of course, you might elect to fit tubular extractors instead.

I'd like to know how this engine does on a dyno test What fuel system is it using - presumably not standard? I think the Pacer comes with a twin-choke carburettor (30/32?) - perhaps a 34/34 carburettor off a Lancia Beta would be appropriate, or there's always twin Weber 36 DCNFs to think about?

-Alex