General 999 fire cylinder heads, melting of

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General 999 fire cylinder heads, melting of

Roperman

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among others i have a fiat panda 4x4, 87', its the high compression 999 (9.8 CR instead of the later 9.5 -- changed over at chassis #4112 510 -- so its *supposed* to use super unleaded/leaded 98 instead of 95 ron). however, during that annoying petrol crisis all my local garages ran out so i had to tank up with 95.
late for a meeting so doing 80-85 and detonates on a slight hill, removing the spark plug from the head, taking the thread in the head with it. is there likely to be any damage aside from the melted head? pistons perhaps? its still compressing to some degree, but cant test obviously.

ive sourced a supposed good 999 head of an injection uno L reg. not bought it yet but close to. do any of you know of any differences between the two heads, and also what fiat changed to adjust the CR when they lowered it in late 87? was it the pistons or something with the head. would i fit my dizzy on there, or is the one on it the same?

i know its long winded. sorry. any advice would be good.

danny
 
Il have a crack at answering some of your questions. The Uno head should fit no problem. The injector is in the manifold not in the head so that can be simply unbolted and your Weber carburettor manifold bolted in its place. If i remember rightly John H replaced an injection pandas head with one off a carb panda with no probs. I would personally use ur Pandas dizzy as i would expect their to be some difference with an injection dizzsy. As for pistons simplest way is just to look at them when you have the head off. If there are chunks missing time to think again
 
I doubt that was the fuel used, we no longer have leaded fuel here and they still work fine. I think it must have overheated from the detonation probably because of something else. I've seen lots of head that had slight melting and it was always caused by detonation, the fuel only affects valve wear;)
 
smokeme said:
I doubt that was the fuel used, we no longer have leaded fuel here and they still work fine. I think it must have overheated from the detonation probably because of something else. I've seen lots of head that had slight melting and it was always caused by detonation, the fuel only affects valve wear;)

I thought higher RON fuel combats against detonation?
 
I thought higher RON fuel combats against detonation?
yep

mine is one of the very early FIREs, before unleaded 95 was even considered for environmental issues. they were built to make best use of the 98 ron leaded fuels available, which gave it more torque than the later lowered CR ones (59 lb ft instead of 57, using CR of 9.8 instead of 9.5). when everyone was going unleaded they lowered the CR, which was quite early on in the engines history, so not too many of these high comp ones.

just wondering if anyone knows what they did to lower CR? dished pistons, or a bigger chamber? the head is *hopefully* coming off today btw.

by the sounds of it as long as ive not holed the piston i should be ok with this head.

thanks

danny
 
smokeme said:
I doubt that was the fuel used, we no longer have leaded fuel here and they still work fine.

yeah they dont miss the lead in the fuel because they are all fitted with hardened valve seats due to them having soft alloy heads instead of cast iron ones of many older engine designs. the very early ones did run a higher compression ratio though.
 
My manual states the headgasket was changed in 1988, the same time the compression changed (not 87 like stated), mine is also a high compression engine and even with all the stuff i've thrown at it it still works great;) .
 
must have bad luck then. usually its ok on 95, except on long high speed journeys or me giving it a hard time. its melted/smashed a few plugs on the motorway before from detonation on 95, and never on 98 so i just assumed it was this. is it the thicker gasket that reduces the CR then?
 
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