1608 BLOWN HEAD GASKET???

[71124spider]

OK ALL YOU FIAT EXPERTS, I WOULD APRRECIATE YOUR OPINION. i was cruzin along in my 71 124 when all of a sudden she started braking up and pinging--so after eliminating the ignition system, i did a compression test--from front to back--first 2 cylinders 140 on the head each--last 2 cylinders 80 each. then i did a cooling system pressure test with my stant cooling system pressure tester holds 15 lbs indefenitley. my question--what would cause a head gasket to blow between 2 cylinders for no reason.? i think thats what happened, i havent pulled the head yet.

[Warren]

Yes, happened to my 1979 between 2 adjacent cylinders at about 80000 miles in 2007; owned car since 2001.

[majicwrench]

Yup got a blown gasket tween the back two.
What caused it?? Well, gaskets don't last forever even when everything is perfect. Any pinging or overheating is hard on it as well. Pull it apart and see what it looks like.
Keith

[RoyBatty]

The good part is that you have a blown head gasket on a fiat twin cam.
The process of R & I on these engines, especially one from the early 70s, is not at all difficult.
Once you disconnect all the obvious lines, hoses and linkage, just remove the exhaust fasteners at the collector and I then you just have 10 head bolts to remove.
You might actually spend more time doing cleanup of the assembly and the bolts and holes in the block, than you will doing the removal and installation.
Do follow the instructions and make sure your threads are clean and in good shape.
And if I remember correct, you are supposed to lube the head bolt threads before installation and torqing.
Have fun.

[71124spider]

is 140 compression good for this motor? it has 84 thousand miles on it.

[majicwrench]

140 is fine.

[71124spider]

THANK YOU TO EVERY ONE FOR YOUR HELP--IT WAS BLOWN RIGHT BETWEEN THE 2 CYLINDERS JUST AS SUSPECTED, MY NEW QUESTION--I'M HAVING THE HEAD DONE--CAN THE VALVE DISC/SHIM CLEARANCES BE SET UP ON THE BENCH COLD? I'M DOING NEW VALVES,GUIDES, AND SEALS--SO I'M SURE IT THROWS EVERYTHING OFF.

[fiat50state]

ok, i worked in a machine shop, so while the head is off, clean and check how the valves are seating, normally done with machinest blueing. you should have a nice seat about the thickness of a pencile line all around the valve. if not a little lapping with some compound should work wonders. whoever is replacing the guides should be checking this. a check of how true the head surface is should also be preformed. A perfectly flat edge is held against the head and a .002 feeler guage is "attempted " to be inserted all across the head. if one can insert the guage, then the head should be milled about .001-.002 thousands. to make it true and seal the new head gasket correctly. if a valve job ( with grinding of the seats ) hasnt been preformed...then id leave the shims alone till its back together and rotate the engine thru a few cycles and see if you still are within tolerences ...hope this helps

[chrisfiat]

my shop always sets the clearances on the bench

[71124spider]

A PROFESSIONAL ENGINE BUILDER IS DOING THE HEAD WORK, BUT HE DOSENT HAVE A LOT OF FIAT EXPERIENCE--HE BUILDS RACE ENGINES--AND I THINK THE CLYMER MANUAL SAYS SET VALVE CLEARANCES WITH THE ENGINE UP TO OPERATING TEMP---THAT WAS MY QUESTION--AM I WRONG? ALSO, WILL GRINDING THE VALVES MAKE THE CURRENT TOLERANCES TIGHTER OR LOOSER?

[narfire]

I've set the clearances on a re built head when cold on the bench. Actually I use one of those "work-mates" as the valves have a place to go when I rotate the cams. After a few weeks on the engine, I checked on a warm engine and for the most part I was still within tolerances. Might have had to reset one or two valves.

[chrisfiat]

grinding will close up the lash clearences on this engine. and any halfway competent shop can work on these heads, these are NOT so unusual or difficult that they must be done by Tony. set the clearences to the looser dimention in tolerence when cold and they will be within spec when hot

[fiat50state]

tecnically speaking. if the valve is ground and we are talking about reconditioning of the seat and its angles and the valve itself,( refaced ) then the valve will seat "deeper" into the head. there by allowing the tip of the valve stem to be closer to the rocker arm/cam surface so the clearance will decrease...Your race engine builder will understand this , its all part of machine shop basics....

[bradartigue]

A PROFESSIONAL ENGINE BUILDER IS DOING THE HEAD WORK, BUT HE DOSENT HAVE A LOT OF FIAT EXPERIENCE--HE BUILDS RACE ENGINES--AND I THINK THE CLYMER MANUAL SAYS SET VALVE CLEARANCES WITH THE ENGINE UP TO OPERATING TEMP---THAT WAS MY QUESTION--AM I WRONG? ALSO, WILL GRINDING THE VALVES MAKE THE CURRENT TOLERANCES TIGHTER OR LOOSER?

Get a FIAT shop manual and machine everything to the tolerances specified. FIAT valve shims are checked and set on a cold engine:

http://www.fiatplus.com/members/valveadj.htm

Race engine builders do things to last about 2 races. Not to knock your friend but I would lean towards the advice of people who build engines to drive on the street and last a long time.

[71124spider]

my engine builder is a reputable builder from my community for the past 30 years when i asked him if he needed me to order the valve shim set-- he said no--because they take the clearance they need off the bottom of the valve stem-- after grinding and lapping the valves---all he said he needed was the specs--what do you think about grinding the valve stem for clearance? anyones thoughts please?