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RWD - Post overheat top end rebuild, now zero compression

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Post overheat top end rebuild, now zero compression 900 1994

Hey

So, 1994 940 turbo wagon, sat for three months waiting for $$$ for suspension parts. Before it was parked, ran like a champ.

I completed the suspension work, and took her out for a victory lap. Checked all fluids etc before departing, nothing amiss.

Got out on the highway maybe five minutes from my driveway and noticed a bit of a stumble and look down to see the temp gauge is pinned. Before I can commence any evasive maneuvers it stalls and I coast to a stop.

Both(!) legs on the vacuum operated plastic heater control valve are broken off, and there isn't a drop of coolant left in the motor.

The wife brings me a couple of gallons of water, and I leap frog it home, filling the cooling system and driving it for maybe three or four minutes until the temp gauge started to climb again, I would pull over, let it cool, refill, rinse repeat until in the driveway.

Things to note from the trip home:

1. dont judge, I was in a hurry to get somewhere and had limited options.

2. The last time I opened the hood to let it cool there was an insane amount of pressure in the cooling system. The expansion tank looked like beer foam. On the last leg the drivers side tank ruptured on the radiator. Upper hose ballooned a bit at both ends.

3. When I was cranking it to start after the overheat, it went whiiiiiiizzzzzzz and kind of worked its way up into running. I assumed this was lack of compression due to blown head gasket.

4. When it was going, until it began to get hot again, everything seemed fine, except that it sounded odd, an overarching phut-phut-phut-phut.

I have been maintaining a fleet of these things for years, so I have a parts car and stuff all over, so I dug in. Now, I've done more than 20 but less than 50 head gasket jobs over the years, so I can get it done now in an afternoon.

First thing I noticed was it spit the shim out from under the lobe of #2 cylinder intake valve. No damage to speak of, so I think it got hot enough in there for the cam bearing tower to grow enough to just let it slide right out. Yikes!

Now I may have been on autopilot a little too much but once I got the head off I didn't notice any holes melted in the pistons, or scored cylinder walls, or anything really out of the ordinary. In fact, the only observation I remember making to myself was a little chuckle over how small the lip is at the top of the cylinder.

Figured the spit shim = trip to machine shop so I pulled the head from the parts car (also ran great until it was taken off the road after kid fender bender that popped the airbag).

Buttoned it all up.


for the TLDR crowd:

overheated. changed head and head gasket.

Turned the key - same whiiiiiirrrrrr. Obviously its not holding compression for some reason.

I triple checked the timing marks, pulled everything apart and redid the timing belt again, even put it 180 out just in case I was going crazy and same thing every time.

Now I'm going out to pull plugs and verify compression, check the crank pulley for a sheared key on the sprocket or failed rubber in the harmonic balancer, or ant other crazy thing I can think of.

I'm stumped.

Any help at this point would be greatly appreciated. It's been a LONG time since I got this boggled over something like this, I know it must be something stupid I'm just not seeing....




 





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New 1 Post overheat top end rebuild, now zero compression [900][1994]
posted by  someone claiming to be Felix_the_caT  on Sun Nov 12 14:24 CST 2017 >

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