Anyone ever heard of this? We were testing at 30 psi and then after a few min it blew. he did a leak down test and said two of the cylinders are low. there was no fluid in the car as its being put back together. Any advice or questions would help. what else could it be


FIXED BY BLOCKING OFF EGR WITH A PLATE

 

anyone?

 

Im confused so you did this with out the motor being installed? or was it installed just had no oil or coolant in the car since you were putting everything back together? In all honesty by doing a "boost leak test" (and someone correct me if Im wrong) if your seeing 30 psi then that would mean the head and also the open valves leading into the combustion chamber (depending on what cycle your on) would also feel that much pressure. It honestly could lift the head if everything isnt Tourqed right. Ive just never heard anything like that happening. And when you guys did the leak down test was each cylinder at TDC?

 

Well a buddy is doing the rebuild for me, we got the trans and tcase rebuild, cam's injectors, licp, and lots of other stuff. Well he had it all back together doing a final boost leak test there was no fluids in the car just testing for leaks. Well from what i heard was he filled it to 30 and something happened. a pop and all the air went out, he did the leak down and two of the cylinders were low of the test, he is thinking the gasket gave. Ive read of people blowing seals in odd places im hoping its a simple fix.

 

There is no way 30 psi should take out a head gasket. pressure during combustion is much, much greater than that.

 

cylinder compressions are ~ 140+ psi... im pretty sure your buddy just doesn't know what he's doing.

 

Before the spark plug fires it might be 140, after - lots more.

 

Tow your car to a real shop and have them finish the build. And you two will remain friends, if not, your friendship will be compromised because of him not knowing what he is doing.

 

I'm very confident in his work. Its not his first build. I appreciate all your concern's. I was a very odd thing but I'm sure it will be fine.

 

Was a boost leak performed or a compression check? They are different.
you could check around to see if a vac hose popped of. Some setup details would help. If your head gasket blew with 30 psi your motor was doomed well before you even thought about doing this.

Head and block where decked? head bolts or studs torqued correctly?

 

the issue you are likely having is that your boost leak test blew the vac lines off the EGR valve and the EGR valve is now open and making it seem like the gasket is blown.

i bet if you test it again, you can hear the compressed air coming from the tail pipe.

put an EGR block off plate on it and never worry about it again.

 

Why would someone reference cylinder compressions with a spark? No one checks engine compression when the engine is running.

 

It would be an interesting test if one could do it. You pointed out that the gasket has to withstand the pressure of compression, which you can test for, but no, it has to withstand the shock, heat and pressure of combustion.

On an interesting side note, the gasket also has to withstand the movement of the head on the block every time the engine is run because the coefficient of expansion is different for cast iron and aluminum. When aluminum heads first appeared the gasket makers were quite proud of the fact that they could come up with a working gasket. This is also why our engines, when overheated, warp the heads.

So, saying that 30 psi blew out the gasket is saying something is seriously wrong. I also agree that it is unlikely to be true. But you never know, some large foreign particle could have gotten between the head and the block.

 

no way in hell will a head gasket blow at 30PSI

 

Vac line blew off....don't forget to tell your friend...puff puff pass