Head trouble - 4AC - Toyota Nation Forum : Toyota Car and Truck Forums

c_r_a_i_g · 06-25-2006, 06:09 AM

Hi all

About a year ago I replaced the head gasket on my 4ac (ae71 station wagon) and it has gone again.

I am certain, as far as I can be, there were no overheating problems.

I think that I was a little slack on the job last time. Can anyone tell me from experience how clean the head/block have to be. I remember having a real job of it trying to get every last trace off last time and giving up and just putting it back together.

I ought to have gotten more than a year out it, so basically does anyone have any tips, common oversights etc for head overhauls.

Looking to do it cheap as the car is full of rust so can't justify a full reco.

Flatness appears to be within limits but I can't fully trust the straight edge I am using.

Any help appreciated.

Flashmn · 06-25-2006, 06:28 AM

The head has to be machined flat, or you'll blow gaskets all the time.

c_r_a_i_g · 06-25-2006, 06:32 AM

Thanks for the reply - are you saying I need to get it machined even if the feeler guage says it's within the limit? The Gregory's say .005 mm is acceptable.

Flashmn · 06-25-2006, 07:16 AM

I would get it machined.

c_r_a_i_g · 06-25-2006, 07:28 AM

Cheers - I think I will. I've been told I should have re-torqued the head bolts at 800km's. Is that true? I had planned to do it last time but put it off and forgot about it until it went again.

Flashmn · 06-25-2006, 10:51 AM

Naah, just torque it through the three steps in the book and its fine.

c_r_a_i_g · 06-30-2006, 03:28 AM

Just continuing the story...put the head in to be machined and it turned out to have a hole through an exhaust port into the water jacket, so it is in the bin.

Picked up another 4A head from the wrecker. It's in good nick, but in front of each vavle pair there is a set of valves(?) linked by a rail to vacuum. Wrecker assures me that the head will be okay (the original doesn't have them) and just don't hook them up to any thing.

Does this sound right?

freakinbox · 06-30-2006, 04:13 AM

with machining of the head and block doesn't that mess with the clearance?

c_r_a_i_g · 06-30-2006, 04:20 AM

They only take off the minimum required, it's part of any professional engine reco, so it can't be that bad.

freakinbox · 06-30-2006, 05:16 AM

well I was trying to figure out if they make up the difference with a thicker gasket. Just stuff I need to find out if I am going to get an engine done up for my car :p

c_r_a_i_g · 06-30-2006, 07:22 AM

You can't machine it yourself, you need to go to a machining shop. They'll tell you if it is flat enough to stay within limits after machining. If they have to take a that much off you might be better seeking out a another head. I'm no expert though.

c_r_a_i_g · 06-30-2006, 07:59 AM

and you can get shims to build up the gap, the machinist should be able to tell you what you need if you are doing it yourself.

eg, http://www.innomach.com/shims.htm

freakinbox · 06-30-2006, 03:19 PM

not doing the machineing myself. I don't have the equipment. I was saying I plan to build the engine myself.

thats all I was wondering craig, thanks. I have always seen this stuff on tv and such with them having the block machined. I'll be taking myself to campsell engines close to me. Guy build race engines. And a guy at the shop recommended him and they have their machining work done by him. He will also be the one that does the valve terrain work to my cylinder head.