Machining needed for head gasket change ?? 1998 s70

peterz · Post by **peterz** » 12 Mar 2007, 16:08

Low compression in 2 cylinders and have to replace head gasket (Likely head gasket failure according to mech). Does head automatically need to be machined, or do I just have the machining done only if out of tolerance? Mech claims need to automatically machine head as part of gasket change.

Post by **billofdurham** » 12 Mar 2007, 16:25

If the head is warped or has deep scratches in it then it will need machining. Check it with a straight edge and feeler gauges to check it is straight.

Bill.

bugeye58 · Post by **bugeye58** » 12 Mar 2007, 22:12

I would think that any competent mechanic would surface the head in conjunction with a gasket change. It eliminates one possible source for another failure, and "comebacks" don't pay the bills!
Jeff

bobsnow100 · Post by **bobsnow100** » 13 Mar 2007, 08:40

I have done at least a dozen head gasket replacements on various cars including an 1994 850 volvo wagon I had, I have never had to have a head machined. You do need to check it with a straight edge and feeler guages. If you pick up a Haynes repair manual there are pics of the maximum clearances at various points on the head, also be careful you don't scrape the surface of the head or the engine block, I always get some very very fine wet sandpaper to clean the surfaces and keep the surface wet while I am just basicly polishing the surface of the head to get off all the old head gasket (black dis-colorization)that always seems to be left once the gasket is removed. When putting the new gasket on,the last thing I do is clean both surfaces(block and head) with carburator cleaner and wipe it with lint free paper towels,make sure nothing is in the head bolts holes in the block too. Follow the proper torque sequence also. I remember on my volvo that you lightly oil the head bolts before installing them so you get proper torque. I remember also the last step in torqueing was to turn the bolt 130%(i think) more, What I did was to use a breaker bar and I also got a piece of cardboard and in the middle I cut a hole out for my socket and drew degrees on it from the hole cutout. That way where ever my breaker bar was,I would line up the 0% with where the wrench started and would turn it until I hit the 130% mark on the cardboard scale

Post by **billofdurham** » 13 Mar 2007, 12:39

I remember also the last step in torqueing was to turn the bolt 130%(i think) more

Good memory.

Stage 1 - 20nm.
Stage 2 - 60nm.
Stage 3 - tighten through a further 130 degrees.

My gauge is made out of 3mm plywood but the principle is the same as yours.

Bill.

Trilarry · Post by **Trilarry** » 13 Mar 2007, 14:26

If it has high mileage I would take it in to a machine shop and let them look at it. They could probaby tell you if the valves/guides are good on the 2 cylinders that have low compression. I had all this done for 215.00 out the door. After they took the valves out all I needed was the exhaust guides changed out.I had them put in new valve seals that came with the head gasket set from Grotons.

Peace of mind and no second guessing is what I got. I installed it 3 weeks ago and it's like having everything new on top.
Tri