Head gasket - valve job question

[shadetree]

I'm replacing the head gasket on a '93 Nissan Altima due to overheating (DOHC 2.4L 4 cylinder).

Removed the head and took it to a machine shop for checking. It's not cracked but slightly warped.

However, they said that it may need a valve job. I watched as they put the head upside down, poured solvent on the valve area, and some solvent came through one of the intake port.

I tried it at home with putting the head on it's side and pouring solvent into the intake ports. All the valves leaked, one cylinder more than the others.

Is this a good test? The problem is a valve job is $200, plus it costs another $200 to have the valves adjusted (the valves are adjusted with shims, which are labor intensive to adjust).

The car has >100k miles and I don't want to sink too much into it.

It seemed to run OK before, but it seemed like the timing chain was making noise.

[BigBry]

Way over my head, but what we did was had the head swapped at National Cylinder Head exchange. They put in all the new valves after doing a thorough cleaning and check of the head.

Total price was about 200 bucks.

[vetteonr]

Nail on the head time BigBry. With the price of heads what they are, it's just easier to do a swap.

[raceman6135]

The test they did is valid, albeit low tech. Many rebuilder shops now have a device that applies a vacuum to the chamber (from the piston side) or to the runner (from the manifold side), and can then measure the vacuum leakage past the offending valve.

Any leakage over 10% is suspect. If you already have the engine torn down this far, like the others said, an exchange head is probably much more cost efficient for a vehicle of this age.

DJS

[shadetree]

Originally posted by raceman6135
The test they did is valid, albeit low tech. Many rebuilder shops now have a device that applies a vacuum to the chamber (from the piston side) or to the runner (from the manifold side), and can then measure the vacuum leakage past the offending valve.

Any leakage over 10% is suspect. If you already have the engine torn down this far, like the others said, an exchange head is probably much more cost efficient for a vehicle of this age.

DJS

Thanks! I'll try to find a shop with a vacuum tester. I'd like to know how bad it is. I wouldn't mind spending $200 to do it right, but I'm a little reluctant to spend >$400 on just the head for this age of car.

Unfortunately, the price on a rebuilt head is $425 - $500. That's because it has to include the double overhead cams. The cams have to be installed in order for the head to come with the valves adjusted.

My understanding is that the problem is that this head uses a solid "cup" lifter with shims to adjust the valves (similar to Toyota). If a valve job is done, or a rebuilt head (without cams) is purchased, it costs another $200 for a mechanic to adjust the 16 valves using various combinations of shims.

So, if the valve(s) are leaking > 10%, it would pay to spend the $425+ on a rebuilt head?

[danny]

at this point if the valves are leaking and head is off then swap the head and finish the job. the valves are leaking if fluid can exit the valves while closed, test is done. don't waste more money finding the degree of leakage. just saying what i would do in your position.

[towtrucks]

I take a shop light and place the light up against the intake or exhaust port and check for light coming from around the valve seat area.

[Trader Ray]

A good shop is hard to find, they all claim to be the best. We have a machinist in this area that works out of a garage, you would not beleive how far you can travel and hear his name mentioned. Every tool imagineable in his old garage. I could not believe my eyes when I took a set of heads there. Once you get used to the big giant dog standing in the door or where ever he wants to, it is alright. This is a shadetree set up that is as professional as any place you can get.