Replacing Head Gasket- what else should I look into?

Hi all,:wave1:

This is my first post on the forum. I got my 96 s/c last year. She performed splendidly on a cross-country trek, but shortly thereafter the head gasket blew. When head gasket seepage was suspected, I used block seal to both test and band-aide. She ran perfectly for probably 5k miles or so, but the leak came back even worse. I will be changing the gasket myself, and while I have everything apart, I want to take advantage of the opportunity and look into potential problem areas. It has 170,000 miles on it and has been well maintained (it was in my family since almost new, so I know it's history).

Things I plan on doing:
-It has rather new plugs and wires, and I will look at cap, rotor, pvc
-Clean throttle body including egr passages
-Thoroughly clean combustion chambers including taking head to machine shop for inspection & potential servicing
-Replace valve seals
-Lap valves, if needed (is it important to lap the valves if no solvent leaks past them?)

Other items:
-After 170k, I would expect that rings and bearings might do well to be replaced, but, that said, they showed no symptoms of ill function. Oil changes had been timely. --Are the original factory parts of such good quality that I should leave them alone if they don't exhibit problems? I'm used to working on 80's GM engines where replacement of rings and bearings is simple and inexpensive. Is there any added complication to doing the same work on a 96 Toyota? This engine seems much more refined than the 86 gm 2.5l, which leads me to wonder if there are other particulars to consider.
-Also, the transmission is functional, but it feels like it has a lot of miles on it. I have never worked on an automatic transmission. Are there particular parts I should check, replace or adjust while I'm in there? What wears out? It has had its fluid changed, but it hasn't been serviced otherwise. Torque converter? Seals? Is there anything to be gained by opening it up and looking at the condition or cleanliness of anything?

Thanks everyone for your help and all the great write ups I've been reading. I'm happy to be a part of the TVT community:thmbup:
-Michael

And thanks Timsrv for your write-up on doing this same job!

Welcome to the Previsti
I've had two Previa engines apart thus far. One had been overheated due to coolant loss at the water pump/front cover junction, and the other a simple and sudden head gasket failure. Both had around 250k on them. The wear on the bearing shells was minimal on both engines, and I expect that had they been reassembled without a change they'd have provided service for a long time.
By the time you've got the engine out, on a stand, and torn down to the point where the head can be removed, though, it's a small job to get the pistons and rods out. From here you can clean the pistons (you'll find them pretty crusty) and hone the cylinders. New rings don't cost much. I'd recommend going that far at least, especially if you've already got experience with such things. I don't think you'll find anything weird or exotic compared to a Fiero engine.
Once the piston/rod assemblies are out, of course, pulling the crank isn't difficult either. You have to take the front cover off first, and the rear seal plate. But you might as well replace those seals while you're in that deep also. At this point you're looking at a crank-up rebuild. OEM rod and main bearings can be had to restore the factory clearances for around $200. After market bearings are much cheaper, but will likely result in clearances larger than the stock used bearings you're replacing. With the front cover off you can assess the timing drive parts, chances are they're fine.
You've gotta take my recommendations with a grain of salt. I do this kind of thing for fun. To me stripping an engine to the crank is not something I do because I have to, but because I can.

if it ain't broke, don't fix it!

Had this same question actually. Are there any other things to look into while the top half of the engine is taken apart?

I've identified that I need to change the following:

- head gasket - possible warped head, big time white smoke coming out exhaust, no compression in cylinders 3 and 4
- water pump - think that it might original and I have 162,xxx miles on the van (my mom said she had it changed out, but I don't see it in her maintenance records)
- SADS couplings - still original and very worn and cracked

Right now, I'm hoping to do the HG job with the engine still in the van. Also, I don't think that I have the experience to look at rods and pistons and the such (just a backyard weekend mechanic). I'm just more interested in things that are along that way that are good to replace while it's apart.

Just as an example, for a timing belt job on the Toyota Camry, people usually recommend changing not only the timing belt, but the water pump, thermostat, oil pump seals, crankshaft seal, camshaft seal, power steering belt, alternator belt, valve cover gasket. There's a lot of "along the way" stuff people will change at the same time. Is there something similar for the Toyota Previa?

I found these 2 other threads that might be helpful to other people:

http://www.toyotavantech.com/forum/showthread.php?1303-A-twist-on-Previa-engine-removal

http://www.toyotavantech.com/forum/showthread.php?1885-97-s-c-Head-gasket-replacement-summary-W-part-s

Welcome to the forums.

I bought my previa with a blown head gasket with intentions of rebuilding it. Since I bought my van with 245,000, I figure it would be best to replace things as I go along. I plan to have this van for a very long time, so I didn't mind the amount of money I put into it.

You could simply replace the head gasket and have the head checked and replace water pump and that could be it.

My mentality was to make the engine new as possible and to gradually change parts out as I go through each system. I also take the preventative maint. approach since I want this van to be reliable. This can be expensive, but it is the approach I am taking. I wanted to buy a new Sienna, but figured, I could do the same to a Previa and make it "new".

So I had my motor fully redone. I did have high mileage and I dont know if the previous owner drove it with the BHG or how long it sat, so I figured I needed to address the cooling system.

As you have the motor out, it is good to clean out the EGR system.

The beginning of the year, my transmission started to fail and then my first gear would felt like neutral. I came upon the same dilemma, do I replace or rebuild. I took it to a ATRA transmission shop and he gave me a good price with a fully rebuild transmission (gears and all) and even with a shift kit. Even changed out the transmission mounts (which were shot anyway). I asked the owner of the shop if he was going to swap transmissions and he told me he rebuilds them from the ground up.

For me, it is worth it and I absolutely enjoy my van. So much, I'm buying a motor to take apart and put together and buy another previa when it is all done (there area few for around $500 with BHG on CL).

I just updated my rebuild list (I just changed out the front end steering components and wheel bearings).