'98 DOHC Head Gasket Replacment

[amgarb]

The SL2 I bought for my son had the gasket fail back in January. Just now getting around to working on it. Started tearing it apart last night, mainly for evaluation purposes. Depending on how bad things look, it may just go to the scrap yard. Basically, if I can fix it for $100-200 then I will, otherwise...

Is a there a good thread describing head gasket replacement for the DOHC? I've looked at some of the SOHC threads but didn't find one specific to the DOHC.

Question: Is it best to leave the intake in the car or lift it out with the the head? Is there room to lift it out without "rolling" the engine forward?

I did replace the intake manifold gasket on my other son's SC1 a short while ago. The DOHC appears to have even less room to work with!

[billr]

The head can be removed easily with the intake attached. There is a brace bracket from the underside of the manifold to the rear of the block that must come off; don't overlook that. I removed my head with the intake on and re-installed the head with the intake off so I would it would be lighter and more compact as I was trying to gently position it on the head. The intake was easy to install with the head in place. Got it? Your choice, it is reasonably easy either way.

Head gasket leaks are, and should be, very rare; but aluminum blocks/heads do not take kindly to over-heating. Check both the head and block surfaces for flatness.

I did not use new head screws, but I have many years of experience and a good feel for how a screw is stretching as it is tightened.

[Waiex191]

OldNuc's head installation procedure:
http://www.saturnfans.com/forums/sho...48&postcount=6

Page 11 of my thread, head installation pics.
http://www.saturnfans.com/forums/sho...230898&page=11

I'd go with a Fel-pro gasket. I used new bolts. They are torque to yield.

[amgarb]

Got the head off this morning. Now I'm at a crossroads and need to make a decision.

The block was flat. I put a straight edge on it (multiple directions) and couldn't get my smallest feeler gauge (0.002) under it anywhere.

The head is a different story. Seems to be roughly 0.005 gap in the middle of the head, especially in the narrow areas between the cylinders.

So I'm torn between putting $50-60 worth of gaskets in it and seeing what happens or taking the head to local shop.

What kind of money (range) do you think I'd be looking at to have the head inspected and redone by a shop?

[amgarb]

Or does anybody know of a reputable rebuilder who may have one in stock?

[billr]

Post a picture of the head surface, with the spots with the most dip high-lighted, so I can give a better guess.

That .005" over a 10" distance would not worry me, but .005" over just an inch would be iffy, and .005" over 1/4" might be impossible to seal.

Can you tell where it was leaking before, was it in those "low spots"?

[Waiex191]

Where are you located? Pakes machine shop in Janesville, WI did an awesome job on our head and whole engine.

[amgarb]

Originally Posted by billr

Post a picture of the head surface, with the spots with the most dip high-lighted, so I can give a better guess.

That .005" over a 10" distance would not worry me, but .005" over just an inch would be iffy, and .005" over 1/4" might be impossible to seal.

Can you tell where it was leaking before, was it in those "low spots"?

Couldn't really tell where it was leaking.

I'll try to post one tomorrow. I was going by Alldata which says max 0.004" longitudal for the service limit.

I also took the cams out and filled the intake and then exhaust ports with water. I've got 5 intake valves and 3 exhaust valves leaking.

History of the car: 170xxx miles. Bought it used (very cheap) as it had a cracked radiator. No idea if or how bad it may have been overheated. Fixed radiator and my kid started driving it. Had slow coolant loss. Then he said it puked coolant all over the place so he got it home and parked it. Next day, I looked at it and it wouldn't start. Did compression test (cold, because it wouldn't start) and had 100-120 psi on first two cylinders and 0 on the last two cylinders. Bubbles in overflow tank if I pressurized cylinder 3.

Can still see some light crosshatching in the cylinder walls.

[amgarb]

Photos attached. Hope this is what you had in mind.

The sharpie arrows identify the leaking valves.

hor.jpg

diag.gif

[amgarb]

I also managed to ding the surface on the dowel pin.

ding.jpg

[billr]

You did a thorough job in checking the flatness, thanks. That all doesn't look so bad to me, even the ding. Smooth any high point on the ding with a small flat file or emery board and use a god coating of Copper Coat or similar gasket sealer. I'm now going to recommend that you do use new head screws, though. Let's give this beast the best possible chance.

[amgarb]

What do you think about water running through my valves?

Think I should pull and lap them?

[Waiex191]

Originally Posted by amgarb

What do you think about water running through my valves?

Think I should pull and lap them?

I probably would. I had that happen on my VW heads. Those were new bug heads that were defective. In that case I replaced them instead of lapping them.

[billr]

Valves that are visibly leaking fluid should be inspected and fixed. You are wasting time and money to re-install the head if the head is known to be bad because of leaking valves!

PS: I use gasoline, alcohol, or paint-thinner to check valves; and fill the combustion chamber side. That takes less fluid to see if one is leaking and no chance of rusting the valve stems/guides

[amgarb]

Ordered parts (gaskets and tools) earlier this week. Lisle tool came yesterday so I started pulling out the valves. Plan is to gently clean them on brass wire wheel and then lap them before reassembling with springs and retesting for leaks.

If all that checks out OK, I'm considering taking it to a local engine guy that I found on facebook to resurface it. (As long as his price is reasonable.)

Any idea how much can be machined off without causing interference issues between the valves and cylinders?

[fetchitfido]

0.0196" (0.5mm) seems to be average for getting the head back into spec while the daredevils take off 0.04" (1mm). It turns into a timing issue before it turns into a pistons contacting valves issue. In my area at work we don't have any gauges that'll measure that large, the best we can do is 0.002"

Depending on how crazy you want the rebuild to get it may be worth the effort of getting '91-'93 valves, a '91-'92 header (inc downpipe) and a 2nd '91-'98 intake cam to replace the exhaust cam.

[amgarb]

Not going crazy on rebuild. Just trying to resurrect a junkyard-bound car on the cheap, if possible.

From my measurements, 0.008" should be plenty to make it flat again.

[billr]

I would pass on the head surfacing, try it as-is.

[amgarb]

Well, it appears the car will live to die another day. I'll feel better about declaring victory after putting a couple tanks of gas through it.

Got it all back together today. Fired right up. Only drove it for a few miles because the valve cover gasket (new) was leaking at one corner of the timing cover. Parked it and pulled the cover and applied some RTV around the perimeter. After checking Alldata, I didn't realize it was only required at the timing cover joints. Guess I should have checked Alldata first.

Got one extra bracket that I can't figure out where it goes. Didn't take good enough notes. Anybody recognize it from the attached photo? Kind of looks like the one behind power steering reservoir that goes to intake manifold but I already have one there. Is there supposed to be two?

I ended up having the head resurfaced. He took 0.015" off, said it was really warped at one of the bolt holes. This put it under minimum thickness so I had to buy a shim to go between the block and head gaskets. It cost me $80 for the machining plus the shim and shipping. I think I probably got $250 in the repair with all the gaskets and fluids.

[ssicarman]

From poor memory the bracket looks like it could be for power steering pump. Maybe something to do with the intake.