ammonman

Just need to vent for a minute. As some may know I've spent the winter re-sealing a 100k mile '88 engine I purchased from Gary Knox to replace my 230k lump that has seen better days. Finally got it started up yesterday and ran it today long enough to heat up the trans and top up the trans fluid and discovered the new passenger head gasket I installed is seeping coolant at the bottom front corner. I used new head bolts, made sure the washers didn't rotate as I tightened the oiled bolts per the WSM procedure of 20nm then two 90 degree rotations. I debated whether to use the old racers trick of letting the gaskets sit 30 minutes, then re-doing the torque procedure and decided that the engineers in Stuttgart were paid well to determine the correct torque procedure so I followed the WSM to a Tee. Frustrated that I'm not done with this saga cause the motor sounds great compared to my old lump and it is peak driving season here. Plus, I just love driving a 928. Debating whether to pull the engine back out and completely re-do that head gasket, do the head gasket with the engine in the car, or just drain the coolant and try re-doing the torque on the bolts. I'm not too concerned about the new bolts being over-stretched so that will save a couple hundred dollars (the 180mm bolts have doubled in price from $9.80/ea to over $18 /ea since I bought the set for this job.)

What say the group?

Mike (bummed in Arkansas)

Update: looks like the issue is with the powder coated water bridge leaking, not the head gasket.

polecat702

I'd PM Greg Brown. He'll give ya the best advice, Mike.

worf928

If any of the hoses at the water bridge have a leak, it can look exactly like the passenger-side head is leaking at the bottom front.

Let the engine cool. Put paper towels stuffed under the water bridge hoses.

Then pressurize the coolant system with a tester (rent one from AutoZone or Advanced Auto Parts, or NAPA, etc.)

Then check to see if your paper towels are wet or the head is actually leaking.

ammonman

Thanks Dave. Already fixed a leaking rad hose by rotating the clamp so it could be tightened completely. I'll double check the rest to be sure.

Mike

davek9

Also check your Water bridge to block seals, a Pressure tester is great advice it's very hard to see a small leak with the engine running

GregBBRD

Runs around the front corner, down the head, drips off of the tensioner, and onto the A/C compressor below? Also fills the small valley in front of the filler neck and to the left (as you look at the engine from the front) of the water crossover where it inserts into the block?

ammonman

Dripping off the side of the block just forward and below the protrusion for the locating dowel onto the compressor shield, then off the shield onto the back of the compressor. But, the car is on stands with the front a bit higher than the rear so gravity might be at work. I just stuffed the under-bridge area with towels and ran the engine until the fans cycled twice. Should have coolant pressure so we will see.

Thanks for talking me down off the ledge everyone.

Mike

ammonman

Well, preliminary results are that there is a leak at the coolant bridge as after putting towels under that area and running the coolant up to temp I haven't had any drips so far. I re-used the bridge that came with the engine I got from Gary Knox and it has been powder coated. Hopefully the powder coat isn't too slick. I seem to remember others here that have had issues getting the hoses to seal to powder coated nozzles. At any rate, that will still be easier than dealing with a bum headgasket.

Mike

SeanR

If the bridge is powder coated you could be in for some fun games with it besides sealing the hoses. If you didn't already, you need to ensure the contact surfaces are coating free on the bridge, the bolts, and the two temperature sensors. After fighting issues with them I won't install PC'd water bridges any longer.

GregBBRD

Very doubtful that it is a head gasket....you would have to leave a giant chunk of old gasket stuck to the block or head for this to be an issue. Warping of these engine is very uncommon. I assume that you had the "pits" in the head where the head gasket contact repaired....or the pits we minimal and required no attention (I surface every cylinder head that comes off of one of these engines, these days....and most of them get, at the very minimum, minor welding of the "problem pits". Some get large amounts of welding.)

The most common problem is for the rear adapter for the heater to warp slightly. The other problem is that the adapter in 1988 was of the two piece design and could leak where the hose attachment piece is glued into the main body. Always replace this piece with the "updated" version 928 104 713 02. Combine this with the very soft Victor Reinz gasket under this....and 18 ft lbs of torque and the gasket will split. Additionally, ANY additional sealant applied to this gasket will make it "slip" and leak. The fluid runs forward along the trough where the head meets the block and runs down the front of the head surface.

Of course, the front water cross-over can also be a source of a leak....this is also a very tricky area to get to seal. Many people "powder coat" the water cross-over....this is generally a disaster! The hoses can't get a grip and blow off, the gasket surface is too uneven to seal where it attaches to the head. The temperature sender won't get a good ground....the list goes on and on. I shudder every time I get an engine in with this piece powder coated. I will not assemble an engine with this piece powder coated....I just throw it away and get another one.

There are very specific things that need to be done at these junctions, for them to not leak.....I've tired many different approaches before I found what reliably works.

ammonman

Thanks for the insight Greg. I didn't skim the heads as none of the small pits were anywhere near the sealing areas (fire ring or gasket "bead" area.) I just scraped the head and block surfaces clean with a razor blade till everything was clean. I will drain off some coolant and swap the powder coated bridge for the original "bare" unit from my old engine as I suspect this is the source of all the problems.

Mike

GregBBRD

Good find. Getting rare to find no pits near the fire rings. As you figured out, minor pits in other areas do not matter.

Use the stock red silicone gaskets on the water crossover . Thin.layer of Drei Bond on the two flanges (including some on the red silicone), to help with any imperfections in the surfaces....no paper gaskets on this end.

worf928

Thoughts on why the factory started using both the red and paper gaskets on the water bridge in '90?

The Forgotten On

I used the paper gaskets in my 81 ion the water bridge and it started leaking coolant again after 2 months. They were the VR gaskets.

At least this time the bolts wont pose a problem...

GregBBRD

There's a significant difference between factory gaskets and Victor Reinz, BTW. When I use a Victor Reinz gasket set, I pick out the gaskets and seals that don't work as well, in the Victor Reinz kit, and substitute in factory pieces. (Contrary to common beliefs, "cheaper" is very seldom better, unless one is price shopping for the identical part or product.) The people that don't do 928 engines on a daily basis and are not aware of the differences/inadequacies of each individual part in the Victor Reinz kit would be better served buying a factory gasket set. (It is now to the point where the substituted and missing parts in the Victor Reinz kit almost make up the price difference for the factory gasket kit.)

I used to install factory gaskets in addition to the red silicone seals, under the front crossover, before I figured out that Drei Bond worked better.

I generally use factory gaskets on the rear of the head, except in special circumstances.

BTW......Drei Bond on any paper gasket is, in general, a mistake.

On a personal note, I'm not very "fast" at what I/we do. We, very rarely, get anywhere near "flat rate" allowed job times. I/we think about the implications and potential problems with every single piece we use. Every single used piece we install is clean enough to lick and has been inspected for flaws or damage. Every single new piece has to perform as well or better than a factory new part, as installed 30 years ago.

There's no way around the fact that quality takes time. There's also no way around that doing something a second or third time sucks.