Finally got time to let this twin SU-H6 B20B in my '69 144s run for a good long time, following R&R of the choke cable to recover the chafed sheath which was grounding out to the steering column support.

The entire time the engine ran (30 minutes), even after warm up, there was a steady stream of white, steam-like exhaust.

I could not attribute this to the mild, humid weather, as my other cars were not showing similar exhaust.

My concern is coolant in the combustion, as I was always told white smoke/steam indicated cooolant leaking into the block, cylinders, or a bad head gasket.

(I now have marked the coolant resevoir bottle to watch for coolant loss)

After shut down, I got these results on a check of engine compression:

In order of 1-2-3-4

155 - 160 - 155 - 145

Just in case gas was washing the cylinder walls by the time I did #4, I added a little oil and retested #4 at 153 psi.

Aren't these reading too low for a B20B? Haynes says it should be 170-185.
-28 psi is said to be bad, so, #4 is borderline at -25 psi.

Further, this is not the original head. It looks like an early carbbed model, but I don't know for sure. Could be from a 70-71 FI which has its injector holes bolted closed. It is definitely not a later FI unit.

Is the white exhaust and low compression telling me there is a problem? Or, could it just be low compression due to the different head and, maybe, a too-thick head gasket?

Or a head that is supposed to give compression in the 150-165 range?

Also, the plugs, which I had just cleaned, are dry fouled (black soot)

You didn't mention if you drove the car or just let it idle for 30 minutes. It could be that half of your exhaust is full of condensed water. Drive it for 30 minutes, with a good amount of 2nd gear and higher rpms to ensure that there is no longer water being boiled off.
Your compression numbers look good. The black soot on the plugs could be from just idling and slightly rich. Drive that car, it's more fun than sitting there and thinking the worst!

Klaus
--
(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)

No, it was idling for 30 minutes.

After posting this, I found some things online which lead me to believe sooting from running rich at idle is normal, depending on which of 350+ needles you have in the carbs.

http://www.triumphclub.co.nz/su_carbs.html

Can't drive the thing now, as the brake system is all apart for overhaul, and the right reear hind quater inner-inner wheel arch, which contains the reinforcement plats for the rear shock, is a large, gaping rust hole you could put a fist through.

And, I have a couple of daily drivers needing attention for inspection, etc.

Someday.

On 89 Octane, unleaded fuel, with "lead Addative"

Unless you have recently overhauled the engine that is pretty good compression.
135 is pretty normal for an old one still in fairly good shape.
I have run them with less than 100. Used some oil.

You may not be able to tell from the coolant bottle - better to pop the
radiator cap, fill it level full and watch for bubbles. You may get some
bubbles initially and then they will quit. That is probably normal. But if
they continue that is a sign of combustion product leakage into the coolant.
Be sure it runs long enough for the thermostat to stay open a while.

There are also testers that will test the coolant or headspace for combustion
products.

I'm curious about your head. Does it or does it not have the holes for the
injectors? They would be 7/8" in diameter and about 1/8" deep over all intake
ports, with about a 7/16" hole at an angle toward the valve near the center
of the depression. Mighty few were made in 70-71 (the famous "E" head). It
would also have an angled or blended area on both sides of the center headbolt
adjacent to the manifold surface. A carbed head may have the flat surfaces
over the ports but will NOT have the 7/8" diameter depressions machined into
them.
Later heads will have a blended area on one side of the center headbolt but
a square edge on the other side (72-73) and the 8-bolt engine heads will have
a square edge on both sides of the center headbolt (74-75). Nearly all of
these will be machined for injector mounts.

The injector depression is admirably filled by a 7/8" freeze plug. Some
caution that a backfire will blow them out but I have never had that happen.
I've been using the freeze plugs since about 1984.
--
George Downs Bartlesville, Heart of the USA!