Amazon: The Amazing B18

[volvogv]

Lately I've been experiencing a loss of power when climbing hills. Usually a quick reset of the carb mixtures would bring it back. Normal tuning helps somewhat but the engine shakes and it won't run at normal idle speed.

Took a closer look at the engine. Cleaned and gapped the plugs. No change. Cleaned the carb domes. No change. Timing good, dwell angle good.

Pulled the spark plugs and ran a compression test:
1) 142 psi
2) 142 psi
3) 142 psi
4) 1 psi

That's right! 1 psi. It's amazing to me that the B18 can run with a dead cylinder and still keep up with freeway traffic.

I looked at the rockers to make sure they move (they do). I'm unable to open the engine until after June but I have a couple of theories to explain a total loss of pressure:

- Hole burned in piston.
- Severely burned valves.

I would think a failed head gasket or worn rings would still build up some pressure? Any ideas?

Mike

[Underdrive]

I think a holed piston would allow some oil past and this would cause some blue smoke to appear from the exhaust. I had a similar problem a while back and the car still got me a few hundred miles back home, compression test showed virtually no compression on one cylinder but I still haven't taken the head off to check it out, just substituted it for another engine I had.

[RSready]

A leak down test would give you an answer.

[Ron Kwas]

Mike;

First, I'd confirm your reading to assure that you didn't have an error using the compression-gauge (that would be a great simple answer and much preferred to just about any other possibility at this point)...but if 0psi reading is confirmed, there is obviously a big problem which will likely need the head to be removed (at least). It's either valves, or piston (with a blown head gasket, there would still be a certain amount of compression made).

Before removing head, I'd remove valve cover and verify both valves are fully closed and showing rocker to valve-stem clearance when #4 is at TDC (seat recession from unleaded fuel can cause exhaust valve not to fully close which would prevent compression...intake valves do not exhibit this issue). If you have access to bore-scope (micro)camera, you might want to take a look around the combustion chamber, to see what is not right (I expect the cause should be pretty obvious when you look around).

If it's a valve issue, removing head will be a good start...if it's a holed piston, engine needs a rebuild, but question is: What caused this in the first place? Super-lean mixture, way retarded timing, something you haven't told us of, etc? It would be mighty bad to install a fresh engine only to have it be hurt again by the original cause! Determine and fix root cause!

RS; A leakdown test is not going to tell Mike anything he doesn't already know...it is typically performed to confirm a leak in what is supposed to be a sealed volume...what Mike has is a catastrophic leak in his volume (combustion chamber) which is preventing compression...and he already knows that...

Good Hunting from Connecticut...let us know how you make out!

[Derek UK]

"Seat recession from unleaded fuel can cause exhaust valve not to fully close which would prevent compression...intake valves do not exhibit this issue."

Just the opposite of that. Inlets normally OK. Seat recession gradually closes the valve clearance and can get to the point that the valve doesn't close at all. This situation will mean no compression on that cylinder. Check all of your valve clearances, especially that one. If you take the rocker gear off and put a straight edge along the valve tops, it's unlikely that they will be exactly in line but the exhaust valves are the ones to check. the amount they vary will denote the amount of recession. It is possible that some thousands of miles back the head was off and the seats recut without adding inserts for lead free and because of this the exhaust valve levels might not be equal if different seats needed different amounts of cut. In this case you could still have good compression. i.e. the 3 that are good might show some difference.
A totally flat cam lobe can kill a cylinder without much loss of compression if the valve clearances are OK. It just won't lift much. Turn the engine over and watch that cylinder's valves. The lack of lift will be obvious.