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Classic Saab 900: Mikes Head Gasket Guide

Thanks to Mike M from NY - USA, 91 Saab 900 16v

This article recounts my misadventures installing a new head gasket on my wife's 91 Saab 900 16v. The head gasket had failed prematurely at 65K miles. By announcing my own blunders, perhaps I can help others avoid repeating my mistakes, and also suggest a now time-tested solution to a related problem of cylinder head etching.

My wife called me at work one day, advising (complaining?) that her car's engine wouldn't crank over. She usually gives me an accurate description of the problems she has with her car, so I was fairly confident that it simply needed a battery charge. This would not have been the first time that the dog switched on the dome light while crossing from the back seat to the front, causing the battery to go flat.

When I got home that evening, I went out to check the car and to my surprise, it started normally. However, a plume of steam continued to pour from the exhaust long after the normal warm-up period. When I got a whiff of the stuff, I immediately noticed the sweet smell of burning antifreeze. Apparently when my wife attempted to start the car, the cylinders had been hydraulically locked with antifreeze which then slowly leaked down to the crankcase during the day. I knew that this particular model engine (its nomenclature is B212) has a history of head gasket leakage and figured that was the job I was in for.

When I removed the cylinder head, I found the #1 (rearmost) cylinder fire ring blown through to a coolant passage. In addition, the cylinder head surface had been badly etched in two places where the head gasket intentionally blocks off coolant passages. Replacing the head gasket was not going to be a problem, but the cylinder head looked too badly etched for resurfacing.

I had seen a similar problem occur on Jaguar engines from the late 80's. I remembered a factory service bulletin that recommended filling the etched surface with an epoxy filler, such as JB Weld. If its good enough for Jag, it is good enough for me. The epoxy compound nicely filled the etched cavities. I finished the repaired area level to the surrounding surface with a fine, flat file.

A mail order parts source sent an OEM head gasket set to me overnight. I had the cylinder head back on and the engine running within 2-days from its failure. It might be valuable to note that while the service manual warns that new cylinder head bolts should be fitted each time the cylinder head is removed, I had no problem getting a solid reading and feel at the specified torque-angle on this assembly.

As I sat in the driver's seat waiting for the lifters to pump up, I thought, this is going better than I could have hoped. After about ten minutes, the engine went quiet at idle. That seemed like a long wait considering that the lifters had been pre-bled before installing them, but then this was my first SAAB head gasket and maybe it was normal.

No such luck. As soon as the engine reached 3000 RPM, it clattered as if all of the lifters had pumped down. The service manual suggests that this situation can occur if air is trapped in the oiling system, and that the system should be bled at the appropriate cam bearing bolts. Then additional mileage should cure the problem. Once again, no such luck. After bleeding the oiling system and about 30 miles of hoping and waiting for the engine to quiet down, I resigned myself to replacing the lifters which I surely must have damaged when attempting to bleed them

Once again, the mail order stockist came through with next day shipping of a new set of lifters. They were installed quickly, ... and made no improvement. Now what? I knew I had created this problem somehow or another, so it was going to be a case of retracing my steps. Off with its head again. At least this gave me the opportunity to check the condition of the epoxy repair, which still looked perfect.

Nothing seemed wrong with my work initially. But careful inspection revealed a narrow, polished ring at the circumference of each piston crown. When I laid the head gasket in place, I found that the fire ring intruded into each cylinder by, perhaps, half a millimeter, enough for the piston crown to contact it. Once the engine got hot, thermal expansion somehow made things just clear at idle, but reciprocal loading at higher RPM caused the connecting rod to stretch and once again let the piston hit the fire ring. What a combination of circumstances!

Some research in the repair manual solved the mystery. Another SAAB engine, the B203, is almost identical to the B212 except that it has a slightly smaller bore and longer stroke. Apparently, I was supplied an incorrect head gasket set for the B212. Another set (from a different mail order supplier) had the correct gasket which cleared the cylinder bore by at least a millimeter.

Upon reassembly this time the cylinder head bolts had stretched. I could not achieve the torque-angle without a spongy, non-progressive feel on the wrench. Empirically, I'd put a limit of one reuse (two torque cycles) on the cylinder head bolts. A new set of bolts put it right. This time, the engine was immediately quiet throughout the rev range (and so it should be now that it has a new set of lifters, arghh.). The engine has been in service now for over a year and has been fine with no sign of trouble from the repair.

I hope this article sheds some light on potential pitfalls of what should be a straight forward job.

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