Re: Low compression

Posted by Owen_Dyneto On 2014/4/29 10:50:32

Following on from Richter's advice above, after cleaning things up (and DO NOT used sandpaper, the grit will get where you can't see it and cause rapid wear) I'd rotate the engine and examine the cylinder walls individually top to bottom for signs of scuffing, scoring (evidence of broken rings), etc. And examine the top of the pistons carefully for broken or cracked lands; take note of any oversize markings. How extensive is the ridge at the top of the cylinder wall? I'd pay especially close attention to that cylinder at the end whose combustion chamber looks wet and different from the others (or is it just illumination that makes it look so different?). You might try to borrow a bore micrometer and make some measurements of bore wear and taper. If everything looks good to the point, I'd remove the valves (keep them in order), examine the valve seats for condition (hoping no cracks are seen - especially on the exhaust seats) and do a complete valve grind, replacing any questionable valves and worn guides. If the cylinder walls all looked good, more than likely the low compression (and we don't what that is, right?) was due to valve wear - valve jobs about every 50,000 miles was pretty much standard stuff in that era. And for sure - never even think about reusing a head gasket.

When I was younger and with a restricted budget we often gave engines like this what we called a "semi-overhaul" and lots of garages made their bread and butter on this type of work. In addition to the valve job, we'd pull the pistons and if the cylinder wall taper was less than something in the range of 0.007", we'd hone the walls, install new or sometimes the original pistons (perhaps knurling the skirts to expand them a bit), new rings and wrist pins, and assuming the crank journals were good, new rod and perhaps main bearings, timing chain, etc. All of this can be done with the engine in the car, working from above and below. Was this as good as a true rebuild? Of course not, but often it was enough to get another 30,000 or more miles of reasonably good performance.