Orange peel on top of piston

[Petros]

It is possible to save the bore and the crank without going to the machine shop, if they are not too badly worn. You can lightly hone the cyl and hand polish the crank journals.

If the crank and bearings are scoured it sounds like it was run dry of oil. Make sure you clean out all of the oil galleys (use a fine bottle type brush, available at auto parts stores), and your oil pump and the by-pass valve is working properly and within spec. I have seen many blown engines from poor oil pressure caused by bad oil pumps or gummed up by-pass valves (the over-press valve, if stuck partly open it does not allow full oil pressure).

low oil can cause low compression since the rings are sealed with a light coat of oil. Though generally wasted bearing will not have much of an affect on compression (unless they are really bad). The test of low compression being rings or not is to squirt motor oil into the spark plug hole and re-do the compression test, if the compression goes up from the "dry" test, than the rings are worn, if the compression does not go up much, than it is either leaky head gasket or valves. Not possible to do after you dismantle the engine.

As far as the overhaul is concerned. IF you can hone the cyl. AND it is still within the max allowable spec for piston to cyl. wall clearance, you are okay to just hone it. It has been my considerable auto engine experience that a small mount of vertical scoring will not have a noticeable affect on compression or engine performance (I have pulled apart engine with good compression that had rather bad vertical scoring). The key is worn cyl. walls, if they are out of spec after a light honing, than you have to overbore the engine and replace the pistons with oversized ones. Also make sure the piston skirt is also not worn out of spec, often if run low on oil or with real dirty oil (which will not only ruin bearings, but will also scour the piston skirts and cyl.) it will wear out the piston skirts. Too much piston to cyl. wall clearance can lead to piston slap and eventual skirt failure.

A way to get a top notch cyl. hone is to heat the block up as warm as possible. In a water cooled engine this is easy by plugging the coolant inlets/outlest and fill it with boiling water before you hone it. On light engines many machine shop also use a "torque plate", a large alum or steel plate that gets torqued to the block like a head, but allows you to hone the cyl. it can look like a head with large holes through it over each cyl. The idea is that both torquing the head in place, and the heating of the block during running will distort the bore, and both using a torque plate and heating it will make a more precision hone since it will be closer to the condition when running. But I have seen tests that show heating the block is more import than a torque plate, and it is easy to do at home. I have had excellent results by filling the block with boiling water when I hone it (several water changes are required to keep it warm during honing).

I have done low budget overhauls, and just honed the cyl and replaced rings, willing to live with a sloppy piston fit. Sometimes this works okay, sometimes it does not, after the piston skirt fails you have to rebuild it again anyway, and if you are lucky the damage is limited to the piston. So there is no economy in doing a low budget rebuild if it does not last very long (the cheapest way to overhaul an engine is to do it only once!). If you have piston to wall clearance within acceptable limits after you hone it, you should be okay just to replace the rings. If not, either replace the engine or get oversized pistons and overbore the block.

If the crank bearings are not too bad they can be hand polished to a smooth shinny finish. It cost almost nothing to do yourself. Use a strip of 800 grit wet and dry sand paper, with a light honing oil or solvent (I use spray carb cleaner). loosely tape the strip around the journal so it turns freely (with solvent or lite honing oil), and wrap it several times with a length of cotton or nylon cord, and pull back and forth on each end of the cord. This will turn the paper around the journal and put even pressure on it. the action is like polishing a shoe, you pull back and forth on the cord ends as the paper works back and forth on the journal. It only takes about 30 to 60 seconds of this to clean up most journals. Keep checking until the journal is smooth. After polishing carefully measure the journal dia. to make sure it is within spec for min. dia. I have found it will seldom take much off to clean up the journals, like .0003-5" (well within wear limits). If you have only one or two deep scour lines, but the rest of the journals are good, it would be okay to leave these and run it. All they do is slightly reduce the surface area of the bearing, and if it is otherwise good there is no reason to regrind the crank just because of that.

OTOH, if they are badly scoured and gouged and you can not polish them out and be with in spec, they need to be reground. If you have to regrind the crank consider having it rebalanced too.

If the bearings in the cages are scoured or have blue discoloring, they need to be replaced. If the crank is within spec after polishing, you can use standard size bearings, if the crank needs to be reground than you need over-sized bearings.

The key on both honing the cyl. and hand polishing the crank is the clearance spec. You need to have accurate measuring devices, if you do not own them many auto parts stores will rent them to you. Sometimes you can take the block and crank into the parts stores or machine shop after you work on them and they will measure them for you to tell if they need to be machined. Same is true with the pistons, if you do not have access to accurate measuring devices, take them to the parts store or machine shop and they can measure them for you.

Do not feel intimidated by this, most engine overhauls I do I hand polish the cranks and go with standard size bearings. About half of the time I can just replace rings after honing the cyl. I will never spend more than I have to, OTOH every time I cut corners I ended up redoing the job within a few months. these are hard lessons learned for a cheap skate home mechanic (former full time mechanic). But there are a lot of parts that can be reused as long as they are serviceable. Many parts stores will tell you to replace the oil pump, valves, and other parts, but if they are in working order, use them. I have even reused gaskets! If you can get them off without damage, they can be reused. The only exception is the head gasket (unless you have an all metal head gasket, they can be re-used if not damaged). I love metal gaskets, I reuse them all the time without issue.

Good luck.

[robbyt8165]

Could I replace my crankshaft from a different year? My engine is 1987 and have found a crankshaft from a 1986 at a decent price (less than $200 including shipping).

Also am going to take my crankshaft to a shop to see if they can clean up the journal without getting it out of spec. Upon closer look, half of journal is smooth and the other half is more pitted than scored. Since the bearing melted, some of this may even be build-up rather than erosion. I tried the sandpaper-rope. It polished the smooth side nicely but isn't cutting through the pitted side significantly.

Thanks for replies.

[Frosty]

Did I say you need a new short motor? Oh yes I did, I just wanted to make sure I did because in my young days I tried so hard to repair this stuff!!!!