427 cylinder condition questions....

[Greg L.]

I know this might be tough to answer with only pics to look at but I thought I'd give it a shot so here goes.

The engine is from my 69 and it's an L36, std size and only de-glazed once by me about 15k miles ago back in 88. At the time the car had about 51k miles. Back then I remembered some cylinder scuffing and a few scratches but nothing seemed too bad and it wasn't smoking so I just did a quick de-glaze, installed new rings and bearings and called it good. The only issue I ever had with it was that the thermostat stuck closed once and it got pretty hot...not hot enough to give it that "cooked" smell but the needle was right up to the red! Before I shut the engine off about 4 years ago I let it run for about a half hour and noticed that the right side was smoking a little. I don't remember it being oil smoke but more like moisture from the muffler which makes sence with the heat riser being on the right side... Also further down you'll see pics of each cylinder bank with the right side being relatively oil free but the left side not so much.

Fast forward to now and I'm trying to decide if I can get away with a quick de-glaze again or if I should go .020 over and make it "perfect". The pros of that are that it will still be std bore, cheaper and 0% chance of a machine shop messing something up. The con is that it might smoke...I really doubt it but I'm not sure...

Anyways here are some pics of what I feel is the "worst" cylinder-(#3). All the cylinders seem to have the same degree and amount of marks, I just decided to pick on #3. Note the long tapered marks as they appear to not have been touched by the rings because they still have fresh looking de-glaze markings from 15k miles ago! The first pic also shows where some oil looks like it is passing because it has washed the carbon from the piston head but the washed area is not where the long tapered marks are so I'm not sure what is going on there...





Piston-(#3)



Here is cyl #5. Still more of those long tapered marks with nice clean de-glaze marks but there is no indication of oil passing these rings so I don't know if these marks are an issue or not....I would think not?


Piston #7, it's cylinder is a lot like the #3 cylinder.


Remember how I said that the right side seemed to smoke but I didn't think it was oil? Well I don't see much indication of oil passing on the right side(a little starting on #2) but it looks like a little more was passing on the left side. Yes I did remember correctly which side smoked...it's written down in fact.

Left cylinder bank.


Right cylinder bank.


So at this point I wasn't sure just what to think of the whole situation. No they are not perfect but they just might still be serviceable. So why then do some rings appear to be passing oil and others are not given that the cylinder marks are pretty much in all cylinders but only the left bank seems to be passing a bit of oil?

Could this be the reason?


These are the top and second ring from #3 and they have obviously lost a fair bit of tension. These were Hastings cast rings and should have lasted a lot longer than 15k miles...unless they got overheated... Could that "little" overheat that I had a while back with the stuck thermostat actually been hot enough to cook these rings and cause the oil to pass a bit on a few cylinders? I've taken engines apart before that have been overheated and this lack of tension is typical of their rings. Those engines often have this cooked/burnt smell though that mine doesn't so I wasn't thinking that it got hot enough but maybe it did.

Sorry for the long drawn out story but I just wanted to explain this dilema of mine as best as I could.

So all things considered, do I have to go .020 over or will a light de-glaze and new rings make it servicable or as good as it was before it got hot?

Any advice here is greatly appreciated!!

Greg Linton
#45455

[Timothy B.]

Re: 427 cylinder condition questions....

Greg,

Why not find a good machine shop in your area that does engine rebuilding and let a pro look at that block. There is no way to tell cylinder condition without checking with mic. Does not look bad to my eye and I bet if it's within .003 of standard bore a proper hone and knourl(sp) piston skirt with new stock type rings will be fine. After you cross this hurtle pay attention to rods, engine balance and compression then of course head work. Did the engine use oil? What did the spark plugs tell you?

[Greg L.]

Re: 427 cylinder condition questions....

I have one of those cheap ebay bore gages so I'll measure up one of the cylinders and post what I find. I guess I could take it to a shop that I know of but I get the feeling that any shop will want to bore it "just to make it right"...

This actualy is my last hurtle because the heads are already done. AND, if I can get away with the original pistons then I have nothing to worry about in regards to the rods, balance and compression. The rods will stay the same regardless but if I have to change pistons then I'll have to make sure that I get the right ones in regards to compression. Never thought about engine balance... Again if I keep the original pistons I won't worry about that but if I change them what all needs to get balanced? ...maybe one more reason I see to try and stay with the original pistons...

The plugs looked all about the same. I think maybe one or two were a little more wet but then again the engine sat for about 4 years so something may have gotten up to them during that time. There was no heavy fouling on any and they looked pretty much like the tops of the pistons that you see in the pics. Oil usage...I can't really say. I never added any oil between oil changes which were once a year but then again the most I ever drove it in one year would only be about 2-3k miles and that was before it overheated. The last 10 years the car was hardly used so I can't say if it would have used oil of not.

Keep in mind that this is not a race engine, never was nor ever will be so I'm trying to keep it as close to original as possible.

[John H.]

Re: 427 cylinder condition questions....

I see bore distortion and scuffed piston skirts - I don't think "de-glazing" is going to get it done. I'd get it measured and go to the next largest bore size you can get pistons for, moly-faced rings, bearings, balance, and put it back together. You don't want to go back in there again.

[Greg L.]

Re: 427 cylinder condition questions....

I measured that one cylinder and I get .002" taper on the thrust side (90 degrees to the block center line) and no measurable taper fore and aft. Those long tapered marks show up as being maybe .0005" at the most. Given the appearance of the cylinders I was a little surprized that the wear wasn't greater. I think I'll measure the rest of them as per the overhaul manual and see what I come up with. Worst case senario I think will be .020 oversize. That shouldn't hurt the value too much should it?

Now about balancing...what do I have to get balanced and why? Shouldn't the replacment pistons be close enough to the originals so that balancing won't be required?

[John H.]

Re: 427 cylinder condition questions....

Greg -

It would be a real stroke of luck (and highly unlikely) to find replacement pistons that weigh exactly the same as the originals; just spend the extra $150 and have it balanced - it's worth it.

If I was looking for a car, I'd see the rebuild, new pistons and rings, and balance as a plus (assuming it was done right); no need to go back in there for many years.