I decided to pull my engine and transmission this week as an interlude to a full-on "tricked out" restoration that will start later in the future. I had the top-end of the engine out, and didn't want the block exposed to moisture and debris if I store the car in a shed. I pulled the oil pan off today and everything looked good right away. After looking around and thinking about pulling the oil pump, I saw two large 1" pieces of clean metal sitting back on the bottom surface of the block, right next to the rear main cap. I cleaned them up and did a little thinking on where they could have came from. My first thought was that they were from the crankshaft. It's a cheap nodular crank from Dallas Export Sales in TX (could be a China crank for what I know). I thought well maybe if some of the balancing work wasn't perfect and if the crank was of poor quality, maybe a corner surface could have broken off. And I almost believed that, but these pieces looked too big. I looked the pieces over some more, and I noticed that they both had a chamfer on the one side of them. That was the giveaway. I looked at the bottoms of the skirts on the pistons and some of them "WERE MISSING". After more looking, 4 sections to be exact. 3-5-7 and 8. I found the other two, I believe they all fell into the oil pan when they came off, and so the other two that I didn't see right away probably fell inside the pistons when I rotated the engine on the stand.

Now i'm thinking to myself (jokingly), is this a breakin characteristic? :rolleyes: :eek: Probably not 1500 miles on the engine. The Comp Cams Magnum cam survived breakin with springs set up for .600 lift, and the piston tops survived DCR's of 8.3:1 with 87/89 octane fuel, but the skirts couldn't stand 375 HP tops? Think i've only had the engine up to 6500 rpm once during its current life.

What's your take on this? :D

I allways thought KB pistons were pretty good,hhhmmmm!!!

Sounds to me like the bores were too big, allowing the piston to rock back and forth at the bottom of the stroke, cracking the skirts ? Only other possibility is that the crank counterweights were barely touching the piston skirts and ended up cracking them off. Look on the crank to see if there is any evidence of that happening.

Bill,

I think your second answer is it b/c my old junk301 with, I swear I pushed a .015" or maybe a .020" feeler gage down beside my pistons, ran fine except for knocking and a hammering upon a cold start up.

Cast W/JCW, 1/8" over, 1/8" half round 283" el-cheapo $34 or was it $39/set pistons!! I think they were Simplex'es???

And I ran her hard above 7,000 rpm's many, many times until a stock rocker gave out and kicked a solid lifter out!! AND I wasn't smart enough to realize the old junk301 motor was STILL FINE!!!

Sure she used alotta oil, but she would STILL rpm above 7 easy with no more than the old Duntov cam!!

pdq67

After looking at the assembly, don't see that the crankshaft hitting the pistons would be a possibility.

The P/W clearance is another issue. There isn't an over abundance of clearance when measured at a right angle to the piston pin. And there wasn't a real simularity among the cylinders. Some cylinders I could fit a .003" feeler gauge into, some I couldn't fit a .0015" into. I'm not sure if this is the way it's supposed to be, but there is more clearance on the piston pin sides of the P/W than there is when measuring on the side with the longer skirt. Might even be a difference in clearance from the one side of the piston to the other side. Also, I don't know if it's a coincidence, but the pistons that have a piece of skirt broke off have it broke on the inside "side" of the engine, not on the outside. Any coincidence there?

Usually broken shirts are from WAAAY too much clearance like I was talking about.. Revving her hard, cold too!!

Or extremely high rpm's, but then the engine usually loses a piston completely and self destructs!!

pdq67

If I remember right, I believe KB recommended .015-.025" P/W clearance at the skirt. Does that sound too much? That was for the street engines.

Any reason to be worried about the "not being able to fit a feeler gauge in between" on some cylinders?

I left the 3, 5, 7, & 8 pistons in the block, in case anyone knows of anything else that I can check. Would it run fine that way?

Also, I don't know if it's a coincidence, but the pistons that have a piece of skirt broke off have it broke on the inside "side" of the engine, not on the outside. Any coincidence there?


Correct me if I am wrong BillK but isn't the "Inside" side the "thrust" side? If so then that might explain why the skirts broke only in that position.

I agree about "piston slap" and pushing the engine too hard on a cold morning.

I may pull a rod cap or two on the ones that are left in there to see if there are any noticeable wear spots on one side of the bearing.

Top or bearing half in the rod instead of the one in the cap??

Detonation, but I would think your piston tops would go first????

Donno, just donno?????????

pdq67

The thrust side of the piston is the passenger side (right side when sitting in car) on all engines except "reverse" rotation ones. So the thrust side is only the inner side on the left bank pistons.

Yeah, I figured with detonation that I would have ring issues. No signs of detonation anywhere, but i'm real suprised.

Well, so far all of the bearing halves have been located fine. 3 out of the 4 bad are on the left bank, but they all look like they were damaged the same. I'll have to check the rod bearings after dinner here.

Thanks

Have you talked to anyone at Keith Black? I would be interested in what they have to say, especially since I used there pistons in my 427 build up!

I haven't speaked with any representative.

I checked the bearings tonight and no noticeable load to the one side of the bearings. I did find two cylinders that had copper stripes on the bearings, don't know what was going on there, but that doesn't have anything to do with the pistons.

FWIW, I measured the cylinder bore at the top with a mic, and I got 4.025. Is this correct? Couldn't get an accurate reading at the bottom, still have the crank in.

I haven't speaked with any representative.

I checked the bearings tonight and no noticeable load to the one side of the bearings. I did find two cylinders that had copper stripes on the bearings, don't know what was going on there, but that doesn't have anything to do with the pistons.

FWIW, I measured the cylinder bore at the top with a mic, and I got 4.025. Is this correct? Couldn't get an accurate reading at the bottom, still have the crank in.

The stripes on your bearings most likely came from the debris off off the broken piston pieces..

Scott