Weird 390 wrist pin issue

[TomP]

I found a 390 in the back of my garage that i never knew i had. I pulled it apart and found a couple of issues.
 On one piston the one snap ring was broken in half. Never found the other half but the snap ring groove is fairly chewed up, the rod bushing is worn away to nothing on one edge, fairly evenly all the way around and the still intact end of the bushing hangs out past the rod. The piston looks fine, no scrapes on that cylinder either.

What could cause that?

The other issue is the crank end thrust is almost 1/4". Crank has such a deep groove in the back of the journal you could almost fit another thrust bearing in place. I would guess a torque convertor not into the second set of splines. The engine appears to be very low miles, D4TE block and standard bore and bearing sizes with hardly any wear, very clean inside too. No obvious grit from that worn crank thrust surface.

[SMorton67FB]

Sounds like the crank moving that much put side pressure on the rod and caused uneven wear on the rod bushing.

[TomP]

That makes sense. It doesn't appear the rod was hitting anything but i suppose pinch against the inside of the pin boss would do that.

It has so much thrust wear it looks like i could leave that bearing in the groove and there would still be room for a new bearing. I wonder if that can be spray welded or something to reuse the crank.

One other thing. The drill bit test shows the block is the same cores as my 69 428CJ block.

[mike7570]

If you need a crank, I have one in classifieds.

[wowens]

Sounds like the crank moving that much put side pressure on the rod and caused uneven wear on the rod bushing.

Wouldn't other rods show the same issue if thrust caused it? Both issues could all be directly related to the broken snap ring.

[pbf777]

Wouldn't other rods show the same issue if thrust caused it? Both issues could all be directly related to the broken snap ring.

    And or, the rod is bent or mis-machined, in either case look for the pin bore and the big-end bore being not parallel as this could have caused both failures.       

    Scott.

[427John]

Wouldn't other rods show the same issue if thrust caused it? Both issues could all be directly related to the broken snap ring.

    And or, the rod is bent or mis-machined, in either case look for the pin bore and the big-end bore being not parallel as this could have caused both failures.       

    Scott.

X2 any misalignment from parallel on the big and small end will be like a little hammer trying to drive the wristpin out, the small end bushing being worn on 1 end is another indicator.

[AlanCasida]

I have ruined two crankshafts in my 427/452 the same way you said yours is...excessive wear on the thrust surface. I first thought is was my converter not having the bevel on the back side of the converter snout where it engages the pump. I fixed that and made triple sure I had enough clearance between the converter and the flexplate when I put it back in the car(with a new Scat crank) After about 750 miles I took it apart and the crank was ruined in the same way. The only thing I could think is causing is the converter being somehow pushed forward under pressure.  I have yet to decide how, though.

[winr1]

Tom..... the crank have a bushing in it ?? 



Alan .... can ya install a new thrust bearing in block and check to see if square ??

If ya have a known good crank, use some blue and turn with pressure against crank perhaps

Is the 3rd main cap native to the block ??

Caveman way but might give a hint



Ricky.

[TomP]

I'd say mine was from an automatic, it had no pilot bushing. No idea the history on it, someone had the pan and timing cover off before... they were almost permanently attached with Right Stuff. But original standard pistons and original Ford standard bearings.

[427John]

Maybe they ran it without the spacer plate between the trans and engine block?

[427John]

That makes sense. It doesn't appear the rod was hitting anything but i suppose pinch against the inside of the pin boss would do that.

It has so much thrust wear it looks like i could leave that bearing in the groove and there would still be room for a new bearing. I wonder if that can be spray welded or something to reuse the crank.

One other thing. The drill bit test shows the block is the same cores as my 69 428CJ block.

Some FT blocks had the the thick walls I've seen a C6 FT block that had the thick walls and even had the 428 cast into the bottom of the water jacket,this particular block also had the bosses for the crossbolt caps like the old C4AE-A blocks,it was machined at 4.05 bore and had the large distributor shaft hole for the FT distributor.Does yours have the large hole or been bushed?

[brettco]

 Is it c6ft or c6me? Would it have a scratch on the back? I found a c6me-a block with a c4ae-b  crank. Trying to figure out what it is.

[427John]

Is it c6ft or c6me? Would it have a scratch on the back? I found a c6me-a block with a c4ae-b  crank. Trying to figure out what it is.

I can't remember if it was a C6ME or a C6AE but it was definitely an FT truck engine out of a u-haul truck there was no scratch on the back,but did have the little 428 cast into the bottom of the water jacket though that is not always on the thick wall blocks,I've also seen a factory warranty 428cj shortblock with a 105 D3 or D4TE block in a 69 mercury cyclone gt r-code that had its blown engine replaced by the dealer in 1974 or 1975,I had read about those blocks being used after the supplies of original blocks dried up but took it with a grain of salt until I saw that car.I was looking at the car thinking of purchasing it so I looked it over pretty well including the receipts he had,but I had just bought a 69 cyclone CJ and couldn't convince my wife that they weren't 2 of the same car.

[brettco]

 Thanks. I think I found a Nov. 66 428 block with the 4 bolt bottom end. They made some of everything.