Hi Iam just starting to teardown a 1990 7.3 to replace the gaskests and seals before I put in it my E250 van camper. My first surprise was the timing marks on the gears. Crank to cam look good but cam to Ip gear is off by 2 teeth. And it was a running engine when I took it out of the donor van And so far I have one head off and I have what looks like 4 pistons that have a crack in them. Ill try and post some pics http://img.photobucket.com/albums/v2...amper73002.jpg

 

And heres a pic of the pistons http://img.photobucket.com/albums/v2...amper73017.jpg

 

The pistons could be cracked due to timing being too far advanced, from the way it looks on the gear, the advanced timing would cause higher cylinder temps which would cause the cracking. Were your glow plugs burned on the end?

 

No but they are not real old. they have been replaced in the past at some time.

 

That, or someone used Ether on top of working glow plugs.....KABOOM!

 

Sounds like liquid fire(ether) Thats whats wrong with the 87 block I got in the garage....the guy who gave me the motor used ether with a half-assed glow plug system and the cracks developed in the middle like those ones are....do all the pistons look like that?

 

I have only removed one head so far and all 4 have a crack in them

 

those lines are definitely drawn on and I cant see the real timing marks in the picture. There should be a Y and a O stamped in the cam gear that lines up the corresponding Y and O on the crank and IP gear. Id go by those, since its possible for someone to draw the lines wrong.

 

I drew the lines on the gears .The lines that I drew are on the "O" s and the "Y" s timing marks Crank and cam line up but cam and IP do not

 

those pistons crack when overfueled and timing off combined, ether damage rips the ring lands off.

Normally wouldnt say this to a guy, nice crack

Make sure the piston oilers are good, that is a heat crack.

 

keep tearing it down, set of new pistons are not that expensive. .Pm answered.

 

Id HATE to hear what that engine sounded like... LOL...

 

amen on that

 

Wow im suprised it even ran that way

 

From what i understand its common to have stress fractures on the pistons when the egts are too high. I guess this happens to 7.3 power strokes too. Don't be fooled you can run high egts on a N/A just as much on a Turbocharged engine. My guess is the crack doesn't go through the whole of the piston.