new motor or just rebuild mine

[dsmtunner123]

OK so i have had a very strange noise coming form my motor and i took the head off and to my suprise i have a bad wrist pin on my #3 piston and the noise was the piston hitting the head so now i am in a major dilemma because i am not sure to just buy another motor or to rebuild mine. What do you think?

 

[4GSixty3]

I would rebuild it...alot cheaper to do that then to get a motor you dont know what has been through.

 

[skier_du]

I'm assuming that since your car is a '93 it is a 7bolt. While it is possible to successfully rebuild a 7bolt, it is difficult.

I have rebuild some 7bolts, and a 6bolt after those attempts. The problem lies in the thrust bearing, of course. It is not to difficult to line up the the thrust bearing, however the problem of CW may still arise.

One of the major problems I noticed on my rebuilt 7 bolts was the main bearing cap, or girdle. The main bearing caps on the 7bolt are smaller than the 6 bolt and have bridges between them. The problem that occurred was that with age, incorrect maching, abuse, inferior material usage in the caps, or whatever (who knows exactly what or combination of things), caused the cap to warp slightly. I noticed this same thing on another engine that CWed. I could tell because of the uneven wear on the thrust bearing. The bearing was aligned fine, but twisted slightly. I had a very competent machine shop measure one of the rebuilt motors after I came up with this theory, and they confirmed that the cap was indeed off, twisted actually.

After this I decided to quit screwing around to build a 7 bolt and hope it would work (it was a 1g 7bolt, by the way) and just go 6bolt. The cost of acquiring a 6bolt is not great (often just a couple hundred for a rebuildable), the maching is the same, and if you are going to build up you only need the block, main caps, and crank anyway. Stock for stock, there is little comparison between the 6bolt's ultimate strength and 7. Yes the 7 is very strong, but any fool can look at the 2 side by side and see how much bigger the rods, bearing journals, main caps, and just about every other stressed part of the block is. The 7bolt will still rev slightly faster because of its lower inertia than the 6bolt, it has smaller parts which are lighter weight. However you can still have weight removed from a 6bolt and it will still have great throttle response either way.

Ultimately, with a very competent machine shop measuring everything, it is possible make sure the thrust is lined up in all directions. Thus resulting in a possible successful rebuild, as long as other problems (e.g. oil starvation, yes, I had that happen to a rebuild to. It had nothing to do with squirters; don't get a Topline oil pump as I am not the only person I know who had this problem with a new pump from them)don't cause crank walk. It has been done, and will be done again.

The previous was my experience. Do some more research and don't just listen to what one person has to say, but several reputable people. Then make your choice.

Good luck.

 

[oddrob]

The question might be answered by what kind of shape your old motor was in. If the piston was hitting the head, did it cause any damage? Did the pin score the wall?