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Replace 3.3 V6 with a 2.5 L4? Is it possible? Preferable? Am I insane?

4K views 7 replies 6 participants last post by  mishagos 
#1 ·
Had some very bad clunking noises on startup after about 6 months of lifter noise that wouldn't go away. I'm assuming I lost the lifter and that was the #1 valve clunking against the piston. It's now stuck.

SO: I figure at best I need to remove the front bank head and get some valve work, clean up the mess if there is any (luckily, the engine was just starting), and put it all back.

Since the 3.3 gets such god awful mileage, I was wondering if anyone's ever put a 2.5 in to replace it? I assume I'd need another trans, too? Or can I make the current one work? Ditto computer?

I'm just a bit attached to this one since I got it painted all nice, and it's otherwise in great shape (ignoring the sagging headliner).

Thoughts?

Feel free to tell me I'm bat-guano crazy.

Thanks!
 
#2 · (Edited)
I'm going to vote for insane. The poor 4 banger will have to work harder than the v6 to pull the weight of the van. You can do it, but will most likely not see any improvements in MPG.
 
#3 ·
The 3.3 is a good engine, better than the 4 cylinders. I'd keep it.

Are you sure the valve hit the piston? A "ticking" lifter is usually one that is compressed and won't "pump up". If it isn't pumped up, no way that it could cause the valve to open enough to contact a piston. Maybe a pedestal in the head broke and now the rocker is hitting the valve cover and knocking, and the valve isn't opening so it misfires. You might only need a cylinder head.
 
#4 ·
I would say fix the 3.3L. The 2.5L swap would be a lot of work to make an under powered van.
What kind of "god awful mileage" are you getting? I'm still regularly getting 23 MPG on the open road.
 
#5 ·
I got good fuel mileage on my 2nd gen vans. The mileage on the 2.5 liter wouldnt be much better,
Hank
 
#6 ·
I'm going to get around to ripping it apart this week to see what's really going on. I'll give an update once I find out. Thanks everyone.

I guess I'll skip the engine changeover.

I usually get about 17mpg, 20 tops. It only has about 140k on it.
 
#7 ·
A few comments (in no particluar order):
  • Having a lifter go south on you will not cause a valve to interfere with the piston
  • Once you get inside you might well find a rocker arm shaft boss broken and a subsequently snapped rocker arm shaft. If this is the case, then the best way to repair it is to replace the head.
  • Another possibility is that you'll find a damaged rocker arm; a relatively easy fix except that any fix will likely be temporary until the next one gets damaged as well due to oil starvation.
  • If you simply have a bad lifter, then I'd replace the lifter, the pushrod, and the rocker assembly for that lifter and then carry on.
 
#8 · (Edited)








OK, so here's what most likely happened, sorted out with help from the machine shop:

One of the oil galleys to the rocker arm was clogged. That lead to unusual wear on the valve-facing surface of the rockers. The hole you see in #1 exhaust rocker arm was from ongoing wear without proper lubrication. Finally, the valve stem broke through the rocker arm, and stuck there momentarily, enough time for the valve stem retaining ring to break, and then the valve fell into the cylinder; gouging the piston. Luckily this happened just on starting, so the piston and head wasn't completely destroyed. It's repairable!

Now here's the weird part: this is pretty much unheard of. But when it happened, I thought, "that's a bizarre thing; it sounds like the valve got sucked into the cylinder! Nah, that can't happen... "

Apparently, it did.
 
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