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Author Topic: AAZ engine hassles  (Read 5024 times)

May 06, 2020, 09:01:59 pm

rattlenbang

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AAZ engine hassles
« on: May 06, 2020, 09:01:59 pm »
Hi all, I've got a non-running '82 diesel westy with an AAZ engine, that I bought as a project. Discovered that one of the exhaust lifters had shattered, marking up the lifter bore pretty bad. Pulled the head, and while everything down below looked normal, each piston had a slight mark where exhaust valves had kissed it in the past. I'm assuming that's why the lifter was broken.

Fortunately, the van came with a spare used AAZ engine, and I pulled that head to swap. I'm thinking this head was not original as it showed little wear on cams, no cracks between valves and looked exceptionally clean, on an engine that supposedly had higher mileage (270k?). But what shocked me was to see those piston crowns had also been kissed. None of these are deep marks, maybe a few thou, but they sure shouldn't be there. They were shiny and not carboned up, showing that not a lot of use since they were hit.
I did some looking online where some dude was rebuilding his AAZ, and sure enough, his pistons also showed the same marks.
What the hell? Do all these engines show the same problem? What I'm left with here is should I be worried about my replacement head? Was it installed as new one because of the past damage shown by those marked pistons? Or did this head do that damage? How do you tell? The valves look fine and are seating fine.

I'm not sure if I should replace my lifters and valves, just my lifters or just install these very clean looking head? Is there really a concern for the valves given that there's barely any mark on the pistons? Valves aren't cheap; rockauto wants $34 each.



Reply #1May 07, 2020, 01:22:57 am

libbydiesel

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Re: AAZ engine hassles
« Reply #1 on: May 07, 2020, 01:22:57 am »
The pistons and valves do not touch unless someone or something screws up.  If the timing is not done exactly right, then the pistons can touch the valves.  It can also happen if the cam or crank sprocket timing slips.  The AAZ is known for having issues with the crank sprocket keyway.  The issue is presumed to be caused by the AAZ serpentine alternator which came with a solid pulley.  Later alternators came with a clutched pulley which reduces the back and forth stress on the crank sprocket.

It is extremely unlikely that the head itself is the cause of the piston/valve contact.   

You should absolutely most definitely replace any valves that came in contact with the pistons.  Even if they look fine, the valve stem has been weakened and they are known to drop the head off the valve a couple few thousand miles later. 

Lifters should be replaced if they are damaged (cracks or mushroomed top, etc...).

Reply #2May 07, 2020, 11:05:30 pm

rattlenbang

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Re: AAZ engine hassles
« Reply #2 on: May 07, 2020, 11:05:30 pm »
Another fellow insisted that along with valves I should also do guides and must get the valve seats cut to fit the new valves. I like to stay away from machine shops as much as possible, but I'm unfamiliar with these engines.

It's always hard to know just how far to go when tearing into 25 year old motors. 

I checked the crank sprocket keyway and it's good, thankfully. 

Reply #3May 08, 2020, 01:41:52 am

libbydiesel

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Re: AAZ engine hassles
« Reply #3 on: May 08, 2020, 01:41:52 am »
You can hand lap the valves rather than having the valves/seats cut.  When you go to remove the valves, you can feel the play side to side.  If there is not significant wear, then there is no need to replace the guides. 

 

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