AVCS Heads
 

Hi
I am in the process of rebuilding an engine and on inspection of the heads found that there are cracks around the plugs.
I assumed this made the heads scrap but was told otherwise today.
Any feedback on this welcome.
Dave


https://cimg0.ibsrv.net/gimg/www.sco...3d5a924865.jpg

How far up the threads do the cracks go ?

Very hard to see how deep, on one valve seat it does look like it is very close to seating area.
The other seats seem clear but this is outside my expertise.
I was hoping to soda blast the heads prior to rebuild but saw this and now have lost the wind in my sails.
The engine is turning out to be a bag of worms, the mechanic that had my car never finished the job of performing an engine swap and on recovering my car I have neither the original engine or replacement engine. His workshop is now closed and I have no recourse so was rebuilding the engine that came back.
That turns out to be 3 engines, V2 block, V5 inlet and V7 heads.
The towel is in my hand ready to throw it in.
Taking a breath to try and make a non angry decision so looking for any guidance re-the engine.
Dave

They don't look to wide, although you have 4 cracks per plug, if they only go up 4 threads by eye, they are usually about 6 if using crack testing dye, if is about 6 threads on a fresh build I would look for another head, which finding crack free 2.0 avc,s heads is getting very hard, the real killer is if you have cracks from valve seat to valve seat.

Thanks for feedback. I will pop the plugs out and take a closer look on the weekend.
It was not visible until I soda blasted and not done the other side yet.
I hope to also get some advice from a local engineering shop (local being Munich) after cleaning.
Looks too fine for welding but has anyone ever tried any other fix?
Starting to look like I have a boat anchor!
In the process of getting quotes for a new engine.
Dave

in fairness a v2 block with sti 7 heads is a good upgrade that makes use of the newest parts available -
have to admit i looked at loads of pictures of cracked 2nd hand heads from various sellers when i was looking for replacements for my ver 8 heads .very few low mileage cars left now with uncracked centres in the heads.
rather than haemorage money on an old engine it might pay to look for a fresh 2nd hand engine? especially if the car isnt mega tuned

Thanks to all for feedback. I decided to go new engine path. Engine Builders in Plymouth will build me a new 2.1 stroked V5. It includes a nitrided 79mm crank, K1 rods, Wossner forged pistons, ACL Race bearings, fully balanced assembly with Roger Clark Motorsport head gaskets, head stud kit, cam belt kit, water pump and an 11mm oil pump. We fully overhaul the heads including guides. all other gaskets and seals are genuine Subaru. I hope this will be the final engine for the car!
Next to work on the plumbing and electrics...

I'm a little bit confused about this issue myself. Is there a reason why the area can not be filled up with a tig welder, and then have the spark plug thread re-threaded, and combustion chamber cleaned up?

I've seen heads and alu blocks welded for various projects, but it seems to be shunned on imprezas.

seems a shame to scrap heads if they can be salvaged, especially if they're becoming rare.

Hi
I had some horrendously looking heads welded and repaired in the past by Tim Radley of http://www.racedevelopments.co.uk/
Give him a shout and see what he can do , he's very good
Cheers Ian

It all depends on cost, you really need the seats removing, welding, re machine the welded area, inc valve seats & spark plug thread, all new valve seats & fitting, it would be cheaper to buy new bare castings, & a lot reliable after the welding process.

NEW Engine
 

Chaps
Thanks for feedback and I have decided that due to other as yet undiscovered surprises I will get a replacement engine from Engine Tuners of Plymouth.
I will break the engine for parts as its already 90% there.
For me I feel that the head welding and re-working is a compromise compared to the other tasks needed to get it together.

Not sure if to re-assemble the heads and sell as a set with crack deceleration or sell as parts.
Replacement is going to be a V5 top to bottom with 2.1 stroker kit.
Then I know its a 0-mile engine so I can focus on building the rest of the car back to its former glory.
This also saves me the task of swapping the Alcatek as it setup for a V5 and was planned to be changed.
I also now have 2 V5 manifolds, the red one that was with the engine and one I had reworked and powder coated to match the car scheme, yes its going to be a bit of a tart!
Wiring harness is stripped and has been cleaned for re-wrapping and fuel rails and injectors serviced.
So back to non ACVS engine.
Dave
The heat of Subaru beats in this car...

https://cimg3.ibsrv.net/gimg/www.sco...3e31b1757c.jpg




https://cimg5.ibsrv.net/gimg/www.sco...dca1a5c585.jpg

https://cimg6.ibsrv.net/gimg/www.sco...e25ca7dc0c.jpg

Any pictures of the car with the WINGS fitted...................:eek:

Love it :thumb:

Where we are going we don't need wings :)
700kg, 320hp
No driver aids
No assisted power brakes
Should be fun...

Hi David , Im rebuilding my WRX after some bottom end knock, so had a short block from Ashley Wilks in UK delivered last week.
But just took a look at my WRX My05 heads after pulling them off the old engine and found mine are cracked as yours. :(


A problem with WRX heads is diparate thermal expansion and contraction on the edge of the spark plug bore right at the flame front.


Im not going weld my heads , but I will be setting the spark plugs down into the cylinder so that the edges of the thread are flush , with area under the thread just slightly over proud to the chamber. (by removing 2-3 mm from the sparkplug seating other side of the head) this is standard practice on the Group N engine build.


The idea behind it is two fold.


First the Aluminium thread is more equally cooled (i.e at same rate) by the steel thread of plug's body when the thread is set right to it's base.


Secondly the burn start is induced slightly deeper ( i.e towards middle of combustion chamber ) which produces a cleaner burn ( with a single spark plug. the best you can do )


Further light grind off work can be done to relieve the stress focus points , which you can see are followed into by the cracks in your photos
basically the smoother the better as all sharp edges heat first and disapate slower. that causes the crack to creep.


Hope to see you pass me sometime at the ring.. ;)

New engine
 

I will scrap the old engine so splitting for parts.
New engine coming from Engine Tuner in Plymouth.
The heads are clean and maybe someone would re-work but not for me.