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My $0.02 is very seriously consider dumping the block. There are plenty of donor engines out there. If you troll around enough may even find a rebuild project someone bailed out of like I did. Obviously this a high output engine - M28/11,12,21,22? I don't see a year. Finding those here stateside is fairly difficult but you only need a block of matching displacement. Honing (misnomer) the block isn't black magic but you need the right chemicals and compound to do the bore etching. If you hone it you with turn it into a low compression air compressor If you know Greg Hagis over there he may be able to help. He builds high HP N/A 928s and what not. BTW I love that valve! Put that on ebay =
I wish someone would have turned me on to the plentiful blocks. it took me YEARS to find a good used 5.0L short block!
928 International had to get rid of a lot of engines last winter. They have many 5.0 engines to get bottom ends from. It's where I got mine for my 5.0 16V hybrid.
928 International had to get rid of a lot of engines last winter. They have many 5.0 engines to get bottom ends from. It's where I got mine for my 5.0 16V hybrid.
Unfortunately when I asked the only one they had available had a broken AC mount.
Take the oversize piston, rings, and block to a machine shop familiar with BMW, Porsche, new VW. Get them the WSM instructions on conditioning the surface after boring. They should be able to sort it out.
Hi Adam , like Greg ( slate blue ) asked , what depth is the gouge in the alusil cylinder ? , it might just be an optical illusion , but in the photo it looks as if the depth of the gouge taken out of the cylinder wall appears 2 mm + , I think the next step is to send the crankcase ( engine block with cradle attached and torqued down ) to one of the Australia's machine shops who are very familiar with Alusil crankcases/ engine blocks get a professional idea of a safe way ahead with this engine , it would be nice to keep the original engine number with the car as opposed to just installing another 2nd hand 4.7L engine with unknown issues
The depth of the cylinder wall ( deepest point ) damage will determine what will be the outcome , be it a dry sleeve or a wet sleeve & then choice of piston ( same weight ,same dia , same compression ratio , pin off set , and rings to suit the cylinder chosen )
That valve looks new. Was the head recently rebuilt?
I thought so too, don't know of any recent works in last 6 or so years.....
Originally Posted by dr bob
OP's questions:
Yes, you can safely bore one cylinder only to match the available piston you find. the WSM shares some of the details for the work on the bore, including the special honing requirements for the alusil surfaces. If your machine shop has done 944 and 968 blocks, they are familiar with the requirements. Know that more than a few good pistons have trashed and been trashed by poorly prepared bores.
That valve is truly a bit of art in itself. Looks like a keeper or retainer let go, allowing the valve to drop way down in the cylinder. Perhaps a bit of carelessness when working on or "assembling" a head whilst still bolted to the block? More typical 928 valve damage is from a timing belt mishap, leaving just the big end of the valve slightly bent over. The guide supports the rest of the stem, so it all stays straight except for he slightly cocked head.
Thanks, that would be my preferred option right now.
The valve now sits pride of place on my desk!!
The valve collet is still intact on the top end of the valve (complete with the spring washer), the valve has broken just below the washer. The outer valve spring is also broken - not sure if the spring broke causing the valve to break or the other way around..... Which ever is now not important, it will be getting all new valves and springs and what ever else the heads need...
Originally Posted by JET951
Hi Adam , like Greg ( slate blue ) asked , what depth is the gouge in the alusil cylinder ? , it might just be an optical illusion , but in the photo it looks as if the depth of the gouge taken out of the cylinder wall appears 2 mm + , I think the next step is to send the crankcase ( engine block with cradle attached and torqued down ) to one of the Australia's machine shops who are very familiar with Alusil crankcases/ engine blocks get a professional idea of a safe way ahead with this engine , it would be nice to keep the original engine number with the car as opposed to just installing another 2nd hand 4.7L engine with unknown issues
The depth of the cylinder wall ( deepest point ) damage will determine what will be the outcome , be it a dry sleeve or a wet sleeve & then choice of piston ( same weight ,same dia , same compression ratio , pin off set , and rings to suit the cylinder chosen )
Regards
Bruce Buchanan
Hi Bruce, yes a used block could have lots of unknown issues plus getting hold of one in Australia for a reasonable price is a challenge (I have been looking into this now for almost 6 months and one has come up that would be suitable and it sold before I got a chance to act!)
The gouges are less than 0.5mm. I am fully prepared to go the full custom piston route and bore the engine out to 98.0mm (+/-), but if I don't need to then why? My engine (83 4.7 M28/12) has about 150000km on it and everything else looks fine and was a good strong engine. What ever happens I will be (most likely and hopefully!!) fixing what I have.
I will add some other damage caused by this valve breakage and update as I go - is there any way to change the thread title?
The valve was only bouncing around for a few seconds but did a bit of damage to the head, none of it is bad and can be fixed. The valve as I have said above is broken just below the collet (retainer).
Looking down the intake port!!
All of the bits of aluminium from the intake port blew back into the intake plenum and were ditributed to all remaining cylinders, did not damage any bores though!
The 79 my wife drove for years tried to digest the screw from an extra intake boot clamp......that was enough to split the cylinder. Obviously much smaller than that valve.😥
Hi guys,
I have answered the buying of a used block/ engine, but will go into more detail if you wish.
I have extensively looked into getting a used engine/ block and to go from there, trouble being there are very few, if any, in Australia - there is a Japan spec 4.7 (but I believe this to be the same low comp as the US one $3500+) or there is another for about $4k - paying this sort of $$ for an unknown quantity makes no sense to me. I looked at the 5.0 litre hybrid option, the Aus spec one is low compression so not suited (unless you put in new pistons....) so one from the US is needed. The one that 928 Int have for $750US with the broken Alt mounting is the only one I could find, I thought long and hard about buying this, but decided against - can you easily weld an Alusil block plus It would cost in the region of $2500+ to get to me (AUD) plus what ever else you may find.....
None of these options make any sense. Paying a lot to get what is essentially an unknown does not make any sense to me. For me to bore my current engine and put in new custom pistons (Wossner or Arias) is in the region of $3500 AUD........
I came here asking if I could feasibly fit the one piston as per the Porsche workshop manual, it turns out that this possible and at a total of around $700 +/- makes a lot of sense! If I still need to bore my whole block out and fit new pistons so be it, it is what I originally allowed for when the death rattle happened. And if the rod is bent there are plenty of used ones available, although the piston reaches the same height at TDC as the rest. I will also makes sure the crank bearings are ok, or replace with new with either polishing or grinding as required. The heads will need to be refurbed as well, but finding Euro 2V ones is not easy as well......
This way I know exactly what I have and what I will end up with.
03-16-2018, 10:22 PM
If you know Greg Hagis over there he may be able to help. He builds high HP N/A 928s and what not. BTW I love that valve! Put that on ebay =
