parrothead

Disassembled the engine tonight and the three cylinders with bad leak down results all have broken piston rings. Cylinders 5,6, & 7. Anything signifigant about those 3? The block is in the back of the Jeep so hopefully results from the machine shop will be promising.
So while I have the engine out anything worthwhile I should do under the empty hood? I will be replacing motor mounts but anything else to consider since I have the access?
Thanks
- Eric

John Struthers

Parrot,
You probably know this already but...
If I'm not mistaken there is a special procedure for honing the bore for silicon exposure.
I don't think you should drop the block off for honing/boring unless you and the shop have the straight skinny on the procedure.
There should be info on the procedure in the WSM, the archive -particularly the 6.0 Liter posts and last but not least contact the guy's at 928 International and Devek for "The Word'.
If you haven't cleaned the pan you might want to run a magnet thru the bottom and check for metal, ask Mark Anderson or Jim Bailey at 928 International about oil starvation -#6 sounds familiar- and results thereof. If you run her hard or track the beast you might be in the market for a drilled crank.
Good luck.

2V4V

Eric,

What John said, times 10. There is NO room to scrimp on engine internals or machine work. (there are things you can cheat if you just gotta, but anything internal ain't them things)

Buy a used block/engine before taking down to a machine shop that has not done a fair number of 928/944 blocks lately. Really.

If you have a good shop that knows Porsche blocks, then you're golden. But, ship it out to someone who does them before letting your block be the 'training aid'.

Greg

slate blue

I just had my GT motor lapped, cost about $400 USD, it had very minimal wear.


Note when I took this photo, I was trying to show the worst aspects of the block, that is where it had maximum wear. You can barely feel the wear in the block, but it was border line according to the specs. What made me get it done was that there was no score marks of any signifigance.

You should also note that the block was decked with a diamond tool. Nothing else will give you as good a finish. If you intend on boring the block you will need oversize pistons which aren't commonly available. I do have a complete set. You are probably better off with Nicasil, about 2k with the Je pistons. That is the cheapest route, remember just because you are putting new rings, don't think that will sovle all your problems. Porsche note that engines with high oil consumption need new pistons.

Old & New

<eric starts to consider a 5 liter block>

GlenL

Or instead of spending big buck you could do what I did when I found broken rings, and pistons, on my 4.7l Euro S: Ignore small scratches and put it back together. Haven't done a compression test but the dyno showed 262 rwhp DIN out of the 300 bhp DIN at-the-engine spec.

Have the machine shop inspect and clean the block. You don't _have_ to have any machine work done on it unless there's a real issue. If there are problems then you can consider getting a new (used) block including going to a 5.0l.

parrothead

Thanks. So is the 5 liter block the same as the 4.7 but a larger bore? John thanks for your input. I had been reading awhile on the problems with alusill?? and that the need of a special machine shop. My local 928 wrench recommended a machine shop that should handle this. I brought the block by the shop over lunch and he seemed knowledgable of the process and said he can handle it, but he was going to make a few phone calls to verify first.
Apparently the one bad groove has him thinking that I might need to go to the next larger piston size. It sounds like that is where it starts getting expensive.
Greg - My oil consumption was mainly blow by after I would red line it. I resembled a mosquito spray truck.
Thanks for the responses. The quest continues...
- Eric

GlenL

The 5l block into '86 will work with the heads, but the pistons have to be notched. Someone, somewhere has a template for this...